structural characterization of natural loess and remolded loess under triaxial tests this paper characterizes the microstructural evolution of saturated natural loess from a site in jingyang china during triaxial test along two stress paths for comparison the same soil in remolded state is also characterized mercury intrusion porosimetry mip scanning electron microscopy sem and environmental scanning electron microscopy esem were used for the microstructure investigation results show that the microstructure of natural loess is similar to that of remolded loess before the consolidated undrained cu triaxial tests including conventional triaxial compression ctc test and reduced triaxial compression rtc test on the contrary their microstructures are different after the tests deeper examination shows that loading led to a significant change of inter aggregate pores without modifying the intra aggregate pores in addition the volume of inter aggregate pores after the rtc test is greater than that after the ctc test under the same consolidation stress the microstructure features of natural and remolded loess after the tests are further used to analyze the macro mechanical behavior for better understanding the relationship between them the results show that it is the cementation bonds of which breakage is influenced by stress path and confining pressure that play important roles in the strength and deformation behavior

physical simulation of ground fissures triggered by underground fault activity abstract numerical modeling and physical simulation experiment are two important steps to investigate the stress and strain fields of overlying strata but sometimes it is very difficult to do the test of the physical experiment on a large scale soil sample due to the financial consideration and the available test site to investigate the features of the ground fissures prevailing in xi an city we undertook in this study a series of physical simulation tests on the large scale soil sample to analyze the stress and displacement fields caused by the underlying normal fault activity comparing with the fracturing modes of the ground fissures and the failure patterns of construction building it is evident that the experiment results coincide with the failure patterns of the building but not with the fracturing modes of the ground fissures which indicate that the ground fissures in xi an may be an old fracture surface having already spread to superficial layer covered by a very thin layer of loose soils and the groundwater over pumping is just a factor to make them exposed on the ground surface

microstructural constraints on geotechnical properties of malan loess a case study from zhaojiaan landslide in shaanxi province china abstract the microstructure of malan loess a late pleistocene loess deposit in china dominates its macroscopic geotechnical properties when subject to inundating or humidifying conditions the distinct metastable structure of the malan loess is sensitive to collapse thus its geotechnical properties undergo change the results of triaxial and uni axial compression tests under the humidifying conditions on undisturbed loess samples demonstrate that its geotechnical properties of the top loess were dominated by metastable structure while the basal loess were more influenced by inter particles cementation bond based on analyses from scanning electron microscopy images change of the loess pore structure can be primarily attributed to the ratio of metastable pores 5 m accordingly an end member model is proposed to illustrate how varying in the size and distributions of very large pores 200 m large pores 50 200 m medium pores 5 50 m and small pores

mercury intrusion and permeability of louiseville clay several theories have been proposed to correlate the permeability hydraulic conductivity with the pore size distribution of soils and it seemed interesting to determine if these theories could be applied to natural clays for this purpose permeability and mercury intrusion porosimetry tests were performed on a champlain sea clay for both intact and remoulded conditions after compression of the specimens to strains varying from 0 to 42 the results show that for either intact or remoulded soil conditions there is a relationship between the pore size parameters and the permeability of the clay however there is no unique relationship for both intact and remoulded clays and for the silt and clay considered in previous studies consequently mercury intrusion porosimetry alone cannot be usepto evaluate the permeability of soils in general plusieurs thkories ont ctc proposces pour corrcler la permiabilite conductivitk hydraulique avec la distribution des grosseurs de pore des sols et il a semblc intiressant de verifier si ces theories pourraient 2tre appliquees aux argiles naturelles a cette fin des essais de permcabilitc et de porosimctrie a intrusion de mercure okt ctc rcaliscs sur l argile de la mer champlain dans des conditions tant intactes que remanikes apris la compression des specimens a des dcformations variant de 0 a 42 les rcsultats demontrent que pour des conditions soit intactes ou remanices il existe une relation entre les paramitres de grosseur de pore et la permcabilitc de l argile cependant il n existe pas de relation unique pour les argiles tant intactes que remanices et pour le limon et l argile ctudics antkrieurement en conscquence la porosimctrie a intrusion de mercure ne peut pas a elle seule tre utilisce pour cvaluer la permcabilitc des sols en general mots clds permcabilitc argile porosimctrie a intrusion de mercure structure traduit par la rcdaction

non darcian flow in loess at low hydraulic gradient abstract determining the mechanism of water flow in loess involves many problems that are vital to science and engineering water flow through loess has usually been assumed to follow darcy s law but this has not been properly validated the main objective of this study is to validate the applicability of darcy s law for loess for this purpose we conducted constant head permeability experiments and mercury injection porosimetry mip on loess specimens of different dry densities the results indicate that darcy s law is not suitable for describing water seepage in loess at low hydraulic gradient since there is a threshold hydraulic gradient i0 below which no flow is observed and a critical hydraulic gradient icr below which the relationship between the hydraulic gradient i and seepage velocity v is non linear the mip results show that variation in hydraulic conductivity is closely related to the pore size distribution psd in loess specimens i0 is positively correlated with the content of pores with diameters in the range of 0 01 1 m and negatively correlated with the content of pores with diameters larger than 3 m the existence of bound water on loess is the main reason that its permeability deviates from darcy s law the mechanism of water movement in loess can be fully understood by considering the effect of bound water

monitoring of land subsidence and ground fissures in xian china 2005 2006 mapped by sar interferometry the city of xian china has been experiencing significant land subsidence and ground fissure activities since 1960s which have brought various severe geohazards including damages to buildings bridges and other facilities monitoring of land subsidence and ground fissure activities can provide useful information for assessing the extent of and mitigating such geohazards in order to achieve robust synthetic aperture radar interferometry insar results six interferometric pairs of envisat asar data covering 2005 2006 are collected to analyze the insar processing errors firstly such as temporal and spatial decorrelation error external dem error atmospheric error and unwrapping error then the annual subsidence rate during 2005 2006 is calculated by weighted averaging two pairs of d insar results with similar time spanning lastly gps measurements are applied to calibrate the insar results and centimeter precision is achieved as for the ground fissure monitoring five insar cross sections are designed to demonstrate the relative subsidence difference across ground fissures in conclusion the final insar subsidence map during 2005 2006 shows four large subsidence zones in xian hi tech zones in western eastern and southern suburbs of xian city among which two subsidence cones are newly detected and two ground fissures are deduced to be extended westward in yuhuazhai subsidence cone this study shows that the land subsidence and ground fissures are highly correlated spatially and temporally and both are correlated with hi tech zone construction in xian during the year of 2005 2006

hydroconsolidation and subsidence of loess studies from china russia north america and europe abstract various approaches to the widespread problem of the hydroconsolidation and subsidence of loess have been suggested these include considerations of rheology thermodynamics phase movements particle packing interparticle bonding pore structure and distribution catastrophe theory topology and simple structural frameworks chinese north american and most european investigators tend to concentrate on mechanisms of loess collapse the russian literature however retains an extra dimension two approaches the syngenetic and the epigenetic approach to the formation of subsiding loess have been defined in the literature most investigators follow a syngenetic approach which appears to be a consequence of the aeolian idea of loess deposition some russian writers in contrast promote an epigenetic approach in which collapsibility can develop in an originally noncollapsible material which can then suffer from hydroconsolidation and subsidence the basis of the phenomenon is a change in the packing structure of the major loess particles and this can be modelled using simple monte carlo methods to develop appropriate structures this paper aims to review the work done on this important subject serious investigation of hydroconsolidation and subsidence of loess began in the early nineteen forties fifty years ago and this has been reported in a piecemeal manner a detailed critical review of this diverse work is now overdue and this is presented herein in the light of recent work in the united kingdom an attempt is made to describe the process in a phenomenological and a structural sense inherent in this the role of n ya denisov as subsidence pioneer is considered

evolution of microstructure in compacted london clay during wetting and loading the influence of fabric on mechanical behaviour is explicitly considered in some of the current constitutive models for unsaturated soils these are based on assumptions regarding the interaction b

influence of structure on shear characteristics of the unsaturated loess in lanzhou china abstract loess is typically a kind of soil with metastable structure which makes loess sensitive to collapse and sliding upon wetting such structure has thus profound influence on loess s mechanical behavior however there have been arguments about how the metastable structure influences on loess s mechanical behavior and what the mechanism behind is in this study the influence of structure on shear characteristics of the unsaturated loess in lanzhou city of china was investigated with comparison of variation of shear strength and its parameters between six pairs of the undisturbed and remolded samples it is found that the peak shear strength and strength parameters of the loess significantly reduced once its structure was destroyed while shear behavior of the loess showed little change strength parameter c was much more sensitive to structure of the loess than shear strength reduction of the loess due to change of structure should be largely attributed to breaking up of cementation bonds between particles evidenced by the difference in pore size distribution and microstructure of soil fabrics between the undisturbed and remolded samples the bonds provided by clays and carbonates contributed the most to structure of the loess with minor by soluble salts while matric suction played little role in structure of the loess

summary of collapsible behaviour of artificially structured loess in oedometer and triaxial wetting tests this paper summarizes experimental studies on wetting induced collapsibility in loess using single oedometer double oedometer and triaxial wetting tests artificially structural loess samples with interparticle bonding calcite caco3 and a large void ratio were tested in the laboratory to avoid sampling disturbance of natural loess the comparison between the single and double oedometer tests confirms that the wetting induced deformation is independent of the sequence of wetting and loading the conventional triaxial apparatus was enhanced for investigating the collapse deformation in response to different water content increments when subjected to different stress levels the wetting induced strain subjected to high confining pressure develops in two steps it increases with increasing water content and reaches a relatively stable plateau and then increases rapidly again until a final stable state is reached the initial collapse surface was found by plotting the wetting induced strain vectors obser

evolution and origin of the ground fissures in xian china large scale extraction of ground water in xian has resulted in significant drawdown of the phreatic surface and in land subsidence across this ancient capital of china it has also triggered the rejuvenation of the normal faults in the upper portions of the quaternary deposits underlying the city leading to surface rupturing and the development of ground fissure zones across the city these ground fissure zones are structurally controlled in the sense that they are directly linked to the normal faults in the quaternary deposits all trending in an east northeasterly direction in essence they are the surface expressions of the deeper faults under current drawdown conditions the ground fissures have resulted in extensive property damage along their paths of propagation this paper describes their occurrence their possible causative mechanism and the resultant damage of necessity xian will still be dependent on ground water supply to a large extent in the years ahead however ground water extraction will have to be managed in an environmentally sustainable manner in order to minimize the geological hazards associated with the ground fissures

pore structure characteristics of debris flow source material in the wenchuan earthquake area abstract wide grading loose soils wgls are a special slope deposit that often serve as a source for debris flows in the western mountainous area of china previous research indicated that rainfall infiltration induced the migration of fine particles within soil slopes and lead to the initiation of shallow failure and subsequent debris flows clearly soil pore structure exerts a profound influence on seepage during rainfall infiltration which is closely related to soil permeability and corresponding internal erosion the current understanding of the mechanisms of fine particle migration is limited because of the complexity of wgls micropore structure the challenge lies in how to systematically characterize wgls pore structure so that it provides a foundation for future numerical simulations of fine particle migration induced debris flows in this study the characteristics of wgls pore structure were analyzed quantitatively using scanning electron microscopy the results revealed that wgls predominantly contained micropores and mesopores the pore size distribution exhibited a bimodal nature with one peak occurring at a pore diameter of 12 m and another at 72 m the pore complexity of all samples exceeded 0 75 which indicates a low aspect ratio for each pore the average diameter of the fine particles that migrated was then determined with a laboratory seepage test a preliminary jamming probability analysis based on three dimensional micropore reconstruction and average fine particle diameter indicate that jamming is most prevalent along the slope

changes in tensile strength and microstructure of loess due to vibration abstract loess soils typically have an open and metastable structure humidification and vibration can modify their microstructure and thus influence their mechanical behavior in the present study to investigate the influence of train vibration on the tensile strength behavior of loess the tensile tests were performed on loess specimens that had been vibrated at a low amplitude for a long period using a modified horizontal extensograph in addition the microstructures of vibrated and non vibrated loess specimens before and after the tensile tests were characterized changes in the loess microstructure due to vibration and that in the tensile test were analyzed the results show that the relationship between uniaxial tensile strength and water content in soil specimen could be represented using a power function the axial displacement at failure varies at the same manner as tensile strength with respect to water content in comparison to intact loess occurrence of less clay bridges and clay buttresses between aggregates or coarse particles is identified in the disturbed specimens while aggregates are seen to be a very little more loose in vibrated specimens after the tensile tests than that before the tensile tests this indicates that vibration reduces the tension resistance and ductility of loess soil structure which could be attributed to loss of bonding strength as a result of breakage of clay cementations and disintegration of aggregates in the tensile test the soil structure goes through two distinct phases of change i e stretching phase and cracking phase in the stretching phase the tensile deformations take place throughout the specimen without altering the contacts between soil particles significantly in the cracking phase weak cementations fail to resist tensile deformation and suffer from breakage once a through crack is developed the specimen breaks in two leading to a catastrophic drop of tensile stress

study of the structure of a sensitive champlain clay and of its evolution during consolidation scanning electron microscopy and mercury intrusion porosimetry are used in parallel to identify the structure of a medium sensitivity champlain clay the clay structure is observed firstly on intact remolded and oven dried soils and secondly on soils consolidated at various levels in one dimensional compression both methods of investigation reveal for the intact soil the existence of an aggregated structure characterized by an interaggregate and an intra aggregate porosity remolding affects interaggregate links but does not destroy aggregates the observation of clay structure at various levels of one dimensional compression shows that the collapse of the structure is progressive the largest interaggregate pores being the first affected as the consolidation proceeds smaller and smaller pores are affected for a given pressure increment only the largest existing pores are affected a structure anisotropy has been seen to develop with increasing compression the scanning electron microscope and the me

the water retention properties of a natural unsaturated loess from northern france the water retention properties of a natural loess from northern france were investigated on intact block samples that were excavated along a high speed train line tgv that experienced stability problems during heavy rain episodes suction measurements were made by using the filter paper method and an in house constructed high capacity tensiometer hct so as to determine the water retention curve of the loess the results showed that an alternative approach using a previously wetted filter paper could fruitfully be used with suction values reasonably compatible with the hct measurements the water retention curve obtained exhibited a peculiar form with no hysteresis observed around the natural water content 14 4 and two hysteresis loops on both the wet and dry sides of the curve it is hypothesised that this zone with no hysteresis corresponds to the natural variations of the water content under seasonal changes providing a range of natural suction between 20 and 80 kpa and it is suggested that th

microstructure and soil water retention behavior of compacted and intact silt loess abstract there are an increasing number of mega engineering projects of removing the top of hills to fill in the valley for new land creation in the loess plateau of china which significantly changes the hydrological and geological equilibrium state of the site the formation of a new hydrological equilibrium state is associated with the water movement in the compacted and intact loess layers most disasters occurring in the loess area are related to water the soil water retention curve swrc is the key to the implementation of unsaturated soil mechanics in engineering practice and is required to numerically model the movement of water in the soil in this study the swrcs and microstructure of intact and compacted specimens from lanzhou and yan an two typical cities that have new land creation projects are investigated the swrc is obtained using the filter paper method the mercury intrusion porosimetry mip and scanning electron microscope sem techniques are used to explore the microstructure the results highlight that the intact loess has a higher air occlusion value aov and a similar slope of swrc in the transition zone compared with the remolded specimens that compacted at the natural water content the normalized swrc i e degree of saturation versus suction avo of the intact specimen is approximately the same as the remolded specimens compacted as the natural water content the difference in the microstructure between intact and compacted specimens originates from different existing states of the clay particles and further contributes to the variation of the swrc

reply to the discussion by ling xu on weak tensile characteristics of loess in china an important reason for ground fissure by ping sun jian bing peng li wei chen yue ping yin and shu ren wu engineering geology 108 2009 153 159

water retention and volumetric characteristics of intact and re compacted loess a laboratory testing program was conducted to investigate the effects of microstructure on the water retention curve wrc and wetting drying induced volume change in loess the axis translation an

ageing effects in a compacted bentonite a microstructure approach it is suspected that the as compacted state of heavily compacted clays used as possible engineered barriers for nuclear waste disposal is time dependent and that further change may occur in the material even at constant water content and density this paper presents an investigation of the time dependent microstructure changes of an mx80 clay bentonite compacted at various dry densities and water contents microstructure investigation is based on mercury intrusion pore size distribution measurements and scanning electron microscopy sem results obtained by other researchers by using x ray diffraction at low angles are also used statically compacted samples of mx80 were kept at constant volume and water content for various periods of time 1 30 and 90 days prior to mercury intrusion and sem micro structure investigation a significant change in micro structure with time was observed characterised by a decrease in the inter aggregate porosity and an increase in the very thin porosity not intruded by

the mechanics of a saturated silty loess and implications for landslides the results from an intensive experimental investigation on a loess that was retrieved from a typical silty loess zone in the north western chinese loess plateau are presented and interpreted triaxial and oedometer tests were performed on intact and reconstituted samples in a saturated condition the soil behavior was found to be strongly affected by structure the compression paths of the intact samples crossed the intrinsic compression line of the reconstituted soil and reached well defined gross yield points after which the compression paths converged towards the intrinsic compression lines two critical state lines were defined for the intact and reconstituted soils in the volumetric plane as a result of a robust element of natural structure comparisons were made with a structured clayey loess retrieved from the south eastern loess plateau it was found that the effects of structure on the behavior of the two loess soils are similar though they are very different in natural properties this indicates that their natural structures might have experienced similar forming processes perhaps related to their common origin catastrophic flowslides commonly occur in the study area and the patterns of behavior observed in the laboratory tests may create some new insights into mechanisms of landslide initiation and subsequent movement as discussed in the study

the structure degradation of a silty loess induced by long term water seepage abstract loess is a typical silt sized aeolian soil that is widely deposited and possesses a fragile soil structure susceptible to collapse upon wetting the instability of shallow loess slopes is well documented but deeper failures triggered by rainfall and irrigation can also occur in the case of long term seepage clay particles and salts have been observed to leach out of the loess slopes this paper presents a systematic laboratory study of the effects of water conditions on the mechanical behaviour of silty loess with isotropic compression and bender element tests carried out on natural and reconstituted loess recovered at 10 m depth from a site in china the results show that saturation causes reduction in both the compression yield stress and small strain stiffness of the soil and that after being exposed to seepage they decrease further the possible mechanism of structure degradation is investigated by means of microscopic and chemical analyses and it is found that seepage will cause the pore ions concentration to reduce with a loss of clay mineral bonding strength resulting in the detachment of silt particles from aggregates this work highlights the importance of monitoring the water outflow in the field at the loess slope edge since it may causes large deformation in the long term

post earthquake changes and prediction of debris flow scales in subao river valley beichuan county sichuan province china subao river lies along the beichuan yingxiu fault in beichuan county which has been heavily impacted by the wenchuan earthquake on 12 may 2008 and has become sources of many geo hazards on 24 september 2008 a rainstorm triggered a large debris flow in the catchment causing several deaths and significant damages a case study on changes of the debris flow was conducted in the river the peak discharges were calculated in the guanmenzi huangnidi and daanshan gullies results indicated that the peak discharges corresponded to various return periods in different gullies 200 years in daanshan 100 years in huangnidi and 50 years in guanmenzi however the triggering precipitation in these three gullies was only of a 20 year return period the debris flows had undergone significant changes analysis indicated that the changes should be ascribed to the flow characteristics initiation conditions and the channel blockage impacted by the rapid accumulation of loose material channel blockage was the principal factor increasing the scale of the debris flow the values on the blocking coefficient were presented based on density height and other characteristics of dams finally all of the peak debris flow discharges of the subao river valley for a 20 year return period were calculated using the recommended blocking coefficient values

weak tensile characteristics of loess in china an important reason for ground fissures by means of uniaxial tensile tests we analyzed the tensile characteristics of undisturbed and disturbed loess samples taken from the areas where ground fissures are prevalent the study shows that the tensile strength and ultimate tensile strain of loess are very small no more than 25 kpa and 0 5 respectively water content and dry density are the two important factors for the tensile strength of loess and show a decreasing exponential and increasing exponential relationship with the tensile strength respectively from the results of tensile tests on loess and the mechanism of ground fissure development in loess areas we may draw a conclusion that the weak tensile strength the loose structure and the collapsibility are the important contributing factors to the development of ground fissures in china s loess areas

the distribution and geotechnical properties of loess soils lateritic soils and clayey soils in china in china various soils covering vast regions occur loess soils of the yellow river in northern china lateritic soils in southern china and clayey soils in central china the special geotechnical properties of these soils are briefly described the relationship of their material components and microstructural features with their geotechnical properties is studied it is shown that the special geotechnical properties of these soils depend mainly on their material component and microstructural features the distribution of these soils is studied in relation to geographical environment and climatic conditions it is suggested that the formation of the geotechnical properties of these soils have undergone three different development stages

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

sulfur isotopic disequilibrium and fluid rock interaction during metamorphism of sulfidic black shales from the waterville augusta area maine usa abstract sulfur isotope ratios of pyrite py and pyrrhotite po from regionally metamorphosed graphitic sulfidic schists and related rocks from south central maine usa were analysed using so2 and sf6 techniques there is a broad range in 34s values for both pyrite and pyrrhotite at most outcrops up to 8 and overall the values are isotopically light averaging 27 for the entire data set suggesting that the rocks have not been grossly isotopically disturbed by regional metamorphism from their inferred organic rich sedimentary origins at all temperatures from chlorite to sillimanite grades sulfide analysed from veins and blebs within the schists show predominantly disequilibrium fractionations ranging from 34 s py po 3 0 to 3 5 as do matrix sulfides from rocks that attained temperatures 500 c do matrix pyrite pyrrhotite pairs with polygonal or aligned granoblastic microstructures approach isotopic equilibrium at millimeter to centimeter scales suggesting that the process that favoured equilibration was recrystallization accompanying metamorphism and deformation this disequilibrium may be a function of preferential interaction of one of the phases with an infiltrating fluid but the lack of any systematic trends in the data particularly with both negative and positive 34spy po at some outcrops does not permit ready identification of fluid sources fluxes or compositions by combining published fluid fluxes for the area and a knowledge of the mass of sulfur contained in the rocks and the inferred infiltrating fluid it appears that sulfur should have been homogenized over at least 10 s to 1000 s of meters if equilibrium had been attained between rock sulfides and an infiltrating fluid of constant composition that this did not occur was probably due to lack of equilibration between sulfides and the fluid but may also have arisen because of channelling of fluid flow along rather than across layers or a lack of fluid infiltration through this unit

a microstructure approach to the sensitivity and compressibility of some eastern canada sensitive clays investigation of micro macro relationships in soils most often concerns granular soils in which both the elemental unit the grain and the physical laws governing inter grain interactions appear to be better known the situation is different for clays because the elementary unit and the inter unit interactions at the micro scale are more difficult to characterise in fine grained soils it has been shown that an intermediate level corresponding to the way clay and fine grained particles are arranged together had to be considered so as to link microscopic features to macroscopic behaviour an investigation of the change in microstructure during compression carried out some time ago on a sensitive clay from canada demonstrated that studying the changes in pore size distribution provides a satisfactory description of microstructure changes during compression the analysis is applied here to six other sensitive clays first a careful examination of the intact and remoulded microstructure is conducted in o

undrained shear behavior of loess saturated with different concentrations of sodium chloride solution abstract a series of ring shear tests was conducted on saturated loess to investigate the effects of nacl concentration in pore water and desalinization on the shear behavior under undrained conditions the loess samples were taken from the ground surface of a frequently active landslide in china were saturated by de aired distilled water with different concentrations of nacl and then were sheared undrained after that the samples were retrieved remolded re set into the shear box and re saturated by passing through de aired distilled water such that the samples were desalinized and then were sheared undrained again through comparing the undrained shear behavior the effects of nacl in the pore water and desalinization on the undrained shear behavior of loess were examined the results showed that the variation of nacl concentration in pore water can strongly affect the shear behavior of saturated loess both the peak shear strength and steady state strength increased with increase of nacl concentration until a certain value after which they decreased with further increase of nacl concentration meanwhile the peak shear strength and steady state strength of the desalinized samples recovered to those of the original sample hence the effects of salinization are reversible these findings may be of practical importance to better understand the repeated occurrence of some irrigation induced loess landslides in china

origin of ground fissures in the shanxi graben system northern china abstract since the 1950s hundreds of ground fissures have occurred in the shanxi graben system in northern china the fissures and related subsidence and differential settlement have caused and are causing substantial damage to homes agricultural land roads canals and other infrastructure although generally similar in appearance the fissures have different origins 1 some fissures coincide with northeast trending faults trenching shows that the fissures extend into the near surface faults increasing vertical offset clay beds and other stratigraphic markers at depth and therefore are probably the surface expression of fault movements 2 some fissures are demonstrably related to accelerated groundwater withdrawal this is particularly apparent in xi an city where groundwater levels have declined by about 15 m within 4 years 3 other fissures owe their origin to the well known process of soil collapse this is particularly common in the silty loessial sediments that occur within most of the valleys that comprise the shanxi graben system

pore pressure generation and fluidization in a loess landslide triggered by the 1920 haiyuan earthquake china a case study abstract during the 1920 haiyuan earthquake numerous catastrophic landslides were triggered in the loess area in northwest china we investigated in detail a large example of these landslides referred to as dangjiacha landslide in this paper this landslide originated from a slope of about 20 and the displaced soil mass traveled about 3200 m damming a valley we performed a field survey and found that standing water existed in the landslide area and the loess had high porosity we infer that it was the liquefaction of the water saturated loess layer rather than the suspension of silt in the pore air in the loess that caused the great mobility of this landslide to test this inference we performed undrained triaxial compression and ring shear tests on loess samples to examine the shear behavior of loess saturated by either air or water the test results showed that the water saturated loess soil was highly susceptible to flow liquefaction failure fast shear tests on naturally air dried loess samples revealed that the generated pore air pressure was small under the undrained condition and no significant reduction in the shear resistance was observed implying that air entrapped in the loess was unlikely to be the main contributor to the high mobility of this large scale landslide