karst collapse susceptibility assessment a case study on the amalfi coast southern italy abstract this paper presents a study to evaluate the collapse susceptibility of a karst cave located along a slope on the amalfi coast southern italy and the presumable geomorphological evolution of the whole slope as a result of cave roof collapse in the study area several natural karst caves with volumes varying between 1000 and 10 000 m 3 were inventoried and the most likely genetic processes were identified some of them proved to be remnants of already collapsed caves while others were in precarious stability conditions the caves are usually located upslope or very close to the main populated resorts a detailed geological geomorphological and geostructural study was performed on a very wide deep cave called the saraceno cave on which the resort town of conca de marini has been built the study was carried out through a multidisciplinary approach which included classical field geological observations sometimes requiring the support of rock climbing geologists experts in photogrammetric surveys and terrestrial laser scanning techniques tls tls surveys allowed the reconstruction of an accurate geometric and geostructural model of the cave and its relationship with the upslope conca de marini resort furthermore it allowed the thickness of the cave overburden to be determined in detail ground surfaces most susceptible to collapse were also identified in the event of possible widespread collapse several buildings and transportation infrastructures could be involved as the cave is located on a very steep slope a debris avalanche could be triggered in the event of a catastrophic failure and the landslide debris characterized by a presumably high magnitude and velocity could involve a wide slope area down to the coast the failure evolution could be very similar to that which took place in amalfi in the late 19th century

an analytical solution for circular tunnels excavated in rock masses exhibiting viscous elastic plastic behavior abstract investigating time dependent behavior of tunnels driven in rocks has been the topic of interest for many years the majority of researches were conducted with the assumption that the behavior of the surrounding rock masses is viscoelastic in this paper an analytical solution is proposed for circular tunnels under hydrostatic stress field whose surrounding rock mass is isotropic homogenous obeying viscous elastic plastic constitutive model it is assumed that the rate of excavation is infinitely large therefore the solution is proposed for unlined tunnels when the advance of tunnel face is halted or after lining installation when the tunnel face is far from the studied section the results were compared with those predicted by finite difference numerical model which exhibited a good agreement for both lined and unlined tunnels except for large times where numerical model results slightly exceed the values predicted by the proposed solutions for lined tunnels

a novel rockbolt formulation for a gpu accelerated finite discrete element method code and its application to underground excavations abstract rockbolting is widely used in civil and mining engineering to increase the inherent strength of the rock mass and reduce deformations around underground excavations rockbolt design by means of computer aided numerical simulations has been playing an increasingly important role in geotechnical engineering the research work presented herein introduces a novel rockbolt logic for the finite discrete element method fdem a numerical modelling approach capable of explicitly capturing brittle fracturing in complex geological media adoption of a gpu based implementation was required to achieve substantial simulation speed ups compared to conventional cpu computing rockbolts are discretized by 1d structural elements which are coupled to the solid finite element mesh by dedicated spring slider connectors representing the bolt anchoring system the formulation is verified by comparing simulated stress distributions with closed form solutions for the cases of i a pull out test on a fully grouted rockbolt and ii a circular tunnel excavated in a bolted elastic medium the effectiveness of the method for practical design applications is demonstrated by simulating the behavior of a bolted underground excavation in a heavily jointed rock mass the effect of bolt spacing on the fracturing and deformational response of the rock mass is analyzed together with the force distributions in the rockbolts

influence of borehole diameter on the formation of borehole breakouts in black shale abstract we performed a series of borehole breakout tests on posidonia shale to study the influence of borehole diameter on borehole stability in unconventional black shale thick walled cylindrical samples 20 80 mm long 10 50 mm in diameter with varying borehole diameters of 1 19 mm drilled perpendicular to bedding were loaded under increasing hydrostatic pressures until formation of borehole breakouts the critical hydrostatic pressure for breakout formation decreased significantly from about 275 mpa for samples with 1 mm borehole diameter to 89 mpa for those containing a 19 mm borehole approaching the uniaxial compressive strength of the material the observed scale effect was fitted to various failure criteria predicting fracture initiation at a depth of about 0 15 mm around the borehole wall in the fine grained shale

excavation damaged zone depths prediction for tbm excavated roadways in deep collieries the excavation works at underground mines create excavation damage zone edz in surrounding rocks around roadway geometry the edz depth is a critical parameter for stability analysis risk assessment support design and toxic waste leakage this paper proposed an innovative edz depth prediction based on a modified nonlinear mohr failure criterion and modification of conventional analytical solution by means of perturbation method a set of cyclic loading tests of surrounding rock of roadways are conducted and a modified mohr failure criterion of rocks under cyclic loading path of tbm excavation is established on the basis of test results moreover perturbation method was introduced for enhancing calculation accuracy in order to verify the proposed analytical solution a set of in situ digital panoramic borehole camera image monitoring was carried out within the roadways and the monitoring results correlated well with the proposed analytical solution the edz geometries of roadways in deep mines are typically oval and the edz depth is influenced by ground stress magnitude lateral coefficient and support stress significantly through the proposed analytical solution a more accurate prediction of edz depth of roadways can be obtained conveniently before the excavation works

a new approach for analyzing circular tunnel in strain softening rock masses although it is relatively a simple problem to study circular tunnels excavated in isotropic rock masses under hydrostatic stress fields the results of stresses and displacements around circular opening can be insightful for ground support design and stability evaluation moreover the solutions are useful in the validation of constitutive models and numerical codes in the several decades past many scholars studied this kind of problem in the mohr coulomb m c media the hoek brown h b media and the generalized h b media and considered the elastic perfectly plastic elastic brittle plastic and strainsoftening models with associated flow and non associated flow rules according to the existing literature surveys most 1 13 of the researches are about elastic perfectly plastic and elastic brittle plastic models because closed form solutions or numerical solution can be easily obtained under certain assumptions however hoek and brown 14 suggest that the average quality rock masses behave in a strain softening mode in the field of underground rock engineering therefore it is of practical importance to study the mechanical behavior of normal rock masses with strain softening behavior by means of the classical theory of plasticity materials with perfectly brittle plastic and perfectly plastic constitutive model can be easily described and simulated in numerical methods such as the finite element method 15 16 etc but it is more difficult to model the strain softening material due to the negative slope in the stress strain coordinates even for the above mentioned excavation of circular tunnel in strain softening materials fewer attempts have been made 17 23 thus far the reason is that the relationship among the stresses plastic strain and the strength

mechanical analysis and interpretation of excavation damage zone formation around deep tunnels within massive rock masses using hybrid finite discrete element approach case of atomic energy of canada limited aecl underground research laboratory url test tunnel the construction of an underground opening leads to changes in the in situ stress regime surrounding the excavation the opening influences the rock mass owing to the redistribution of the stresses

influence of structure and water pressure on the hydraulic conductivity of the rock mass around underground excavations abstract in this study in situ water injection tests and numerical modeling in conjunction with core logs and television image measurements were applied for an investigation of the hydraulic properties of the rock mass around underground excavations the aim of our work was to investigate the influence of rock structure and water pressure on the hydraulic conductivity of the rock mass around underground excavations thus water injection tests were conducted in four boreholes that were drilled in the rock mass in underground tunnels in china seepage connection initiation and steady state seepage were proposed to identify the seepage evolution course within the rock mass by combining the results of pressure and hydraulic conductivity generally hydraulic conductivity is strongly related to rock structure and water pressure the results also revealed that a rearrangement of rock structure would occur in the damage zone resulting in an increase in hydraulic conductivity of nearly one to several orders of magnitude the results from the modified numerical model showed that the pore water distribution and the groundwater inflow rate are affected by both the hydraulic conductivity and the thickness of the damage zone and they are influenced more by the thickness of this zone

reconstruction of a 3700 ma transgressive marine environment from isua greenland sedimentology stratigraphy and geochemical signatures abstract the rare preservation of a stratigraphy in the northwest of the eoarchean isua supracrustal belt greenland demonstrates the world s earliest recognised marine transgression stratigraphically lowest is the 3710 ma solvang volcanic formation of picrites basalts and basaltic andesites with arc like geochemical signatures close to its erosional top this formation s volcanic rocks show increase in k2o with depletion of na2o depletion in sr with no alteration in eu abundance and 18ovsmow increase to 16 interpreted as subaerial weathering at 3700 ma the sedimentary snowpatch formation was deposited unconformably on the solvang volcanic formation locally the unconformity is marked by the laterally discontinuous conglomerate member dominated by rounded quartz clasts but also with clasts of basalt and andesite up to 10 cm across layered chert and ultramafic rocks the conglomerate member carries sparse detrital zircons the youngest of which are 3710 ma the conglomerates are succeeded by the sandstone and dolostone member of layered quartz and dolomite clastic sandstones that locally preserve relict shallow marine cross bedding with scoured layers tempestite breccia beds and very rare stromatolite horizons the sandstone and dolostone member is succeeded by the 3695 ma bif member the snowpatch formation quartz dolomite sandstones and interlayered stromatolites have seawater like ree y trace element patterns variably modified by a negligible to significant influx of a terrigenous component trace element signatures such as ti v ratios and normalising ree y data to a 3710 ma weathered volcanic rock rather than post archean average shale suggest this component was derived from a juvenile arc source resembling the basement solvang volcanic formation the detailed field and geochemical evidence such as positive correlation between fe mg and pr yb in the snowpatch formation dolostones and bif banded iron formation indicates that the dolomitic lithologies developed in a shallow water setting with clastic sedimentation during a marine transgression over a weathered 3710 ma volcanic arc basement followed by bif deposition in deeper water thus by 3700 ma shallow water exposed settings had already been established which were the site of stromatolite development

simplified method for estimating the hoek brown constant for intact rocks abstractthe constant mi is a fundamental parameter required for the hoek brown hb criterion to estimate the strength of rock materials to calculate mi values triaxial tests need to be carried out however triaxial tests are time consuming and expensive in this research a simplified method is proposed that can estimate mi values using information on rock types and the uniaxial compressive strength ucs of intact rocks to evaluate the reliability of the proposed method mi values estimated from the proposed method are used in the hb criterion to predict intact rock strength the predicted intact rock strength is then tested against experimental intact rock strength using existing triaxial tests and tests in the authors laboratory results from the comparison show that mi values calculated from the proposed method can be used reliably in the hb criterion for estimating intact rock strength when triaxial test data are not available

the influence of water on the strength of neapolitan yellow tuff the most widely used building stone in naples italy neapolitan yellow tuff nyt has been used in construction in naples italy since the greeks founded the city then called neapolis in the sixth century bce we investigate here whether this popular building stone is weaker when saturated with water an issue important for assessments of weathering damage and monument preservation to this end we performed 28 uniaxial compressive strength measurements on dry and water saturated samples cored from a block of the lithified upper member of the nyt our experiments show that the strength of the zeolite rich nyt is systematically reduced when saturated with water the ratio of wet to dry strength is 0 63 complementary experiments show that two other common neapolitan building stones piperno tuff and the grey campanian ignimbrite both facies of the campanian ignimbrite deposit devoid of zeolites do not weaken when wet from these data and previously published data for tuffs around the globe we conclude that the water weakening in nyt is a consequence of the presence of abundant zeolites the block tested herein contains 46 wt of zeolites these data may help explain weathering damage in nyt building stones due to rainfall rising damp and proximity to the sea or water table and the observed link between rainfall and landslides rock falls and sinkhole formation in naples and the weathering of other buildings built from zeolite rich tuffs worldwide

the petrographic and geomechanical properties of some sandstones from the newspaper member of the natal group near durban south africa abstract sandstones are by far the most important rock type in the natal group which is mainly a terrestrial succession formed during ordovician silurian times the most notable member of the group is the newspaper member from which sample material was obtained most of the material sampled was fine to medium grained arkosic sandstone they are well cemented with generally low porosity accordingly sandstones of the newspaper member tend to be very strong and of low deformability few of the petrological properties of these sandstones have a notable influence on the mechanical properties however increasing clay content tends to lower the unconfined compressive strength whilst increasing quartz content tends to enhance it on the other hand many of the mechanical properties are interrelated significant or highly significant relationships occur amongst the strength parameters and between hardness and strength young s modulus also has significant relationships with strength and hardness another property which has a significant influence on strength and deformability is porosity

an enhanced equivalent continuum model for layered rock mass incorporating bedding structure and stress dependence abstract layered rock masses exhibit significant anisotropy in both the deformability and strength properties of this rock mass are largely affected by its bedding structure and also by the stress state change for the purpose of characterizing these salient features using the equivalent continuum concept an enhanced model is proposed in this paper based on the ubiquitous joint model in the enhanced model the intact bedded rock is assumed to behave as a transversely isotropic elastic body a modified anisotropic strength criterion is adopted to describe the direction dependence of the strength of intact bedded rock in addition stress sensitive parameters are utilized for both the intact rock and bedding plane among which the dilation angle and strength parameters of intact rock are influenced by confining pressure and loading history whereas the stiffnesses of bedding planes are closely related to the current normal stress the effect of layer thickness on the mechanical behavior of rock mass is reflected by continuously updating the global stiffness matrix after failure of bedding plane and by conditions for conducting bedding plane related calculations determined by the relative scales between element size and layer thickness preliminary validation of this model is conducted by comparing with the closed form solutions and with laboratory tests generally good agreements can be achieved between numerical simulations and theoretical experimental results which indicate that applicability of the enhanced model on underground engineering issues related to layered rock mass is promising

analytical solution for determining the plastic zones around twin circular tunnels excavated at great depth abstract many existing planar elastoplastic analyses have been limited to the case of only one tunnel excavated in rock mass the mohr coulomb failure criterion which is widely used in rock engineering is considered in this paper to propose an analytical method for determining the plastic zones around twin circular tunnels of equal size excavated at great depth the premise is that the plastic zone around each tunnel can completely enclose the tunnel edge and the two plastic zones are not connected the unknown elastic zone on the physical plane is mapped onto an annular region on the image plane using the conformal transformation in the complex variable method which transforms the problem of determining the elastoplastic interfaces into solving the mapping function coefficients on the basis of the stress continuity conditions along the two elastoplastic interfaces the nonlinear equations about the mapping function coefficients are established and then solved effectively by the differential evolution algorithm in which the coefficients are considered as design variables the presented solution is verified by numerical solution the influence of tunnel spacing cohesion internal friction angle and in situ stresses on plastic zones are analyzed

hoek brown parameters for predicting the depth of brittle failure around tunnels a review of underground openings excavated in varying rock masstypes and conditions indicates that the initiation of brittlefailure occurs when the damage index di expressed as theratio of the maximum tangential boundary stress to the laboratoryunconfined compressive strength exceeds approx0 4 when thedamage index exceeds this value the depth of brittle failure around a tunnel can be estimated by using a strengthenvelope based solely on cohesion which in terms of thehoek brown parameters implies that m 0 it is proposed that inthe brittle failure process peak cohesion and friction are notmobilized together and that around underground openings thebrittle failure process is dominated by a loss of the intrinsiccohesion of the rock mass such that the frictional strengthcomponent can be ignored for estimating the depth of brittlefailure an essential component in designing support for theopening case histories were analyzed using the hoek brownfailure criterion with traditional frictional parameter

monitoring velocity changes caused by underground coal mining using seismic noise we use passive seismic interferometry to monitor temporal variations of seismic wave velocities at the area of underground coal mining named jas mos in poland ambient noise data were recorded continuously for 42 days by two three component broadband seismometers deployed at the ground surface the sensors are about 2 8 km apart and we measure the temporal velocity changes between them using cross correlation techniques using causal and acausal parts of nine component cross correlation functions ccfs with a stretching technique we obtain seismic velocity changes in the frequency band between 0 6 and 1 2 hz the nine component ccfs are useful to stabilize estimation of velocity changes we discover correlation between average velocity changes and seismic events induced by mining especially after an event occurred between the stations the velocity decreased about 0 4 based on this study we conclude that we can monitor the changes of seismic velocities which are related to stiffness effective stress and other mechanical properties at subsurface caused by mining activities even with a few stations

the elasto plastic response of underground excavations in rock masses that satisfy the hoek brown failure criterion abstract this paper is intended to illustrate the relationship between the hoek brown parameters describing the strength of rock masses and the mechanical response of underground openings a formulation of the elasto plastic behavior of rock in terms of the hoek brown criterion is presented the analysis assumes that the joint system present in the rock mass has no preferred orientation so that the medium can be considered to behave as an isotropic continuum it is shown that appropriate scaling of the hoek brown parameters leads to considerable simplification in defining the elasto plastic response of the rock mass the classical case in which the excavation process is treated as a uniform reduction of internal pressure in symmetrically loaded cylindrical and spherical cavities is considered closed form expressions are given for the extent of plastic behavior and the related stress and displacement fields a dimensionless graphical representation of these solutions is provided that allows accurate estimates of the response of excavations in hoek brown materials to be made quickly and easily examples are given to illustrate the use of the graphs illustrative applications of the derived closed form solutions are also described the construction of ground reaction curves for the design of cylindrical tunnels according to the convergence confinement method and a case study of stability analysis of spherical cavities produced by underground nuclear explosions in french polynesian atolls are discussed

large deformation of tunnels in longwall coal mines large deformation of tunnels in longwall coal mines creates massive cracks in the surrounding rocks which may cause groundwater loss and threaten the coal mine safety rock mechanical characterization is crucial for understanding the large deformation of underground openings based on the theoretical analysis and laboratory triaxial tests this study aims to propose a strength degradation model of the rocks for a deep understanding on the large deformation of underground openings the proposed model captures the non linear post peak rock strength degradation which is dependent on the plastic strains accumulated under the decreasing confining pressures the stress dependent elastic properties were not considered in this study the proposed model was incorporated in a finite difference package flac3d for engineering application the simulated surface convergence of the underground opening matches the in mine measurements which supports the proposed model more importantly the simulated crack zone after tunnel excavation agrees with the observations from borehole images therefore the proposed model provides a helpful tool to evaluate the safe margin of an underground tunnel if it is close to a subsurface water bearing formation it also sheds lights on the underground tunnel design to prevent the adjacent groundwater from inrush

analytical solution of displacement and stress induced by the sequential excavation of noncircular tunnels in viscoelastic rock abstract the sequential excavation of a tunnel cross section is usually employed in large scale tunnel construction to reduce the excavation impact on surrounding rock time dependent sequential excavation combined with rock rheology makes the mechanical response of the surrounding rock a complex function of time and it is possibly closely related to the excavation path this study presents new analytical solutions that account for an arbitrary sequential excavation of the tunnel s cross sections the ground s viscoelastic properties arbitrary tunnel shapes and pressures exerted at the internal tunnel boundaries due to liners or water pressures the time dependent analytical solutions for the stresses and displacements in each excavation step are derived by complex variable theory conformal mapping and the laplace transform technique the solutions agree very well with the fem numerical results for models that are completely consistent and they are qualitatively consistent with the field data in addition the mechanical mechanism of the time dependency of the displacement is analyzed in detail for two types of viscoelastic models then parametric analyses are conducted for the sequential excavation of a rectangular tunnel a semi arched tunnel with a vertical wall and a horseshoe tunnel to investigate the influence of the excavation sequences excavation time and the supporting pressures on the ground displacements and stresses the proposed analytical solutions can help reveal the particular mechanical mechanism of the time dependent ground responses due to sequential excavations combined with rock rheology as well as provide an alternative method in the preliminary designs of future tunnels

fracture initiation growth and effect on stress field a numerical investigation a numerical investigation was made of the relationships between fracture initiation growth stress field and boundary conditions two dimensional plane strain continuum models were used in which fractures appeared as zones of strain localization developed through application of a strain softening mohr coulomb constitutive model r and r fractures developed first followed by y fractures at larger strains the models showed that equal development of conjugate r and r fractures is easily changed to favor one or the other set by minor variations in model initial conditions strength loss in fractures caused stress field rotations in regions bounded by fractures altering the orientation of subsequent fractures the amount and sense of stress field rotation is dependent on the strength loss during displacement on the fractures the orientation of fractures and on the boundary conditions y oriented fractures could be explained on the basis of a mohr coulomb failure criterion provided that stress field rotation is accounted for monitoring of fracture slip activity showed that under conditions of constant boundary velocity slip was discontinuous in time alternating on fractures throughout the model

application of alternative methods for determination of rock quality designation rqd index a case study from the rožna i uranium mine stražek moldanubicum bohemian massif czech republic a comparison of rock quality designation rqd parameters obtained by drill core analysis and the rqd determined using alternative methods is presented using metamorphic rocks such as migmatized gneisses migmatites and amphibolites methods of borehole wall imaging using high resolution acoustic logging optical televiewer and simple video inspection as well as the structural analysis of exploration drift walls oriented subparallel to the analysed boreholes are used for alternatively evaluated rqd values results show that in most cases the rqd index measured directly on a drill core section reaches lower values about 10 30 than the rqd evaluated by alternative methods significant differences in determination of the rock mass failure degree using classical and alternative methods may occur especially in sections with higher frequency of the metamorphic foliation planes created by biotite rich bands or by dark coloured melanosome layers the nature of biotite itself is favourable for the creatio

estimating the support effect of energy absorbing rock bolts based on the mechanical work transfer ability abstract an interaction model is proposed to describe the interaction between the energy absorbing rock bolt and the rock mass based on the plane strain axial symmetry assumption and the incremental theory of plasticity the equilibrium equations and compatibility equations of rock mass as well as the response of the energy absorbing rock bolt are deduced theoretically the proposed method was programmed in a visual basic environment and a semi analytical solution for the coupling model was achieved the reinforcement mechanism of the energy absorbing rock bolt in conventional tunneling is clearly demonstrated through an illustrative case study the reinforcement effect of the energy absorbing rock bolt under different conditions was estimated quantitatively and its mechanical work transfer ability is presented in addition the validity of the proposed method was verified through numerical simulations finally a number of derivative cases were investigated to reveal the influence of the bolt and rock properties on the reinforcement effect and the bolt work transferred on the rock mass in the case of higher in situ stress or low strength rock mass the support effect of the energy absorbing rock bolt is significantly improved and the bolt absorbs more energy increasing the bolt installation density could always be helpful for the stabilization of the surrounding rock mass however additional rock bolt length could hardly affect ground reinforcement because the bolt section embedded in the elastic region of the rock mass could barely help to constrain the elastic displacement release the bolt should be installed no later than the stage of critical inner pressure namely when the plastic region occurs

end bearing response of open ended pipe piles embedded in rock abstract prediction of bearing capacity of steel pipe piles in rock masses is an important consideration in civil engineering especially as such prediction influences the safety of the supported superstructures as well as the pile integrity in pile driving operations provided that the rock mass is described as a linear elastic and perfectly plastic material obeying the hoek brown failure criterion a finite element analysis is performed to investigate the embedment depth effect on the annular base bearing capacity and the failure mechanism of typical open ended pipe piles in sedimentary rock masses the pipe pile has smooth walls and rough toe surface annular toe resistance of pipe piles can serve as an estimate of the rock mass resistance to driving in a fully coring mode which is usually expected for large diameter open ended pipe piles pipe pile results are also extended to circular piles and embedded strip foundations socketed in rock masses the analysis is shown to highlight the influence of the annular geometry of the pipe pile causing an unsymmetrical failure mechanism with respect to pipe wall center as well as an inclination of rock mass reaction which if sufficiently large may lead to pile convergence and damage during pile driving operations the failure mechanism legitimates the plug tendency to rise up in the pipe and explains the plug formation the study demonstrates that in most practical applications the bearing capacity of pipe piles approaches a limiting value which is less than or at most equal to the end bearing capacity of an embedded strip foundation of width equal to the pipe wall thickness a comparison has been made with experimental data it is shown that the results are relatively in good agreement with test data in terms of rock mass resistance and the mechanism of rock plug formation

exact and approximate solutions for displacements around circular openings in elastic brittle plastic hoek brown rock abstract a simple exact solution is presented for the elastic brittle plastic plane strain analysis of displacements around circular openings in an isotropic hoek brown rock subjected to a hydrostatic in situ stress the integration involved in the solution is carried out by using a standard mathematical software results produced by using the present exact method are found to be identical to those obtained by using a recently published closed form but complicated solution based on a transformation technique an extremely simple but approximate closed form solution was earlier derived by making a simplifying assumption for the evaluation of the elastic part of the total strain in the plastic zone several example cases are analyzed to show that the simplifying assumption made in the derivation of the simple closed form solution has an insignificant effect on the results for displacements for practical problems the innovative approximation technique may be used to obtain simple solutions of a wide variety of complex plasticity problems in rock mechanics

post yield plastic frictional parameters of a rock salt using the concept of mobilized strength abstract salt slabbing spalling and fallout surrounding underground salt storage cavern are closely associated with the nonlinear deformability and post yield property of rock salt a better understanding of the pre and post yield behavior of rock salt helps the designer in predicting displacements and failure zones around the salt cavity more accurately as well as in the optimizing design and operation in the present study an approach to determine young s modulus and poisson s ratio from triaxial test plots has been discussed a series of compression tests was performed to explore the nonlinear deformability and post yield strength properties of a rock salt the rock salt specimens were prepared from jintan salt deposit china it is found that the error in modulus obtained by directly computing the gradient of stress strain curve is relatively small and can be used in analysis however error in poisson s ratio is large the post yield strength characteristics were described by nonlinear empirical evolution law of mobilized strength components with maximum principal strain during the process of strain softening hardening the proposed generalized mohr coulomb strength criterion with cohesion weakening and frictional strengthening was proved effective to capture the post yield behavior of rock salt

considerations of the dilatancy angle in rocks and rock masses the present study responds to the poor treatment given to dilatancy in classical rock mechanics post failure problems such as tunnel or mine pillar design a comprehensive review of the literature and observations in regard to published test results would indicate that dilatancy is highly dependent both on the plasticity already experienced by the material and confining stress moreover it also appears that scale may play a non negligible role in our article we provide a detailed analysis of published test data with a view to proposing a sufficiently significant but conveniently simple formulation of the dilatancy angle that reflects these dependencies and that can be readily implemented in numerical codes the model is then tested demonstrating that it is capable of representing rock sample strain behaviour in compressive tests finally the model is applied to the resolution of ground reaction curves for tunnels in poor to average quality rock masses showing a good correlation with results obtained using practical rock engineering techniques r 2005 elsevier ltd all rights reserved

the 1793 eruption of san martin tuxtla volcano veracruz mexico abstract san martin tuxtla n18 562 w95 199 1659 masl is a basaltic volcano located in southern veracruz a mexican state bordering the gulf of mexico it rises in a volcanic field strewn with monogenetic volcanic cones maars and three other large volcanoes mostly dormant since the late pliocene santa marta san martin pajapan and cerro el vigia the latest eruptive event of san martin occurred in 1793 and was described by don jose mariano mozino a naturalist under the commission of the viceroy of the then new spain in this work we present results of the study of this eruption based on historical accounts and field observations we identified an ash deposit around the volcano related to the 1793 eruption mapped its distribution and determined its granulometric petrographic and geochemical characteristics these studies suggest that the volcano began its activity with explosive phreatomagmatic explosions which were followed by strombolian activity this period lasting from march to october 1793 the activity continued with an effusive phase that lasted probably 2 years the eruption covered an area of about 480 km2 with at least 1 cm of ash the fines reaching distances greater than 300 km from the crater a total mass of about 2 5 1014 g was ejected and the volcanic columns probably reached altitudes of the order of 10 km during the most explosive phases the lava emitted formed a coulee that descended the northern flank of the volcano and has an approximate volume of 2 0 107 m3

influence of plastic shear strain and confinement dependent rock dilation on rock failure and displacement near an excavation boundary abstract excavation induced rock failure and displacement near an underground opening boundary is closely associated with rock mass dilation a better understanding of rock mass dilation around the excavation helps us to predict or anticipate displacements and extent and shape of the failed zone and subsequently assist design of proper ground support systems a calibrated cohesion weakening and frictional strengthening cwfs model with a constant dilation angle can capture the stress induced brittle failure shape in hard rocks however the use of a constant dilation angle in either cwfs mohr coulomb perfectly elasto plastic or mohr coulomb strain softening models cannot simulate the displacement distribution near the excavation reasonably in the present study numerical simulations are performed to study excavation induced displacement around tunnels located in different rock mass types i e coarse grained hard rock medium grained hard rock fine medium grained soft rock and fine grained soft rock using a mobilized dilation angle model that depends on both confining stress and plastic shear strain it is illustrated from a few examples that displacement distributions obtained from the dilation angle model are more reasonable when compared with the general trend measured underground

the brittle deformation regime of water saturated siliceous sandstones summary we present here new experimental data on the mechanical behaviour of water saturated bentheim and fontainebleau sandstones deformed in the brittle failure regime bentheim sandstone samples were stressed at room temperature and subjected to confining pressures pc ranging from 12 to 120 mpa and pore pressures pp ranging from 1 to 70 mpa for all samples the evolution of the volumetric strain first shows compaction eventually reversing to dilation of the pore volume when approaching the peak stress all samples failed localized on a single shear zone critical stresses that is onset of dilatancy and peak stress can be uniquely defined as a function of the effective pressure peff pc pp the failure curve parameters when fitted with the hoek brown criterion or a parabolic envelope are consistent with previous values obtained on similar material when compared to data obtained on dry samples of the same rock the present data show no notable effect of the presence of water on the critical stress levels the same conclusion holds for the stress strain curves when dry and water saturated experiments under equivalent effective confining pressures are compared when compared to previously published data obtained on various quartzose rocks which show a quite variable water weakening effect our results lead to the conclusion that the quasi exclusive presence of quartz grains bonded together by a quartzose cement combined with the absence of clayey minerals may explain the absence of this effect in bentheim sandstone moreover this conclusion is supported by complementary results obtained by fontainebleau sandstone with similar microstructural and compositional characteristics a previously developed micromechanical model based on the interaction of pore cracks has been used and modified to take into account the presence of water when compared to the experimental data the results of the model show good agreement for low to intermediate effective confining pressures critical stresses as well as deformation curves are well reproduced as was the case for the dry rock provided that effective pressure is introduced at higher effective pressures a mix of mechanisms including shear enhanced compaction may explain the progressive discrepancy between the modelled and the experimental curves when approaching the apex of the failure envelope

intraplate paleostresses reconstructed with calcite twinning and faulting improved method and application to the eastern paris basin lorraine france this study deals with the reconstruction of intraplate paleostresses calcite twinning inversion provides paleostress directions and differential values even in poorly outcropping areas however existing methods are not well adapted to multiphase deformation cases and the calculation of stress values provides unreliable estimates modifications were brought to a calcite twinning inverse method and to the processing of results in a new twin data separation process the whole set of data is used to calculate each tensor the variability of yield stress value for twinning with strain hardening is taken into consideration a first order yield stress calcite grain size dependence function has been established with a sample showing various grain sizes this modified method of calcite twinning inversion was applied in the eastern paris basin lorraine france in this platform area measured fractures are preferentially trending ne sw and nw se at all scales the meso cenozoic paleostress succession reconstructed with fault slips is complex jurassic sedimentation occurred during the tethys rifting a mainly strike slip phase with r1 successively striking nnw and nne is attributed to the tertiary pyrenean orogenesis and is followed by wnw extension in the oligocene after local ene compression wnw compression was probably due to the alpine late miocene collision the calcite twinning inversion has confirmed these tectonic events and their succession order and the directions of stress axes were specified using grain size and strain rate sensitive yield stress values the differential stresses can be estimated with an uncertainty of few mpa they range between 20 and 30 mpa depending on the tectonic event the oligocene paleodepths of the sampled calcite estimated using differential stress values are structurally sensible thus the original calcite twinning inverse method has been improved complex paleostress successions such as in platform areas may be deciphered by combination with fault slip inversion even if additional improvement is possible this calcite twinning inverse method opens new ways to determine stress distributions in tectonic plates d 2004 published by elsevier b v

determining the size and shape of blocks from linear sampling for geotechnical rock mass classification and assessment classifying and assessing geotechnical aspects of rock masses involves combining parameters in various ways guided by empirical considerations to derive quantitative geotechnical parameters geological structures and the deformation history of rocks underpin the nature of rock masses the kinematics of a deforming rock mass may occur as sliding along throughgoing discontinuities or as distributed sliding on block faces distributed sliding will tend to disrupt the continuity of planar structures such that data on the size and shape of blocks is needed rather than relying on discontinuity orientation data alone orientation and spacing data can be combined to provide a geometric analysis of block systems from linear samples such as drill core dihedral angles and spacing of sequential pairs of discontinuities provides a sample of the size and shape of blocks that can be interpreted stereologically further detail can be derived by combining neighbouring intersections that enclose or partially enclose individual blocks the shape and size of a block can be represented on a stereograph with the enclosing faces shown as poles and their perpendicular distance from an arbitrary point inside the block shown as a number identifying the size and shape of specific blocks rather than relying on statistical methods is beneficial to critical aspects of design such as analysing keyblocks that would be exposed during excavations the detailed characterization of block size and shape is also a step toward interpreting the kinematics of rock mass deformation and the analysis of rock masses as ultra close packed dilatant granular systems

empirical and numerical analyses of support requirements for a diversion tunnel at the boztepe dam site eastern turkey abstract this paper presents the engineering geological properties and support design of a planned diversion tunnel at the boztepe dam site that contains units of basalt and tuffites empirical theoretical and numerical approaches were used and compared in this study focusing on tunnel design safety rock masses at the site were characterized using three empirical methods namely rock mass rating rmr rock mass quality q and geological strength index gsi the rmr q and gsi ratings were determined by using field data and the mechanical properties of intact rock samples were evaluated in the laboratory support requirements were proposed accordingly in terms of different rock mass classification systems the convergence confinement method was used as the theoretical approach support systems were also analyzed using a commercial software based on the finite element method fem the parameters calculated by empirical methods were used as input parameters for the fem analysis the results from the two methods were compared with each other this comparison suggests that a more reliable and safe design could be achieved by using a combination of empirical analytical and numerical approaches

reliability of hoek brown estimates of rock mass properties and their impact on design this technical note examines the reliability of a slope stability calculation and a tunnel support design calculation

a new method of estimating the ratio between in situ rock stresses and tectonics based on empirical and probabilistic analyses this paper describes a new procedure for assessing the ratio between in situ stresses in rock masses by means of k k h v being h and v principal stress and tectonics for purposes of engineering geology and rock mechanics the method combines the use of the logic decision tree and the empirical relationship between the tectonic stress index tsi and a series of k in situ values obtained from an extensive database the decision tree considers geological and geophysical factors affecting stress magnitudes both on the regional and local scale the tsi index is defined by geological and geomechanical parameters the method proposed provides an assessment of the magnitude of horizontal stresses of tectonic origin results for several regions of europe are presented and the possible applications of the procedure are discussed

analytical solution for a circular opening in an elastic brittle plastic rock abstract this paper deals with the analytical solutions for the prediction of displacements around a circular opening in an elastic brittle plastic rock mass compatible with a linear mohr coulomb or a nonlinear hoek brown yield criterion three different cases of definitions for elastic strains in the plastic region used in the existing solutions are mentioned the closed form analytical solutions for the displacement in the plastic region are derived on a theoretically consistent way for all the cases by employing a non associated flow rule the results of the dimensionless displacements are compared using the data of the soft and hard rocks to investigate the effect of different definitions for elastic strains with the dilation angle

rock mass response model for circular openings the main parameters affecting the failure and deformation state of the rock mass around a circular opening are the level of vertical and horizontal in situ stresses the characteristics of the rock mass the diameter of the opening and the support pressure the influence of all these parameters on the stress induced final deformations around circular openings was investigated by a finite difference based two dimensional numerical simulation for both hydrostatic and nonhydrostatic stress field conditions from the results of the parametric studies the variation of tunnel strain versus the ratio of uniaxial compressive strength of the rock mass to in situ vertical stress and the ratio of radial support pressure to in situ vertical stress for fair quality and poor quality rock masses was statistically analysed as a result of the three dimensional nonlinear regression analysis and surface curve fitting process by means of a large number of models a best fit model with the best correlation with these dimen