coupled thmc models for bentonite in an argillite repository for nuclear waste illitization and its effect on swelling stress under high temperature abstract subsurface manipulations such as those expected from the disposal of heat emanating radioactive waste in deep repositories can induce strongly coupled thermal t hydrological h mechanical m and chemical c processes adequate coupled thmc models are highly desirable or even indispensable for performance assessment of such repositories for examples for the analysis of bentonite based engineered barrier system ebs surrounding the emplaced waste in this study we present coupled thmc model simulations of a generic nuclear waste repository in an argillite with a bentonite based buffer the objective is to evaluate the chemical changes in the ebs bentonite and their effect on mechanical behavior under high temperature attempting to shed light on whether ebs bentonite can sustain temperatures higher than 100 c without significant impact on barrier s performance two scenarios were simulated for comparison a case in which the temperature near the waste canister peaks at 200 c and a case in which the temperature at the same spot culminate with about 100 c simulations for a generic case with kunigel vi bentonite as backfill and opalinus clay as host rock were conducted for 1000 years and reported in the previous study zheng et al 2015 in this paper simulations for 100 000 years have been done for two types of bentonite based buffer materials kunigel vi and febex bentonite this enables us to evaluate how different types of bentonite behave in terms of the illitization and its impact on swelling stress and whether we can generalize these results to support decision making the simulations show the occurrence of illitization in the bentonite buffer and the enhancement of illitization under high temperature however febex bentonite undergoes less illitization mainly due to the higher ion concentration in pore water and the lower content of k feldspar in the bentonite mineral composition moreover the reduction of swelling stress by chemical changes is more pronounced for kunigel vi bentonite than for febex bentonite overall the results of our model simulations suggest that an argillite repository with a bentonite based ebs that is similar to febex bentonite could sustain temperatures much higher than 100 c as far as illitization concerns model results also reveal that illitization is stabilized after about 2000 years in bentonite near the waste package but continues in bentonite near the bentonite argillite interface which manifests the strong effect of geochemical interaction between ebs bentonite and host rock on long term illitization in bentonite

no flat wadati benioff zone in the central and southern central andes abstract the wadati benioff zone wbz is an approximate plane defined by earthquakes hypocentres observed in convergent plate boundaries and that usually dips at angles greater than 30 in some areas of the andes where there are gaps in volcanic activity and where heat flow is abnormally low this plane in most studies has nearly horizontal dip at a depth of about 75 100 km and it has been associated to flat subduction of the oceanic lithosphere this situation has been taken as the present day analogue of the laramide orogeny of western north america for which a flat slab episode has been proposed in the past years in this work the observed low heat flow in areas of the andes is assumed to be due to low radiogenic heat generation in geologically old and allochthonous terranes constituting large regions of western south america on the basis of geotherms obtained for areas of ecuador peru chile and argentina and of rheological results describing the partition between brittle and ductile regimes the seismic activity observed both in the lower crust and at depths of about 75 100 km is thoroughly explained at these depths earthquakes occur within the subcontinental upper mantle and then there is no flat wbz associated to subduction of the oceanic lithosphere there is evidence from recent seismological observations that the real wbz lies not horizontally and deeper in the tectonosphere

modeling of damage permeability changes and pressure responses during excavation of the tsx tunnel in granitic rock at url canada this paper presents numerical modeling of excavation induced damage permeability changes and fluid pressure responses during excavation of a test tunnel associated with the tunnel sealing experiment tsx at the underground research laboratory url in canada four different numerical models were applied using a wide range of approaches to model damage and permeability changes in the excavation disturbed zone edz around the tunnel using in situ calibration of model parameters the modeling could reproduce observed spatial distribution of damage and permeability changes around the tunnel as a combination of disturbance induced by stress redistribution around the tunnel and by the drill and blast operation the modeling showed that stress induced permeability increase above the tunnel is a result of micro and macrofracturing under high deviatoric shear stress whereas permeability increase alongside the tunnel is a result of opening of existing microfractures under decreased mean stress the remaining observed fracturing and permeability changes around the periphery of the tunnel were attributed to damage from the drill and blast operation moreover a reasonably good agreement was achieved between simulated and observed excavation induced pressure responses around the tsx tunnel for 1 year following its excavation the simulations showed that these pressure responses are caused by poroelastic effects as a result of increasing or decreasing mean stress with corresponding contraction or expansion of the pore volume the simulation results for pressure evolution were consistent with previous studies indicating that the observed pressure responses could be captured in a biot model using a relatively low biot willis coefficient 0 2 a porosity of n 0 007 and a relatively low permeability of k 2 10 22 m2 which is consistent with the very tight unfractured granite at the site

a model approach to radioactive waste disposal at sellafield one of the great environmental problems of our age is the safe disposal of radioactive waste for geological time periods britain is currently investigating a potential site for underground burial of waste near the sellafield nuclear plant future leakage of radionuclides depends greatly on subsurface water flows these must be understood from the past to predict hydrogeology 104 105 years into the future we have taken information from the present day published by the government company nirex and used a finite element steady state fluid flow computer code to examine water flows in the subsurface we find that flow directions at the planned repository are persistently upwards and that geologically significant flow rates could occur flow rates are particularly sensitive to uncertainties of rock permeability conductivity measurements made from site investigation boreholes the hydrogeology at this site needs longer term investigation before a confident and credible prediction can be made

substorms under northward interplanetary magnetic field statistical study it was recently noted that substorms can occur even under prolonged northward interplanetary magnetic field imf conditions based on the substorm list obtained from the image spacecraft we perform a statistical study on the features of substorms during northward imf interval the strength of the substorm is represented by the al index decrease and the total intensity of the auroral bulge four main features have been found as follows 1 most substorms occur soon after a southward imf and intense substorms are more likely to occur for short duration of northward imf period 2t t5th whereas no intense substorms occur after prolonged northward imf condition 2 there is a positive correlation between the strength of the substorm and the two solar wind parameters the imf by and the solar wind dynamic pressure pd 3 the average strength of the substorms during the storm period is much larger than that of the substorms during the period without storm meanwhile nearly all strong storm time substorms occurred either during the intense storm period or during the late main phase or the early recovery phase of the storm 4 about half of substorms either an increase or a decrease in the solar wind dynamic pressure are found within 30tmin preceding each onset time such features indicate that the energy stored in the magnetotail during a previous southward imf period is the main energy source for substorms under northward imf condition especially for intense substorms and both the imf by and the solar wind dynamic pressure play an important role in the energy accumulation during the northward imf period

a study of thermal pressurization and potential for hydro fracturing associated with nuclear waste disposal in argillaceous claystone abstract we present coupled thermo hydro mechanical thm modeling of geologic nuclear waste disposal in argillaceous claystone focusing on thermally induced pressure changes and the potential for such pressure changes to induce hydro fracturing to investigate this possibility we first conduct a three dimensional repository scale model with host rock properties repository design and nuclear waste decay heat functions derived from the french concept of geologic disposal in argillaceous claystone the model simulations show that the highest potential for hydro fracturing occurs between emplacement micro tunnels cells at the center rather than at the edge of the repository we further investigate the use of a two dimensional single cell model as a simpler surrogate for a full three dimensional model our results reveal that such geometric simplification is reasonably accurate for modeling coupled thm processes at the center of the repository though it overestimates the likelihood for hydro fracturing and substantially overpredicts ground surface uplift a parameter study shows the importance of adjacent higher permeability geological layers that play a significant role in dissipating overpressure in the host rock layer finally the study shows the importance of the spacing between emplacement tunnels which if too short results in a higher fluid pressure and a strongly increased potential for hydro fracturing overall the study suggests the limiting factor in the thermal management and design of a repository is not necessarily the maximum temperature in the engineered barrier system near the waste packages but rather the more modest host rock temperature between emplacement tunnels due to the potential for thermal damage

structure of the crust and upper mantle beneath the great valley and allegheny plateau of eastern pennsylvania 2 gravity modeling and migration of wide angle reflection data linear inversion of p composites for three different profiles suggests that the lower crust beneath eastern pennsylvania consists of material with high averaged p wave velocities 6 8 7 5 km s compared with 6 4 7 1 km s for most crustal models derived for surrounding areas within the appalachians and the grenville province of the canadian shield interpretations of these velocities in terms of rock type are limited by the low resolving power of the data and by the nonuniqueness in inferring rock type from p wave velocity alone the high averaged p wave velocities could be associated with substantial volumes of mafic rock perhaps emplaced by underplating or with high grade metamorphic assemblages of intermediate composition and sedimentary origin similar to those found in the ivrea zone in northern italy because of the sparseness of the s wave data averaged shear wave velocities are not well enough resolved over most depth ranges to distinguish among the different compositional models computations of gravity anomalies for two dimensional models using various linear velocity density relations however suggest that at least part of the crust beneath the scranton gravity high is mafic moreover if the entire basement section beneath this anomaly consists of mafic material then the gravity studies indicate that the lower crust beneath the great valley must be mafic as well migrated shot gathers show a concentration of reflectors at depths between 35 and 45 km a result that is controlled in part by the limited range of offsets used but that is also consistent with recent observations of a highly reflective lower crust reflections that are migrated to depths within the uppermost mantle could be multiples or primary reflections from upper mantle layering although the data are rather sparse the interpretation of these later arrivals as primary reflections is supported by their small ray parameters which suggests that they are not converted phases and by their large relative amplitudes which suggests that they are not multiples layering within the upper mantle could be in the form of alternating high and low velocity zones perhaps related to emplacement of eclogites or garnet granulites in the uppermost mantle during the process of underplating

thermo hydro mechanical response of granite to temperature changes this paper examines the thermo hydro mechanical behaviour of a granitic rock the cylindrical sample of granite contained a sealed fluid filled cavity which was subjected to a cycle of temperature changes on its outer surface the temperature and fluid pressure changes in the fluid filled cavity were measured since the measurement of fluid pressure and temperature in the sealed cavity is experimentally feasible the technique is a common feature in thermo hydro mechanical experiments however it was observed that regardless of how precisely the cavity was filled with de aired water air bubbles can still exist in the cavity and influence the fluid pressure changes a novel technique is suggested for taking into account the influence of the volume of trapped air and eliminating its effect in the estimation of permeability the experiment was computationally modelled using the finite element code comsol multiphysics and the experimental results were compared with the computational estimates

hydro mechanical response of a fractured granitic rock mass to excavation of a test pit the kamaishi mine experiment in japan a thermo hydro mechanical experiment was conducted in a fractured granitic rock mass at the kamaishi mine in japan the experiment consists of the excavation of a cylindrical test pit on the floor of an experimental drift the test pit was then filled with bentonite with an embedded heater during the excavation of the test pit the hydro mechanical response of the surrounding rock was monitored this paper presents the efforts of four research teams to numerically simulate the hydro mechanical response of the rock mass during excavation while the total inflow rate to the test pit the flow distribution on the pit walls and the displacements in the rock mass away from the pit could be reasonably predicted the pore pressure in individual boreholes and the expansion behaviour of the pit were less successfully simulated the reasons for these discrepancies are discussed in the paper

tectonics and topography for a lithosphere containing density heterogeneities the purpose of this paper is to clarify the dynamic role of lithospheric density heterogeneities in particular with respect to mountain building and other processes of intraplate deformation density anomalies within or just beneath the lithosphere constitute major sources for tectonic stress fields the product of their magnitude by their depth is shown to characterize their ability to induce deformation this rule of the density moment directly yields the lithospheric thickening or thinning rate when applied to structures of large lateral extent for anomalies of lateral extent that is small in comparison with their depth the deformation is vertically inhomogeneous and has been computed with the help of simple physical models of a stratified viscous newtonian lithosphere the analytical treatment is based on fourier transform continent continent collision thickens not only the crust but the entire lithosphere the cold root underlying a mountain chain induces strong regional compressive stresses able to sustain the mountain bulding process without further help from forces transmitted from far away thus the continental lithosphere is in a somewhat metastable mechanical state adiabatic i e rapid thickening or thinning tends to grow further once initiated tectonic phases of strong compression correspond to the climax of such instabilities the response of models with cold lithospheric roots of various intensities has been computed both in two and three dimensions they yield velocity distributions and stress fields instructive comparisons are made with earthquake focal mechanisms and in situ stress measurements in the alpine and appalachian regions in the presence of lateral variations of the mechanical properties of the lithosphere the tectonic style is not only function of the local topography and of the nature of its compensation deformations in neighbouring provinces are coupled as shown by 3 dimensional models for example thickening sustained by a cold lithospheric root may generate extension in peripheral zones of weakness these last results illustrate the point that the computation of regional tectonic stresses requires the knowledge of the density anomalies within the lithosphere on the one hand and of geometrical constraints related to lateral mechanical heterogeneities on the other

a numerical model for thermo hydro mechanical coupling in fractured rock coupled thermo hydro mechanical codes with the ability to model fractured materials are used for predicting groundwater flow behavior in fractured aquifers containing thermal sources the potential applications of such a code include the analysis of groundwater behavior within a geothermal reservoir the capability of modeling hydro thermo systems with a dual porosity fracture flow model has been previously developed in the finite element code fehm fehm has been modified to include stress coupling with the dual porosity feature fehm has been further developed to couple the dependence of fracture hydraulic conductivity on effective stress within two dimensional saturated aquifers containing fracture systems the cubic law for flow between parallel plates was used to model fracture permeability the barton bandis relation was used to determine the fracture aperture within the cubic law the code used a newton raphson iteration to implicitly solve for six unknowns at each node results from a model of heat flow from a reservoir to the moving fluid in a single fracture compared well with analytic results results of a model showing the increase in fracture flow due to a single fracture opening under fluid pressure compared well with analytic results a hot dry rock geothermal reservoir was modeled with realistic time steps indicating that the modified fehm code does successfully model coupled flow problems with no convergence problems

coupled thm processes in edz of crystalline rocks using an elasto plastic cellular automaton this paper aims at a numerical study of coupled thermal hydrological and mechanical processes in the excavation disturbed zones edz around nuclear waste emplacement drifts in fractured crystalline rocks the study was conducted for two model domains close to an emplacement tunnel 1 a near field domain and 2 a smaller wall block domain goodman element and weak element were used to represent the fractures in the rock mass and the rock matrix was represented as elasto visco plastic material mohr coulomb criterion and a non associated plastic flow rule were adopted to consider the viscoplastic deformation in the edz a relation between volumetric strain and permeability was established using a self developed epca2d code the elastic elasto plastic and creep analyses to study the evolution of stress and deformations as well as failure and permeability evolution in the edz were conducted results indicate a strong impact of fractures plastic deformation and time effects on the behavior of edz especially the evolution of permeability around the drift

in situ behaviour of a stiff layered clay subject to thermal loading observations and interpretation the paper presents an interpretation of an in situ heating test carried out on opalinus clay in the mont terri underground laboratory opalinus clay is a stiff strongly bedded mesozoic clay of marine origin when subjected to thermal loading saturated stiff clays exhibit a strong pore pressure response that significantly affects the hydraulic and mechanical behaviour of the material the observations gathered in the in situ test have provided an opportunity to examine the integrated thermo hydro mechanical thm response of this sedimentary clay coupled thm numerical analyses have been carried out to provide a structured framework for interpretation and to enhance understanding of thm clay behaviour numerical analyses have been based on a coupled theoretical formulation that incorporates a constitutive law especially developed for this type of material the law includes degradation of bonding by damage by performing three dimensional computations it has been possible to incorporate anisotropy of m

thermally induced mechanical and permeability changes around a nuclear waste repository a far field study based on equivalent properties determined by a discrete approach abstract a numerical investigation is conducted on the impacts of the thermal loading history on the evolution of mechanical response and permeability field of a fractured rock mass containing a hypothetical nuclear waste repository the geological data are extracted from the site investigation results at sellafield england a combined methodology of discrete and continuum approaches is presented the results of a series of simulations based on the dfn dem discrete fracture network distinct element method approach provide the mechanical and hydraulic properties of fractured rock masses and their stress dependencies these properties are calculated on a representative scale that depends on fracture network characteristics and constitutive models of intact rock and fractures in the present study data indicate that the large scale domain can be divided into four regions with different property sets corresponding to the depth the results derived by the dfn dem approach are then passed on to a large scale analysis of the far field problem for the equivalent continuum analysis the large scale far field analysis is conducted using a fem code rocmas for coupled thermo mechanical process the results show that the thermal stresses of fractured rock masses vary significantly with mechanical properties determined at the representative scale vertical heaving and horizontal tensile displacement are observed above the repository observed stress and displacement fields also shows significant dependency on how the mechanical properties are characterized the permeability changes induced by the thermal loading show that it generally decreases close to the repository however change of permeability is small i e a factor of two and thermally induced dilation of fracture was not observed note that the repository excavation effects were not considered in the study the work presented in this paper is the result of efforts on a benchmark test bmt2 within the international co operative projects decovalex iii and benchpar

fracture dominated flow in the borrowdale volcanic group at sellafield nw england the identification of potential flowing features development of conceptual models and derivation of effective parameters

a study of caprock hydromechanical changes associated with co2 injection into a brine formation a numerical study of hydromechanical changes during a deep underground injection of supercritical co2 in a hypothetical brine aquifer caprock system is conducted the injection process is simulated using a newly developed computer model for multi phase analysis of co2 and brine water flow coupled with heat transfer and rock deformations in this modeling co2 is injected at a constant rate over a 10 year period at a depth of 1 300 1 500 m the injection zone is overlain by a 100 m thick caprock located at 1 200 1 300 m which in one of the studied cases is intersected by a vertical fault the hydraulic mechanical as well as hydromechanical responses caused by the injection are studied this includes the spread of the co2 plume effective stress changes ground surface uplift stress induced permeability changes and mechanical failure analysis the analysis shows that most hydromechanical changes are induced in the lower part of the caprock near its contact with the injection zone whereas the sealing mechanism of the upper part may remain intact despite an injection pressure close to the lithostratic stress value

lithospheric structure of tibet and western north america mechanisms of uplift and a comparative study we seek to determine the mantle lid thickness of the lithosphere and to constrain the mechanisms that are responsible for the cenozoic uplift of the tibetan plateau located behind the himalaya collision zone and the western united states located behind the san andreas transform convergent plate boundary selected first p arrivals of international seismological centre isc data at distances less than 22 are analyzed by the two station method to constrain the upper mantle structure of the basin and range br colorado plateau cp great plains gp and tibetan plateau tp the data are presented as plots of apparent velocity versus distance to the second station we show that these observations of apparent velocities versus distance as well as those that concern the attenuation of sn provide estimates of the mantle lid thicknesses we obtain the following mantle lid thicknesses br 20 40 km cp 35 50 km gp 150 195 km and tp 135 180 km sn is not observed for paths beneath the br and cp while sn efficiently propagates beneath the gp sn is also observed beneath most of tibet except in the north central part of the tp a possible interpretation of our observations is that indian continental lithosphere underthrusts only about the southern 2 3 of tibet

the seismic 8 discontinuity and partial melting in continental mantle strong scattered reflections beyond 8 degrees 8 offset are characteristic features of all high resolution seismic sections from the continents the reflections identify a low velocity zone below approximately 100 kilometers depth beneath generally stratified mantle this zone may be caused by partial melting globally initiated at equal depth in the continental mantle solid state is again attained at the lehmann discontinuity in cold stable areas whereas the zone extends to near the 400 kilometer discontinuity in hot tectonically active areas thus the depth to the lehmann discontinuity may be an indicator of the thermal state of the continental mantle

a mathematical model for seepage of deeply buried groundwater under higher pressure and temperature summary deeply buried groundwater such as brine is an important industrial raw material with high economic value because brine frequently exists under higher temperature and pressure the quantitative prediction of its seepage field is very difficult here we study the migration of deeply buried groundwater by using a numerical simulation based on laboratory test results in particular we express the pressure and temperature variation of seepage parameters such as hydraulic conductivity k and specific storage coefficient s in terms of the corresponding variation of the solid skeleton s permeability k porosity n compressibility coefficient s and seepage fluid s viscosity and compressibility coefficient w then through mathematical transformation and linearization methods the mathematical model with pressure and temperature dependent coefficients is reduced to the same form as the standard one for seepage flow the results are successfully applied to the moxi structure in sichuan basin the results show that the effect of higher pressure and temperature should be taken into account for quantitative study of deeply buried groundwater and that the effects are easily included by the transformation of the mathematical model to standard form

a mathematical model for consolidation in a thermoelastic aquifer due to hot water injection or pumping a mathematical model is developed for the areal distribution of fluid pressure temperature land subsidence and horizontal displacements due to hot water injection into thermoelastic confined and leaky aquifers the underlying assumption is that the aquifer is thin in relation to the horizontal distances of interest and hence all dependent variables of interest are average over the thickness values the solid matrix is assumed to be thermoelastic following the development of three dimensional conservation of mass and energy equations and equilibrium equations in terms of horizontal and vertical displacements the mathematical model is derived by averaging the three dimensional model over the vertical thickness of the aquifer subject to conditions of plane total stress the effects of viscous dissipation and compressible work have been included in the formulation the resulting averaged coupled equations are in terms of pore water pressure temperature and vertical and horizontal displacements which are functions of x y and t only the equations are nonlinear and have to be solved simultaneously due to the coupling that exists among them equations and appropriate boundary conditions in radial coordinates have also been presented for an example of a single injecting or pumping well

multiphysics processes in partially saturated fractured rock experiments and models from yucca mountain 1 the site investigations at yucca mountain nevada have provided us with an outstanding data set one that has significantly advanced our knowledge of multiphysics processes in partially saturated fractured geological media such advancement was made possible foremost by substantial investments in multiyear field experiments that enabled the study of thermally driven multiphysics and testing of numerical models at a large spatial scale the development of coupled process models within the project have resulted in a number of new advanced multiphysics numerical models that are today applied over a wide range of geoscientific research and geoengineering applications using such models the potential impact of thermal hydrological mechanical thm multiphysics processes over the long term e g 10 000 years could be predicted and bounded with some degree of confidence the fact that the rock mass at yucca mountain is intensively fractured enabled continuum models to be used although discontinuum models were also applied and are better suited for analyzing some issues especially those related to predictions of rockfall within open excavations the work showed that in situ tests rather than small scale laboratory experiments alone are essential for determining appropriate input parameters for multiphysics models of fractured rocks especially related to parameters defining how permeability might evolve under changing stress and temperature a significant laboratory test program at yucca mountain also made important contributions to the field of rock mechanics showing a unique relation between porosity and mechanical properties a time dependency of strength that is significant for long term excavation stability a decreasing rock strength with sample size using very large core experiments and a strong temperature dependency of the thermal expansion coefficient for temperatures up to 200 c the analysis of in situ heater experiments showed that fracture closure opening caused by changes in normal stress across fractures was the dominant mechanism for thermally induced changes in intrinsic fracture permeability during rock mass heating cooling and that fracture shear dilation appears to be less significant significant effort was devoted to predicting the long term stability of underground excavations under mechanical strength degradation and seismic loading perhaps one of the most challenging tasks within the project we note that such long term strength degradation is actually an example of a chemically mediated process governed by underlying microscopic stress corrosion and chemical diffusion processes in the yucca mountain project such chemically mediated mechanical changes were considered implicitly through model calibrations against laboratory and in situ heater experiments at temperatures anticipated to be experienced by the rock a possible future research direction would be to simulate such processes mechanistically in a complete coupled thmc framework where c denotes chemical processes

global scale ionospheric flow and aurora precursors of auroral substorms coordinated superdarn and image wic observations we use global scale polar cap flow vector measurements from the super dual auroral radar network superdarn with the concurrent auroral observations from the wideband imaging camera on board imager for magnetopause to aurora global exploration image wic to study the polar cap flow and auroral precursors during a substorm onset on 26 december 2000 we show for the first time close connection between the dayside and nightside polar cap flow enhancements with the enhanced dayside flow preceding the nightside one by several minutes and the ensuing poleward boundary intensification pbi streamer and the later onset forming a complete preonset sequence for a substorm onset our results supplement our previous study by providing further evidence that the dayside polar cap flow disturbance may be the key to initiate the whole process of a certain type of substorm by triggering reconnection somewhere in the tail via applied field or flow perturbations on the nightside plasma sheet boundary layer our results also indicate that a preexisting double oval structure is likely a favorable precondition for a certain type of substorm to be triggered by polar cap flow disturbance and the associated pbis streamers on the other hand not all our global scale preonset auroral sequences support the recent revised onset scenario proposed by nishimura et al 2010a using the all sky imagers of the time history of events and macroscale interactions during substorms mission this suggests that the preceding pbi streamer is not a sufficient condition to trigger a substorm it may not even be a necessary condition considering the existence of various types of substorm onsets

a new model of upper mantle p wave velocity below the baltic shield indication of partial melt in the 95 to 160 km depth range abstract the subcrustal mantle to about a depth of 160 km below the baltic shield can be divided seismically into two main intervals the upper interval between ca 45 and 100 km is characterized by refracted waves with velocities between 8 0 and 8 6 km s interpreted as a sandwich layered model of intermixed high and low velocity layers the lower interval is a ca 40 km thick zone of relatively low average velocity at a depth increasing from 95 km in the southern part to 120 km in the northern part of the shield seismic sections show that isolated bodies in this interval generate scattered reflections with substantial amplitude variation over short distance the maximum velocity difference at the reflectors is 1 0 km s which is larger than in the upper main interval our model is based on a general gap in correlation of seismic arrivals at offsets between 800 and 1100 km at larger offsets we observe continuous linear first arrivals indicating a relatively homogenous layer of high 8 6 km s velocity below a depth of 160 km petrologically the lower reflective interval is explained by partially melted small bodies with patches of carbonatitic or kimberlitic magma of horizontal extent less than 20 km this new model of the upper mantle is based on seismic data from the baltic shield and there is clear indication that it is equally valid for other shield and platform areas

analysis of thermo hydrologic mechanical impact of repository for high level radioactive waste in clay host formation an indian reference disposal system in our study a coupled hydrologic mechanical analysis is done of the excavation damaged zone before the emplacement of nuclear waste this is followed by a coupled thermal hydrologic mechanical analysis to evaluate the impact of nuclear waste repository in porous water containing rock mass this analysis has been under taken in accordance with the indian reference disposal system the paper considers the changes in pore pressure and stresses due to excavation of disposal holes a critical study of rock mass permeability porosity thermally induced stresses strains and temperature distribution after the emplacement of nuclear spent fuels in disposal holes has also been done coupling to the mechanical constitutive equations is done via effective normal strain rates

excavation damaged zone division and time dependency deformation prediction a case study of excavated rock mass at xiaowan hydropower station abstract rock mass excavation is accompanied by rock deformation during unloading which degrades the quality of rock mass and significantly affects the safety and stability of rock mass engineering taking the excavated rock mass from the dam foundation of xiaowan hydropower station as the study object long time single hole acoustic tests shat were conducted in the dam abutment rock mass with the changes in the acoustic wave velocity recorded then a new method quantifying the excavation damaged zone edz was proposed according to the cumulative degradation rate of acoustic wave velocity and a time dependency model for evaluating the evolution of the excavation heavily damaged zone ehdz was established the results indicated that the cumulative degradation rate curves of the wave velocity along the boreholes exhibited significant differences in time and space the depth corresponding to the inflection point on the curve can be regarded as the bottom boundary of the ehdz which could be used to generate time dependency curves and demonstrate the spatiotemporal evolution process for the ehdz the time dependency curves can be classified into three categories the differences between the classified curves are related to the depth of the initial ehdz ehdz0 rock mass elastic modulus e and unloading stress u the time dependency model for the ehdz evolution process follows a negative exponential function the ehdz0 depth e and u can determine the coefficients of the model the model provides an effective method to predict ehdz depths at different times after rock mass excavation the prediction results are of considerable significance for researches on the unloading failure and the selection of rock mass reinforcement which would ensure the stability and safety of the rock mass engineering during construction and operation

heat induced moisture movement in a clay barrier i experimental modelling of borehole emplacement abstract the paper presents the results of a series laboratory experiments which were conducted to study the heat induced moisture movement in a bentonitic clay buffer region in the experimental investigations hygro thermal phenomena are induced by a cylindrical heater which is placed within the compacted buffer material located in a borehole centrally situated in a granite block the paper summarizes the experimental methodologies and presents results for the time dependent distribution of temperatures within the granite block and the residual moisture distribution within the buffer at the termination of the experiment

analysis of the thm behaviour in a clay based engineered barrier system ebs modelling of the he e experiment mont terri url to understand the complex thermo hydro mechanical thm processes and their evolution in a clay based engineered barrier systems ebs during the closure phase of a geological repository for radioactive waste a 1 2 scale in situ heating experiment he e experiment has been ongoing since 2011 in the mont terri rock laboratory based on the experimental data a fully coupled thm 3d simulation using the finite element program opengeosys was carried out the main objectives of the simulation were to interpret the experimental observations to understand the thermally induced thm interactions and to analyse the different material properties five experimental phases were numerically interpreted in order to take into account the changes in the temporary material properties during experimental operations these included the tunnel excavation the ventilation the emplacement of the bentonite ebs the heating phase and the phase after shutdown of the heater a non isothermal richards flow model was used to take into account the evaporation and vapour diffusion during the heating the material behaviours of ebs in association with the saturation dependent thermal conductivity and the water retention behaviour under high temperatures were analysed in detail the strong thermal hydraulic and mechanical anisotropic properties of the opalinus clay were described by a transversely isotropic model

rainfall infiltration induced groundwater table rise in an unsaturated porous medium increased rainfall associated with climate change is becoming a common occurrence and can lead to a variety of geoenvironmental hazards infiltration during rainfall and deformations of a soil mass are coupled and the water table can easily experience a rise during these events a study of the coupling process is important to increase our knowledge concerning the impact of a water level rise on the environment based on the theory of seepage and flow in porous media the theory of elasticity and the soil water characteristic curve a two dimensional hydro mechanical model for an unsaturated porous medium is developed and incorporated in the comsol multiphysics software the numerical procedure is capable of considering the influences of the soil water characteristic curve the effects of varying the boundary conditions on the coupled unsaturated infiltration and deformation equations are investigated the examples demonstrate that the coupling effects significantly influence the position of the groundwater levels the rate of change in the water table is closely related to the coupled infiltration and deformation in an unsaturated porous medium

influence of pressurized water influx on the hygro thermal behaviour of an engineered clay barrier in a waste emplacement borehole this paper presents the results of a series of experiments conducted to examine the hygro thermal behaviour of a compacted internally heated engineered clay barrier consisting of a mixture of bentonitic clay and sand compacted in a laboratory scale model simulating a waste emplacement borehole located in a granitic rock the experiments considered the supply of water at a prescribed pressure at the outer cylindrical and plane boundaries of the compacted engineered clay barrier the experiments examined the manner in which the water supply conditions influenced the extent of the moisture uptake within the compacted clay barrier the experimental results presented in this paper include contours of the time dependent variation of temperature within the granite block the time dependent variations of temperature at the midsection level of the internally placed heater and along the axis of the experimental facility and the residual volumetric moisture content distribution determined at the termination of the experiments

an international model comparison study of controlled fault activation experiments in argillaceous claystone at the mont terri laboratory abstract we present results from an international model comparison study involving a series of controlled fault activation experiments in opalinus clay at the mont terri laboratory switzerland the fault activation experiments were conducted in situ by water injection at variable pressure from boreholes targeting different parts of the main fault crossing several tunnels and galleries of the mont terri laboratory the model simulations focused on 1 an experiment activating a discontinuity fracture or minor fault within the damage zone of the main fault and 2 an experiment activating discontinuities close to the core of the main fault the experimental data consist of coupled hydraulic and mechanical responses monitored at an injection borehole and a monitoring borehole located a few meters away after overcoming several modeling issues along with necessary model developments a reasonably good agreement was achieved between the modeling results and the field observations the fault activation experiments displayed an abrupt flow rate increase associated with a sudden fracture opening and rupture propagation after the injection pressure reached above the estimated normal stress on the fracture this was followed by an abrupt flow rate decrease indicating hydraulic closing once the injection pressure decreases to an estimated 1 2 mpa below the stress normal to the opened fracture the models were able to capture this abrupt hydromechanical behavior including an observed dominant opening behavior along with the rupture propagation while the spatial extent of the shear rupture and the quantity of peak injection flow were the most challenging to predict

thermo hydro mechanical modeling of carbon dioxide injection for enhanced gas recovery co2 egr a benchmarking study for code comparison the objective of this paper was to investigate the thm coupled responses of the storage formation and caprock induced by gas production co2 egr enhanced gas recovery and co2 storage a generic 3d planer model 20 000 3 000 100 m consisting of 1 200 m overburden 100 m caprock 200 m gas reservoir and 1 500 m base rock is adopted for the simulation process using the integrated code tough2 eos7c flac3d and the multi purpose simulator opengeosys both simulators agree that the co2 egr phase under a balanced injection rate 31 500 tons year will cause almost no change in the reservoir pressure the gas recovery rate increases 1 4 in the 5 year co2 egr phase and a better egr effect could be achieved by increasing the distance between injection and production wells e g 5 83 for 5 km distance instead of 1 2 km in this study under the considered conditions there is no evidence of plastic deformation and both reservoir and caprock behave elastically at all operation stages the stress path could be predicted analytically and the results show that the isotropic and extensional stress regime will switch to the compressional stress regime when the pore pressure rises to a specific level both simulators agree regarding modification of the reservoir stress state with further co2 injection tension failure in reservoir could occur but shear failure will never happen under these conditions using tough flac a scenario case is also analyzed with the assumption that the reservoir is naturally fractured the specific analysis shows that the maximal storage pressure is 13 6 mpa which is determined by the penetration criterion of the caprock

an experimental study of the flow of gas along synthetic faults of varying orientation to the stress field implications for performance assessment of radioactive waste disposal critical stress theory states that fault transmissivity is strongly dependent upon orientation with respect to the stress tensor this paper describes an experimental study aimed at verifying critical stress theory using a bespoke angled shear rig designed to examine the relationship between gas flows along a kaolinite filled synthetic fault as a function of fault dip a total of 22 gas injection experiments were conducted on faults oriented 0 15 30 and 45 to horizontal both with and without active shear gas flow was seen to be complex repeat gas injection testing showed a consistent gas entry pressure but considerably different nonrepeatable gas peak or breakthrough pressure gas flow occurred along discrete dilatant pathways the physics governing the pressure at which these features formed was repeatable however permeability was dependent on the number distribution and geometry of the resultant pathways the nonrepeatable gas response suggests that the number of pathways was dependent on very subtle variations in gouge properties no fault orientations were seen to exhibit nonflow characteristics although critical stress theory predicted that two of the investigated fault angles should be effective seals however a small variation in gas entry pressure was seen with fault angle as a result of varying normal and shear stress acting on the gouge material shear was seen to enhance gas movement by reducing gas entry pressure and increased permeability once gas became mobile therefore in kaolinite gouge filled faults shear is not an effective self sealing mechanism to gas flow

numerical methods in rock mechanics the purpose of this civilzone review paper is to present the techniques advances problems and likely future development directions in numerical modelling for rock mechanics and rock engineering

a coupled hydro mechanical model for simulation of gas migration in host sedimentary rocks for nuclear waste repositories abstract in a deep geological repository dgr for nuclear wastes several mechanisms such as waste form degradation and corrosion could lead to gas generation the produced gas can potentially overpressurize the repository alter the hydraulic and mechanical properties of the host rock and affect the long term containment function of the natural host rock and engineered barriers thus the understanding of the gas migration within the host rock and engineered barriers and the associated potential impacts on their integrity is important for the safety assessment of a dgr in this paper a coupled hydro mechanical model for predicting and simulating the gas migration in sedimentary host rock is presented a detailed formulation coupling moisture liquid water and water vapor and gas transfer in a deformable porous medium is given the model takes into account the damage controlled fluid gas water flow as well as the coupling of hydraulic and mechanical processes e g stress deformation the model also considers the coupling of the diffusion coefficient with mechanical deformation as well as considers the modification of capillary pressure due to the variation of permeability and porosity the prediction capability of the developed model is tested against laboratory scale and in situ experiments conducted on potential host sedimentary rocks for nuclear waste disposal the model predictions are in good agreement with the experimental results the numerical simulations of the laboratory and field gas injection tests provide a better understanding of the mechanisms of gas migration and the potential effects of excessive gas pressure on the host sedimentary rocks this research work has allowed us to identify key features related to gas generation and migration that are considered important in the long term safety assessment of a dgr in sedimentary host formations

x lines in the magnetotail for southward and northward imf conditions utilizing associated observations of geotail and ace satellites from the year of 1998 to 2005 we investigated the x lines in the near earth tail under different interplanetary magnetic field imf conditions the x lines are recognized by the tailward fast flows with negative b z statistically the x lines in the tail can be observed for southward as well as northward imf but more frequently observed for southward imf a typical case on 26 april 2005 showed clear evidence that the x line can occur for northward imf while the geomagnetic activity is particularly quiet further analysis showed that the x line related solar wind has stronger e y and b z components for southward than northward imf in addition the x line related geomagnetic activities are stronger for southward than northward imf

geohydromechanical processes in the excavation damaged zone in crystalline rock rock salt and indurated and plastic clays in the context of radioactive waste disposal abstract the creation of an excavation disturbed zone edz or excavation damaged zone edz is expected around all man made openings in geologic formations macro and micro fracturing and in general a redistribution of in situ stresses and rearrangement of rock structures will occur in this zone resulting in drastic changes of permeability to flow mainly through the fractures and cracks induced by excavation the edz may have significant implications for the operation and long term performance of an underground nuclear waste repository various issues of concern need to be evaluated such as processes creating fractures in the edz the degree of permeability increase and the potential for sealing or healing with permeability reduction in the zone in recent years efforts along these lines have been made for a potential repository in four rock types crystalline rock salt indurated clay and plastic clay and these efforts have involved field laboratory and theoretical studies the present work involves a synthesis of the ideas and issues that emerged from presentations and discussions on edz in these four rock types at a cluster conference and workshop held in luxembourg in november 2003 first definitions of excavation disturbed and edzs that may be applicable to all four rock types are proposed then an approach is suggested for the synthesis and intercomparison of geohydromechanical processes in the edz for crystalline rock salt indurated clay and plastic clay comparison tables of relevant processes associated factors and modelling and testing techniques are developed a discussion of the general state of the art and outstanding issues is also presented a substantial bibliography of relevant papers on the subject is supplied at the end of the paper

ridge forces absolute plate motions and the intraplate stress field torque poles are calculated for a variety of possible forces acting on the plates including ridge push slab pull and collisional resistance these torque poles are then compared to the directions of absolute plate motions there is a strong correlation between ridge torque poles and the azimuth of absolute plate motions for the north american south american pacific cocos and eurasian plates simple slab pull torques correlate well with absolute motion azimuths for the pacific nazca and cocos plates and moderately well with the absolute motion azimuth of the indoaustralian plate collisional resistance torque poles correlate with the absolute motion azimuth of the eurasian plate only the correlations are presented as further evidence that the absolute reference frame for plate motion is determined by the surface plates themselves torque poles for various forces are also compared with several long wavelength features of the global intraplate stress field that also tend to be aligned with absolute motion directions in general ridge torque directions agree well with the orientations of maximum horizontal stresses for stable north america western europe and south america and provide an alternative explanation for the alignment in terms of ridge push forces rather than basal drag collisional resistance forces can also explain the alignment of stresses in western europe for the indoaustralian plate the torque pole for collisional resistance forces is consistent with the general pattern of stresses in at least the western half of the plate but is not a good predictor of the entire data set for the plate other processes in addition to collisional resistance must be important for the indo australian plate ridge push forces may account for a significant portion of the long wavelength features of the intraplate stress field especially away from continental collisions such a conclusion is consistent with negative buoyancy of the slab being an important component of the driving mechanism as previously suggested slab forces may be largely balanced within the subducted slab itself and thus have limited effect on deformation of the surface plates

modeling the thermal hydrologic processes in a large scale underground heater test in partially saturated fractured tuff the drift scale test dst is being conducted in an underground facility at yucca mountain nevada to probe the coupled thermal hydrological mechanical and chemical processes likely to occur in the fractured rock mass around a potential high level nuclear waste repository thermal hydrological processes in the dst have been simulated using a three dimensional numerical model the model incorporates the realistic test configuration and all available site specific measurements pertaining to the thermal and hydrological properties of the unsaturated fractured tuff of the test block the modeled predictions were compared to the extensive set of measured data collected in the first year of this 8 year long test the mean error between the predictions and measurement at 12 months of heating for over 1600 temperature sensors is about 2 degrees c heat pipe signature in the temperature data indicating two phase regions of liquid vapor counterflow is seen in both the measurements and simulated results the redistribution of moisture content in the rock mass resulting from vaporization and condensation was probed by periodic air injection testing and geophysical measurements good agreement also occurred between the model predictions and these measurements the general agreement between predictions from the numerical simulations and the measurements of the thermal test indicates that ourmore fundamental understanding of the coupled thermal hydrologic processes at yucca mountain is sound however effects of spatial heterogeneity from discrete fractures that are observed in the temperature data are not matched by simulations from the numerical model which treat the densely spaced fractures as a continuum less

thermohydromechanics of partially saturated geological media governing equations and formulation of four finite element models this paper presents the general governing equations for coupled thermohydromechanical thm processes in saturated and unsaturated geologic formations and reviews four finite element codes for modeling of such system three of the codes are developed for the special purpose of analyzing coupled thm processes in unsaturated porous and fractured geological media and the fourth is a commercial code that has been used in its standard version with a few adaptations for this specialized problem the basic assumptions and fundamental equations for coupled thm processes in unsaturated porous fractured rock are presented and formulations of the four finite element models are compared

tomography of the western united states from regional arrival times first arrival times from regional distances 200 1200 km in the western united states extracted from the international seismological centre isc data set were inverted in a tomographic study to map the laterally varying pn velocity structure of the uppermost mantle i e the mantle lid and to estimate the crustal static delay at each seismograph station synthetic data were used to evaluate resolution results correlate well with major tectonic features we find low uppermost mantle velocities v 7 9 km s these low apparent pn velocities are primarily due to the effects of isostasy hotspot volcanism and crustal extension we interpret the low apparent pn velocities beneath the sierra nevada 7 6 7 7 km s to be the result of time delays introduced by ray paths tunneling through the deep crustal root the yellowstone hotspot migrating along the snake river plain has left low velocity 7 6 7 8 km s hot upper mantle in its wake lower pn velocities 7 8 km s beneath the extensional basin and range are also presumably due to hotter uppermost mantle based on station static delays for the basin and range we infer that moho depths there do not vary significantly from 30 km normal continental pn velocities 8 0 km s as well as thicker crust 40 50 km underlying the rocky mountains wyoming basin province colorado plateau and the northern columbia plateau indicate the presence of relatively cool uppermost mantle beneath these regions

the interaction of a magnetic cloud with the earth ionospheric convection in the northern and southern hemispheres for a wide range of quasi steady interplanetary magnetic field conditions this is the second of three papers which study a large interplanetary magnetic cloud and its interaction with the earth s magnetosphere here the authors study flows within the ionosphere during the passage of the magnetic cloud on jan 13 15 1988 this is the first study of ionospheric convections during prolonged periods of stable and different imf orientations which result from the stable but spatially varying field structure within the magnetic cloud data from imp 8 and dmsp f8 are analyzed for this work this observation gave information on ionospheric responses to greater than 10 hour period of northward and southward imf with a gradual change from one to the other issues studied included strengths of peak flows for north and south imf changes in cross polar cap potential with imf b sub z types and variations of convective patterns vs imf variations in size of the polar cap etc

western u s upper mantle structure regional three dimensional inversions of upper mande p wave velocity structure are created from teleseismic p wave travel time residuals recorded by many of the high density high frequency regional arrays operated within the western united states these inversions are adjusted to a global international seismic centre reference and merged to obtain an image of the upper mantle beneath western united states the p wave velocities in the upper mantle are slow on average and the structure is very heterogeneous where resolution is good coherent upper mantle structures are imaged that extend as deep as 200 km the juan de fuca and gorda slabs which penetrate to greater depths are exceptions and deviate from the average velocity at a given depth by as much as 4 lateral resolution of these structures usually is very good although the magnitude of the actual seismic variations is probably greater than that imaged the long wavelength part of the imaged mantle structure defines coherent elongate features with wavelengths of 200 500 km within 250 km of the pacific coast these structures have a wavelength of 250 km and trend parallel to the surface physiography and young tectonic structures beneath the continental interior where use is made of additional seismic studies to infer average structure in regions of poor teleseismic data coverage structures have a wavelength of 500 km and trend northeasterly this northeast orientation is discordant with young tectonic structures but aligns with young volcanic activity

on the nature of mantle heterogeneities and discontinuities evidence from a very dense wide angle shot record abstract a seismic survey with a receiver spacing of 50 m provided one of the most densely sampled wide angle seismic reflection images of the lithosphere this unique data set recorded by an 18 km long spread reveals that at wide angles the shallow subcrustal mantle features high amplitude reflectivity which contrasts with a lack of reflectivity at latter travel times this change in the seismic signature is located at approximately 120 150 km depth which correlates with the depth estimates of the lithosphere asthenosphere boundary lab of previous dss studies this seismic signature can be simulated by two layer mantle model both layers with similar average velocities differ in their degree of heterogeneity the shallow heterogeneous layer and the deeper and more homogeneous one correlate with the lithosphere and the asthenosphere respectively studies involving surface outcrops of ultramafic massifs and mantle xenoliths infer that the upper mantle is a heterogeneous mixture of ultramafic rocks lherzolites harzburgites pyroxenites peridotites dunites and small amounts of eclogites laboratory measurements of physical properties of these mantle rocks indicate that compositional variations alone can account for the wide angle reflectivity a temperature increase would homogenize the mixture decreasing the seismic reflection properties due to melting processes it is proposed that this would take place below 120 150 km 1200 c the lab

mathematical modelling of groundwater flow at sellafield uk abstract sellafield in west cumbria was a potential site for the location of the uk s first underground repository for radioactive intermediate level waste ilw the repository was to lie around 650 m beneath the ground surface within rocks of the borrowdale volcanic group bvg a thick suite of sw dipping fractured folded and metamorphosed ordovician meta andesites and ignimbrites these are overlain by an onlapping sequence of carboniferous and permo triassic sediments in situ borehole measurements showed that upward trending fluid pressure gradients exist in the area of the potential repository site and that there are three distinct fluid types in the subsurface fresh saline and brine at depth to the west of the site simulations of fluid flow in the sellafield region were undertaken with a 2d steady state coupled fluid and heat flow simulation code oilgen in both simplified and geologically complex models topographically driven flow dominated the regional hydrogeology fluids trended persistently upwards through the potential repository site the dense brine to the west of the site promoted upward deflection of topographically driven groundwaters the inclusion in hydrogeological models of faults and variably saline sub surface fluids was essential to the accurate reproduction of regional hydraulic head variations sensitivity analyses of geological variables showed that the rate of groundwater flow through the potential repository site was dependent upon the hydraulic conductivity of the bvg and was unaffected by the hydraulic conductivity of other hydrostratigraphic units calibration of the model was achieved by matching simulated subsurface pressures to those measured in situ simulations performed with bvg hydraulic conductivity 100 times the base case median value provided the best fit comparison between the calculated equivalent freshwater head and that measured in situ regardless of the hydraulic conductivity of other hydrostratigraphic units transient mass transport simulations utilising the hydraulic conductivities of this best fit simulation showed that fluids passing through the potential repository site could reach the surface in 15 000 years simple safety case implications drawn from the results of the study showed that the measured bvg hydraulic conductivity must be less than 0 03 m year 1 to be simply declared safe recent bvg hydraulic conductivity measurements showed that the maximum bvg hydraulic conductivity is around 1000 times this safety limit

modelling groundwater flow changes due to thermal effects of radioactive waste disposal at a hypothetical repository site near sellafield uk high level radioactive waste hlw and spent fuel from nuclear power plants sf require very long duration disposal because of its long lived toxicity specific repository design is necessary to accommodate the associated large heat generation from continual decay conceptual designs propose geological containment within salt claystone or crystalline bedrock however while many studies have investigated the safety of disposal in these host rocks the interaction of near field heat coupled to far field groundwater flow for uk relevant conditions has not been fully investigated using an excellent dataset from a repository investigation in saturated fractured rock at sellafield uk with deep groundwater flow a preliminary investigation of the effect of the addition of heat from hlw and sf on regional groundwater flow is undertaken a coupled thermo hydrogeological groundwater flow model dependent on fluid density and viscosity has been calibrated to field data before heat is added to simulate waste substantial heating reduces fluid density and dynamic viscosity groundwater flows upwards through permeable damage zones of high angle faults and increases natural velocity by 1 5 elevated groundwater temperatures are predicted at the surface in just hundreds of years travel times for conservative chemical species from the hypothetical repository to the st bees sandstone aquifer are reduced by over one third if engineered barriers fail at the point of containment and remain reduced by hundreds of years for particles released thousands of years after containment the results imply that in conditions similar to those modelled the high performance guarantee of the engineered barrier is essential to repository safety a very good understanding of the coupled interaction of near field heat and far field groundwater flow will be important for safety cases especially accuracy concerning heterogeneous fault discontinuities it is necessary to model heat advection and faults at fractured sites

closing the gap between regional and global travel time tomography recent global travel time tomography studies by zhou 1996 and van der hilst et al 1997 have been performed with cell parameterizations of the order of those frequently used in regional tomography studies i e with cell sizes of 1 2 these new global models constitute a considerable improvement over previous results that were obtained with rather coarse parameterizations 5 cells the inferred structures are however of larger scale than is usually obtained in regional models and it is not clear where and if individual cells are actually resolved this study aims at resolving lateral heterogeneity on scales as small as 0 6 in the upper mantle and 1 2 3 in the lower mantle this allows for the adequate mapping of expected small scale structures induced by for example lithosphere subduction deep mantle upwellings and mid ocean ridges there are three major contributions that allow for this advancement first we employ an irregular grid of nonoverlapping cells adapted to the heterogeneous sampling of the earth s mantle by seismic waves spakman and bijwaard 1998 second we exploit the global data set of engdahl et al 1998 which is a reprocessed version of the global data set of the international seismological centre their reprocessing included hypocenter redetermination and phase reidentification finally we combine all data used p pp and pwp phases into nearly 5 million ray bundles with a limited spatial extent such that averaging over large mantle volumes is prevented while the signal to noise ratio is improved in the approximate solution of the huge inverse problem we obtain a variance reduction of 57 1 synthetic sensitivity tests indicate horizontal resolution on the scale of the smallest cells 0 6 or 1 2 in the shallow parts of subduction zones decreasing to approximately 2 3 resolution in well sampled regions in the lower mantle vertical resolution can be worse up to several hundreds of kilometers in subduction zones with rays predominantly pointing along dip important features of the solution are as follows 100 200 km thick high velocity slabs beneath all major subduction zones sometimes flattening in the transition zone and sometimes directly penetrating into the lower mantle large high velocity anomalies in the lower mantle that have been attributed to subduction of the tethys ocean and the farallon plate and low velocity anomalies continuing across the 660 km discontinuity to hotspots at the surface under iceland east africa the canary islands yellowstone and the society islands our findings corroborate that the 660 km boundary may resist but not prevent present day large scale mass transfer from upper to lower mantle or vice versa this observation confirms the results of previous global mantle studies that employed coarser parameterizations

the role of gravitational potential energy in active deformation in the southwestern united states in orogenic belts intrinsic buoyancy and extrinsic boundary forces act on the continental lithosphere determining the relative importance of these forces is fundamental to understanding the dynamics of continental deformation in the western united states estimates of gravitational potential energy show that given available constraints on rheology buoyancy forces are sufficient to produce the wide variety of rates and styles of observed deformation including absence of deformation this underscores the importance of gravitational potential energy for deformation in orogenic belts

coupled thermal hydrological mechanical analyses of the yucca mountain drift scale test comparison of field measurements to predictions of four different numerical models abstract the yucca mountain drift scale test dst is a multiyear large scale underground heating test designed to study coupled thermal hydrological mechanical chemical behavior in unsaturated fractured and welded tuff as part of the international cooperative code comparison project development of coupled models and their validation against experiments four research teams used four different numerical models to simulate and predict coupled thermal hydrological mechanical thm processes at the dst the simulated processes included heat transfer liquid and vapor water movements rock mass stress and displacement and stress induced changes in fracture permeability model predictions were evaluated by comparison to measurements of temperature water saturation displacement and air permeability the generally good agreement between simulated and measured thm data shows that adopted continuum model approaches are adequate for simulating relevant coupled thm processes at the dst moreover thermal mechanically induced rock mass deformations were reasonably well predicted using elastic models although some individual displacements appeared to be better captured using an elasto plastic model it is concluded that fracture closure opening caused by change in normal stress across fractures is the dominant mechanism for thermal stress induced changes in intrinsic fracture permeability at the dst whereas fracture shear dilation appears to be less significant this indicates that such changes in intrinsic permeability at the dst which are within one order of magnitude are likely to be mostly reversible

effects of joint surface roughness and orientational anisotropy on characteristics of excavation damage zone in jointed rocks abstract investigating the mechanical behavior of the excavation damage zone edz in jointed rocks is essential for underground openings in this numerical study the effects of joint surface roughness and orientational anisotropy on the size and shape of edz in jointed rocks were examined based on a diversion tunnel excavated in columnar jointed rocks at the baihetan hydropower station the results showed that failure zones are usually at the two ends of the tunnel roof both open and shear zones are dependent on the jrc joint roughness coefficient averages and standard deviations with increasing standard deviations of jrc the depths and areas of both open and shear zones generally increase as the jointed rocks changing from anisotropic to isotropic the shapes of edz are similar but rotate in jointed rocks under effects of water pressures larger open zones appear in the lateral tunnel walls and the depths of shear zones increase

a multisatellite study of a pseudo substorm onset in the near earth magnetotail this paper reports the multisatellite and ground observations of two pseudo substorm onset events that occurred successively at 0747 ut and 0811 ut may 30 1985 with more attention to the 0747 ut onset the distinguishing features of the 0747 ut event are as follows 1 the substorm associated tail reconfiguration started in a very localized region in the near earth magnetotail 2 the magnitude of the current disruption decreased markedly as the disruption region expanded tailward 3 on the ground the onset of a very small negative bay 40 nt was observed simultaneously with the onset of the current disruption but over a much wider local time sector than the near earth tail reconfiguration positive bay onsets at mid latitudes also had a longitudinally wide distribution from these features we infer that in the present event the current disruption took place filamentarily near ampte cce at 8 8 re it is also inferred that pseudo substorm onsets are distinguished from standard substorm onsets by the absence of a global expansion of the current disruption and that the spatial scale of the onset region in the magnetosphere is not a major difference between the two the present study suggests that the spatial distribution of the magnetic distortion before onsets is an important factor to determine the expansion scale of the current disruption it is also suggested that the current disruption is basically an internal process of the magnetosphere

numerical simulation of excavation damaged zone under coupled thermal mechanical conditions with varying mechanical parameters understanding of the formation and subsequent spatial and temporal evolution of excavation damaged zone edz under coupled thermal mechanical tm conditions is of great importance for evaluating the long term performance of underground radioactive waste repository thermal stress induced damage and temperature dependent rock parameter change are two main ways that thermal effects influence the mechanical parameters of rock under tm conditions this paper begins with formulation of a coupled thermal mechanical tm model based on elastic damage principle next the model is numerically implemented and validated against theoretical solution and some existing experimental observations finally damage zone evolution in a granite specimen under a variety of thermal and mechanical conditions is numerically simulated where the influence of elevated temperature on the rock parameters such as elastic modulus and strength is taken into account it is noted that the damage zone is dominantly controlled by the lateral pressure coefficients and the thermal effect may promote the tensile damage and restrain the shear damage in particular temperature induced parameter change is also an important way causing rock damage and the final damage pattern of rock depends on the combined loading path of elevated temperature and external loading

a case study on the influence of thm coupling on the near field safety of a spent fuel repository in sparsely fractured granite in order to demonstrate the feasibility of geological disposal of spent candu fuel in canada a safety assessment was performed for a hypothetical repository in the canadian shield the assessment shows that the maximum long term radionuclide release from such repository would meet international criteria for dose rate however uncertainties in the assumed evolution of the repository were identified such uncertainties could be resolved by the consideration of coupled thermal hydro mechanical chemical thmc processes in task a of the decovalex thmc project thm models were developed within the framework of the theory of poroelasticity such model development was performed in an iterative manner using experimental data from laboratory and field tests the models were used to perform near field simulations of the evolution of the repository in order to address the above mentioned uncertainties this paper presents the definition and rationale of task a and the results of the simulations from a repository safety point of view the simulations predict that the maximum temperature would be well below the design target of 100 c however the stress on the container can marginally exceed the design value of 15 mpa however the most important finding from the simulations is that a rock damage zone could form around the emplacement borehole such damage zone can extend a few metres from the walls of the emplacement holes with permeability values that are orders of magnitude higher than the initial values the damage zone has the potential to increase the radionuclide transport flux from the geosphere the effect of such an increase should be taken into account in the safety assessment and mitigated if necessary by the provision of sealing systems

upper mantle s velocity structure of north america we have inverted fundamental and higher mode rayleigh waveforms from 685 vertical component broadband seismograms with wave paths over north america to obtain an image of the upper mantle s velocity structure down to 660 km among the well resolved features of the new model are 1 a high velocity root beneath the north american craton which extends no deeper than 250 km except near the archean core of the craton where depths of 350 km are reached 2 a weak band of low velocity along the eastern margin of the north american craton which reaches into the transition zone 3 a low velocity slab window beneath the western united states down to a depth of 300 km 4 areas of low uppermost mantle velocity beneath the cascade volcanoes the yellowstone hotspot track the colorado plateau the sierra madre occidental and the grabens bordering the jalisco block and 5 a pronounced band of high velocities in the transition zone coinciding with the expected location of the subducted trailing fragments of the farallon plate we introduce several improvements to the method of partitioned waveform inversion which was used to compute the new model rather than to correct for an estimated depth to the mohorovicic discontinuity we leave the crustal thickness as a free though yet poorly resolved parameter in the inversion we also improve the windowing and filtering operator used to select uncontaminated waveforms

damage induced permeability changes in granite a case example at the url in canada abstract this paper concerns both in situ measurements of permeability and numerical modelling of changes in permeability induced by microcrack growth hydraulic experiments including pulse tests with the seppi probe are in progress these tests are a part of the tunnel sealing experiment tsx at the 420 m level of canada s underground research laboratory whose aim is to estimate the in situ hydraulic properties of lac du bonnet granite based on laboratory investigations the anisotropic damage model developed by homand et al comput geotech 22 1998 135 and recently reviewed by shao et al int j rock mech min sci 36 1999 1001 has been extended in order to account for changes in permeability induced by microcrack growth we have implemented this extension in the three dimensional code flac 3 d triaxial compression tests with permeability measurements carried out on two different granites provide a verification of the numerical implementation with a good agreement between experiments and predictions comparison between in situ measurements of permeability and predictions indicates that both the results of numerical modelling and observations are globally in agreement finally numerical modelling as well as the in situ measurements indicate that a depth of 50 70 cm is a good estimation of the extent of excavation disturbed zone in the tsx tunnel

can intense substorms occur under northward imf conditions 1 this paper reports on several substorms observed under northward interplanetary magnetic field imf conditions the intensity of which was at least as significant as that of typical substorms under moderately southward imf conditions such northward imf periods were identified during the recovery phase of three strong storms in the case of each storm two or more substorms occurred successively being separated by 1 8 5 h while the imf condition continued persistently northward the substorms are clearly evidenced by auroral and other complementary observations for the most intense substorms the auroral breakup occurred at the magnetic latitude of 58 and for the others it was between 60 and 65 the polar cap size prior to each onset was substantial despite the northward imf conditions the auroral expansion following each onset lasted from a few up to several magnetic local time hours and exhibited a clear poleward expansion feature for most of the events studied geosynchronous magnetic dipolarizations preceded by field stretching and or energetic particle injections occurred the occurrence of such intense substorms implies that a certain large amount of energy remains in the tail even under northward imf conditions the occurrence of two or more successive substorms further implies that even after the release of a certain amount of energy triggered by the substorm the tail can still have a substantial amount of energy left which can be released by a subsequent substorm s we conjecture that an intense substorm during a northward imf period can be expected when such a period belongs to the recovery phase of an intense storm mainly because of large energy loading done by preceding southward imf bz during the storm s main and some early recovery phase in addition we argue that substorm energy can also be supplied by other mechanisms of the solar wind magnetosphere coupling under northward imf conditions such as dayside reconnection in the presence of a substantial imf by component

path dependent regional phase travel time corrections for the international monitoring system in north america the software developed for the comprehensive nuclear test ban treaty ctbt international data centre idc in vienna austria uses the iaspei91 seismic travel time tables as default however in reality travel times as a function of source location are different for each station especially at regional distances this is not modeled by a global one dimensional model such as iaspei91 the software therefore allows the application of a suite of travel time corrections for improved travel time prediction and consequently more accurate hypocentral locations to account for path dependency we have developed gridded source specific station corrections ssscs for pn sn pg and lg phases for 22 international monitoring system ims stations in north america in deriving the ssscs and associated modeling errors we used a methodology that had been successfully applied previously for fennoscandia we first compiled regionalized one dimensional travel times for north america then we assigned travel times as weighted sums of the travel times in each region to calculate ssscs validation testing of the ssscs was conducted using two separate sets of north american ground truth gt events with location accuracies within 10 km gt0 gt10 these events were recorded at ims stations between 1995 and 1999 and distributed throughout north america test event location results with ssscs applied show reductions in both mislocations and error ellipses for gt events with location accuracies better than 2 km the median change in location was a 5 km improvement and the median area of the 90th percentile error ellipses was reduced from 2550 km 2 to 910 km 2 using ssscs for both data sets the median improvement is less than 5 km the testing emphasized that gt events with accuracies 5 km or better are crucial for validating ssscs using ssscs for all 51 gt0 gt10 events used in the validation testing the median area of the error ellipses was reduced to less than 1000 km 2 and the error ellipse reductions were achieved without significant degradation of coverage the modeling errors used in this study may be somewhat underestimated however leaving the target goal of error ellipses less than 1000 km 2 still somewhat in question we expect the ssscs event locations and uncertainties can be improved by future refinement of travel times and modeling errors these corrections were implemented in the operational prototype idc system located in arlington virginia in march 2000 and have been delivered to the vienna idc in january 2001

early miocene continental extension related basaltic magmatism at walton peak northwest colorado further evidence on continental basalt genesis the walton peak lavas erupted directly onto c 1 8 ga basement and were interbedded with subaerial sediments four new k ar dates for the lavas average 22 8 0 3 ma associating them unambiguously with the earliest large scale extension related magmatism in nw colorado the lavas are basalts trachybasalts and shoshonites there is also one 100 m thick composite flow of trachydacite containing pillow like basic masses up to tens of metres in size with chilled margins elemental data and sr and nd isotopic ratios suggest that the trachydacite evolved from the basalt type forming most of the pillows by a combination of fractional crystallization and crustal assimilation nevertheless post evolution magma mixing during and immediately before extrusion of the flow has obscured the details of this process a proportion of the pillow like basic masses in the composite flow are shoshonites that did not take part in the magma mixing they are relatively rich in incompatible minor and trace elements e g nb 41 46 ppm in the shoshonites and 20 25 ppm in all other walton peak basic lavas the sr and nd isotopic ratios of the nb rich and nb poor compositions overlap open system processes in a long lived pre existing magma chamber are considered unlikely to be the main cause of the diverse basic magmas because the walton peak lavas directly overlie precambrian basement likewise crustal contamination models using either upper or lower crustal rock types of this region do not give satisfactory mechanisms to relate the nb rich and nb poor mafic liquids a genetic model invoking variable degrees of partial melting of lithospheric mantle containing hydrous minerals does not explain why the nb rich and nb poor compositions are bimodal and not a range a variety of sparse ultrapotassic magmas minettes to lamproites accompanied the basalt dominated neogene volcanism of nw colorado and surrounding area their elemental and isotopic compositions support the view that the ultrapotassic liquids originated by fusion of hydrous and halogen rich metasomatized zones within the subcontinental lithospheric mantle addition of about 15 of lamproitic melt to the low nb walton peak basic magmas reproduces the main geochemical and isotopic characteristics of the high nb magmas such a process seems to have been widespread throughout nw colorado neogene igneous activity although wholly lithospheric mantle sources for all the mafic magmas cannot be ruled out there is evidence that both subduction related calcalkaline and ocean island basanitic melts of asthenospheric origin formed the dominant components of the nw colorado volcanics addition of as little as 10 of lamproitic melt during their uprise through the subcontinental lithospheric mantle was sufficient to imprint on them continental incompatible element and radiogenic isotope characteristics

on the poleward boundary of the nightside auroral oval under northward interplanetary magnetic field conditions 1 in this paper we examined the dependence of the poleward boundary of the nightside auroral oval on interplanetary magnetic field imf conditions in particular we performed the study for periods after the imf bz becomes northward at or some time during the recovery phase of major storms for the selected periods we used the precipitating particle energy flux observed by the defense meteorological satellite program satellites to determine the poleward boundary of the nightside oval the following results were obtained 1 we confirmed the expected result that under a more strongly northward imf bz the poleward boundary of the nightside oval tends to be located more poleward implying a smaller polar cap 2 however it tends to take a very long time after the imf bz turns northward for the polar cap size to substantially reduce e g 15 h or longer for a poleward movement by 5 this is likely because the magnetosphere during the selected northward imf periods was still under the substantial influence of the preceding southward imf conditions associated with the storm s main phase and also because a finite imf by can support dayside reconnection to sustain an open polar cap region of substantial size 3 we found that for a given sign of the imf by the poleward boundary of the nightside oval is asymmetric between premidnight and postmidnight regions in a given hemisphere and between hemispheres at a given magnetic local time region for example for a positive imf by the northern southern hemispheric oval boundary is more poleward equatorward in the premidnight region and the situation is opposite in the postmidnight region and for a negative imf by we suggest a possible reason that may be responsible for the asymmetry 4 a similar in an opposite sense asymmetric feature can be seen with the imf bx but only when the imf happens to be of a parker spiral angle type we conclude that the magnetosphere during the recovery phase of major storms likely remains open even after the imf turns northward and the polar cap field lines are still connected to the imf the role of the finite imf by is prominent in determining both the size and shape of the polar cap which can affect details of the dynamical evolution during the storm recovery phase

on the impact of temperatures up to 200 c in clay repositories with bentonite engineer barrier systems a study with coupled thermal hydrological chemical and mechanical modeling abstract one of the most important design variables for a geological nuclear waste repository is the temperature limit up to which the engineered barrier system ebs and the natural geologic environment can be exposed up to now almost all design concepts that involve bentonite backfilled emplacement tunnels have chosen a maximum allowable temperature of about 100 c such a choice is largely based on the consideration that in clay based materials illitization and the associated mechanical changes in the bentonite and perhaps the clay host rock could affect the barrier attributes of the ebs however existing experimental and modeling studies on the occurrence of illitization and related performance impacts are not conclusive in part because the relevant couplings between the thermal hydrological chemical and mechanical thmc processes have not been fully represented in the models this paper presents a fully coupled thmc simulation of a nuclear waste repository in a clay formation with a bentonite backfilled ebs for 1000 years two scenarios were simulated for comparison a case in which the temperature in the bentonite near the waste canister can reach about 200 c and a case in which the temperature in the bentonite near the waste canister peaks at about 100 c the model simulations demonstrate some degree of illitization in both the bentonite buffer and the surrounding clay formation other chemical alterations include the dissolution of k feldspar and calcite and precipitation of quartz chlorite and kaolinite in general illitization in the bentonite and the clay formation is enhanced at higher temperature however the quantity of illitization is affected by many chemical factors and therefore varies a great deal the most important chemical factors are the concentration of k in the pore water as well as the abundance and dissolution rate of k feldspar less important ones are the concentration of sodium and the quartz precipitation rate in our modeling scenarios the calculated decrease in smectite volume fraction in bentonite ranges from 1 to 8 of the initial volume fraction of smectite in the 100 c scenario and 1 27 in the 200 c scenario chemical changes in the 200 c scenario could also lead to a reduction in swelling stress up to 15 18 whereas those in the 100 c scenario result in about 14 15 reduction in swelling stress for the base case scenario model results also show that the 200 c scenario results in a much higher total stress than the 100 c scenario mostly due to thermal pressurization while cautions should be taken regarding the model results due to some limitations in the models the modeling work is illustrative in light of the relative importance of different processes occurring in ebs bentonite and clay formation at higher than 100 c conditions and could be of greater use when site specific data are available

the febex benchmark test case definition and comparison of modelling approaches abstract the febex full scale engineered barriers experiment in crystalline host rock in situ test was installed at the grimsel test site underground laboratory switzerland and is a near to real scale simulation of the spanish reference concept of deep geological storage in crystalline host rock a modelling exercise aimed at predicting field behaviour was divided in three parts in part a predictions for both the total water inflow to the tunnel as well as the water pressure changes induced by the boring of the tunnel were required in part b predictions for local field variables such as temperature relative humidity stresses and displacements at selected points in the bentonite barrier and global variables such as the total input power to the heaters were required in part c predictions for temperature stresses water pressures and displacements in selected points of the host rock were required ten modelling teams from europe north america and japan were involved in the analysis of the test differences among approaches may be found in the constitutive models used in the simplifications made to the balance equations and in the geometric symmetries considered several aspects are addressed in the paper the basic thm physical phenomena which dominate the test response are discussed a comparison of different modelling results with actual measurements is presented and a discussion is given to explain the performance of the various predictions

successive substorm expansions during a period of prolonged northward interplanetary magnetic field 1 we have studied successive substorm expansions that occurred in spite of a period of prolonged northward interplanetary magnetic field imf after the northward imf persisted for almost 19 h a series of 11 very weak to moderate substorm expansions occurred during the following 6 h interval of northward imf on 19 january 1998 separated from each other by a few tens of minutes most of these substorm expansions did not accompany significant changes of the solar wind and the imf as for typical substorms that occur under southward imf conditions spacecraft and ground based instruments observed auroral breakups and enhancements of the westward auroral electrojet and large scale convection in the ionosphere together with plasmoids and dipolarizations in the magnetotail in association with the substorm expansion onsets these signatures suggest that the mechanism of substorm expansion onsets is the same as for typical substorms even under prolonged northward imf conditions we suggest that the large imf by affects large scale convection and energy accumulation in the magnetotail and that the enhanced convection due to the large imf by effect and substorm expansions can be an important factor for the promotion of succeeding substorm expansion onsets

characterising and modelling the excavation damaged zone in crystalline rock in the context of radioactive waste disposal this paper describes current knowledge about the nature of and potential for thermo hydro mechanical chemical modelling of the excavation damaged zone edz around the excavations for an underground radioactive waste repository in the first part of the paper the disturbances associated with excavation are explained together with reviews of workshops that have been held on the subject in the second part of the paper the results of a decovalex demonstration of coupled models and their validation against experiment research funded by an international consortium of radioactive waste regulators and implementers http www decovalex com research programme on modelling the edz are presented four research teams used four different models to simulate the complete stress strain curve for avro granite from the swedish aspo hard rock laboratory subsequent research extended the work to computer simulation of the evolution of the repository using a wall block model and a near field model this included assessing the evolution of stress failure and permeability and time dependent effects during repository evolution as discussed all the computer models are well suited to sensitivity studies for evaluating the influence of their respective supporting parameters on the complete stress strain curve for rock and for modelling the edz

thermohydromechanical modelling of the buffer container experiment abstract in order to investigate how heat affects the performance of a dense bentonite sand buffer material a full scale in situ experiment the buffer container experiment bce was conducted by atomic energy of canada limited aecl in the bce an electric heater simulating the heat output of a disposal container of used fuel was installed vertically in a 1 24 m diameter by 5 m deep borehole surrounded by bentonite sand buffer the borehole was drilled in the floor of a room excavated in canadian shield granite on the 240 level of aecl s underground research laboratory url the thermal hydraulic and mechanical responses were monitored in the bentonite sand buffer and in the surrounding rock power was provided to the heater for approximately 896 days in order to get a better understanding of the coupled thermohydromechanical t h m process in the bce numerical simulations were conducted using code bright to model the evolution of the temperature thermally induced pore water pressure and mechanical response in the bentonite sand buffer and the surrounding rock the thermal response in the experiment was successfully modelled the simulated water seepage from the rock to the borehole was compared with measured results for the bce the thermally induced moisture movement in the buffer was also reasonably well simulated the comparison of the simulated pore water pressure in the rock with the measurement indicates that the influence of temperatures on the hydraulic parameters of rock should be further studied the modelled vertical displacements in the rock are also compared with the measured data in the bce and the analysis of the rock displacement suggested that the in situ thermal expansion coefficient of the rock could be much higher than the coefficient determined in the laboratory

coupled thermo hydro mechanical analysis of a heater test in fractured rock and bentonite at kamaishi mine comparison of field results to predictions of four finite element codes four computer codes were applied for a prediction of coupled thermo hydro mechanical responses during an in situ heater experiment which simulates a nuclear waste deposition hole with a waste over

fractured rock hydromechanics from borehole testing to solute transport and co2 storage the paper was prepared with partial support of the us department of energy under contract no de ac02 05ch11231 with the lawrence berkeley national laboratory

modelling the mont terri he d experiment for the thermal hydraulic mechanical response of a bedded argillaceous formation to heating coupled thermal hydrological mechanical thm processes in the near field of deep geological repositories can influence several safety features of the engineered and geological barriers among those features are the possibility of damage in the host rock the time for re saturation of the bentonite and the perturbations in the hydraulic regime in both the rock and engineered seals within the international cooperative code validation project decovalex 2015 eight research teams developed models to simulate an in situ heater experiment called he d in opalinus clay at the mont terri underground research laboratory in switzerland the models were developed from the theory of poroelasticity in order to simulate the coupled thm processes that prevailed during the experiment and thereby to characterize the in situ thm properties of opalinus clay the modelling results for the evolution of temperature pore water pressure and deformation at different points are consistent among the research teams and compare favourably with the experimental data in terms of trends and absolute values the models were able to reproduce the main physical processes of the experiment in particular most teams simulated temperature and thermally induced pore water pressure well including spatial variations caused by inherent anisotropy due to bedding

characteristics of deep groundwater flow in a basin marginal setting at sellafield northwest england 36cl and halide evidence abstract a number of chemical and physical processes inside and outside a sedimentary basin e g evaporite dissolution and topographic drive respectively affect groundwater flow near the basin s margin contrasting formations at the margin typically basinal sedimentary rocks and basement are host to the interplay between these processes so that groundwater flows and compositions change within a relatively small volume to interpret how groundwater flow and geochemistry have evolved interactions between these processes must be understood such interactions were investigated near the margin of the east irish sea basin in nw england by sampling deep groundwaters to 1500 m below sea level from ordovician volcanic basement rocks and carboniferous to triassic sedimentary cover rocks variable br cl ratios and cl concentrations in deep saline waters and brines indicate mixing patterns variations in 36 cl cl constrain the timing of mixing relatively low br cl ratios ca 1 10 3 by mass characterise brine from the western sedimentary cover and reflect halite dissolution further west saline water with relatively high br cl ratios ca 2 10 3 by mass of uncertain origin occupies the eastern basement these two waters mix across the area however mixing alone cannot explain variable 36 cl cl ratios which partly reflect differing in situ 36 cl production rates in different rock formations most 36 cl cl ratios in groundwater sampled from the eastern metavolcanic basement mean 25 10 15 and western sedimentary cover mean 10 10 15 are at or close to equilibrium with in situ 36 cl production these variations in 36 cl cl across the site possibly took 1 5 ma to be attained implying that deep groundwater flow responded only slowly to the quaternary glaciation of the site interplay between varied processes in basin marginal settings does not necessarily imply flow instability

intraplate earthquakes and a seismically defined lateral transition in the upper mantle we show that the lateral transition in the upper mantle between the cratonic central eastern and the tectonically active western regions of north america is narrow and deep reaching by travel time analysis of early rise explosion seismic data a concentration of enigmatic intraplate earthquakes coincides with the transition differential potential energy from density changes across the transition may generate a high compressional stress level which locally exceeds the shear strength of the lithosphere the resultant deformation is ductile in most parts of the lithosphere but in the brittle upper crust it explains the enigmatic intraplate earthquakes around the lateral transition in the upper mantle

a comparative simulation study of coupled thm processes and their effect on fractured rock permeability around nuclear waste repositories this paper presents an international multiple code simulation study of coupled thermal hydrological and mechanical thm processes and their effect on permeability and fluid flow in fractured rock around heated underground nuclear waste emplacement drifts simulations were conducted considering two types of repository settings 1 open emplacement drifts in relatively shallow unsaturated volcanic rock and 2 backfilled emplacement drifts in deeper saturated crystalline rock the results showed that for the two assumed repository settings the dominant mechanism of changes in rock permeability was thermal mechanically induced closure reduced aperture of vertical fractures caused by thermal stress resulting from repository wide heating of the rock mass the magnitude of thermal mechanically induced changes in permeability was more substantial in the case of an emplacement drift located in a relatively shallow low stress environment where the rock is more compliant allowing more substantial fracture closure during thermal stressing however in both of the assumed repository settings in this study the thermal mechanically induced changes in permeability caused relatively small changes in the flow field with most changes occurring in the vicinity of the emplacement drifts

why is it downhill from tonopah to las vegas a case for mantle plume support of the high northern basin and range a major abrupt southward decline in elevation 800 m with an accompanying increase in bouguer gravity anomaly 80 mgal crosses a seismically active region of southern nevada at about 37 n the steepness of the gravity gradient requires significant crustal density contrast some of which is probably caused by the plutonic roots of voluminous tertiary volcanism to the north but the amplitude of the anomaly requires additional contrast within the mantle the topographic step probably developed in mid miocene time coincident with the arrival of the starting head of the yellowstone thermal plume at the base of the lithosphere a plausible combination of crustal and deep buoyancy sources related to the heat and melt input of an anomalously hot asthenospheric source is consistent with gravity seismic heat flow and isotopic observations and explains the origin of the topographic step

migration of radionuclides from a high level radioactive waste repository in deep geological formations the paper presents the development of an analytical model to estimate the migration of radionuclides through a single fracture with right circular cylinder geometry from a high level radioactive waste repository in deep geological structures the processes considered are advection dispersion surface sorption and radioactive decay for transport in the fracture diffusive loss to the host rock radial diffusion adsorption and radioactive decay for transport in the host rock the model is applied to a typical case of high level radioactive waste repository in deep geological rock formations the concentrations showed an increasing trend with increasing dispersion in fracture or reducing dispersion in the host rock or reducing porosity it is shown that the models which do not consider the dispersion of radionuclides within the fracture underestimate the radionuclide concentrations in the fracture water also the effect of dispersion reduces with increase in fracture water velocity the concentration of radionuclides in the fracture water in general increases with increase in fracture radius until a critical radius is reached the model development is targeted for the performance assessment of high level radioactive waste repositories

coupled thermal hydraulic mechanical phenomena in saturated fractured porous rocks numerical approach the fundamentals of the theory of consolidation and thermoelasticity are recast into the formulation of a phenomenon called thermohydroelasticity subsequently a variational principle and galerkin formulation are combined with the finite element method to develop a new technique to investigate coupled thermal hydraulic mechanical behavior of liquid saturated fractured porous rocks a code to code verification of the method is performed finally the environment of a heater emplaced in hard rock is simulated the effects of the coupled thermal stresses in the fractured rock are evident from the dramatic reduction of permeability due to the deformation of the fractures these results can improve the understanding of observations and displacement measurements made in the in situ experiments at the stripa mine in sweden 46 references

excavation induced damage studies at the underground research laboratory the underground research laboratory url is situated in the lac du bonnet granite batholith in southeastern manitoba canada the url was developed to study issues related to the deep geologic disposal of used fuel from nuclear reactors and has developed into an international atomic energy agency recognized geotechnical center of excellence extensive rock mechanics research has been conducted including work to understand the character and extent of excavation damage experience at the url has shown that damage exists around underground openings and that the damage develops from the energy imparted to the rock by the excavation method and by redistribution of the in situ stress field around the excavated openings subsequent near by excavations removal of loose material from the existing tunnel thermal loads and pore pressure changes will all influence the development and extent of rock damage as does the rock type and its fabric studies at the url have shown that in highly stressed rock damage will develop around underground openings even when a low energy excavation method is used and that properly designing the excavation geometry and orientation plays a major role in constructing stable openings two zones of excavation affected rock have been shown to exist from studies at the url 1 a zone of irreversibly damaged rock surrounding the excavation which may include failed zones inner and outer damage zones and 2 a zone of excavation disturbance where the in situ stresses are influence by the excavation no damage is measurable measurements of the properties of the damaged rock ultrasonic velocity transmissivity using a variety of instruments have shown that a less intensively damaged outer zone surrounds a more highly damaged inner zone the inner damage zone may have zones of failed rock depending on stress concentrations relative to rock strength and damage imparted by excavation method the inner damage zone is attributed to the effects of the excavation method and stress redistribution and the outer damage zone is attributed to the effects of stress redistribution alone in lower stressed rock the extent of the outer zone is much less than for an opening in highly stressed rock with the same excavation shape and orientation relative to in situ stresses the excavation disturbed zone describes the volume of rock surrounding the damage zone where the stress redistribution is too small to permanently change rock properties unless some other stress increase such as thermal loading is added and it is also characterized non permanent but potentially long term changes in hydraulic head