why permafrost rocks become unstable a rock ice mechanical model in time and space in this paper we develop a mechanical model that relates the destabilisation of thawing permafrost rock slopes to temperature related effects on both rock and ice mechanics and laboratory testing of key assumptions is performed degrading permafrost is considered to be an important factor for rock slope failures in alpine and arctic environments but the mechanics are poorly understood the destabilisation is commonly attributed to changes in ice mechanical properties while bedrock friction and fracture propagation have not been considered yet however fracture toughness compressive and tensile strength decrease by up to 50 and more when intact water saturated rock thaws based on literature and experiments we develop a modified mohr coulomb failure criterion for ice filled rock fractures thatincorporates fracturing of rock bridges friction of rough fracture surfaces ductile creep of ice and detachment mechanisms along rock ice interfaces novel laboratory setups were developed to assess the temperature dependency of the friction of ice free rock rock interfaces and the shear detachment of rock ice interfaces indegrading permafrost rock mechanical properties may control early stages of destabilisation and become more important for higher normal stress i e higher magnitudes of rock slope failure ice mechanical properties outbalance the importance of rock mechanical components after the deformation accelerates and are more relevant for smaller magnitudes the model explains why all magnitudes of rock slope failures can be prepared and triggered by permafrost degradation and is capable of conditioning long paraglacial response times here we present a synoptic rock and ice mechanical model that explains the mechanical destabilisation processes operating in warming permafrost rocks

diagenetic stabilization of aragonite and low mg calcite i trace elements in rudists abstract cretaceous rudists with thick multilayered bimineralic aragonite and low mg calcite shells have been studied for the effects of meteoric diagenesis on their textural and chemical attributes the original fine compact prismatic or cellular prismatic microstructures of low mg calcitic layers have been preserved frequently despite the vagaries of their subsequent diagenetic histories these layers usually suffered only partial recrystallization which caused fusion of crystal units rounding of prism comers and partial cementation confined to intercrystalline and intraparticle pore spaces in contrast the originally aragonitic parts of the shell usually suffered either complete dissolution or at best retained some vestiges of their crossed lamellar or complex crossed lamella microstructures synsedimentary submarine diagenetic events such as borings by endolithic fauna internal micritic and or peloidal sedimentation and submarine aragonite and or high mg calcite cements within the primary inter and intraparticle pore spaces were coeval with rudist accretion the subsequent meteoric cementation has been characterized by the formation of bladed and equant ferroan calcites which occluded the residual primary and secondary porosities diagenetic stabilization of aragonite to diagnetic low mg calcite and low mg calcite to diagenetic low mg calcite is believed to have been a two stage process initially sr and na have been partially depleted during an early meteoric diagenetic phase calcitization of metastable phases with expulsion of sr at a slower rate than that of na this stage is followed by incorporation of more mn fe and mg due to precipitation of late ferroan calcite stabilization of aragonite causes more pronounced trace element repartitioning than the stabilization of low mg calcite however the degree of repartitioning depends not only on mineralogy but also on the structural buildup of a given shell layer suggesting that factors such as water rock ratio surface kinetics are of considerable sig ificance for the process of diagenetic stabilization rudist skeletal components with preserved original mineralogy and texture have trace element chemical signatures analogous to holocene marine bivalves this similarity argues for comparable chemical composition of the cretaceous and holocene seawater as well as for similar modes of incorporation of trace elements into mollusc shells

shear behaviour of idealized infilled joints under constant normal stiffness the shear behaviour of soft joints containing infill materials was investigated in the laboratory under constant normal stiffness cns conditions tests were conducted on joints with asperities having inclinations of 9 5 type 1 and 18 5 type ii under a given range of initial normal stresses no 0 30 to 1 10 mpa and at a constant normal stiffness of 8 5 kn mm it was found that the shear strength of joints decreases considerably even with the addition of a thin layer of infill results also show that the effect of asperities on shear strength is significant up to an asperity height to infill thickness t a ratio of 1 4 1 8 whereas the shear behaviour is controlled by the infill alone beyond this critical ratio the shear displacement corresponding to the peak shear stress is considerably reduced once the infill starts to govern the shear behaviour of the joint in this study the drop in peak shear stress under cns conditions has been modelled by a hyperbolic relationship in relation to cle

shear rupture under constant normal stiffness boundary conditions abstract a grain based distinct element method and its embedded grain based method are used to simulate the fracturing processes leading to shear rupture zone creation in a calibrated massive non jointed brittle rock specimen deformed in direct shear under constant normal stiffness boundary conditions under these boundary conditions shear rupture zone creation relative to the shear stress versus applied horizontal displacement load displacement curve occurs pre peak before the maximum peak shear strength is reached this is found to be the result of a normal stress feedback process caused by the imposed shear displacement which couples increases in normal stress due to rupture zone dilation with shear stress producing a complex normal shear stress path that reaches and then follows the rock s yield strength envelope while the yield envelope is followed the shear strength increases further and shear stress oscillations repeated stress drops followed by re strengthening periods in the load displacement curves occur due to fracture creation as the rupture zone geometry smoothens once the maximum peak strength is reached after a series of shear stress oscillations the largest stress drops occur as the ultimate or residual shear strength is approached the simulation results provide insight into the fracturing process during rupture zone creation and improve the understanding of the shear stress versus applied horizontal displacement response as well as the stick slip behaviour of shear rupture zones that are being created under constant normal stiffness boundary conditions

shear strength of rock joints influenced by compacted infill abstract discontinuities such as fault planes joints and bedding planes in a rock mass may be filled with different types of fine grained material that are either transported or accumulated as gouge due to weathering or joint shearing previous laboratory studies have mainly examined the role of saturated infill that exhibits the minimum shear strength however in practice the infill materials are often partially saturated generating matric suction within the joint that can contribute to increased shear strength to the authors knowledge this is the first study to examine the influence of compacted unsaturated infill on the joint shear strength a series of laboratory triaxial tests on idealised model joints and imprinted natural joint profiles was carried out with constant water contents of the infill being maintained from the laboratory results it is observed that the peak shear strength of infilled joints increased with the decrease of degree of saturation from 85 to 35 for both idealised joints and replicated natural joints based on the laboratory observations an empirical model for describing the infilled joint shear strength was developed

strength of jointed rock masses jointed rock masses comprise interlocking angular par ticles or blocks of hard brittle material separated by discontinuity surfaces which may or may not be coated with weaker materials the strength of such rock masses depends on the strength of the intact pieces and on their freedom of movement which in turn depends on the number orientation spacing and shear strength of the discontinuities a complete understanding of this problem presents formidable theoretical and experi mental problems and hence simplifying assumptions are required in order to provide a reasonable basis for estimating the strength of jointed rock masses for engineering design purposes this paper summarizes some of the basic information upon which such simplifying assumptions can be made a simple empirical failure criterion is presented and its application in engineering design is illustrated by means of a number of practical examples des masses jointives de rochers comprennent des particules angulaires enchevetrees ou des

comparison between models of rock discontinuity strength and deformation one important component in the design of tunnels in urban areas is a correct assessment of the interaction between the underground excavation with other structures in the vicinity in this sense a correct stress strain response by the model representing the rock mass behavior is essential the shear and normal displacement of rock discontinuities and their shear and normal stiffness control the distribution of stress and displacement within a discontinuous rock mass in conditions where an equivalent continuum based approach is not applicable the joint material model should be able to describe important mechanisms such as asperity sliding and shearing post peak behavior asperity deformation and the effect of soft infilling the distinct element code udec was used to simulate the direct shear tests on a natural joint profile and the prediction of two existing models of discontinuity strength and deformation were then compared with a new soil infilled joint model and with experimental data for clean and soil infilled rock joints a numerical modeling of a cavern excavated in a jointed medium is also presented to illustrate the response of different models the proposed soil infilled joint model described more comprehensively the occurrence of dilation and compression with lateral displacements and also better represented the double peak shearing in relation to the adopted squeezing mechanism that could not be captured by the two existing models

tectonic control on sediment accretion and subduction off south central chile implications for coseismic rupture processes of the 1960 and 2010 megathrust earthquakes based on a compilation of published and new seismic refraction and multichannel seismic reflection data along the south central chile margin 33 46 s we study the processes of sediment accretion and subduction and their implications on megathrust seismicity in terms of the frontal accretionary prism fap size the marine south central chile fore arc can be divided in two main segments 1 the maule segment south of the juan fernandez ridge and north of the mocha block characterized by a relative large fap 20 40 km wide and 2 the chiloe segment south of the mocha block and north of the nazca antarctic south america plates junction characterized by a small fap 10 km wide in addition the maule and chiloe segments correlate with a thin 1 km thick and thick 1 5 km thick subduction channel respectively the mocha block lies between 37 5 and 40 s and is configured by the chile trench mocha and valdivia fracture zones this region separates young 0 25 ma oceanic lithosphere in the south from old 30 35 ma oceanic lithosphere in the north and it represents a fundamental tectonic boundary separating two different styles of sediment accretion and subduction respectively a process responsible for this segmentation could be related to differences in initial angles of subduction which in turn depend on the amplitude of the down deflected oceanic lithosphere under trench sediment loading on the other hand a small fap along the chiloe segment is coincident with the rupture area of the trans pacific tsunamigenic 1960 earthquake mw 9 5 while a relatively large fap along the maule segment is coincident with the rupture area of the 2010 earthquake mw 8 8 differences in earthquake and tsunami magnitudes between these events can be explained in terms of the fap size along the chiloe and maule segments that control the location of the updip limit of the seismogenic zone the rupture area of the 1960 event also correlates with a thick subduction channel chiloe segment that may provide enough smoothness at the subduction interface allowing long lateral earthquake rupture propagation

fore arc structure and plate boundary earthquake sources along the southwestern kuril subduction zone 1 the geologic structure and gravity anomalies of the fore arc wedge along the southwestern kuril arc were compared with the sources of seismic waves and tsunamis of the 1952 1973 and 2003 plate boundary earthquakes the source areas are generally located beneath fore arc basins in the upper slope which has been subsiding except for the tsunami source of the 1952 earthquake while the slip amount varies beneath the basins large slip of seismic sources of the 1952 and 2003 earthquakes occurred under the low gravity anomaly zone of a fore arc basin and a structural ridge along the n s oriented collision zone between the kuril and ne japan fore arcs where there is inferred to be a zone of a strong basal erosion of the overriding plate the tsunami sources are located under the subsiding area to the east of the collision zone these comparisons indicate that the source areas are primarily restricted to the region under the subsiding area of the upper slope and the lateral change of slip amount in the source areas is related to the collision tectonics of the fore arc sliver the 1952 tsunami source extended seaward which was presumably induced by the slip of the larger seismic source under the upper slope the lack of large scale slope failure or splay faults in the middle to lower slope suggests that the slip along the plate boundary is responsible for tsunami generation a subducting seamount presumably prevented the seaward propagation of the rupture beneath the middle to lower slope

development and applications of a synthetic material to simulate soft sedimentary rocks due to the fact that a model material can be made homogeneous the influence of different variables on behavioural mechanisms can be investigated independently consequently large experimental scatter attributed to inherent variables generally unknown of a natural material can be avoided this paper presents the development of an artificial material which can effectively simulate the behaviour of an array of weak sedimentary rocks this synthetic soft rock was constituted with gypsum cement fine sand and water and characterized with homogeneous and isotropic properties with insignificant variability from one batch to another it can be easily manufactured in the laboratory and can be cast either in large or small volumes to occupy any predetermined shape of given physical dimensions an experimental application to study the behaviour of reinforced composites simulated bolted rock is also described in this paper puis qu une matiere modele peut etre rendue homogene il est possible d etudier de fac

contributions to geotechnique 1948 2008 engineering geology rock mechanics and rock engineering throughout its history geotechnique has regularly published papers on the fundamentals of engineering geology the core concepts of rock mechanics and the practice of rock engineering in totality these papers provide a concise history of the development of these areas of geotechnics here a review of many of these papers is presented in terms of the specific themes of engineering geology rock slope instability behaviour of intact rock and discontinuities in rock field measurements in rock mechanics discontinuous rock masses numerical modelling and rock engineering papers covering a wide range of issues within these themes are outlined together with an indication of how they have influenced later developments the review clearly demonstrates how geotechnique has been at the forefront of rock mechanics rock engineering and engineering geology for the whole of its 60 year existence

tsunamigenic structures in a creeping section of the alaska subduction zone segments of subduction zones that are capable of generating tsunamigenic earthquakes appear to have characteristic structural configurations these structures include heterogeneous plate interfaces a small wedge of deformed sediment at the toe of the overriding plate the frontal prism and splay faults in the crust of the overriding plate that root within the plate boundary megathrust here we use seismic reflection imaging to show that these features also exist within a creeping segment of the alaska subduction zone the shumagin gap we identify an active crustal scale normal fault system that dips landward and resembles that involved in the 2011 tohoku oki earthquake in japan we also find that the shumagin gap has a small frontal prism a deep water splay fault and that the plate interface here is rough and thinly sedimented we propose that lateral propagation of rupture from a neighbouring segment into the shumagin gap may explain a tsunamigenic earthquake that occurred there in 1788 and that tsunamigenic potential should be considered in hazard assessments for the region our results demonstrate that structural configurations similar to those in tohoku may exist in other subduction zones including within creeping segments or segments with no record of historical megathrust earthquakes but are under recognized identifying similar configurations globally may improve our ability to anticipate regions capable of generating large tsunamis creeping subduction zones are unlikely to generate tsunamigenic earthquakes analysis of a creeping part of the alaskan subduction zone reveals fault structures similar to those in tohoku suggesting it may host large earthquakes and tsunamis

effect of soil infilled joints on the stability of rock wedges formed in a tunnel roof abstract the use of an equivalent continuum for a rock mass is not always suitable for situations where the failure is structurally controlled by discontinuities as in the case of wedges in the tunnel roof in these instances discontinuum approaches are usually preferred rock joints that are filled with soft infill are likely to be the weakest planes in a rock mass having a dominant influence on its overall shear behaviour in this case the joint material model adopted for the discontinuities should be able to describe important mechanisms such as asperity sliding and shearing post peak behaviour asperity deformation and the effect of the soft infilling the latest version of a soil infilled joint model is discussed here it describes more comprehensively than previous models the occurrence of dilation and compression with lateral displacements and also represents the hardening mechanism related to asperity interference as observed in the laboratory that cannot be readily captured by the existing joint models an analytical approach for the analysis of rock wedges structurally controlled by soil infilled joints and a numerical simulation based on a metro station collapse which occurred in brazil in 2007 are presented

dynamic modelling of fault slip with barton s shear strength model abstract barton s shear strength model has been incorporated into the flac3d code as a ubiquitous joint model using the plastic flow rule to analyze the potential effect of fault slip bursts on mine openings comparison of the incorporated model with the classical mohr coulomb model is conducted through a case study of a primary fault that is parallel to a steeply dipping tabular ore deposit which is mined out by the sublevel stoping method based on the results obtained from the numerical analyses seismic source parameters are calculated and compared for each case the results show that faults having rough surfaces tend to cause much larger seismic events than faults with smooth surfaces in addition parametrical study with respect to fault surface roughness shows that seismic moment and radiated energy significantly vary with the fault surface roughness and the seismic moment does not necessarily correlate with the radiated energy peak particle velocity excited by seismic waves arising from the simulated fault slips is also examined it is found out from the results that peak particle velocity is strongly dependent upon the fault surface roughness and has a correlation with the radiated energy but not with seismic moment

shear strength model for overconsolidated clay infilled idealised rock joints saturated infilled joints can contribute to the instability of rock masses during undrained shearing this paper reports an experimental investigation into the effect of the overconsolidation of infilled rough joints on undrained shear behaviour a revised model is presented for predicting the shear strength of rough infilled joints on the basis of experimental tests carried out on idealised sawtoothed joints with natural silty clay as the infill material tests were conducted under consolidated undrained conditions in a high pressure triaxial apparatus on joints having a dip angle of 60 pore pressure development in the infill materials was monitored the results show that the effect of asperities on shear strength is significant up to a critical asperity height to infill thickness ratio t a whereas the shear behaviour is controlled by the infill alone beyond this critical value the proposed model for predicting the shear strength of rough infilled joints describes how the ocr influences the shear strength pore water pressure development and critical t a ratio

use of a rotary shear box for testing the shear strength of rock joints this note describes a rotary shear machine similar to those designed by bishop green garga andersen brown 1971 and bromhead 1979 but suitable for testing rock surfaces especially the shear strength of rock surfaces separated by an infilling of weaker material the machine was constructed in 1986 and has recently been used to complete a series of trial tests on clean flat rock surfaces and similar surfaces separated by clean rock gouge it was specifically designed to accurately measure shear parameters up to peak failure and to follow these parameters beyond failure to their residual or basic angle of friction this permits an accurate study of the mechanisms governing shear resistance in rock joints which are subjeced to large displacements

frontal wedge deformation near the source region of the 2011 tohoku oki earthquake 1 we report an uplift of 5 m with a horizontal displacement of more than 60 m due to the 2011 tohoku oki earthquake the uplift was measured by an ocean bottom pressure gauge installed before the earthquake on a frontal wedge which formed an uplift system near the japan trench horizontal displacements of the frontal wedge were measured using local benchmark displacements obtained by acoustic ranging before and after the earthquake the average displacements at the frontal wedge were 58 m east and 74 m east southeast these results strongly suggest a huge coseismic slip beneath the frontal wedge on the plate boundary the estimated magnitude of the slip along the main fault was 80 m near the trench our results suggest that the horizontal and vertical deformations of the frontal wedge due to the slip generated the tremendous tsunami that struck the coastal area of northeastern japan

tsunamis and splay fault dynamics 1 the geometry of a fault system can have significant effects on tsunami generation but most tsunami models to date have not investigated the dynamic processes that determine which path rupture will take in a complex fault system to gain insight into this problem we use the 3d finite element method to model the dynamics of a plate boundary splay fault system we use the resulting ground deformation as a time dependent boundary condition for a 2d shallow water hydrodynamic tsunami calculation we find that if the stress distribution is homogeneous rupture remains on the plate boundary thrust when a barrier is introduced along the strike of the plate boundary thrust rupture propagates to the splay faults and produces a significantly larger tsunami than in the homogeneous case the results have implications for the dynamics of megathrust earthquakes and also suggest that dynamic earthquake modeling may be a useful tool in tsunami research

a simple shear strength model for interlayer shear weakness zone interlayer shear weakness zone iswz is a widespread zonal weak geotechnical system with variable thickness in rock masses representing a potential threat to the overall stability of structure constructed on or within the rock mass due to their relatively poor mechanical properties its shear behaviour depends on both the interlayer soil and the interlayer soil host rock interface soil rock interface in this study a dynamic approach is adopted by treating iswz as an unfilled joint rock rock interface that is increasingly filled with interlayer soil of variable thickness based on the available experimental data a simple shear strength model is developed capable of describing both the shear behaviours of interlayer soil and soil rock interface because the geometric factors i e the thickness of interlayer soil and the morphology of interface and the mechanical conditions i e normal stress uniaxial compressive strength of rock and shear strength of interlayer soil are all taken into account the combining mechanical effect of interlayer soil and soil rock interface on the iswz is totally included in the model this is partly confirmed by the good agreement between the model prediction and the experimental results from laboratory and field tests

three dimensional inversion of regional p and s arrival times in the east aleutians and sources of subduction zone gravity highs free air gravity highs over forearcs represent a large fraction of the power in the earth s anomalous field yet their origin remains uncertain seismic velocities as indicators of density are estimated here as a means to compare the relative importance of upper plate sources for the gravity high with sources in the downgoing plate p and s arrival times for local earthquakes recorded by a seismic network in the eastern aleutians are inverted for three dimensional velocity structure between the volcanic arc and the downgoing plate a three dimensional ray tracing scheme is used to invert the 7974 p and 6764 s arrivals for seismic velocities and hypocenters of 635 events one dimensional inversions show that station p residuals are systematically 0 25 0 5 s positive at stations 0 30 km north of the aleutian volcanic arc indicating slow material while residuals at stations 10 30 km south of the arc are 0 1 0 25 s negative both features are explained in three dimensional inversions by velocity variations at depths less than 25 35 km tests using a one dimensional or a two dimensional slab starting model show that below 100 km depth velocities are poorly determined and trade off almost completely with hypocenters for earthquakes at these depths the locations of forearc velocity highs in the crust of the upper plate correspond to the location of the gravity high between the trench and volcanic arc free air anomalies calculated from the three dimensional velocity inversion result match observed gravity for a linear density velocity relationship between 0 1 and 0 3 mg m 3 km s 1 when a 50 km thick slab is included with a density of 0 055 0 005 mg m 3 values outside these ranges do not match the observed gravity the slab alone contributes one third to one half of the total 75 150 mgal amplitude of the gravity high but predicts a high that is much broader than is observed the inclusion of upper plate velocity anomalies predicts the correct width of the anomaly 100 150 km where the anomaly is most positive because the forearc gravity high is continuous along the entire aleutian arc and is found in most arcs globally high upper plate forearc velocities are suspected to be a common feature of the upper plate of most subduction zones the forearc mass excesses appear to be sustained by upward regional flexure of the upper plate that partly balances the depression of the lower plate at the trench thus elevating high density and high velocity material thus a part of the downward flexure of the subducting plate is regionally compensated by shallow positive mass anomalies in the upper plate and the strength of the upper plate helps generate the forearc gravity highs

laboratory testing and parameters controlling the shear strength of filled rock joints the shear strength of iofilled rock joints has been studied for a long time but a complete understanding of the mechanisms and of the parameters controlling the process has never been reached this paper reviews test results in the literature and compares them with results obtained by the authors the main parameters controlling the shear strength of infilled joints are discussed and a framework for understanding the failure mechanisms involved in the shearing of such discontinuities is given la resistance au cisaillement des joints rocheux remplis a ete etudiee depuis tres longtemps mais le mecanisme et les parametres controlant le processus n ont jamais ete totalement compris cet article passe en revue les resultats des essais publies et les compare avec les resultats obtenus par les auteurs les parametres principaux controlant la resistance au cisaillement des joints remplis sont discutes et un cadre pour comprendre les mecanismes de rupture associes au cisaillement de telles discontinuites est donne

a shear strength model for idealised infilled joints under constant normal stiffness infill materials found in natural rock joints may cause a reduction in joint shear strength influencing rock mass stability this paper reports a study aimed at developing a semi empirical methodology for predicting the shear strength of infilled joints taking into account joint surface characteristics and the properties of the joint and infill materials a new model for predicting the shear strength of infilled joints is presented on the basis of a series of tests carried out on two types of model joint surface having asperity angles of 9 5 and 18 5 with graphite and bentonite used as infill materials all tests were carried out in a large scale shear apparatus under constant normal stiffness cns conditions the results indicate that at low infill thickness to asperity height ratio t a the combined effect of the basic friction angle b and the joint asperity angle i is pronounced but it diminishes with increasing t a ratio so that the shear strength converges towards that of the infill al