thermal mechanical and chemical influences on the performance of optical fibres for distributed temperature sensing in a hot geothermal well structural well bore integrity is an important issue for sustainable provision of geothermal energy raman scattering based fibre optic distributed temperature sensing dts can help to monitor the status of a well and therefore help to optimize expensive work over activities this study reports on the installation of a fibre optic cable in the cemented annulus behind the anchor casing in the high temperature geothermal well he 53 hellishei i geothermal field sw iceland although the cable has been damaged during the installation temperature data could be acquired during the entire length of installation down to 261 3 m temperature measurements were performed during the installation in spring 2009 during the onset of a flow test in summer 2009 and after a 8 5 month shut in period in summer 2010 during the flow test maximum temperatures of 230 c were measured after 2 weeks fluid production using optical time domain reflectometry otdr attenuation measurements at 850 and 1 300 nm enabled to identify mechanical thermal and chemical degradation along the optical fibre the observed degradation led to erroneous temperature readings and limits due to the optical budget of the dts system the accessible length of the fibre the characteristics and the influence of the different degradation mechanisms on the accuracy of the dts measurements are discussed and recommendations for an optimized installation are given

one dimensional compression and consolidation of shales abstract this paper presents a comprehensive methodology for analysing the compression and consolidation behaviour of shales an apparatus was designed to perform oedometric high pressure tests by applying a maximum vertical total stress of 100 mpa and simultaneously controlling the pore water pressure of the specimen an analytical method was formulated to analyse the shale consolidation behaviour which allows information to be gathered on the coefficient of consolidation stiffness poroelastic properties secondary compression and permeability of the tested material as a function of the applied stress conditions results obtained on opalinus clay shale using the developed methodology are presented and discussed

mantle convection with a brittle lithosphere thoughts on the global tectonic styles of the earth and venus summary plates are an integral part of the convection system in the fluid mantle but plate boundaries are the product of brittle faulting and plate motions are strongly influenced by the existence of such faults the conditions for plate tectonics are studied by considering brittle behaviour using byerlee s law to limit the maximum stress in the lithosphere in a mantle convection model with temperature dependent viscosity when the yield stress is high convection is confined below a thick stagnant lithosphere at low yield stress brittle deformation mobilizes the lithosphere which becomes a part of the overall circulation surface deformation occurs in localized regions close to upwellings and downwellings in the system at intermediate levels of the yield stress there is a cycling between these two states thick lithosphere episodically mobilizes and collapses into the interior before reforming the mobile lid regime resembles convection of a fluid with temperature dependent viscosity and the boundary layer scalings are found to be analogous this regime has a well defined nusselt number rayleigh number relationship which is in good agreement with scaling theory the surface velocity is nearly independent of the yield stress indicating that the plate motion is resisted by viscous stresses in the mantle analysis suggests that mobilization of the earth s lithosphere can occur if the friction coeycient in the lithosphere is less than 0 03 0 13 lower than laboratory values but consistent with seismic field studies on venus the friction coeycient may be high as a result of the dry conditions and brittle mobilization of the lithosphere would then be episodic and catastrophic

mechanical properties of a carbonate sand from a dredged hydraulic fill this paper focuses on the properties of a crushable uncemented carbonate sand retrieved from an artificial island to be used for petroleum production offshore of the united arab emirates the sa

3m analytical method evaluation of shaft friction of bored piles in sands abstractthis study presents 3m an analytical method to estimate the skin friction of bored piles in sands it is based on the fundamental mechanic behavior of sands and keeps track of the major mechanisms occurring in the soil close to the pile during loading these include the development of a shear band its potential expansion as induced by soil dilatancy and the ensuing increment of horizontal stresses owing to the restraining effect of surrounding soils the resulting analytical equations are easy to apply and insert in a worksheet the procedure to evaluate the shear band expansion is calibrated against results of direct shear tests at constant normal load whereas the increment of horizontal stresses is evaluated by the closed form solution for the expansion of a cylindrical cavity into a dilatant elastic perfectly plastic medium the effectiveness of the 3m method in predicting shaft friction has been checked against numerical results centrifuge and full scale pile load tests nevertheless pr

discussion of test fill on soft plastic marine clay at onsoy norway 1 the comprehensive technical article by berre 2014 on the plastic marine clay at onsoy norway merits further examination we attempted to determine c cc for onsoy clay using the cc and c values in table 1 the computed values of c cc based on tests oed 1x to oed 4x were however dissimilar and some of the values of c cc for example for test oed 4x do not seem reasonable fortunately the author has carefully defined the cc and c values that are listed in table 1 it turns out according to the list of symbols that the compression index cc has been calculated for the steepest part of the a versus a plot above pc on the other hand the values of a at which c wasmeasured are clearly shown on figs 20 to 23 for computing c cc for any soil c and cc must be defined at the same consolidation pressure e g a or v mesri and godlewski 1977 mesri and castro 1987 it is readily possible to determine from figs 20 to 23 the values of tangent cc 1 eo where eo is the initial or preconstruction void ratio at consolidation pressures at which secondary compression was allowed to determine c note that the values of eo ei are also listed in table 1 the values of cc determined from figs 20 to 23 together with the corresponding values of c from table 1 are listed in table d1 the computed values of c cc for the four oedometer tests data are nearly identical and the average c cc for onsoy marine clay is near the most representative value of 0 04 for inorganic soft clays terzaghi et al 1996 table 16 1 p 110 berre 2014 reports a ko value for onsoy plastic clay equal to 0 60 determined by hydraulic fracturing tests in the field it is interesting to compare the ko value of 0 60 by hydraulic fracture with the values of ko computed by the empirical equations proposed by mesri and hayat 1993 for ko of soft clay deposits

role of the lithosphere in mantle convection plate geometry and kinematics generally reflect the mechanical properties of the solid lithosphere rather than those of the fluid mantle underneath and plate formation and subduction account for most of the heat transport from the earth s interior correspondingly mantle convection models must incorporate a stiff but mobile boundary layer like the lithosphere before they can reproduce the main features of mantle convection a relatively easy way to accomplish this in numerical models is to combine a temperature dependent viscosity with an imposed piecewise constant surface velocity boundary condition it is shown how surface heat flux topography gravity and geoid but not plate velocities or stresses can then be derived numerical models confirm that a lithosphere has a first order effect on the underlying flow structure for internally heated models approx imating the case of whole mantle convection the calculated surface signatures are in first order agreement with observations a level of empirical success which hitherto has not been approached by models of mantle convection companion papers exploit the observations more fully to constrain the main features of mantle convection

interaction of rising and sinking mantle plumes the frequency of plume formation in fully developed thermal convection is determined experimentally because the fluid has a temperature dependent viscosity the cold and hot thermal boundary layers have different thicknesses and viscosities as a result plumes are released from these layers with different frequencies there also appears to be a direct temporal interaction between the cold and hot boundary layers in particular whereas there is a single frequency for cold plume formation hot plumes form with multiple frequencies one of which is similar to the frequency of cold plumes the measurements thus suggest that cold sinking plumes may induce hot rising plumes

engineering properties of fibrous peats this state of the art paper presents an interpretation of the permeability compressibility and shear strength of fibrous peats using data from laboratory tests on undisturbed block samples of two fibrous peats as well as extensive laboratory and field data from the literature on fibrous peat deposits engineering properties of fibrous peats are significantly different from those of most inorganic soils however the same fundamental mechanisms and factors determine behavior of both inorganic soils and fibrous peats fibrous peat deposits possess very high initial permeability typically 1 000 times the initial permeability of soft clay and silt deposits upon compression the permeability of fibrous peats decreases dramatically with a ratio of permeability change index to in situ void ratio equal to 0 25 as compared to 0 50 for soft clay and silt deposits fibrous peats display extreme compressibility to the increase in effective vertical stress with compression index values right after preconsolidation pressure 5 to 20 times the corresponding compressibility of typical soft clay and silt deposits among geotechnical materials fibrous peats display the highest ratios of secondary compression index to compression index in the range of 0 05 to 0 07 the values of coefficient of earth pressure at rest for normally consolidated young fibrous peat deposits are in the range of 0 30 to 0 35 as compared to 0 45 to 0 65 for inorganic soils the values of friction angle from triaxial compression tests for fibrous peats are in the range of 40 to 60 as compared to less than 35 for soft clay and silt compositions for fibrous peats the ratios of undrained shear strength in compression to preconsolidation pressure are usually in the range of 0 50 to 0 75 as compared to 0 32 for soft clay and silt deposits for surficial fibrous peat deposits the ratio of vane shear strength to preconsolidation pressure is near 1 0 as compared to 0 12 to 0 35 for inorganic soft clay and silt deposits for fibrous peats the ratio of undrained young s modulus to undrained shear strength is in the range of 20 to 80

estimating horizontal stresses for mudrocks under one dimensional compression abstract we examine horizontal stresses in mudrocks for the case of one dimensional mechanical compression through laboratory measurements of the horizontal to vertical effective stress ratio i e k 0 previous empirical relationships which predict horizontal stresses as a function of depth or overburden stress are site specific and cannot easily be generalized the k 0 values of various resedimented mudrocks from a diverse range of geologic origins have been investigated for effective stresses ranging from 0 1 to 100 mpa the value of k 0 during normal compression k 0nc varies systematically as a function of both stress level and mudrock composition k 0nc generally increases with stress level and values as high as 0 90 have been measured at effective stresses approaching 100 mpa this finding implies that high horizontal stresses can develop at depth solely due to normal mechanical compression and that tectonic stresses creep or geologic unloading are not necessary correlations have been developed which allow k 0nc to be estimated from a mudrock s liquid limit an easily and inexpensively measured property which reflects both the quantity and type of clay minerals present in a mudrock high liquid limit smectite rich mudrocks display a more rapid increase in k 0nc with increasing stress compared to more silty low liquid limit mudrocks k 0 measurements made on laboratory resedimented specimens compare well with measurements made on intact core samples as well as in situ tests tests carried out to examine k 0 for overconsolidated materials show that k 0 during unloading can be well approximated by a power law function originally proposed by schmidt 1966 an original equation is proposed to describe k 0 during reloading our experimental results reveal sediment behavior at high stress levels that has not been previously observed and provide useful information on how horizontal stresses evolve within basins

normally loaded inclined strip anchors in cohesionless soil plate anchors are among the most effective anchorage systems that are widely used to resist horizontal and inclined uplift loads in many offshore and onshore applications previous research on plat

mechanical properties of two expansive clay soils from sudan the mechanical responses of two highly expansive plastic alluvial soils from sudan are reported when wetted from their in situ state such soils frequently lead to damage of civil engineering structures disturbed samples of a black cotton clay and a more plastic red clay were collected from two locations in the vicinity of khartoum intrinsic properties were established from reconstituted samples using oedometer and triaxial apparatus natural undisturbed block samples of the black cotton clay were obtained and tested in an unsaturated state as found in situ basic characteristics of both soils are presented detailed information on the intrinsic properties of both clay soils was established and found to conform with burland s earlier published framework shear planes formed during shearing in almost all triaxial samples and strengths reduced to post rupture values k0 consolidated reconstituted samples exhibited a more brittle response to undrained shearing compared with isotropically consolidated sam

discussion of cyclic tests on high quality undisturbed block samples of soft marine norwegian clay the article by wichtmann et al 2013 presents a comprehensive set of laboratory test data on the cyclic undrained shear strength of soft marine norwegian onsoy clay the tests were performed on specimen quality designation sqd b specimens andresen and kolstad 1979 terzaghi et al 1996 cut from block samples taken by the sherbrooke sampler lefebvre and poulin 1979 this article is a valuable contribution because compared to data and interpretation for sands undrained cyclic strength data for soft clays are rare e g andersen and lauritzen 1988 andersen et al 1988 furthermore the previous norwegian geotechnical institute ngi tests on soft marine norwegian drammen clay were performed on specimens consolidated to the compression range beyond the pre consolidation pressure p whereas the tests on onsoy clay have been performed using high quality specimens subjected to the in situ effective stress condition ho vo before undrained shear a meaningful impression of undrained shear strength behavior of soft clay deposits is obtained by normalizing undrained shear strength with respect to pre consolidation pressure as both su and p represent points on the yield envelope skempton 1948 mesri 1975 mesri and huvaj 2007 the cyclic undrained shear strengths of sands have been commonly normalized with respect to effective overburden pressure vo because it is not readily possible to determine pre consolidation pressure of sand deposits this discussion concerns cyclic triaxial shear data on specimens cut from samples taken in the depth range of 10 50 to 11 37 m and consolidated before undrained shear to the in situ effective stress condition the onsoy clay samples had a pore water salt content of 32 5 g l natural water content of 63 to 65 liquid limit of 63 and plasticity index of 33 to 34 lunne et al 2006 at the depth range of the samples the end of primary eop pre consolidation pressure p corresponds to p vo 1 4 note that i reduced values of p from the constant rate of strain crs tests by a factor of 0 912 because the imposed strain rates i in the ngi tests were about 10 times the eop strain rate p mesri et al 1994 the in situ values of ko ho vo can be determined according to the following empirical equations mesri and hayat 1993

in situ evaluation of k0 in eastern canada clays an approximate value of the horizontal effective stress in an overconsolidated clay deposit is often determined from an estimate of the effective stress ratio k0 using the equation it is also generally considered that the parameter is approximately equal to sin for evaluating k0 in sensitive clays of eastern canada a testing program has been initiated on three different sites representing a large range of overconsolidation ratios three different in situ devices were used the cambridge self boring pressuremeter the flat dilatometer and hydraulic fracturing the results show that the different techniques give essentially the same k0 values they also give k0 values larger than those expected with an parameter typically between 0 75 and 1 15 key words clay dilatometer horizontal stress hydraulic fracturing in situ tests self boring pressuremeter

plate motions and the viscosity structure of the mantle insights from numerical modelling abstract the viscosity structure of the earth s mantle is likely to play an important role with respect to the motion of the lithospheric plates a zone of low viscosity in the upper mantle as postulated by seismological studies and also by investigations of postglacial uplift has been proposed to facilitate plate motion another inferred feature of the viscosity profile in the mantle is a significant increase at greater depth we have employed a three dimensional mantle convection model to explore the relation between the appearance of plate motion and the viscosity structure of the mantle beneath the model allows for a complex fluid rheology strong temperature pressure and stress dependence of the viscosity and can so account for the self consistent formation of plates at the surface of the convecting mantle plate like motion appears only in a limited parameter range and we demonstrate that this appearance is closely linked to a specific viscosity structure the viscosity is characterized by a local minimum at shallow depth low viscosity zone and by a local maximum at greater depth self consistent plate motion is only observed if such a viscosity structure exists in order to determine the functional relationship between the viscosity structure and plate motion we also employ an approach in which a certain viscosity profile is prescribed these studies again reveal the importance of the local extrema in the viscosity profile taking into account an increased interior viscosity also obtained by the pressure dependence we find stable plate motion as a general result we observe that the balance of the temperature and stress dependence of the viscosity is necessary to obtain plate motion at the same time we find a viscosity profile showing a minimum at shallow depth and a maximum at greater depth

plume capture by divergent plate motions implications for the distribution of hotspots geochemistry of mid ocean ridge basalts and estimates of the heat flux at the core mantle boundary abstract the coexistence of stationary mantle plumes with plate scale flow is problematic in geodynamics we present results from laboratory experiments aimed at understanding the effects of an imposed large scale circulation on thermal convection at high rayleigh number 106 ra 109 in a fluid with a temperature dependent viscosity in a large tank a layer of corn syrup is heated from below while being stirred by large scale flow due to the opposing motions of a pair of conveyor belts immersed in the syrup at the top of the tank three regimes are observed depending on the ratio v of the imposed horizontal flow velocity to the rise velocity of plumes ascending from the hot boundary and on the ratio of the viscosity of the interior fluid to the viscosity of the hottest fluid in contact with the bottom boundary when v 1 and 1 large scale circulation has a negligible effect on convection and the heat flux is due to the formation and rise of randomly spaced plumes when v 10 and 100 plume formation is suppressed entirely and the heat flux is carried by a sheet like upwelling located in the center of the tank at intermediate v and depending on established plume conduits are advected along the bottom boundary and ascending plumes are focused towards the central upwelling heat transfer across the layer occurs through a combination of ascending plumes and large scale flow scaling analyses show that the bottom boundary layer thickness and in turn the basal heat flux q depend on the peclet number pe and when 10 q pe1 2 and when 1 q pe 1 3 consistent with classical scalings when applied to the earth our results suggest that plate driven mantle flow focuses ascending plumes towards upwellings in the central pacific and africa as well as into mid ocean ridges furthermore plumes may be captured by strong upwelling flow beneath fast spreading ridges this behavior may explain why hotspots are more abundant near slow spreading ridges than fast spreading ridges and may also explain some observed variations of mid ocean ridge basalt morb geochemistry with spreading rate moreover our results suggest that a potentially significant fraction of the core heat flux is due to plumes that are drawn into upwelling flows beneath ridges and not observed as hotspots

the coefficient of earth pressure at rest laboratory experiments on undisturbed specimens of a large number of soft clay deposits as well as previous measurements on clays and granular soils were used to examine and explain the magnitude and behavior of the coefficient of earth pressure at rest k0 i after sedimentation primary consolidation ii during secondary compression aging iii after active or passive preshearing away from the laterally constrained condition iv during a decrease in effective vertical stress and v during an increase in effective vertical stress in the recompression or compression range in terms of the slope of the effective horizontal versus effective vertical stress path the behavior of k0 is explained using the concept of mobilized angle of friction in laterally constrained deformation condition the jaky equation provides in terms of the angle of internal friction a good estimate of k0 of sedimented normally consolidated young clays and granular soils as well as of of presheared clays and sands

global distribution and characteristics of coronae and related features on venus implications for origin and relation to mantle processes coronae on venus range from 60 to over 2000 km across and are characterized by a complex range of morphologies the annuli around coronae range from about 10 to 150 km across and have tectonic features ranging from extensional to compressional to a combination of both topographically coronae are domes plateaus plateaus with interior lows and rimmed depressions a subset of features classified here as coronae corresponds to depressions and is interpreted to consist of large scale calderas a number of features have been identified with many of the basic characteristics of coronae similar interior deformation associations with volcanism high topography but lacking a distinct tectonic annulus these features tend to be somewhat smaller than coronae and may represent failed coronae or coronae in an early stage of evolution the size distribution of coronae and coronalike features with maximum widths greater than about 250 km is well represented by a power law of the form n d kd where n is the number of coronae with maximum widths greater than d km and 3 05 the spatial distribution of coronae is not random the features are concentrated in a few groups and along several chains coronae are similar in many morphologic characteristics to major volcanic shield structures and volcanic rises such as western eistla regio the largest corona artemis is actually larger than several volcanic rises on venus coronae and volcanic rises appear to be surface manifestations of mantle plumes there is no evidence of any systematic variation in age along chains of coronae as occurs in hotspot chains on earth instead a number of multiple and overlapping coronae may indicate limited movement of the surface above a hotspot or mantle plume the morphology and size distribution of coronae highlands and major shields suggest that mantle upwelling on venus operates either on several spatial scales with coronae representing smaller scale upflows and major volcanic rises representing larger convective upwellings or on several temporal scales with coronae representing shorter duration upflows and major volcanic rises representing long term upwellings

axial capacity of bored piles in very stiff intermediate soils there is a major shortage of good quality load test data for bored piles in stiff to hard intermediate soils such as silts and clayey sands this paper presents the results and interpretation of an

corona structures on venus models of origin coronae on venus are circular to elongate structures with maximum widths of 150 1000 km characterized by annuli of concentric ridges surrounding complex interiors the features have raised topography relative to the surroundings they are associated with volcanic activity and most are partially surrounded by a peripheral trough variations in morphology between individual coronae are due to differences in their stage of evolution and or differences in the relative significance of the geologic processes that occur in each stage we examine models for three processes that may be involved in corona origin and evolution 1 a hotspot or rising mantle diapir model 2 a sinking mantle diapir model and 3 gravitational relaxation of topography rising mantle diapirs are caused by heating at depth e g hotspot while sinking mantle diapirs may result from cooling or a phase change causing increased density and negative buoyancy at the base of the lithosphere the hotspot model is most consistent with the major characteristics of coronae with gravitational relaxation occurring as a modificational process the sinking mantle diapir would produce dominant central compression that has not been observed at coronae however higher resolution image and altimetry data from magellan can be used to distinguish more fully between the two models coronae in various states of formation and degradation can be identified in the venera 15 16 data suggesting that the process may be continuing today

simulating the thermochemical magmatic and tectonic evolution of venus s mantle and lithosphere two dimensional models 1 numerical convection models of the thermochemical evolution of venus are compared to present day topography and geoid and recent resurfacing history the models include melting magmatism decaying heat producing elements core cooling realistic temperature dependent viscosity and either stagnant lid or episodic lithospheric overturn in stagnant lid convection the dominant mode of heat loss is magmatic heat pipe which requires massive magmatism and produces very thick crust inconsistent with observations partitioning of heat producing elements into the crust helps but does not help enough episodic lid overturn interspersed by periods of quiescence effectively loses venus s heat while giving lower rates of volcanism and a thinner crust calculations predict 5 8 overturn events over venus s history each lasting 150 myr initiating in one place and then spreading globally during quiescent periods convection keeps the lithosphere thin magmatism keeps the mantle temperature constant over venus s history crustal recycling occurs by entrainment in stagnant lid convection and by lid overturn in episodic mode venus like amplitudes of topography and geoid can be produced in either stagnant or episodic modes with a viscosity profile that is earth like but shifted to higher values the basalt density inversion below the olivine perovskite transition causes compositional stratification around 730 km breakdown of this layering increases episodicity but far less than episodic lid overturn the classical stagnant lid mode with interior temperature rheological temperature scale lower than tcmb is not reached because mantle temperature is controlled by magmatism while the core cools slowly from a superheated start core heat flow decreases with time possibly shutting off the dynamo particularly in episodic cases

mantle convection model with a dynamic plate topography heat flow and gravity anomalies summary surface observables have been calculated for a numerical convection model that includes a dynamic plate that is a stiff but mobile section of the upper boundary layer that is driven entirely by internal buoyancy forces the results for heat flux and topography are virtually identical to those obtained from a partially kinematic model in which plate mobility results from an imposed horizontal velocity on the top surface these results confirm the validity of the partially kinematic approach which has been used previously the partially kinematic approach is more efficient computationally

compaction behavior of argillaceous sediments as function of diagenesis the paper presents the results of laboratory compaction tests on samples of kimmeridge clay taken from two different locations in the uk the main objective of the laboratory tests is to determine how diagenesis affects the hydro mechanical properties and compaction behavior of argillaceous sediments the two kimmeridge clays used in the tests are essentially from the same parent material but have undergone different degrees of mechanical and chemical diagenesis the laboratory tests are designed to determine the effects of mechanical loading and chemical processes on changes in porosity permeability compressibility strength and effective horizontal stress in argillaceous materials another objective of the study is to investigate the adequacy of soil mechanical constitutive models in predicting the response of argillaceous materials to conditions corresponding to burial depths in sedimentary basins the tests on kimmeridge clay are carried out to as high as 150 mpa effective vertical stress corresponding to about 9 km in burial the results indicate that mechanical compaction and burial depth cannot explain the differences in the hydro mechanical behavior of the tested materials the differences in hydro mechanical response are attributed to chemical diagenesis by precipitation of minerals in the pores of the sediment other observed effects of chemical diagenesis on hydro mechanical behavior of lithified sediments are 1 increase in apparent pre consolidation stress 2 decrease in compressibility 3 decrease in permeability and 4 decrease in effective horizontal stress implications of the results to fluid flow and overpressure development in sedimentary basins are discussed

effect of particle fabric on the coefficient of lateral earth pressure observed during one dimensional compression of sand the effect of initial particle fabric on the one dimensional compression response of fraser river sand was investigated one dimensional compression with lateral stress measurement was carried out

arrhenius rheology versus frank kamenetskii rheology implications for mantle dynamics 1 the viscosity of planetary mantle material is strongly temperature dependent this dependence is described by an arrhenius law but for the realistic viscosity contrast that appears over the depth of the mantle strong gradients in the upper thermal boundary layer occur these strong gradients are not realizable in numerical models therefore the frank kamenetskii approximation leading to a linearized exponential viscosity function is commonly used much research on the plate mantle system has been done applying the frank kamenetskii rheology the question though still arises if these results can be reproduced when using the arrhenius law here it has to be kept in mind that in numerical models the realistic viscosity contrast appearing over the mantle can neither be coped with by the arrhenius nor the frank kamenetskii approach thus the computational aspects to date only allow for viscosity contrasts being moderate as compared to realistic values and extrapolations to planet like values have to be made for both rheologies comparing results obtained by the commonly used forms of the arrhenius and the frank kamenetskii approach we observe the same change in flow behavior from mobile lid to stagnant lid convection the differences are only of quantitative nature in the stagnant lid regime some arrhenius formulations lead to a thinner top boundary layer which results in values of lithospheric thicknesses being more realistic here it has to be noted that different forms of the arrhenius law have been used which differ among themselves when properly scaled the differences between the frank kamenetskii and arrhenius rheology can however be strongly diminished to understand general features in the plate tectonics mantle convection system an additional stress dependence of the viscosity has to be considered the discrepancies between the various viscosity formulations are then of even less importance because for an earth like convection regime the top viscosity is more strongly influenced by the stress dependence rather than by the temperature dependence

transient mantle convection on venus the paradoxical coexistence of highlands and coronae in the bat region thecoexistenceofvenusianhighlands attributedtolong livedaxisymmetricmantleplumes anduncompensatedcoronae attributed totransientdiscretemantle thermals isdifficulttoreconcilewithmodelsofmantleconvectionunderthermallysteady stateconditions however cratering and geological studies indicate a uniformly young surface age 700 myr as well as a comparable timescale for resurfacing 100 to 400 myr possibly consistent with a recent lithospheric overturn and a transient mantle thermal regime we use laboratory experiments on free and forced thermal convection at high rayleigh number ra 10 7 in a variable viscosity fluid to investigate the steady state and transient thermal regimes preceding and following such an overturn from analyses of shadowgraph images andtimeseries of global andlocal variations intemperature basal heat fluxandviscosity weestablishsteady statestagnant and active lid states and characterize two intermediate transient regimes flow in steady state stagnant lid is in the form of intermittent thermals consistent with published work during the transition to active lid convection the stagnant lid isstirred into the interior using a conveyorbelt spreadingofthiscoldfluidalongthehotboundaryleadstoatransitiontoa mixedmode offlowfromthehotboundary approximatelyisoviscous thermalsrise from the thermal boundarylayer aheadofthe advancingcoldfrontandlow viscosityplumes rise from behind the front as a result of an enhanced temperature contrast the longevity of this regime and the timescale for the transient depends on the rate of overturn pe and the aspect ratio of the system a the magnitude of local temperature viscosity and heat flux variationsincreaseswithpeandcanexceedsteady statevaluesforactive lidconvection additionalnumericalsimulationsshowthatthe mixed mode regime will occur in the presence of internal heating and for no and free slip boundaries in contrast the transition from active lid to stagnant lid convection is marked by a change from a flow composed of plumes and large scale overturning motions to a regime dominated by risingand sinking thermals on a timescale ofthermal diffusion applied tovenus our resultssupport a hypothesis that the contemporaneous coexistence of the atla and beta highlands regions with interspersed uncompensated coronae is consistent withatransientthermalregimefollowingalithosphericoverturn itisalsoexpectedthatsuchcoronaeformedn250myraftertheupliftof the highlands implications of the thermal origin of coronae for venusian mantle structure are also explored 2007 elsevier b v all rights reserved

resurfacing events on venus implications on plume dynamics and surface topography 1 global resurfacing events explain the relatively young and uniformly aged surface of venus in numerical models featuring these events a variety of plume classes occur ranging from strong stable to smaller wind driven upwellings we investigate this plume dynamics in a 3d cartesian geometry paying special attention to the surface topography while the stable upwellings of the stagnant lid phase correlate with an elevation of the surface the wind driven upwellings of the resurfacing phase do not necessarily correlate with a positive topography signal we rather observe that a thick plate can dominate the topography above upwellings

stress history and sampling disturbance effects on monotonic and cyclic responses of overconsolidated bootlegger cove clays this paper examines the influence of reproducing the stress history of a natural soil deposit during laboratory reconsolidation on the subsequent response and behavior of heavily overconsolidated b

the effect of rheological parameters on plate behaviour in a self consistent model of mantle convection abstract in a three dimensional numerical model of mantle convection we have explored the self consistent formation and evolution of plates this was done by investigating the influence of temperature stress and pressure dependence of the viscosity on plate like behaviour further the role of a depth dependent thermal expansivity and of internal heating was examined first order self consistent plate tectonics can be obtained for temperature and stress dependent viscosity we observe virtually undeformed moving plates and the phenomenon of trench migration however plate motion only appears during short intervals which are interrupted by long phases characterised by an immobile lid an improvement is achieved by adding pressure dependence of the viscosity and of the thermal expansivity to the model this leads to extended plates with continuous plate motion and the appearance of a low viscosity zone internal heating accelerates subduction and gives an increase in plate velocity the plates are otherwise left intact we find that the surface velocity is largely determined by subduction rather than by upwellings plate like behaviour is restricted to a narrow parameter window the window is bordered by an episodic or a stagnant lid type of flow on the one side and by a domain in which convection is akin to constant viscosity flow on the other side with these different convective regimes the behaviour of various terrestrial planets can be described self consistently occasionally even a change from the plate regime to the stagnant lid regime occurs such a type of transition has possibly changed the style of tectonics on some terrestrial planets such as mars

mineral dissolution and the evolution of k0 adequate knowledge of the in situ state of stress can be essential to the analysis of geotechnical systems however the measurement and prediction of k0 remain difficult in particular limited attention has been given to the evolution of k0 during the formation history of the soil and diagenetic processes such as mineral dissolution experimental and numerical results show that grain mass loss due to mineral dissolution produces a pronounced horizontal stress drop under zero lateral strain conditions the state of stress may reach the active shear failure ka condition and internal shear planes may develop while horizontal stress recovery often follows upon further dissolution marked differences in fabric are observed between the pre and postdissolution soil structures

localization of gravity and topography constraints on the tectonics and mantle dynamics of venus summary we develop a method for spatio spectral localization of harmonic data on a sphere and use it to interpret recent high resolution global estimates of the gravity and topography of venus in the context of geodynamical models our approach applies equally to the simple spatial windowing of harmonic data and to variable length scale analyses which are analogous to a wavelet transform in the cartesian domain using the variable length scale approach we calculate the localized rms amplitudes of gravity and topography as well as the spectral admittance between the two fields as functions of position and wavelength the observed admittances over 10 per cent of the surface of venus highland plateaus and tessera regions are consistent with isostatic compensation of topography by variations in crustal thickness while admittances over the remaining 90 per cent of the surface rises plains and lowlands indicate that longwavelength topography is dominantly the result of vertical convective tractions at the base of the lithosphere the global average crustal thickness is less than 30 km but can reach values as large as 40 km beneath tesserae and highland plateaus we also note that an earth like radial viscosity structure cannot be rejected by the gravity and topography data and that without a mechanical model of the lithosphere admittance values cannot constrain the thickness of the thermal boundary layer of venus modelling the lithosphere as a thin elastic plate indicates that at the time of formation of relief in highland plateaus and tesserae the effective elastic plate thickness k was less than 20 km estimates of t at highland rises are consistently less than 30 km our inability to find regions with t 30 km is inconsistent with predictions made by a class of catastrophic resurfacing models

preliminary analysis of an expanded corona database for venus we have conducted an extensive survey of the magellan data to reassess the population of coronae we identify a new type of coronae here referred to as type 2 coronae having the same basic morphology as previously identified coronae type 1 but lacking a significant 50 annulus of closely spaced fractures 106 type 2 coronae are included in the new database giving a total of 515 coronae on venus the characteristics of the expanded population of type i coronae are similar to those of the previously described population but the type 2 coronae are smaller tend to have relatively flat interiors surrounded by a topographic rim and are more likely to be found isolated from other features our observations in particular the morphology and setting of the type 2 coronae may provide supporting evidence for the existence of a depleted mantle layer under the venusian plains

mechanical behaviour of fine grained sediments experimental compaction and three dimensional constitutive model abstract the usual undimensional description of deformations of sediments based on a phenomenological relationship between porosity and the vertical effective stress does not give information about the horizontal stress and moreover is irrelevant for sedimentary structures in which deformation process is not only vertical modelling three dimensional deformation processes in sedimentary basins requires a three dimensional mechanical constitutive model for sediments a special dometric cell was conceived in g 3s this cell allows the measurement of the lateral stress during dometric compaction and so enables us to elaborate a three dimensional model of mechanical behaviour four varieties of fine grained sediments were studied by this cell in a large scale of strain and stresses the modified cam clay model was used for fitting the experimental data and it was shown that this model can reproduce the mechanical compaction of sediments up to 50 mpa of vertical effective stress about 3 km burial depth if its parameters are deduced from dometric zero lateral strain data

experimental characterization of deformation coefficient of earth pressure at rest stiffness and contact force distributions of sand during secondary compression and rebound this paper aims to provide a comprehensive picture of the sand responses during secondary compression and rebound based on experimental characterizations the experiment was carried out on dry leighton buzzard sand using a modified direct shear box equipped with tactile pressure sensors for the stress measurements and bender elements for stiffness i e ghv and ghh monitoring it was found that secondary compression and rebound followed the same deformation trends as primary compression and rebound to continuously contract and expand respectively the deformation characteristics determined the changes in the associated soil properties therefore the opposite soil behavior during secondary compression and rebound was observed during secondary compression the corresponding void change deviatoric strains eq and the deviatoric strain rate e q increased with increasing vertical stress v or deviatoric stress q because the sample crept more easily under a higher v or q the compression deformation ga

neutrally buoyant diapirs a model for venus coronae coronae are typically circular features 100 600 km in diameter characterized by a deformed annular ring that is often topographically high the central region may be raised or depressed relative to the ambient elevation previous studies have proposed an evolutionary progression beginning with dome shaped features which have radiating extensional rifts followed by plateau shaped features which have both concentric deformation and radial extension ending with the classic corona as described above previous dynamical calculations of a rising and spreading diapir simulated the evolution from dome to plateau shaped topography but could not account for the raised rim or depressed central topography of some coronae we demonstrate that these features can be modeled by a diapir that spreads laterally at a depth of neutral buoyancy

corona formation and heat loss on venus by coupled upwelling and delamination coronae are volcanotectonic features that are unique to venus and are interpreted to be small scale upwellings a model in which upwelling causes delamination at the edge of the plume head along with deformation of a preexisting depleted mantle layer produced the full range of topographic forms of coronae if half of the coronae are active delamination of the lower lithosphere could account for about 10 percent of venus9 heat loss with another 15 percent due to upwelling delamination may occur in other geologic environments and could account for some of venus9 heat loss deficit

a coupled thermal mechanical model for corona formation on venus we develop a model of the combined thermal and mechanical evolution of diapirs in the mantle of venus the diapir is treated as an oblate spheroid rising through a viscous fluid and ultimately impinging on a rigid overlaying lid drag forces imposed by the lid cause the diapir to spread and flatten as it rises we parameterize the heat loss from the rising diapir using a nusselt number formulation and treat the resulting loss in buoyancy in our flow calculation the model predicts the evolution timescale and degree of flattening of a diapir as it rises as well as the stresses exerted on the underside of the lithosphere in order to explore diapir behavior further we check our analytical model against the predictions of the finite element code mantle from the combined results of these models and observations of venusian coronae we are able to make a number of inferences about venusian diapirism and mantle properties we find that the diapirs responsible for formation of venusian coronae have an initial size distribution extending from about 30 to 100 km in radius typical evolution timescales for these diapirs are 30 50 myr if venus global average resurfacing age is 300 500 myr then our results are consistent with a rate of diapirism that has been roughly constant over this period and with an effective mantle viscosity of 1021 pa s

carbonates and cementation of glacially derived cohesive soils in new york state and southern ontario cet article presente des resultats se rapportant a la teneur en carbonate de silts et d argiles naturels en fonction de la profondeur de l emplacement geographique et de l origine geologique on etudie aussi l influence de cette teneur en carbonate sur le comportement geotechnique l effet sur la pression de preconsolidation apparente est illustre en detail pour l un des sites etudies la repartition des carbonates a l interieur des varves d un depot glacio lacustre est egalement presentee pour demontrer la variabilite potentielle de la cimentation naturelle des sols les donnees en provenance de quinze sites etayent les relations proposees entre teneur en carbonate et pression de preconsolidation apparente

towards a simple and reliable method for calculating the uplift capacity of plate anchors in sand this paper investigates the uplift capacity of horizontal plate anchors in sand through finite element analyses and centrifuge experiments finite element simulations adopt a sophisticated bounding

recycling the lid effects of subduction and stirring on boundary layer dynamics in bottom heated planetary mantle convection 1 the subduction and stirring of cold oceanic lithosphere governs the thermal regime of the earth s mantle whether upwelling mantle plumes are transient isoviscous thermals or long lived low viscosity plumes depends on the magnitude of the resulting temperature variations in the thermal boundary layer at the base of the mantle previous laboratory experiments suggest that low viscosity earth like plumes occur where the hot thermal boundary layer tbl viscosity ratio h o 10 here the results from two dimensional numerical simulations in which subduction is either forced from above or allowed to arise naturally show that 1 a morphologic transition from upwellings in the form of isoviscous thermals to cavity plumes occurs where h o 10 and is accompanied by a qualitative change in the temporal and spatial dynamics of the hot tbl 2 this transition corresponds to a condition in which the velocity boundary layer vbl is concentrated within the basal part of the tbl for no and free slip boundaries and 3 a regime in which h o 10 can only occur if the total viscosity ratio across the convecting system t o 102 our results support a recent conjecture that low viscosity mantle plumes in the earth are a consequence of strong mantle cooling by plate tectonics moreover earth like plume models may be inappropriate for explaining the origin of surface features on one plate planets such as mars or venus

volcanism and tectonics on venus we review recent developments in the study of volcanism and tectonics on venus venus s crust is basaltic dry and probably about 30 km thick the mantle convects giving rise to plumes and has a similar composition and mean temperature 1300 c but a higher viscosity 10 20 pa s than that of the earth inferred melt generation rates constrain the lithospheric thickness to between 80 and 200 km the elastic thickness of the lithosphere is about 30 km on average the present day lack of plate tectonics may be due to strong faults and the high viscosity of the mantle most of the differences between earth and venus processes can be explained by the absence of water venus underwent a global resurfacing event 300 600 ma ago the cause and nature of which remains uncertain the present day surface heat flux on venus is about half the likely radiogenic heat generation rate which suggests that venus has been heating up since the resurfacing event

determination of erosion thickness by numerical back analysis the case study of badenian clays in the carpathian foredeep czech republic abstract the paper describes an application of the geotechnical numerical back analysis in estimating the thickness of eroded sedimentary overburden in shallow basinal sediments the approach is based on the back analysis of the coefficient of earth pressure at rest k 0 and on estimating the unloading from the obtained k 0 value this approach is compared with the conventional methods represented by baldwin butler s compaction curves and casagrande s concept of preconsolidation stress the results of these two commonly used methods are incorrect if the sedimentary profile is affected by ageing effects such as cementation secondary compression etc the method is demonstrated on the lower miocene marine clay often called tegl which was deposited in the carpathian foredeep in the vicinity of brno czech republic the numerical back analysis was applied to galleries and adits opened during site investigation of the kralovo pole tunnels in brno the application of baldwin butler s equation suggested the erosion thickness of 180 270 m and casagrande s method of 100 800 m while the numerical back analysis of 0 40 m

rayleigh taylor instability as a mechanism for corona formation on venus abstract in this study we explore the idea that coronae have formed on venus as a result of gravitational rayleigh taylor instability of the lithosphere the lithosphere is represented by a system of stratified homogeneous viscous layers low density crust over high density mantle over lower density layer beneath the lithosphere a small harmonic perturbation imposed on the base of the lithosphere is observed to result in gravitational instability under the constraint of assumed axisymmetry topography develops with time under the influence of dynamic stress associated with downwelling or upwelling and spatially variable crustal thickening or thinning topography may therefore be elevated or depressed above a mantle downwelling but the computed gravity anomaly is always negative above a mantle downwelling in a homogeneous asthenosphere the ratio of peak gravity to topography anomaly depends primarily on the ratio of crust to lithospheric viscosity average observed ratios are well resolved for two groups of coronae 40 mgal km 1 consistent with models in which the crust is perhaps 5 times stronger than the lithosphere group 3a rim surrounding elevated central region coronae are inferred to arise from a central upwelling model whereas group 8 depression coronae are inferred to arise from central downwelling observed average coronae radii are consistent with a lithospheric thickness of only 50 km an upper low density crustal layer is 10 20 km thick as inferred from the amplitude of gravity and topography anomalies

stagnant lid convection on venus the effect of strongly temperature dependent viscosity on convection in the interior of venus is studied systematically with the help of finite element numerical models for viscosity contrasts satisfying experimental constraints on the rheology of rocks venus is likely to be in the regime of stagnant lid convection this regime is characterized by the formation of a slowly creeping very viscous lid on top of the mantle venusian lithosphere and is in agreement with the tectonic style observed on venus stagnant lid convection explains large geoid to topography ratios on venus by the thermal thinning of a thick lithosphere the thickness of the lithosphere can be as large as 400 550 km for beta regio and 200 400 km on average geoid and topography data and experimental data on the rheology of rocks provide constraints on the viscosity of the mantle 10 20 10 21 pa s the convective stresses in the interior 0 2 0 5 mpa the stresses in the lid 100 200 mpa the velocity in the interior 0 5 3 cm yr 1 and the heat flux beneath the lithosphere 8 16 mw m 2 parameterized convection calculations of thermal history of venus are difficult to reconcile with a thick present day lithosphere however a sufficiently thick lithosphere can be formed if a convective regime with mobile plates was replaced by stagnant lid convection around 0 5 b y ago one of the possible explanations for the cessation of venusian plate tectonics is that during the evolution of venus stresses in the lid dropped below the yield strength of the lithosphere this model predicts a drastic drop in the heat flux thickening of the lithosphere and suppression of melting and is consistent with the hypothesis of cessation of resurfacing on venus around 0 5 b y ago

venus crater distribution and plains resurfacing models detailed analysis of the distribution of craters on venus using mth nearest neighbor analysis coupled with models based upon surface morphology constraints indicates that the hypothesis of complete spatial randomness csr cannot be rejected but is not a unique model of the observed crater distribution based on morphologic mapping the extensive volcanic plains can be divided into four units that have a spread in age of the order of 0 5t the mean surface age of the planet this four unit plains model along with its derivatives produce test statistics that indicate such models also cannot be rejected further the probability of obtaining a result at least as extreme as the observed test statistic given that the null hypothesis model corresponds to venus is true is lowest for the csr model there is no particular reason to pick a csr model along with its implications for catastrophic resurfacing as a constraint on the evolution of venus and there are geological reasons to choose the multiage models we find that we cannot distinguish statistically among models that have two three or four distinct production ages within the plains however the hypothesis that the variation in crater density within all of the plains is due to a single random process can be rejected for two reasons first the binomial probability that such a process could exist within each of the plains units is 0 05 except the smallest and youngest unit pl1 second using a chi squared statistic to test the hypothesis that four plains units have the same age gives a p value of 10 4 indicating confident rejection of the hypothesis thus csr cannot be used as a constraint on models of resurfacing or planetary evolution of venus because of the non uniqueness in matching such a model to the observed crater distribution and the strong indication of distinct ages within the plains with a significant spread in age geological and geophysical constraints provide our best clues for understanding venus

coefficient of earth pressure at rest for sands subjected to vibration an oedometer instrumented to measure horizontal pressure was used to examine the behavior of the coefficient of earth pressure at rest ko of clean sands subjected to vertical vibration reconstit

behavior of hydrocarbon reservoir sands and sandstones most new oil and gas reservoirs are discovered in sands and weak sandstones and the petroleum industry has therefore generated an extensive amount of data from laboratory tests on these materials some of these data are reexamined in this paper within the context of recent soil mechanics research of key importance to petroleum engineers is the compressibility of the sands and this is shown to be related both to the current density and stress level of the soil and to the location of its normal compression line when present the cement bonds between the particles appear to be weaker than the particles themselves so that the major yield point during compression is still associated with breakage of the particles rather than of the cement bonds the paper also examines the behavior of the sands and sandstones in shearing allowing a more general understanding of the mechanics of the materials to be developed

relating shaft friction of buried piles and cpt resistance in clayey sands this paper examines factors controlling the ultimate shaft friction developed on buried piles in normally consolidated clay sand mixtures and explores the relationship between this friction and the

a conceptual model for the relationship between coronae and large scale mantle dynamics on venus 1 among the most enigmatic features on venus are the more than 500 quasi circular structures collectively referred to as coronae associated volcanism and tectonism suggest that coronae result from small transient mantle plumes although only about 20 have clearly associated positive gravity anomalies indicative of current activity coronae are concentrated within a region defined by the dynamically active highland areas of beta atla and themis regiones bat coronae avoid the lowest or highest topography and geoid subsets of the corona population indicate that the spatial distribution of coronae has evolved from a previously less concentrated global distribution to the current bat concentration recent laboratory experiments on thermal convection at high rayleigh number using fluids with temperature dependent viscosity suggest a straightforward interpretation of these relationships small scale upwellings from a hot lower thermal boundary layer tend to be excluded by longer wavelength downwelling structures from the cold upper boundary layer the relative paucity of coronae in the broad lowland plains regions is consistent with the inference of mantle downwellings beneath the plains coronae are largely excluded from compensated highlands perhaps because the thickened crust is not easily disrupted in these regions laboratory experiments indicate that small transient boundary layer instabilities can coexist with and be focused toward large scale upwellings possibly explaining the spatial concentration of coronae in the bat region thus coronae provide important insights into interacting scales of convective flow in venus s mantle and into the evolution of venus s mantle dynamics direct tests of our model are possible through geological mapping

assessing the coefficient of the earth pressure at rest from shear wave velocity and electrical resistivity measurements abstract determination of earth pressure coefficient k 0 in natural soil deposits is a significantly important issue in geotechnical engineering this paper evaluates the feasibility of predicting k 0 values from measurements of vertical and horizontal shear wave velocities v s vh v s hh and v s hv and vertical and horizontal electrical resistivities s v s h a series of seismic piezocone tests scptu improved crosshole ch tests and soil resistivity tests using a modified laboratory apparatus were carried out at two research sites in jiangsu province of china and results were used to develop two existing k 0 shear wave velocity correlations for prediction of k 0 the seismic and electrical resistivity test results showed that both the shear wave velocity ratios v s hh v s hv or v s hv v s vh and the horizontal to vertical electrical resistivity ratio s h s v may provide a good indicator of the inherent soil anisotropy at these sites the existing v s k 0 prediction framework largely requires determining c s hv c s hh ratio and a simple procedure for evaluating this ratio based on the measured horizontal and vertical electrical resistivities the k 0 values predicted by shear wave velocity at both sites are also compared with values determined by jaky s formula and mayne kulhwy s formula in normally consolidated nc soils the k 0 values predicted from these methods showed good agreement however for over consolidated oc soils at shallow depths certain variations between different methods are noted further investigations of the effects of overconsolidation ratio on k 0 predictions will lead to the correction factors for better prediction of k 0 for oc soils this paper has confirmed that reasonable predictions of k 0 for natural soil deposits can be made using the proposed methodology

behaviour of a sensitive marine sediment microstructural investigation the aim of this study is to characterise along various stress paths the microstructural evolution of a deep water marine sediment from the gulf of guinea gog results obtained at the macroscopic level have shown that the phenomenological behaviour of the gog sediment is explained by the properties of remoulded samples given by the isotropic and critical state lines and by the properties of the intact samples given by the damage evolution of the inter aggregate bonds microstructural investigations conducted by mercury intrusion porosimetry and scanning electron microscopy demonstrate that the volumetric strains measured at the macroscopic level come from inter aggregate pore variations associated with the degrading of the inter aggregate bonds the mechanism responsible for reorienting the particles appears to apply in the case of the remoulded sediment as for the natural sediment it is first necessary to increase the isotropic consolidation stress towards higher values in order to break the bonds between the aggregates before it becomes possible to activate the particle reorientation mechanism and thus approach the remoulded behaviour

earth pressure at rest of sovind marl a highly overconsolidated eocene clay abstract the present study evaluated the earth pressure at rest k 0 of sovind marl a highly overconsolidated eocene clay this clay exhibits extremely high plasticity indices of up to 300 a highly fissured structure and preconsolidation stresses up to 6800 kpa continuous loading oedometer clo tests at a constant rate of strain were performed in the danish clo apparatus this apparatus applies test water at 200 kpa and measures total horizontal stresses via pressure gauges placed in a stiff oedometer ring horizontal and vertical stresses were measured from in situ stresses to various stress levels to estimate continuous k 0 development in the clay normally consolidated earth pressures at rest were 0 42 and 0 68 for sovind marl at two different ages overconsolidated k 0 k 0 oc reached values as high as 6 to 8 in the in situ stress range the correlation between k 0 oc and the overconsolidation ratio ocr reported by meyerhof in 1976 was inconsistent with the k 0 oc development of sovind marl however the development of ocr in the laboratory under the previously applied test stresses ocr lab as an alternative to preconsolidation stresses showed congruent results regardless of sample age when an value of 1 05 was used

soil behaviour through field instrumentation an improved version of the observational method is developed and proposed the method uses field measurements as the direct inputs to the framework of the constitutive behaviour and analyses the be

in situ lateral stress measurement in glaciolacustrine seattle clay using the pressuremeter pressuremeter testing was conducted for the state route sr 99 bored tunnel project in seattle washington to estimate in situ soil stress deformation parameters along the tunnel alignment many of the tests were conducted in a very stiff to hard glaciolacustrine clay known as seattle clay this unit is historically known for deep seated slope failures and many of these failures have been attributed to the release of high locked in lateral stresses estimation in situ lateral stresses along the tunnel alignment was a primary focus of the exploration program due to the hard consistency of this unit and the potential for cobbles neither self boring pressuremeter nor dilatometer testing was feasible therefore prebored pressuremeter testing was used using several lateral stress estimation techniques including a novel in situ creep testing approach the in situ lateral stresses in the seattle clay were estimated to be significantly higher than what would be expected by assuming a simple laterally constrained vertical loading and unloading stress path due to glaciation deformational features commonly encountered in seattle clay indicate its stress history also has included significant lateral shearing the memory of this shearing within the fabric of the clay may influence the in situ stress state and response to lateral unloading

the global resurfacing of venus the impact cratering record on venus is unique among the terrestrial planets fully 84 of the craters are in pristine condition and only 12 are fractured remarkably only 2 5 of the craters and crater related features are embayed by lava although intense volcanism and tectonism have affected the entire planet furthermore the spatial and hypsometric distribution of the craters is consistent with a completely random one including stochastic variations monte carlo simulations of equilibrium resurfacing models result in a minimum of 17 times more embayed craters than observed or unobserved nonrandom crater distributions for resurfacing areas between 0 03 and 100 of the planet s surface these models also are not consistent with the number and nonrandom distribution of volcanoes and the nonrandom distribution of embayed and heavily fractured craters the constraints imposed by the cratering record strongly indicate that venus experienced a global resurfacing event about 300 m y ago followed by a dramatic reduction of volcanism and tectonism this global resurfacing event ended abruptly 10 m y the present crater population has accumulated since then and remains largely intact thermal history models suggest that similar global resurfacing events probably occurred episodically in the past the tesserae statistically have the same average surface age crater retention age as the rest of the planet but they probably represent older rock units deformed by earlier episodes of global resurfacing although they largely survived the latest global resurfacing event their surfaces were severely deformed by it monte carlo simulations indicate that only about 4 6 of the planet has been volcanically resurfaced since the global event and that the lava production rate has been no more than 0 01 0 15 km3 yr during this time this rate is significantly less than the current rate of intraplate volcanism on earth 0 33 0 5 km3 yr most of venus recent volcanism occurs in the beta atla themis region and most of the recent tectonism is associated with the major global scale tectonic disruption zones that lie within and connect the equatorial highlands the approximately 33 of the planet s surface bounded by latitudes 30 n and 30 s longitudes 60 and 300 e contains twice as many heavily fractured craters and 1 4 times more lava embayed craters as the planetary average this region includes most of the major tectonic belts in the equatorial region because the craters are indistinguishable from a statistically random distribution both spatially and hypsometrically this concentration of strongly fractured and embayed craters is considered indicative of a continuing low level of limited extension and volcanic activity in this region over the past 300 m y however these craters are simply fractured and or embayed and very few have been subjected to complete tectonic disruption complete burial and subsequent removal from the surface as was the case during the global resurfacing event we show that neither the present level and style of geologic activity nor anything less than global resurfacing could have produced the observed cratering record the effects of recent geologic activity are much less than those of the earlier global resurfacing event when the record of all the early heavy bombardment and much of the later light bombardment was erased from the surface by massive volcanism and tectonic activity episodic regional resurfacing events that had global effects also occurred on earth e g the mid cretaceous superplume and probably on mars on mars they may have triggered the catastrophic releases of water that formed the outflow channels

a mantle plume model for the equatorial highlands of venus the equatorial highlands of venus consist of four main structures atla beta ovda and thetis regiones each has a circular to oval shaped planform and rises 4 5 km above the mean planetary radius these highlands are associated with long wavelength geoid highs with amplitudes ranging from 35 m at ovda to 120 m at atla they also contain topographic valleys interpreted as extensional rift zones and beta is known to contain shield volcanoes these characteristics are all consistent with the equatorial highlands being formed by mantle plumes an alternative model in which ovda and thetis are interpreted as spreading centers analogous to terrestrial mid ocean ridges fails to explain most of the observed geoid anomalies and topography in these regions some smaller highlands such as bell regio eistla regio and the hathor innini ushas region may also be plume related but most coronae are unlikely to be the direct result of plume activity we have modeled plumes using a cylindrical axisymmetric finite element code and a depth dependent newtonian rheology we compare our model results with profiles of geoid and topography across atla beta ovda and thetis our best model fits are for beta and atla assuming whole mantle convection and that earth and venus have similar mantle heat flows venus must lack an earth like low viscosity zone in its upper mantle in order satisfy the observed geoid and topography for these features this conclusion is consistent with the long wavelength admittance spectrum of venus and with the observed differences in the slopes of the geoid spectra for the two planets one explanation for the different viscosity structures of the two planets could be that the mantle of venus is drier than earth s mantle