fully softened shear strength at low stresses for levee and embankment design abstractshallow slides in levee and other embankment slopes are usually controlled by effective normal stresses less than 12 kpa 250 psf for first time slides in fine grained soils the fully softened shear strength is frequently used to model the strength of embankment soils because it represents the shear strength remaining after the effects of overconsolidation compaction desiccation or other strengthening processes have been removed because of wetting infiltration stress relief swelling and weathering however there is limited fully softened strength data at effective normal stresses less than 50 kpa 1 000 psf so existing correlations in this stress range must be extrapolated this paper presents new fully softened shear strength data at an effective normal stress of 12 kpa 250 psf and recommendations for estimating and modeling the stress dependent fully softened shear strength envelope directly or as a power function in stability analyses

comparison of site specific and empirical correlations for drained residual shear strength analyses of landslides slopes and embankments often require reliable drained residual shear strength estimates for cohesive deposits involving pre existing shear surfaces laboratory tests to meas

drained shear strength parameters for analysis of landslides this paper presents recommendations for selecting the type and magnitude of drained shear strength parameters for analysis of landslides in particular the importance existence and use of the cohesion shear strength parameter is reviewed for slope stability analyses it is recommended that the shear strength be modeled using a stress dependent failure envelope or a friction angle that corresponds to the average effective normal stress acting on the slip surface passing through that particular material instead of using a combination of cohesion and friction angle to represent soil shear strength other recommendations for stability analyses include using an effective stress cohesion of zero for residual and fully softened strength situations to facilitate selection of shear strength parameters for landslide analyses empirical relationships for the drained residual and fully softened strengths are updated from the previous empirical relationships presented by stark and eid finally the paper presents torsional ring shear test results that indicate that pre existing shear surfaces exhibit self healing that results in increased shear resistance the magnitude of healing appears to increase with increasing soil plasticity and this increase could have implications for the size timing and cost of landslide remediation

shear mechanisms and viscoplastic effects during impulsive shearing in clay formations the co seismic reactivation of pre existing landslides involves dynamic shear actions on sliding surfaces characterised by attritive states impulsive shear motions were applied after the attainment of the fully softened and residual conditions by means of an appropriately modified ring shear apparatus the kinematics parameters that characterise shear motions are related to co seismic displacements of rigid landslide bodies as defined by newmark s approach the results of the tests performed on clay samples with different index properties highlight the influence of the initial spatial disposition of particles on the shear mechanisms in addition it seems that these mechanisms control both the inviscid and viscous components of the shear stress for high shear rates an increase of the viscous strength in the residual condition determines a greater viscoplastic strength than that in the fully softened condition on this basis different behaviours in seismically induced reactivat

reduction in fully softened shear strength of natural clays with nacl leaching and its effect on slope stability abstractlandslides and slope failures in natural clay rich materials are frequently observed in coastal areas and other areas where these materials were deposited in a saline water environment high sodium chloride nacl concentration in the pore fluid results from deposition in this environment as shown by the results of this study subsequent reduction in the nacl concentration results in reduction in fully softened shear strength with potentially significant reduction in slope stability fourteen sample materials were collected from seven different landslide areas in niigata prefecture japan to evaluate the effect of saline water on fully softened shear strength fsss the sample materials were collected from the intact mudstones and the sliding surface materials pore waters from the powdered sliding surface materials exhibited low concentrations of nacl however the pore waters in the powdered intact rock samples exhibited a high concentration of nacl washing of nacl from the powdered intact

instability of amuay cliffside this paper presents a case study of cliffside instability geotechnical analyses employing field measurements and laboratory test results obtained over a 30 yr period indicate that rising pore pressures trigger slides along the cliff visual observation surveys and field exploration show that most of the landslides have wedge type failure geometry shear occurs through a nearly horizontal stratum of weak clay brown fat clay the strength of the fat clay decreases with deformation fluids generated by domestic and industrial activities have resulted in a perched water layer above the stratum of fat clay for more than two decades the pore pressure on top of the fat clay has risen a wedge type of stability analysis can give the correct factor of safety i e 1 0 for the slides which have occured asce

drained residual shear strength at effective normal stresses relevant to soil slope stability analyses abstract an extensive torsional ring shear testing program has been conducted to measure the drained residual shear strength of soils at the wide range of effective normal stress 10 to 700 kpa usually mobilized in reactivated and first time landslides soils mudstones and shales of different plasticity and gradation were tested in the program the effects of the change in nonlinearity of shear strength envelope over the utilized normal stress ranges on slope stability analyses were investigated using this data new empirical residual shear strength correlations were developed as a function of soil index parameters and wide range of effective normal stresses in essence the correlations are presented as revised versions of those previously developed for a limited number of normal stresses utilizing the same soil index parameters comparisons were made with a considerable amount of back calculated shear strength data reported in the literature for reactivated landslides as well as results predicted from existing shear strength correlations to verify the increased suitability of the new correlations for use in slope stability analyses a numerical expression was also introduced to express the residual shear strength correlations for direct incorporation in slope stability software

analysis of a sample containing a shear surface from a recent landslip south cotswolds uk the paper reports analysis of a block sample taken from a trial pit hand dug across the shear surface of an active landslide in the south cotswolds the slide is located on the upper fuller s earth some 50m downslope of the overlying great oolite limestone the weathering of which has produced ooliths and gravel sized fragments which are incorporated within the slipped mass sampling at 5 mm intervals confirmed the inverse relationship between the natural moisture content and calcite content in order to assess the significance of changes in moisture content in the fine fraction the influence of the non sorptive calcite was removed and a normalized moisture content profile established examination of the lower shear surface using scanning electron microscopy confirmed the parallel orientation of the clay minerals for a thickness of some 1 m this thin veneer extended over areas of granular material highlighting the importance of obtaining representative samples when shear strength assessment is under

effects of overconsolidation ratios on the shear strength of remoulded slip surface soils in ring shear the drained shear strength of clay soils is independent of stress history though there have been instances in the geotechnical literature of studies that have suggested some dependence of stress history on the drained shear strength accordingly the effect of artificial overconsolidation ratios ocr on the drained shear behaviour and shear strength of a high plasticity clay soil and a loess soil has been discussed from an experimental point of view the slip surface materials of two landslides were remoulded and consolidated from slurry and were subjected to drained shear tests four overconsolidation ratios ocr 1 ocr 2 ocr 4 and ocr 6 were tested under constant effective normal stress in a ring shear apparatus the overconsolidated specimens achieved peak friction coefficients at relatively lesser shear displacements in contrast to the normally consolidated specimens in the kamenose soil the fully softened friction coefficient and the residual friction coefficient showed stress dependency in the ocr 1 bloc of both soils however between the two soils although dissimilar patterns of variation of these two shear strength parameters in the overconsolidated state compared to the normally consolidated state was evident significant differences in the residual friction coefficient attributable to overconsolidation were not found

vp vs characterization of a heavy oil reservoir this article demonstrates a vp vs application for a heavy oil field near plover lake saskatchewan where nexen has applied both hot and cold production methods plover lake field is about 8 km east of the alberta saskatchewan border and about 320 km north of the canada u s border oil sands of the devonian mississippian bakken formation are found in ne sw trending shelf sand tidal ridges that can be up to 30 m thick 5 km wide and 50 km long overlying upper bakken shales are preferentially preserved between sand ridges the bakken formation is disconformably overlain by lodgepole formation carbonates mississippian and or clastics of the lower cretaceous mannville group since sandstones have larger s wave velocities and hence lower vp vs ratios than shales vp vs maps should help to identify thickening sand layers within the target zone we also intend to examine changes within the reservoir due to cold production unlike the steam injection processes used in enhanced heavy oil recovery cold prod

evaluation of common practice empirical procedures for residual friction angle of soils hawaiian amorphous material rich colluvial soil case study the residual strength of soils has received considerable attention after skempton suggested that the stability of reactivated landslides may be governed by residual strength in this respect numerous studies have been conducted to determine the factors affecting the residual strength of soils specifically research effort was focused on determining correlations between the residual friction angle of soils and soil indexes such as atterberg limits and clay fraction some of these researchers suggested that strong correlations exist with soil indexes other researchers claimed that there is no correlation between the soil index and the residual friction of soils thus there is a need to clarify whether there is a correlation between residual friction angle and soil index properties in this effort we describe general properties of landslides in hawaii with an emphasis on an active landslide followed by evaluating correlations between the residual strength and soil indexes the results of this study show that the existing empirical correlations for soil index properties and residual friction angle predict poorly the residual friction angle of colluvial soils that rich in amorphous materials however the results also show that a strong correlation between ll and pi and residual friction angle may exist depending on the soil mineral type

embankment failures at vernon british columbia a section of highway 97 west of vernon b c is located over a soft to firm compressible silty clay subsoil in addition to an extensive site investigation the performance of two test embankments was observed for 2 years before construction was begun on the highway grade between them when the highway fill reached a maximum thickness of about 10 m a failure occurred the design was then changed to include berms on either side but a second failure occurred when the grade was rebuilt an undrained back analysis of the first failure shows the influence of various variables on the factor of safety and illustrates the difficulty of choosing appropriate strength values for design when the site has a strong crust overlying a weaker layer and there is potential for progressive failure observations of settlements pore pressures and lateral movements in the subsoil describe the performance of the embankment during construction and reveal the importance of strain softening as a factor in the failures compa

plane slope failures in the langhe region of italy widespread plane slope failures have occurred in the hilly langhe region nw italy over the past two centuries and more recently in november 1994 the 1994 event caused the deaths of 20 people and major damage to properties this paper is a description of the landslides that occurred in connection to flexural slip the causes of the phenomena are discussed in detail including the variation of the residual strength along the shear surface as a result of specific geological chemical and mineralogical conditions after examining the phenomena that contribute to create slide prone slopes the paper concentrates on the driving mechanisms applying to the case histories investigated

observations and models of simple nocturnal slope flows abstract measurements of simple nocturnal slope winds were taken on rattlesnake mountain a nearly ideal two dimensional ridge tower and tethered balloon instrumentation allowed the determination of the wind and temperature characteristics of the katabatic layer as well as the ambient conditions two cases were chosen for study these were marked by well defined surface based temperature inversions and a low level maximum in the downslope wind component the downslope development of the slope flow could be determined from the tower measurements and showed a progressive strengthening of the katabatic layer hydraulic models developed by manins and sawford 1979a and briggs 1981 gave useful estimates of drainage layer depths but were not otherwise applicable a simple numerical model that relates the eddy diffusivity to the local turbulent kinetic energy was found to give good agreement with the observed wind and temperature profiles of the slope flows

discussion of residual and postliquefaction strength of a liquefiable sand by mandar dewoolkar jay hargy ian anderson pedro de alba and scott m olson

rational design treatment of slides in overconsolidated clays and clay shales during the early part of the past century engineers were repeatedly surprised by unforeseen movements of valley slopes on overconsolidated flat bedded clays and clay shales movements have occurr

analysis of a retrogressive landslide in glaciolacustrine varved clay abstract the largest landslides in estonia are associated with glaciolacustrine varved clays one of the recent slope failures audru landslide was chosen for detailed investigation landslide morphology was instrumentally measured and the underlying geological setting investigated with eight boreholes penetrating the varved clay varve correlation was used to localize the failure zone and estimate the extent of the displaced material within the landslide body field measurements and limit equilibrium models displayed a retrogressive complex of three separate sliding events the first stage of audru landslide was initiated by the river undercutting and was followed by retrogressive slides that caused partial liquefaction of the landslide body the influence of the various modeling parameters on the overall slope stability was also investigated

observations of flow and turbulence in the nocturnal boundary layer over a slope measurements were conducted on an eastern slope of the salt lake basin slb as a part of the vertical transport and mixing experiment vtmx conducted in october 2000 of interest was the nocturnal boundary layer on a slope in particular katabatic flows in the absence of significant synoptic influence extensive measurements of mean flow turbulence temperature and solar radiation were made from which circulation patterns on the slope and the nature of stratified turbulence in katabatic winds were inferred the results show that near the surface 25 50 m the nocturnal flow is highly stratified and directed downslope but at higher levels winds strongly vary in magnitude and direction with height and time implying the domination of upper levels by air intrusions these intrusions may peel off from different slopes surrounding the slb have different densities and flow at their equilibrium density levels the turbulence was generally weak and continuous but sudden increases of turbulence levels were detected as the mean gradient richardson number dropped to rig about unity with a short timescale fluctuated on the order of a few tens of seconds while modulating with rig a longer along slope internal waves sloshing timescale of about half an hour the mixing efficiency or the flux richardson number of the flow was found to be a strong function of similar to that found in laboratory rig experiments with inhomogeneous stratified shear flows the eddy diffusivities of momentum and heat were evaluated and they showed a systematic variation with when scaled with the shear length scale and the rms rig vertical velocity of turbulence

assessment of non linear rock strength parameters for the estimation of pipe jacking forces part 1 direct shear testing and backanalysis abstract a method of backanalysis was used for the assessment of pipe jacking forces from three pipe jacking drives in laminated shale and interbedded lithological units of metagraywacke siltstone greywacke and phyllite found in the highly weathered and fractured lithologies of the tuang formation malaysia direct shear tests were conducted on reconstituted tunneling rock spoils sampled from three pipe jacking sites the direct shear test results were initially assessed using the mohr coulomb failure criterion which demonstrated severe shortcomings in capturing the nonlinear shear strength behavior of the reconstituted tunneling rock spoils subsequently a simple power law function was proposed together with the generalized tangential method to obtain useful equivalent tangential cohesion c t p and friction angle t p for the assessment of pipe jacking forces in fractured lithologies the outcomes from this study show that the tangential mohr coulomb strength parameters can be used to backanalyze the frictional coefficient avg and the vertical stress at the tunnel crown ev these backanalyzed values were successfully related back to the measured jacking forces and jacking speeds for pipe jacking drives in various geological conditions and lubrication efforts the use of the backanalyzed parameters c t p t p avg and ev in the assessment of pipe jacking forces from highly weathered rocks comprising of laminated and interbedded lithological units could lead to the prediction of jacking forces using numerical models a companion paper to this study has also been produced to evaluate the reliability and suitability of these backanalyzed parameters for assessing pipe jacking forces using the finite element method

bayesian estimation of the normal and shear stiffness for rock sockets in weak sedimentary rocks abstract the design of socketed foundations in weak sedimentary rocks is often governed by settlement the shear stiffness of the rock socket sidewalls and the normal stiffness of the rock socket base are the main parameters that affect the settlement of rock sockets at service load conditions and are needed for settlement calculation in load transfer method or using the theory of elasticity in this paper in situ load test data for socketed foundations in weak rocks are collected the shear stiffness of the rock socket sidewalls and the normal stiffness for the rock socket base are respectively estimated based on the measured side shear stress and shear displacement and base contact pressure and normal displacement relationships the parameters affecting shear and normal stiffnesses are discussed a bayesian approach is used to develop probabilistic models for the rock socket shear and normal stiffnesses which are functions of both rock properties and the rock socket size

residual shear strength mobilized in first time slope failures this paper presents a review of long term stability of stiff clay and clay shale slopes and detailed reanalyses of 99 case histories of slope failures in 36 soft clays to stiff clays and clay shales we analyzed 107 sections using the observed actual slip surface in a first time slope failure in clay or shale part or all of the slip surface is unsheared prior to the occurrence of the landslide most stiff clays and clay shales contain stratigraphic discontinuities such as bedding planes and laminations the fully softened shear strength is shown to be the lower bound for mobilized shear strength in first time slope failures in homogeneous soft to stiff clays and on the slip surfaces cutting across bedding planes and laminations for many of the first time slope failures it appears that part of the slip surface is at the residual condition for excavated slopes the residual condition could be present before the final slope is formed or it may develop in response to excavation by progressive deformation along nearly horizontal surfaces including bedding planes or laminations in addition to the permeability dependent rise in porewater pressure and softening delayed first time failure of slopes in stiff clays and clay shales is caused by propagation of the residual condition into the slope on horizontal or subhorizontal surfaces including stratigraphic discontinuities the residual condition is present on the entire surface of reactivated landslides

fourth canadian geotechnical colloquium strength and slope stability in canadian soft clay deposits it is generally admitted that the long term stability of clay slopes should be analysed in terms of effective stresses which necessitates the knowledge of the pore pressure conditions and of the relationship between the shear strength and the effective stresses this paper deals with the determination of shear strength for stability analysis of clay slopes in eastern canada first the various concepts pertinent to slope stability in soft clay are examined and a certain justification of the use of the post peak or large strain strength is demonstrated in a second part 14 case records of natural slopes or permanent excavation slopes are presented and analysed in terms of the post peak strength finally values of post peak strength determined in the laboratory for more than 30 sites are presented and it is attempted to derive correlations by which the shear strength parameters could be readily approximated from other properties such as the apparent preconsolidation pressure or the vane strength

a model study of the strong and weak wind stably stratified nocturnal boundary layer influence of gentle slopes with the exception of intermittency and waves a brief review of the observed and modeled mean structure of the nocturnal boundary layer nbl is presented the effect of gentle slopes on strong and weak wind nbl was investigated here using a one dimensional model with a simple correction term to account for the slope effects identical to the one used by brost and wyngaard 1978 the study indicates that the wind profiles temperature profiles and surface layer turbulence characteristics are extremely sensitive to the imposed geostrophic wind when small slopes are present especially for light winds this is due to the complex interaction between the buoyancy driven slope flow and the imposed geostrophic wind that in turn influence the shear generation of turbulence finally the current issues in the modeling of weak wind boundary layer are discussed

temperature dependent residual shear strength characteristics of smectite bearing landslide soils this paper presents experimental investigations regarding the effect of temperature on the residual strength of landslide soils at slow to moderate shearing velocities we performed ring shear tests on 23 soil samples at temperatures of 6 29 c the test results show that the shear strength of smectite rich soils decreased when temperatures were relatively low these positive temperature effects strength losses at lower temperatures observed for smectite bearing soils are typical under relatively slow shearing rates in contrast under relatively high shearing rates strength was gained as temperature decreased as rheological properties of smectite suspensions are sensitive to environmental factors such as temperature ph and dissolved ions we inferred that temperature dependent residual strengths of smectitic soils are also attributed to their specific rheological properties visual and sem observations of ca bentonite suggest that slickensided shear surfaces at slow shearing rates are very shiny and smooth whereas those at moderate shearing rates are not glossy and are slightly turbulent indicating that platy smectite particles are strongly orientated at slow velocities the positive temperature effect is probably due to temperature dependent micro friction that is mobilized in the parallel directions of the sheet structure of hydrous smectite particles on the contrary the influence of micro viscous resistance which appears in the vertical directions of the lamination is assumed to increase at faster velocities our results imply that if slip surface soils contain high fractions of smectite decreases in ground temperature can lead to lowered shear resistance of the slip surface and trigger slow landslide movement

residual strength of clays in landslides folded strata and the laboratory the post peak drop in drained shear strength of an overconsolidated clay may be considered as taking place in two stages first at relatively small displacements the strength decreases to the fully softened or critical state value owing to an increase in water content dilatancy second after much larger displacements the strength falls to the residual value owing to reorientation of platy clay minerals parallel to the direction of shearing if the clay fraction is less than about 25 the second stage scarcely comes into operation the clay behaves much like a sand or silt with angles of residual shearing resistance typically greater than 20 degrees conversely when the clay fraction is about 50 residual strength is controlled almost entirely by sliding friction of the clay minerals and further increase in clay fraction has little effect the angles of residual shearing resistance of the three most commonly occurring clay minerals are approximately 15 degrees for kaolinite 10 degrees for illite or clay mica and 5 degrees for montmorillonite when the clay fraction lies between 25 and 50 there is a transitional type of behaviour residual strength being dependent on the percentage of clay particles as well as on their nature the post peak drop in strength of a normally consolidated clay is due only to particle reorientation measurements of strength on natural shear surfaces agree within practical limits of variation with values derived from back analysis of reactivated landslides this field residual strength can be recovered by multiple reversal shear box tests on cut plane samples but in high clay fraction materials it is typically somewhat higher than the strength measured in ring shear tests residual strength is little affected by variation in the slow rates of displacement encountered in reactivated landslides and in the usual laboratory tests but at rates faster than about 100 mm min qualitative changes take place in the pattern of behaviour a substantial gain in strength is followed with increasing displacement by a fall to a minimum value in clays and low clay fraction silts this minimum is not less than the slow or static residual but in clayey silts with clay fractions around 15 25 according to tests currently in progress the minimum can be as low as one half of the static value author trrl

large eddy simulation of a katabatic jet along a convexly curved slope part 1 statistical results abstractlarge eddy simulation is performed to study a katabatic jet along a convexly curved slope with a maximum angle of about 35 5 the design of this numerical simulation of turbulent shear flow is discussed and a qualitative assesment of the method is proposed the katabatic flow is artificialy generated by ground surface cooling and a stable atmospheric boundary layer with constant stratification is considered as a reference state a quantitative statistical analysis is used to describe the present turbulent flow with a focus on the outer layer shear of the katabatic jet which extends about 50 m above the jet maximum the prandtl model for a katabatic jet is applied to the present results and revisited versions of the model found in the literature are discussed with an emphasis on specific momentum and turbulent heat diffusion the vertical and downslope variability of the turbulent kinetic energy budget is also discussed and it is shown that advection and production contributions in the downslope

delayed collapse of cut slopes in stiff clay delayed failure of railway cutting slopes in stiff clays excavated in the nineteenth and early twentieth centuries has been studied for some forty years known failures have generally been deep seated more recently failures have been a problem in the slopes of motorway cuttings and embankments although generally these have been shallow the average operational strength at failure in these slides has been significantly less than the peak strength and progressive failure has been postulated as the probable cause of this progressive failure can now be analysed using advanced numerical techniques a series of coupled finite element analyses have been conducted assuming strain softening soil with properties based on the brown london clay and the results are reported they show that progressive failure is considerable and fully explain the observed field behaviour the delays experienced in the field are also recovered by the analyses progressive failure is generated primarily by the high lateral stresse

evaluation of peak side resistance for rock socketed shafts in weak sedimentary rock from an extensive database of published field load tests a limit state approach this paper presents analyses of the measured peak side resistance of rock sockets constructed in weak claystone shale limestone siltstone and sandstone the peak side resistance is obtained fro

the structure of katabatic flows down a simple slope an analysis of the katabatic flow structure is presented based on data collected along a simple slope over a two month period four meteorological stations were deployed along the nearly two dimensional east slope of mt hymettos in greece the study focuses on the momentum and energy budgets of the flows during carefully selected stationary periods with negligible ambient winds in order to achieve a proper selection the mean features of the observed flows are presented along with their response to external winds the observed profiles are successfully compared with the theoretical prandtl profiles bulk quantities of the katabatic layer are compared with proposed experimental values in order to check the representativity of the observed flows these comparisons offer a further test of theoretical considerations and assist in discussions of processes affecting mean flow features the flows were 20 m deep with velocities 1 2 m s 1 during steady state periods the katabatic acceleration was mainly balanced by the surface friction the contribution of advective terms being small the estimated interfacial drag was less important than the surface drag which proved large compared with usually suggested values within the experimental uncertainties values of the drag coefficient of the order of 10 2 seem appropriate the steady state energy balance showed that the downslope advection balanced the turbulent heat flux to the ground surface

drained residual shear strength of some claystones from front range colorado drained residual shear strength data on claystone shale bedrock samples from seven sites along the front range in colorado collected from various sources are summarized the claystone bedrock specimens from these sites were from dawson laramie arapahoe and denver formations the testing procedures included reversal direct shear and torsional ring shear tests upper bound lower bound and average residual shear strength envelopes were developed using the data from the seven sites the secant residual friction angle varied from an upper limit of about 30 to a lower limit of about 5 5 for effective normal stress ranging from 30 to 960 kpa selected published correlations relating the drained residual friction angle to the liquid limit plasticity index clay fraction and effective normal stress were also compared to the data set for this particular data set the plasticity index based correlations compared better than the liquid limit based correlations it is recommended that if any published corr

fill placement on slopes underlain by franciscan melange distress in two housing developments was caused by a deep bedrock landslide triggered by placement of a large upslope fill the large fill was placed to create a visual barrier between the upslope development and downslope housing developments and to balance the cut and fill quantities for the upslope site this case history presents some of the ramifications of fill placement on natural slopes surrounded by urban areas such as overstressing underlying weak material that may exist below the depth of borings typically conducted for single family residences and office complexes the importance of surface and subsurface information in a formation known locally as franciscan complex melange which is a block in matrix rock formation common to the area the shear behavior of serpentinite which is part of the franciscan complex and the importance of natural and man made changes to a slope such as rainfall surficial grading home construction and fill placement it also illustrates the importance of locating the critical slope cross section before construction and the proper use of back analyses in a landslide investigation doi 10 1061 asce gt 1943 5606 0000394 2011 american society of civil engineers ce database subject headings landslides shear strength slope stability subsurface investigations case studies fills author keywords landslides shear strength slope stability subsurface investigation serpentinite franciscan complex melange block in matrix rock

study of preexisting shear surfaces of reactivated landslides from a strength recovery perspective abstract residual shear strength is generally considered in the design of preventive measures for slopes consisting of preexisting shear surfaces of large scale landslides recent research suggests that the preexisting shear surface of a reactivated landslide can regain strength with the passage of time which might also be considered in designing the slope stability measures in this study three reactivated landslide soils were tested in a ring shear apparatus for the discontinued shear periods of 1 3 7 15 and 30 days with the following main objectives i to understand the strength recovery behavior of landslide soils in a residual state of shear after as long as 30 days of discontinued shear ii to understand the comparative pattern of strength recovery in highly plastic and less plastic soils and iii to understand the mechanism involved in strength recovery at a residual state of shear the results indicate that recovered strength measured in the laboratory is hardly noticeable after a rest period of 3 days but recovered strength is lost after a small shear displacement this paper primarily focuses on the effect of strength recovery from residual strength on preexisting shear surface soils and the mechanisms behind it

slope stability analyses in stiff fissured clays results of torsional ring shear direct shear and triaxial compression tests on cohesive soils reveal that the fully softened shear strength is stress dependent and related to the type of clay mineral and quantity of clay size particles an empirical relationship for the fully softened friction angle is presented that is a function of liquid limit clay size fraction and effective normal stress studies of first time slides i e slopes that have not undergone previous sliding in stiff fissured clay with a liquid limit between 41 and 130 suggest that the mobilized shear strength along the failure surface can be lower than the fully softened shear strength recommendations are presented for estimating the mobilized shear strength in first time slides based on soil plasticity soils with a liquid limit greater than 30 exhibit a large difference between the fully softened and residual friction angles in these soils the presence or absence of a pre existing shear surface should be clarified

stress induced response from both natural and construction related processes in the deepening of the peace river valley b c the peace river rises in the rocky mountain trench and flows easterly through the rocky mountains before flowing onto the plains in northeastern british columbia near the alberta border stress measurements conducted at two of three damsites near the boundary of the foothills and the plains reveal high remnant lateral stresses and a k0 of about 2 in proceeding 90 km downriver from the w a c bennett dam past the peace canyon dam to the proposed site c dam near fort st john the stratigraphic section changes from competent massive sandstones of lower cretaceous age to soft weak shales at the top of the lower cretaceous section valley downcutting by the peace river through these highly stressed rocks has led to valley rebound features that have both similarities and differences where observed at each of the three damsites differences in rock strength at each site contribute to the variations in features noted these valley rebound features include vertical relief joints horizontal bedding plane join

seismic pursuit of wormholes cold production has become increasingly popular in the extraction of heavy oil due to the development and widespread use of progressing cavity pumps essentially powerful augers that suck both oil and sand into the well at the onset of production these pumps produce about 60 oil and 40 sand however production can improve to 95 oil with only 5 sand after a few months this increase in oil production and reduction in sand production is attributed to the development of high porosity tubes termed wormholes roche 2002 describes wormhole development as the creation of a network of horizontal wells without using a drilling rig operators who plan infill drilling rely on wormhole distribution information to optimize well spacing it is accepted that aggressive cold production of oil sands will increase oil recovery and this has been demonstrated in several pools both in alberta and saskatchewan so assuming these induced sand channels can boost cold heavy oil production can we map them that s a good question because wormholes have small dimensions compared to seismic wavelengths making their seismic detection extremely difficult this challenge caused us to perform feasibility tests based on a number of models from the literature the following describes the results of these tests we also show some real seismic data with promising indications for wormhole imaging much heavy oil recovery in western canada involves steam injection time lapse seismology plays a major role in monitoring steam fronts and time lapse or 4d seismology is now a standard reservoir characterization tool however steam production injection is costly and heavy oil production now increasingly uses cold flow techniques as stated earlier cold production methods use special pumps known as progressing cavity pumps figure 1 these pumps similar to an auger or archimedes screw within a flexible sleeve lift the oil sand mixtures from the producing formation

the robustness of vp vs mapping multicomponent seismology is a useful tool for enhanced reservoir characterization of heavy oil fields as shown by watson et al 2002 and lines et al 2005 multicomponent data can provide maps of the p wave to s wave velocities vp vs and these vp vs maps provide important information about lithology and reservoir changes in this discussion we show that vp vs mapping as derived from traveltime measurements on vertical and radial component data is a robust procedure we explore two aspects of this type of vp vs mapping first we explore the spectral differences of pp and ps seismic volumes and design band pass filters that can significantly improve the quality of vp vs maps second we perform an error analysis of this mapping and show that the derivation of vp vs maps from reflection traveltime picks is not overly sensitive to the choice of reflecting horizons above and below the reservoir

effects of freeze thaw and softening on a natural clay at low stresses weathering processes such as softening and freeze thaw cycling affect the properties of clays care must therefore be taken when selecting strength and compressibility parameters for analysis of natural slopes compacted clay embankments and trench excavations in which significant proportions of the cross section can be affected by climatic weathering samples of plastic lake agassiz clay from winnipeg were consolidated anisotropically in the laboratory to axial stresses less than or equal to the in situ effective overburden pressure they were therefore all overconsolidated with respect to the field preconsolidation pressure the samples were then loaded under drained or undrained conditions along steeply rising stress paths in p q stress space one group of samples was tested immediately to identify the undisturbed behavior a second group was subjected to freeze thaw cycles and a third group allowed to swell freely before testing the freeze thaw cycling produced increased compressibility and pore

residual strength of slip zones of large landslides in the three gorges area china abstract slip zones of the large landslides in the three gorges area are commonly composed of fine grained soils with substantial amount of coarse grained particles particularly gravel sized particles in this study residual strength of the soils from slip zones of these landslides were examined in relation to their index properties based on a survey of 170 landslides it was found that laboratory determined residual friction angle using gravel free fraction of the disturbed soils from the slip zones was closely related to clay content liquid limit and plasticity index on the other hand in situ residual friction angle of these soils i e including gravel fraction showed very weak correlations with clay content and atterberg limits but was largely dependent on gravel and fines clays silts contents increasing with gravels and decreasing with fines and displayed strong linear correlation with the ratio of gravel to fines contents these observations indicate that among the index properties clay content and atterberg limits can be used to estimate residual strength of the soils finer than 2 mm but they are not appropriate evaluate the residual strength of the soils containing considerable amount of gravel sized particles for the latter particle size distribution particularly the ratio of gravel to fines contents appears to be a useful index additionally it was found that there was no identifiable correlation between relative abundance of individual major clay minerals and residual friction angles of both gravel free fraction of disturbed and in situ soils suggesting that influence of clay minerals on residual strength of these soils can not be simply evaluated based on their abundance

empirical correlations drained shear strength for slope stability analyses empirical correlations provide estimates of parameter values for preliminary design verification of laboratory shear test data and confirmation of back analysis of a failed slope the empirical correlations presented herein use liquid limit clay size fraction and effective normal stress to capture the variability and stress dependent nature of drained residual and fully softened strength envelopes this paper describesthetestingandanalysisusedtoincreasethenumberofdatapointsintheexistingcorrelations expandtheresidualstrengthcorrelation to include an effective normal stress of 50 kpa and develop correlations between values of liquid limit and clay size fraction measured using sampleprocessedthroughano 40sieve astmprocedure andvalues derivedusingball milled disaggregated sample inaddition equations are presented to express the empirical correlations used to develop a spreadsheet that estimates the residual and fully softened friction angles based on entered values of liquid limit and clay size fraction doi 10 1061 asce gt 1943 5606 0000824 2013 american society of civil engineers ce database subject headings shear strength friction clays shale slope stability drainage author keywords shear strength residual friction angle fully softened friction angle empirical correlation clay shale

energy evolution a new perspective on the failure mechanism of purplish red mudstones from the three gorges reservoir area china abstract purplish red mudstones from section four of the badong formation are broadly distributed in the three gorges reservoir area tgra and exhibit special characteristics distinct from the mudstones elsewhere this paper investigates the failure mechanism of such mudstones from a new perspective of energy evolution initially the complete failure process under three stress paths i e loading unloading and cyclic loading unloading is monitored and the related data are acquired methods to estimate the energy parameters i e total absorption energy tae cumulative dissipation energy cde and elastic strain energy ese under cyclic loading unloading conditions are presented two new parameters namely the proportion of cde pcde and proportion of elastic energy dissipation peed are introduced using the data the mechanical properties and energy properties are analyzed and the energy evolution is revealed the results show that the failure mechanism under the three stress paths is different from an energy evolution perspective the mechanical parameters deteriorate under unloading in comparison with those under loading the increase in the cde is similar to that in the tae and the ese strain relationship features a step shaped rise for cyclic loading unloading the tae and the pcde nearly linearly increase with cycle times this work provides a new perspective on the failure mechanism of the purplish red mudstones from the tgra

suction monitored direct shear testing of residual soils from landslide prone areas the apparent cohesion due to soil suction plays an important role in maintaining the stability of steep unsaturated soil slopes with deep ground water table in this paper a modified direct shear box is used to determine the relationships between the value of this additional cohesion and the associated soil suction the apparatus incorporates a miniature tensiometer which allows for the simple and direct measurement of suction during shearing the soil water characteristic curves and shearing behavior of intact residual soils being low to medium plasticity silts as well as silty sand taken from four landslide prone areas in thailand have been investigated the relatively low air entry suctions 0 7 kpa and bimodality of the soil water characteristic curves gives an indication of the structured pore size distribution of the materials tested samples with higher suction tend to display stronger bonding at particle contacts and thus are more brittle the shear strength is found to increase nonlinearly

the selborne cutting stability experiment the paper describes a field experiment in which a 9 m deep cut slope in gault clay was brought to failure by pore pressure recharge the geology of the site is described and the procedures used to

creep and failure of slopes in clays the accumulated experience on slope stability is reviewed with due consideration to the time dependent behaviour of natural clays prior to failure a consistent picture of the behaviour of both man

residual shear strength measured by laboratory tests and mobilized in landslides drained residual shear strength measured by multiple reversal direct shear or ring shear tests has been successfully used for over four decades for stability analyses of reactivated landslides in stiff clays and clay shales a body of literature has accumulated in recent decades claiming that healing or strength regain is realized in time on preexisting slip surfaces already at residual condition in other words the shear stress required to reactivate a landslide is claimed to be larger than the drained residual shear strength determined using laboratory tests this article presents 1 a comparison of secant residual friction angle determined from laboratory tests and secant mobilized friction angle back calculated for reactivated landslides 2 explanations that field evidence used to claim healing can be attributed to alternative factors and the laboratory evidence on strength regain upon reshearing is the result of either the testing apparatus or testing procedure or is inapplicable to stiff clays and shales and 3 laboratory aging test results which show no strength regain on preexisting shear surfaces at residual condition doi 10 1061 asce gt 1943 5606 0000624 2012 american society of civil engineers ce database subject headings clays shale residual strength landslides slope stability laboratory tests author keywords clays shales residual strength landslides slope stability

the failure of carsington dam the upstream slope of carsington dam failed just before its completion in 1984 the slip started on the right abutment and spread across the valley to a length of nearly 500m extensive investigations were conducted and further information was obtained when the dam was reconstructed the initial slip sheared through the core which contained shear surfaces due to rutting and along a layer of yellow clay which contained solifluction shears both materials were brittle with low residual strengths the factor of safety based on measured peak strengths was about 1 4 with reductions to allow for shears it was 1 2 it had been reduced to 1 0 by progressive failure finite element fe analyses in which strain softening was reproduced confirmed this it was concluded that the slide spread by lateral load transfer through sections of the dam with a safety factor greater than 1 in the vailey centre the slide passed through the base of the mudstone fill a combination of fe and limit equilibrium analysis ind

heavy oil reservoir characterization using elastic wave properties this case history describes seismic monitoring efforts at pikes peak field a prolific heavy oil field production exceeding 42 million barrels just east of the alberta saskatchewan border that has been operated by husky energy since 1981

large landslides induced by fluvial incision in the cenozoic duero basin spain abstract the pleistocene opening of the endorheic duero river drainage basin northwestern spain and central portugal has led to river incision creation of steep valley sides and development of large 0 1 km2 and episodically active rotational and roto translational landslides along river reaches where a weak geological lithology has been exposed by river erosion these landslides occur in the central part of the duero basin despite low precipitation weak contemporary seismicity and low regional relief these landslides occurred as a result of the downcutting of the duero river and its tributaries through a sequence of miocene basin fill sediments in the last few thousand years the incision reached a series of high plasticity low strength clay layers within the sedimentary sequence owing to this mechanism these landslides occurred in a specific area at a specific period of time all of the large landslides are located at the outside of meander bends suggesting that river lateral erosion facilitated slip failures recent anthropogenic activities to control river flows and to stabilize river banks have decreased the possibility of future landslides in this area

lias clay slope sections and their implications for the prediction of limiting or threshold slope angles a series of previously published engineering studies of lias clay slopes in the east midlands is summarized along with the description of some further slope sections all the slopes studied show evidence of landsliding though some of it may be of periglacial origin the very disparate nature of the different landslides suggest that various different erosion regimes were responsible for the original slope formation it is believed that the smaller landslides are more typical of the area piezometric observations show that at the present day maximum pore pressures are proportionately less in the larger landslides the average value of the pore pressure parameter ru varying between 0 48 for shallow landslides to 0 32 in the largest stability analyses show that the residual strength is strongly stress dependent r c r 0 varying from 16 in shallow landslides to 10 in the case of the largest these and other factors have important implications for the often used practice of combining laboratory measurements of residual strength with the infinite slope method of stability analysis to predict threshold slope inclinations for landsliding