geological hazards in loess terrain with particular reference to the loess regions of china abstract the considerable morphodynamic energy provided by the continuing tectonic evolution of asia is expressed in high erosional potentials and very high rates of sediment production that make this continent unequalled as a terrestrial source of primary silt many of these environments are hazardous threatening human occupation health and livelihood especially in regions of dense population such as the loess lands of north china dry loess can sustain nearly vertical slopes being perennially under saturated however when locally saturated it disaggregates instantaneously such hydrocompaction is a key process in many slope failures made worse by an underlying mountainous terrain of low porosity rocks gully erosion of loess may yield very high sediment concentrations 60 by weight characteristic vertical jointing in loess influences the hydrology enlarged joints develop into natural sub surface piping systems which on collapse produce a loess karst terrain collapsible loess up to 20 m thick is common on the western loess plateau foundation collapse and cracked walls are common many rapid events following periods of unusually heavy monsoonal rain slope failure is a major engineering problem in thick loess terrain flow slide and spread types being common the results are often devastating in both urban and rural areas an associated hazard is the damming of streams by landslides the human population increases the landslide risk in china notably through imprudent land use practices including careless water management a number of environmentally related endemic diseases arise from the geochemistry of loess and its groundwaters including fluorosis cretinism kaschin beck disease keshan disease and goitre the chinese desert margins also have a major atmospheric dust problem the effect of such dust upon human health in these extensive regions including many large cities has yet to be evaluated but pneumoconiosis is thought to affect several million people in north and west china

the loess of north central china geotechnical properties and their relation to slope stability abstract loess is an aeolian deposit consisting of predominantly silt sized quartz particles and containing variable amounts of clay sized minerals loess is generally classified as a water softening material because upon wetting the loess fabric rapidly weakens or collapses the strain hardening of malan loess and the brittle failure of lishi and wucheng loess are in strong contrast to the failure behaviour of these loess deposits in a remoulded state from tests carried out on samples with varying moisture contents using a modified bromhead ring shear apparatus it was found that the effective apparent cohesion gradually increases and the effective internal friction angle decreases with an increase in moisture content when the moisture content reaches a material specific threshold the effective cohesion decreases rapidly and the effective internal friction angle stabilises at a residual value the frequent failure of loess slopes in the western part of the chinese loess plateau is closely related to progressive weathering along zones in these slopes which causes a dramatic decrease in strength from the peak strength condition progressive weathering is common in the loess slopes in the western part of the chinese loess plateau during the process shear strength reduction along potential slip surfaces may be achieved by leaching of readily soluble salts destruction of cementation bonds and redistribution of particles localized collapse of the loess fabric causes internal deformation and consequently peak strength conditions are concentrated on a progressively smaller area of the failure plane therefore the mode of failure of loess slopes is generally determined by brittle failure of the undisturbed and unweathered central parts of the slopes it is important that both the weathered and unweathered strength of the loessmaterials in this area be established in order to analyze the stability of existing loessslopes many of which are steepand lie directly above domestic and industrial urban areas

geological and geotechnical characteristics of some loess and loessic soils from china and britain a comparison abstract derbyshire e and mellors t w 1988 geological and geotechnical characteristics of some loess and loessic soils from china and britain a comparison eng geol 25 135 175 loess and loessic deposits cover some 630 000 km 2 of the surface of mainland china the loess plateau of shanxi shaanxi gansu and ningxia being the type region of this formation loess thickness generally exceeds 100 m over large areas of the loess plateau the maximum recorded thickness being 335 m in eastern gansu province near the city of lanzhou in britain loess and loessic deposits form part of a group of materials collectively known as brickearth they occur predominantly as sporadic accumulations in the southeast of england and rarely attain a thickness of more than four metres despite their geographical separation the deposits from china and britain have a remarkable similarity in some of their physical and geotechnical characteristics samples from both locations have been examined and tested in the laboratory and the results are presented the scope of the testing programme involved mineralogical analyses soil microfabric studies using a scanning electron microscope index testing including plasticity grading and density measurements and the investigation of the compressibility characteristics of the soils with particular reference to their susceptibility to collapse a soil structure model based on scanning electron microscope studies is presented and discussed in relation to the perceived mode of formation of the soils and their postdepositional history

underwater bleaching of signals from sediment grains new experimental data abstract the results of an underwater bleaching experiment are reported the purpose of the experiment was to evaluate the degree to which thermoluminescence tl and optically stimulated luminescence osl signals are reduced by a three hour exposure to light at different water depths samples of quartz and feldspar separates were annealed in the laboratory and then given fixed doses of laboratory beta radiation before exposure the results indicate that a three hour light exposure is sufficient to zero the optical signals down to water depths of 10 m for feldspar infra red stimulated luminescence and 12 14 m for quartz osl the tl results for the same quartz and feldspar samples exhibit some bleaching effects with tl signals at 14 m water depth being reduced to 50 65 of the initial value scatter of the tl results limits their interpretation

failure mechanisms in loess and the effects of moisture content changes on remoulded strength abstract investigations into the failure mechanisms of loess slopes in the loess region of north central china have shown that a majority of mass movements are associated with shallow slab slides predominantly moving under tension the effects of soil moisture content are of paramount importance when dry vertical slopes in loess may exceed 15 m in height but under conditions close to saturation the structural strength of loess rapidly decreases causing failure of the slopes mass failure of loess occurs as collapse due to hydroconsolidation and disintegration of the loess fabric as a result of liquefaction or fluidization and can be associated with progressive failure processes local destruction of the openwork fabric of the loess can lead to small plastic movements within the loess deposits this is as close as loess can come to creep

modelling the erosional susceptibility of landslide catchments in thick loess chinese variations on a theme by jan de ploey abstract in his 1990 paper catena 17 175 183 jan de ploey proposed a system whereby catchments are viewed as functional units in which geomorphic work results from the combined effects of water erosion and mass movements his measure of erosional susceptibility of catchments es introduced the gravitational potential in addition to the kinetic energy of the eroding agents this modelling of the erosional susceptibility of catchments in terms of energy was being used to explore time dependent variations of es when jan de ploey died also at this time he extended an invitation to the present authors to test and extend his model using our data base on the landslide dominated catchments in the thick loess country of north central china this paper presents a series of new equations expressing variations in es using a data base for over 200 landslides in the loess covered mountainous terrain relative relief up to 1500 m of the lanzhou region of eastern gansu province these equations express the loss of potential energy of the landslide mass in relation to the relative relief and the pressure energy input in the form of rainfall these indices of erosional susceptibility can be used to analyse the differences in response from one catchment to another and through time between the characteristics of vegetation cover including land use hydrology geomechanical behaviour and mechanisms of movement on slopes using certain assumptions on percentage area of catchments affected by mass movement and long term mean annual precipitation in the lanzhou region the es equation suggests an estimate for non clayey materials of about 10 4 m 2 s 2 which is a significantly higher susceptibility value than the mean worldwide value for non clayey materials obtained by de ploey

a long square barrel gravity corer for sedimentological and geochemical investigation of fine grained sediments abstract large volume undisturbed sediment cores 3 m long are obtained using a modified gravity corer the corer is square in cross section 12 7 12 7 cm and is designed to facilitate acquisition and subsampling of fine grained sediments sedimentological and geochemical data demonstrate that the modified gravity corer obtains undisturbed cores and preserves the sediment water interface

collapsibility and deformation characteristics of deep seated loess in china abstract lin z g and wang s j 1988 collapsibility and deformation characteristics of deep seated loess in china eng geol 25 271 282 as part of a comprehensive research program laboratory tests were conducted on samples of deep seated loess from different locations of the loessial regions of northern china including shaanxi gansu shanxi and honan provinces the information thus acquired on some aspects of the engineering properties of the samples such as the unit collapse pressure relationships the initial collapse pressure versus the preconsolidation pressure and deformation pressure characteristics is interesting and may prove useful to geotechnical engineers who work on projects on water poor plateaux or high river terraces in loessial regions throughout the world

controlling factors of loess landslides in western china based on detailed field data from recent geo hazards surveys in the loess plateau region of western china this study analyzes the key factors that control loess landslides the evolution phase of river valleys the geological structure of slopes and the geometry of slopes are all found to play a role in determining the occurrence distribution and other characteristics of loess landslides groundwater and vegetation also contribute to their formation a combination of human engineering activities and precipitation events are the principal triggering factors for the instability of loess slopes

neogene clay and its relation to landslides in the southwestern loess plateau china loess occurs widely in northwestern china covering neogene clay and other sedimentary units that overlie the bedrock the neogene clays of the baoji region of shaanxi province north china including the eolian hipparion and paleo sanmen lake fluvial deposits are typical clays of the southern chinese loess plateau these clays are also sensitive key strata controlling the development of large scale landslides along the slope of the loess tableland surrounding the guanzhong basin to investigate the neogene clay types and landslides in the region soil samples were tested and the macro and micro structures of the clay strata were analyzed comprehensive analysis methods including the pipette method and fine x ray diffraction were applied to quantitatively analyze the sample composition and determine the clay mineral types the neogene clays are mainly composed of illite and montmorillonite mixed layer minerals on the williams discrimination diagram of swelling potential both types of clay are medium to strongly expansive soil two case studies illustrate that rainfall reduces the shear strength of the neogene clay and raises the groundwater level rainfall has gradually destroyed the structure of the neogene clay transforming it to sliding belt soil the sliding belt lies mainly within the neogene clay layers significantly affecting the occurrence and characteristics of landslides in baoji the rise in groundwater level and weakening of the shear strength of the neogene clay are important factors in the occurrence of landslides the long term strength is a key factor affecting the development of loess landslides along the loess tableland in baoji

gravity erosion on the steep loess slope behavior trigger and sensitivity abstract gravity erosion is a dominant geomorphic process on the widespread steep loess slopes yet it is not well understood due to the complexity of failure occurrence and behavior this study conducted a series of experiments in the laboratory to test the stability of different slope geometries and rainfalls and then performed a sensitivity analysis to quantitatively explore the triggering mechanisms of mass failure on the steep loess slope a topography meter designed by the authors was used to quantitatively measure the process of gravity erosion and the increase rate analysis method presented by the authors was also used to analyze the sensitivity of gravity erosion the following three types of gravity erosion were observed landslide avalanche and mudslide in an event of rainfall various types of gravity erosion might emerge in the same period and mass failures with the same mode and similar size often adjacently appeared sometimes a group of mass failures might happen on a large slowly slipping block then the increase rate analysis method was used to evaluate variations in the gravity erosion with respect to changes in other causal parameters of rainfall duration intensity and slope height gradient climate driven factors and topography triggers had prominent influences on gravity erosion whether for the total amount or the peak amount in an experiment the largest sensitivity parameter on both landslides and mudslides was that of rainfall duration in comparison topography was relatively less influential for the total amount in an experiment the sensitivity parameters of rainfall duration on the landslide and mudslide were 24 9 and 19 5 respectively while the sensitivity parameter of rainfall intensity on the avalanche was 2 2 for the peak amount in an experiment the sensitivity parameter of rainfall duration on the landslide and mudslide were 5 5 and 15 6 respectively meanwhile the sensitivity parameter of slope gradient on the avalanche was 4 6 the experimental results obtained here provide an insight into the pre failure mechanisms and processes of steep loess slopes

shear strength characteristics of a residual soil shallow landslides in natural residual soils slopes are common all over the world the slip surfaces associated with these landslides are often situated above the groundwater table therefore it i

laboratory study on soil behavior in loess slope subjected to infiltration abstract in recent years heifangtai plateau in gansu province china has received significant attention as a loess region in which landslides frequently occur this study aims to examine the soil behavior and failure mechanism s of loess slopes subjected to water infiltration high quality samples were retrieved behind the failure plane of a landslide in heifangtai three sets of stress path tests were conducted to mimic the process of loess slope failures these tests include undrained compression on anisotropically consolidated saturated samples drained shear by decreasing mean effective stress at constant axial load on saturated samples and wetting by decreasing matric suction at constant axial load on unsaturated samples loess behavior was evaluated in terms of shear strength deformation upon shearing critical state state parameter and soil water characteristic curve three major observations were drawn from the test results first the anisotropically consolidated saturated loess exhibits a noticeable strain softening behavior upon undrained compression the peak shear strength is mobilized at less than 1 axial strain the ultimate shear strength is only 20 30 of the peak value second when subjected to shear by decreasing mean effective stress at constant axial load the saturated loess exhibits sudden failure when the confining stress is low at higher stresses the soil exhibits progressive failure third unsaturated loess deforms progressively when subjected to a reduction in matric suction i e wetting at constant axial load the failure mechanisms of the loess slopes are discussed based on the experimental findings

problems in predicting the mobility of slow moving landslides abstract this paper discusses problems in predicting the mobility of slow moving landslides three case studies are presented here where research has been carried out by the utrecht university the la valette landslide complex in the french alps the la mure landslide in the french pre alps near grenoble and the hau landslide in switzerland to predict field velocities of these slow moving landslides the viscosity parameters of the material of these landslides were determined by strain controlled tests in a ring shear apparatus based on bishop s design at utrecht university the viscosity parameters from the laboratory proved to be 10 to 1000 times lower than viscosities obtained from back analyses on the observed velocities in the field this discrepancy may be explained by the development of negative pore pressures when the plastic material slides over a rigid wavy slip surface and or by convergent flow effects the associated gain in strength results in a higher apparent viscosity a more detailed analysis is made for the movements of the la valette landslide observed velocities at the la valette landslide are difficult to describe by one parameter set as the response to a change in groundwater level is not the same during a rise or fall in the piezometric level this deviation may be explained by rapid changes in total stresses and consequently changes in pore pressure under partly undrained conditions the emerging hysteresis with local and temporal variations in pore pressure makes it difficult to predict in detail the moving pattern of landslides

a redesigned kasten core barrel and sampling technique abstract a modified kasten core barrel was developed to obtain cores with nearly 100 sediment retrieval while minimizing disturbance of the sediment water interface one side of the 15 15 cm square barrel is doubled by a second movable plate which can be moved upwards by a series of hand screws thus enabling complete sideways extrusion of the core this produces a set of subcores or slabs of equal quality with preserved stratigraphy which can be x rayed subsampled stored or frozen for geochemical studies the new kasten core barrel is effective in rough weather inexpensive to build easy to handle and enables fast core processing on board

characteristics of late quaternary activity along the southern border fault zone of weihe graben basin abstract the weihe graben basin located in the centre of shaanxi china is a tectonic depression on the southern border of ordos massif a subtectonic unit in the sino korean paraplatform in the light of new information exhibited from geological mapping on the scale of 1 50 000 the active history and the feature of the southern border fault zone of weihe graben basin have been researched the fault zone may be subdivided into two segments the piedmont fault of huashan mt in the east sector and the northern border fault of qinling mts in the west sector the research shows that new activity of the piedmont fault of huashan mt is obvious since the late quaternary a great number of relics of earthquake deformation such as the newest fault scarps bedrock fractures loess crevices landslides and mountain creep are distributed along this fault and its two flanks this fault is most likely the causative fault zone of the huaxian great earthquake in 1556 m 8 the analysis of two palaeoseismic profiles shows the earthquake recurrence interval is 2000 2500 years for the huashan mt piedmont fault whereas 2000 4000 years for the northern border fault of qinling mts

long hydroplastic plastic barrel sediment cores suitable for geotechnical testing abstract long large diameter 8 cm sediment cores are obtained by outfitting the pvc core barrels with a sliding weight placed near its bottom no metal barrel is needed laboratory tests prove that the cores thus obtained are undisturbed and suitable for geotechnical testing

occurrence of landsliding on slopes where flowsliding had previously occurred an investigation in a loess platform north west china abstract loess slides in south jingyang platform shaanxi province usually occur on slopes where loess flowslides had previously occurred numerical modeling shows that flowslide occurrence causes conditions that increase shear stress and water content in the subsequent slopes both of these factors move the soil stress states towards its theoretical failure line under these conditions only small increases in water content can cause soil collapse this leads to the backscarps of former flowslides being much more prone to landsliding wetting test results show that the loess can collapse suddenly as the water content gradually increases therefore the wetting process induced by continued irrigation may result in the subsequent slides during constant water content tests of the loess material soil shear strength increases with the development of specimen deformation therefore slide mobilization which may be a relatively slow process is dependent on whether the wetting conditions exist finally a slope evolution model for loess platforms is proposed in this study

irrigation induced loess flow failure in heifangtai platform north west china because the construction of dams and hydro electric power stations of liujiaxia and yanguoxia across the yellow river in west gansu province north west china inhabitants in the reservoir areas were resettled in heifangtai loess platform irrigation thus started in 1968 perched water table was significantly raised and resulted in many loess flow failures in the past 30 years this type of landslide was often featured by long runout distance high speed and recurrence laboratory tests along icu and csd stress paths were performed it is shown that the loess has a strong strain softening behavior and instability can occur in drained condition before undrained liquefaction the failure mechanism of loess flow can be interpreted as the following process with increasing perched water table collapse in loess was first triggered in drained condition and led to undrained loading to adjacent soil in the lower saturated part of the loess platform under gravity loading applied by upper dry loess undrained flow failure mobilized eventually

analysis of the causes of large scale loess landslides in baoji china landslide hazards are common in western china understanding the mechanism of landslides in loess covered regions is particularly important for landslide risk assessment a detailed landslide survey including large scale slide drilling and geophysical exploration was carried out at the edge of the loess plateau on the north side of the wei river in china we reconstructed the geomorphological evolution model of the wei river and analyzed slope structures and lithology engineering geologic conditions and active fault properties in the landslide regions were investigated the results showed that paleogeomorphology of the north slope of the river gradually lowered from south to north ancient landforms showed a gradual transition to the south sanmen lake basin from the piedmont alluvial plain during the pliocene to early pleistocene the lake basin in the southern part of the study area gradually retreated and the wei river formed in the early pleistocene the main river flow shifted northward because of neotectonic movement and periodic climate changes until the holocene and then gradually moved southward to produce the current landforms the active wei river fault at the edge of the loess plateau acted as a route of water infiltration weakening the structural planes erosion and rise of the groundwater table caused old occurrence during the late pleistocene and ancient occurrence before the late pleistocene landslides to form on the edge of the plateau along active fractures and interfaces of pliocene sand gravel and clay these were multiple deep seated rotational slides and or multiple perched translational landslides slope stability analysis indicated that the complex landslides that occurred in the loess areas in recent years were closely related to the distribution of water and pliocene clay

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

heavy rainfall triggered loess mudstone landslide and subsequent debris flow in tianshui china abstract continuous and heavy precipitation triggered a large loess landslide at the southern dagou village of mapaoquan town tianshui city gansu province of china on july 21 2013 the landslide debris rapidly turned into a debris flow that was deposited in the ravine mouth with the volume of 1 9 105 m3 detailed field mapping three dimensional laser scanning aerial photograph interpretation and laboratory tests were carried out to study the formation and moving characteristics of the landslide and subsequent debris flow the results showed that 1 the peak flow velocity and peak discharge of the debris flow were estimated to be approximately 7 2 m s and 730 m3 s respectively the velocity had a tendency to first increase and then decrease from the head to entrance in the dagou gully 2 the analysis of rainfall conditions showed that the effective antecedent rainfall within 7 days and hourly rainfall intensity which triggered the slide debris flows was 239 mm and 20 mm h respectively compared with the critical rainfall in this area the effective antecedent rainfall was found to be more significant in triggering this event 3 the mean and effective particle sizes were approximately 0 73 1 3 mm and 0 036 0 087 mm respectively and had the same distribution along the gully as the velocity which confirmed the process of the variation in the flow velocity 4 the scale amplification was very obvious in the formation and moving process of the slide debris flows

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