centrifuge model study on settlement of strip footing subject to rising water table in loess owing to man made activities and natural conditions the groundwater table experiences considerable changes in lanzhou centrifugal model tests were performed to investigate the settlement of strip

relationships between loess and the silk road reflected by environmental change and its implications for human societies in the area of ancient panjikent central asia rich ancient societies of central asia developed on the basis of trade between east and west their existence was dependent on natural resources that favoured agriculture the branches of the silk road in central asia clearly coincide with loess areas where many settlements were erected based on the presence of fertile loess soil and water the aim of the study was to analyse the environmental factors that led to the growth and decline of one of the most important silk road loess towns ancient panjikent as an example of human and climatic impacts on landscape changes the town established in the fifth century quickly became one of the most important cities of sogdiana local loess material was used for the production of the sun dried bricks rapid population growth led to deforestation and consequently increased the intensity of erosion rates and reductions in cultivation area a period of drought near the end of the first millennium ad influenced the final abandonment of the ancient town and its relocation to the lower terrace of the zarafshan river a decline in natural and agricultural resources and subsequently climatic forces caused a decline in the number of cities in semiarid regions of central asia

qualifying mass failures on loess gully sidewalls using laboratory experimentation abstract the morphology of the failure scar has been a long debated issue concerning the loess plateau of china and the lack of normative data has hampered vital research in this area in this study a series of laboratory experiments were conducted to observe failure geometries and volumes under rainfall simulations the following six failure scar types occurred the sequence of the types described here may be same to that of the following text namely tf cd cu ia ps and co the number of failure masses in the experiment for scar types tf cd cu ia ps and co amounted to 45 26 23 3 2 and 1 of the total and the corresponding volumes were 58 16 20 2 3 and 1 of the total respectively this implies that tf cd and cu were the three major types of failure scars during the process of gravity erosion on a steep loess slope and the scar tf was the most significant the sensitivity coefficient the degree of variation in the target value caused by a change in a crucial factor when other conditions remain unchanged of the slope gradient and rainfall intensity for the total volume of the tf scar were 4 5 and 3 7 respectively in other words a relatively dangerous failure scar tf might appear if the slope became steeper or if the rainfall became more intensive in addition the sensitivity coefficients of the rainfall duration for the total volume of the cu scar was significant being 12 4 this shows that a long duration storm could easily induce a large volume failure with a cu scar the experimental results obtained here provide a morphogenic insight into the gravity erosion control on a loess gully sidewall

particle packing from an earth science viewpoint abstract particle packings are relevant to many aspects of the earth sciences and there is a long history of the study of packings from an earth science viewpoint packings have also been studied in connection with other subjects and disciplines allen 1982 produced a major review which provides a solid base for earth science related studies this review complements allen s work and in particular focuses on advances in the study of random packings over the last ten years transitions from packing to packing may be as important as the packings themselves and possibly easier to model this paper places emphasis on certain neglected works in particular morrow and graves 1969 and the packing transition envelope kahn 1956 and the measurement of packing parameters griffiths 1962 on packings in one dimension and getis and boots 1978 on packings in two dimensions certain packing problems are relevant to current areas of study including structure collapse in loess hydroconsolidation flowslides in very sensitive soils wind erosion jewel quality in opals and the structure and functions of sand dunes the region where interparticle forces become active particles

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

distribution and genetic types of loess landslides in china abstract in this study 14 544 loess landslides collected from the loess plateau of china are used to reveal their distribution and origins main factors considered include landslide density regional tectonics soil properties geomorphic structure rainfall distribution seismic activity and human activity based on these factors the loess plateau is divided into eight zones with high possibilities of landslides that are classified into six genetic types the first genetic type of clustering distribution of loess landslides is related to several main regional active faults the second type is related to broken pieces of loess geomorphic structures the third type is considered to be due to unloading of the geomorphic peripheral slope that can cause the internal structural plane to open and thus controls the prototype and scale of the loess landslide change of hydrogeological conditions in the slope softens the loess pedestal and the slippery layer forming a softening zone and thus controlling the shear crack and slip model of the fourth type of loess landslides the fifth type is due to seismic activities that can generate additional stress to the earth s surface and landform slopes causing the opening of joints and seismic liquefaction the last type of landslides is caused by human activities by changing the geological structure hydrogeological conditions and the inner stress balance of slopes

the influence of loess cave development upon landslides and geomorphologic evolution a case study from the northwest loess plateau china abstract loess caves landslides collapses bank erosion and soil erosion which are independently and interactively shaping the modern loess landscape are widely distributed across the chinese loess plateau the study area is located in a small watershed in huining county gansu province which is one of the areas with the strongest development of loess caves across the loess plateau this area is an ideal site for studying geological hazards and geomorphic evolution on the loess plateau seventeen landslides and 176 loess caves with a density of 887 units km2 were investigated with a uav unmanned aerial vehicle and mapped by gis geographic information system using high resolution uav images and topographic data we carried out an interpretation of loess caves bank erosion and landslides studied the spatial distribution and developmental patterns of loess caves landform morphology and the relationship between loess caves and landslides based on gis spatial analysis mathematical statistics and field surveys and analyzed the influence of loess microtopography on slope landforms finally six typical evolutionary models of soil erosion loess cave development landslide occurrence barrier dam formation are preliminarily proposed the primary slope stage early cave stage accelerated cave stage cave connecting stage landslide creeping stage and landslide dam forming stage this study is a useful exploration and an attempt to reveal the influence of loess cave development on slope stability and disaster chain effects

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

mantle dynamics uplift of the tibetan plateau and the indian monsoon convective removal of lower lithosphere beneath the tibetan plateau can account for a rapid increase in the mean elevation of the tibetan plateau of 1000 m or more in a few million years such uplift seems to be required by abrupt tectonic and environmental changes in asia and the indian ocean in late cenozoic time the composition of basaltic volcanism in northern tibet which apparently began at about 13 ma implies melting of lithosphere not asthenosphere the most plausible mechanism for rapid heat transfer to the midlithosphere is by convective removal of deeper lithosphere and its replacement by hotter asthenosphere the initiation of normal faulting in tibet at about 8 3 ma suggests that the plateau underwent an appreciable increase in elevation at that time an increase due solely to the isostatic response to crustal thickening caused by india s penetration into eurasia should have been slow and could not have triggered normal faulting another process such as removal of relatively cold dense lower lithosphere must have caused a supplemental uplift of the surface folding and faulting of the indo australian plate south of india the most prominent oceanic intraplate deformation on earth began between about 7 5 and 8 ma and indicates an increased north south compressional stress within the indo australian plate a tibetan uplift of only 1000 m if the result of removal of lower lithosphere should have increased the compressional stress that the plateau applies to india and that resists india s northward movement from an amount too small to fold oceanic lithosphere to one sufficient to do so the climate of the equatorial indian ocean and southern asia changed at about 6 9 ma monsoonal winds apparently strengthened northern pakistan became more arid but weathering of rock in the eastern himalaya apparently increased because of its high altitude and lateral extent the tibetan plateau provides a heat source at midlatitudes that should oppose classical symmetric hadley circulation between the equator and temperate latitudes and that should help to drive an essentially opposite circulation characteristic of summer monsoons for the simple case of axisymmetric heating no dependence on longitude of an atmosphere without dissipation theoretical analyses by hou lindzen and plumb show that an axisymmetric heat source displaced from the equator can drive a much stronger meridianal monsoonlike circulation than such a source centered on the equator but only if heating exceeds a threshold whose level increases with the latitude of the heat source because heating of the atmosphere over tibet should increase monotonically with elevation of the plateau a modest uplift 1000 2500 m of tibet already of substantial extent and height might have been sufficient to exceed a threshold necessary for a strong monsoon the virtual simultaneity of these phenomena suggests that uplift was rapid approximately 1000 m to 2500 m in a few million years moreover nearly simultaneously with the late miocene strengthening of the monsoon the calcite compensation depth in the oceans dropped plants using the relatively efficient c4 pathway for photosynthesis evolved rapidly and atmospheric co2 seems to have decreased suggesting causal relationships and positive feedbacks among these phenomena both a supplemental uplift of the himalaya the southern edge of tibet and a strengthened monsoon may have accelerated erosion and weathering of silicate rock in the himalaya that in turn enhanced extraction of co2 from the atmosphere thus these correlations offer some support for links between plateau uplift a downdrawing of co2 from the atmosphere and global climate change as proposed by raymo ruddiman and froehlich mantle dynamics beneath mountain belts not only may profoundly affect tectonic processes near and far from the belts but might also play an important role in altering regional and global climates

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

the effects of slope length and slope gradient on the size distributions of loess slides field observations and simulations abstract in this study we characterize and consider the effects of slope length and slope gradient on the size distributions of loess slides to carry out this study we employ data on 275 loess slides within zhidan county central loess plateau china these data were collected in the field and supplemented by the interpretation of remote sensing images both the field observations and slope stability analysis show that loess slide size increases with the slope length slide sizes is significantly correlated with slope length showing a power law relationship in both cases however the simulation results show that slope gradient is not associated with loess slide size the main part of the link between slope gradient and slide size seen in the observations is only apparent as indicated by the strong connection between slope gradient and length statistical analysis of the field observations reveals that slope gradient decreases with increasing slope length and this correlation interferes with the potential relationship between landslide sizes and slope gradient seen in the field observations in addition the probability densities of the areas of loess slides occurring on slopes of different slope lengths are determined using kernel density estimation this analysis shows that slope length controls the rollover of the frequency size distribution of loess slides the scaling exponent increases with slope length

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

centrifuge model testing of a loess landslide induced by rising groundwater in northwest china abstract considerable artificial irrigation in the heifangtai area has caused the continued rise of groundwater levels which has resulted in several large scale landslides in the loess platform area considering the no 13 landslide of jiaojia in the heifangtai area as a geological archetype a series of centrifuge tests was conducted to study the deformation and failure characteristics of the slope due to the continuous rise in the groundwater level meanwhile the pore water pressure earth pressure deformation and evolution characteristics of the slope were monitored and recorded in real time furthermore isotropically consolidated undrained triaxial testing icu was conducted to investigate the static liquefaction of loess specimens which was related to the slope instability the centrifuge test results showed that a series of parallel and steep tension cracks at the top of the slope were present before the landslide which was caused by the rising groundwater the icu experimental results showed that as the pore water pressure increased strong strain softening and static liquefaction of saturated loess soils were found which was related to the sudden destruction of the slope

wind blown origin of the pliocene red clay formation in the central loess plateau china abstract in order to determine the depositional processes of the pliocene red clay formation deposited directly beneath the plio pleistocene loess in the chinese loess plateau four red clay sections spanning over 400 km are studied grain size analysis of closely spaced samples in the sections shows that the particles of the red clay are very fine with the sand fraction 63 m being negligible and that all the curves indicating changes in different grain size parameters have a similar pattern the grain size records in the upper part of the four sections are almost identical with the median grain size centered at 4 8 m the ree patterns of 28 samples from the jiaxian red clay section are all characterized by lree enrichments relatively flat hree and slight negative eu anomaly being similar to those of eolian loess and the average upper continental crust these lines of evidence point to a wind blown origin of the red clay deposits accumulation of the loess soil sequences in the chinese loess plateau during the past 2 6 ma can be therefore regarded as the continuation of the pliocene atmospheric dust deposition observations of spatial grain size changes in the loess plateau suggest that the eolian red clay might be transported mainly by the westerlies differing significantly from the overlying loess that was transported essentially by the east asia winter monsoonal winds

magnetostratigraphic record of the late miocene onset of the east asian monsoon and pliocene uplift of northern tibet abstract widespread eolian red clay underlying the plio pleistocene loess palaeosol succession in northern china has been dated magnetostratigraphically back to 8 35 ma indicating that the east asian monsoon started at about the same time as the indian monsoon an initial sedimentation rate of 11 m myr increased gradually to 17 5 m myr by 6 ma and then decreased to 6 m myr between 5 ma and 3 5 ma a marked increase in sedimentation rate and grain size beginning between 3 5 ma and 3 1 ma indicates that the east asian winter monsoon strengthened at this time and intensified further after 2 6 ma the temporal coincidence of the stronger winter monsoon and the pliocene uplift of northwestern tibet just before the onset of the northern hemisphere glaciation indicate that the three events could be causally linked

size distribution of loess slides in relation to local slope height within different slope morphologies abstract loess slides are widespread and dangerous gravity induced surface processes on the loess plateau of north central china the local slope height and slope morphology have been considered as important conditioning factors for landslide susceptibility mapping however the quantitative relationship between landslide size and local slope height within different slope morphologies is not very clear in this study an inventory of 155 loess slides was developed based on detailed field investigation and remote sensing image interpretation statistical analysis and gis were applied to find the quantitative relationships between the size of these loess slides and local slope height in different types of slope morphologies the analysis shows that the relationship between the loess slides volume and area exhibits a similar trend within different types of slope morphologies in addition the analysis demonstrated that loess slides are more frequent on local slope height from 40 to 100 m stepped slopes with higher pore water pressure are prone to sliding and approximate 34 19 of total loess slides occur in these stepped slopes moreover the analysis shows that the mean loess slide area and volume rapidly increase with increasing local slope height furthermore the result underlines the fact that both the local slope height and the slope morphology are two fundamental factors that control the occurrence as well as size distribution of loess slides the loess slide size remarkably increases with increasing local slope height within every type of slope morphologies these findings indicate that local slope height can limit the loess slide size and their spatial extent moreover we quantified the correlation between the loess slide size and local slope height using power law form and the scaling exponents of the correlations are different within different slope morphologies

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

characterizing hydrological processes on loess slopes using electrical resistivity tomography a case study of the heifangtai terrace northwest china abstract from the perspective of engineering geology loess has long been considered as a homogeneous and porous material it is commonly believed that water penetrates loess via pores and in some cases causing mass movements however several researchers have expressed doubts about this mechanism as a cause of slope failures in loess and moreover the actual hydrological processes operating in loess deposits and their effect on slope failures have not been fully investigated here we present the results of an electrical resistivity survey of the heifangtai loess terrace in northwestern china designed to characterize the hydrological processes in loess slopes and their relationship with slope failures the heifangtai loess terrace is located on the fourth terrace of the yellow river and consists of 57 m thickness of aeolian loess 2d and 3d electrical resistivity tomography ert was used to monitor the movement of ground water before and after irrigation and rainfall events and the evolution of a sink hole in the toe of the landslide deposits our main findings are as follows 1 based on the 2d ert results the depth of infiltration into the thick unsaturated loess is not more than 5 m in the profile at the top of the landslide 2 electrical resistivity decreased as a result of water infiltration through sinkholes and this process can increase the soil water content and induce soil liquefaction which can eventually result in land sliding 3 landslide deposits block the groundwater drainage channels through the loess which results in the concentration of water in the toe of the landslide consequently groundwater together with rainfall triggers the failure of sinkholes or cracks which may induce a continuing process of new slope failures at the sites of past landslide

environmental geology in loess areas of china there are several unfavorable geological hazards in the loess area of china the major purposes of environmental geology studies in this region are to expound the causes of these hazards and to determine treatments geological hazards include endemic diseases depletion of groundwater land subsidence ground fissures soil erosion and collapsibility of loess this article is a summary of studies regarding these hazards keshan disease and kaschin beck disease for example can be prevented and cured by adding selenates to table salt ponds can be constructed on the loess plateau and dikes around farmlands to collect rainfall to recharge groundwater resources excess extraction of groundwater is the major cause of land subsidence ground fissures in xi an are primarily caused by tectonics but over extraction of ground water strengthens its activity observation stations should be established in order to forecast and prevent landslides planting trees in a regional shelterbelt is the primary measure necessary to prevent soil erosion as a result of these geological studies valuable experience in preventing collapse of loess in china has been gained

petroleum source rock potential of mesozoic condensed section deposits in southwestern alabama because condensed section deposits in carbonates and siliclastics are generally fine grained lithologies often containing relatively high concentrations of organic matter these sediments have the potential to be petroleum source rocks if buried under conditions favorable for hydrocarbon generation in the mesozoic deposits of southwestern alabama only the upper jurassic smackover carbonate mudstones of the condensed section of the lzagc 4 1 cycle have realized their potential as hydrocarbon source rocks these carbonate mudstones contain organic carbon concentrations of algal and amorphous kerogen of up to 1 7 and have thermal alteration indices of 2 to 3 the upper cretaceous tuscaloosa marine claystones of the condensed section of the uzagc 2 5 cycle are rich up to 2 9 in herbaceous and amorphous organic matter but have not been subjected to burial conditions favorable for hydrocarbon generation the jurassic pine hill norphlet black shales of the condensed section of the lzagc 3 1 cycle and the upper jurassic haynesville carbonate mudstones of the condensed section of the lzagc 4 2 cycle are low 0 1 in organic carbon although condensed sections within depositional sequences should have the highest source rock potential specific environmental preservational and or burial history conditions within a particular basin will dictate whether or not the potential is realized as evidencedmore by the condensed sections of the mesozoic depositional sequences in southwestern alabama therefore petroleum geologists can use sequence stratigraphy to identify potential source rocks however only through geochemical analyses can the quality of these potential source rocks be determined less

a study of a flowslide with significant entrainment in loess areas in china flowslides are a frequent type of natural disaster in loess areas and may result in the significant loss of properties and or casualties the dagou flowslide is a typical event in a loess area and is accompanied by significant sediment entrainment to analyze the mechanisms responsible for flowslides and to obtain the parameters for a runout analysis a field investigation was conducted specimens were sampled on site to carry out laboratory tests including a triaxial test sieve analysis and chemical component analysis the parameters were used in the runout study employing an energy based runout model an analytical entrainment model was adopted to calculate the entrainment after considering physical properties and the mechanism of the entrainment process of the loess finally the entrainment model was incorporated into the runout model to simulate the post failure process of this case energy dissipation due to the deformation of slices was considered as it was thought to be important for a slide with a significant deformation the simulation results were compared with the measurements including runout distance total volume erosion depth deposition height at different sections and velocities at specific locations the results indicate that the energy based runout model together with the entrainment model can capture the kinematic characteristics of the dagou flowslide therefore it is feasible to use this model to predict the runout characteristics of flowslides in similar areas copyright c 2017 john wiley sons ltd

human impact on geomorphic processes and hazards in mountain areas in northern spain abstract the temporal occurrence of slope movements their contribution to relief evolution and human influence on those processes in two study areas of northern spain are presented the work is based on temporal analyses covering 100 ka in one study area and 43 years in the other temporal analysis has been the basis for quantitatively assessing the magnitude of human influence and developing landslide susceptibility and hazard models with known independently tested prediction capability the results obtained in one study area show a relationship between landsliding periods and increasing precipitation during upper pleistocene and holocene significant increases of landslide frequency and mobilisation rate were also found around 5500 and 200 years ago those moments coincide with two periods of intensified human presence and activities neolithic and industrial revolutions the increase observed represents about one order of magnitude from pre neolithic to present a similar increase has been found between 1954 and 1997 in the other study area the latter increase shows no relationship with changes in climate parameters or seismic activity a fairly good correlation has been found between landslide frequency and socioeconomic indicators of human activity sedimentation rates in two neighbouring estuaries were determined and significant increases particularly in the second part of last century were also found evidence obtained suggest that the increases observed in the frequency of slope instability events and therefore hazard denudation and sedimentation rates are due to a greater extent to indirect geomorphologic changes caused by human action rather than climate change detailed analysis of landslide frequency during that 43 year period has also been used to produce and validate landslide susceptibility models and obtain landslide hazard maps with known prediction accuracy validation tests were carried out comparing susceptibility maps based on landslides that have occurred in the past with the ones occurring in several later periods prediction capability of models could thus be determined validation of susceptibility maps using data derived from the temporal analysis of landslides was used to obtain hazard maps expressed as probability of new ruptures in a given time period on the basis of past trends in terrain behaviour possible impacts of a growing influence of human activities on the terrain have been incorporated into the assessment of future hazards by considering different scenarios

climate change loess and palaeosols proxy measures and resolution in north china the loess plateau of north china is a key region for the study of records of quaternary climatic change various techniques to abstract climatically sensitive data were first applied to the classic loess palaeosol site at luochuan and current views on climatic change in asia have been strongly moulded by results from this central part of the loess plateau data including the magnetic susceptibility granulometry mineralogy geochemistry micromorphology fossil content and inorganic and organic carbon content of asian loess palaeosol series have been used singly and in combination as surrogate measures of palaeoclimates to infer climatic changes with particular reference to changes in the asian monsoon some of this work is reviewed and the status of a number of parameters as climatic proxies is discussed some lithostratigraphic sequences from which proxy measures of climate have been derived are incomplete as shown by erosion surfaces water laminated zones and truncated palaeosol profiles while others provide records of relatively low resolution most descriptions of quaternary climatic changes based on studies of the loess emphasize alternations in the relative dominance of warm and moist v cool dry and dust laden monsoons some recent studies of the much higher resolution loess palaeosol successions on the western margins of the loess plateau have suggested that such changes may sometimes be out of phase with the inference that the current climate model is too simple means of testing this hypothesis are proposed

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

development and evolution of loess vertical joints on the chinese loess plateau at different spatiotemporal scales abstract the vertical joints of aeolian loess are ubiquitous on the chinese loess plateau clp the distribution variability of which mainly depends on the differences in structural characteristics of loess water drivers e g rainfall or irrigation loess strata e g sedimentary depth and microtopography this study conducted extensive field investigation and experiments to enhance the understanding of morphologies cross scale transformation mechanism and structural bases of loess vertical joints lvjs moreover the development and evolution processes of lvjs were refined by considering loess sedimentary dynamics results show that 1 lvjs are the product of diagenesis in loess strata during loess historical sedimentary process 2 the pore concentration zones and vertical tubular channels in loess are the structural bases of forming original vertical joints ovjs at the micro mesoscale which is supported by the results from the three dimensional computing tomography ct scanning and scanning electron microscopy sem tests and 3 the morphologies of lvjs vary with the microtopography at different spatiotemporal scales and is characterized by the cross scale transformation mechanism i e that they could transform up i e an expansion behavior or down i e a degradation behavior at the micro meso and sub macro scales under the influences of dry wet cycles loess pile thickening and exogenic forces besides we also propose the development and evolution mechanism of ovjs in loess from the viewpoint of unsaturated loess which would help understand the loess anisotropic genesis structural evolution preferential flow and the occurrence of geohazards such as landslides and soil erosion

magnetostratigraphy and paleoclimatic interpretation of a continuous 7 2 ma late cenozoic eolian sediments from the chinese loess plateau an almost 300m thick eolian sequence of late cenozoic sediments which includes 162 5m of quaternary loess paleosols and 126m of late tertiary eolian red clay from the central part of the chinese loess plateau was investigated to determine the magnetostratigraphy the results show that eolian dust accumulation and by inference the related east asia paleomonsoon had begun by 7 2ma as paleomonsoon are largely controlled by the tibetan plateau this implies that the plateau had reached some critical elevation by 7 2ma the section also documents a rapid increase in eolian dust accumulation in the late cenozoic at 3 2ma that is probably due to the influence of global ice volume on the east asian monsoon

temporal patterns of nonseismically triggered landslides in shaanxi province china abstract examination of the temporal patterns of landslide events provides valuable insights into the baseline information used to determine landslide activity and perform risk assessment in a given area we collected a catalog of historical nonseismically triggered landslides that occurred over 22 years in shaanxi province china we found that the annual number of slides was significantly related to the annual number of falls the average annual numbers of slides and falls were approximately 17 and 10 respectively the active and nonactive periods of landslides alternated within the time series of the annual number of landslides an empirical power law correlation exists between the complementary cumulative frequency and the annual number of landslides the monthly distribution of landslide events is significantly associated with monthly rainfall most landslide events occurred in the rainy season between july and october the average time intervals of falls and slides from july to october were approximately 12 days and 8 days respectively moreover the temporal distribution of landslide events is clustered owing to the impact of nonuniformly distributed rainfall activities most of the landslides concentrated in one or two months of a year furthermore the nonzero values in the landslide time series are nonuniformly spaced the complementary cumulative frequency distribution of the time intervals between landslide events can be adequately fitted by an exponential function based on these equations the temporal probabilities of landslide events can be predicted in addition most of the nonseismically triggered landslides in shaanxi province were triggered by long term antecedent rainfall and high intensity intraday rainfall

geological and computer modeling of upper jurassic smackover reef and carbonate shoal lithofacies eastern gulf coastal plain abstract reefs and carbonate shoals have long been known from the upper jurassic smackover formation in the gulf coastal plain however these carbonate lithofacies have unique acoustic properties that make them difficult to define using 3 d seismic reflection technology in the eastern gulf coastal plain microbial reef and shoal buildups occur on pre jurassic paleotopographic basement features on a carbonate ramp margin development of these buildups is a result of the interplay among paleotopography sea level changes and carbonate productivity geological and computer modeling indicates that smackover reef and shoal development is restricted to the flanks of high emergent relief structures while reef and shoal development occurred on the crest and flanks of low relief structures submergent for these submergent features modeling indicates that carbonate productivity during reef growth was significantly greater than during shoal development in addition to the initial paleorelief the rate of sea level rise the level of carbonate productivity and duration of reef growth appear to be critical factors in determining thickness and distribution of the reef lithofacies subsidence and compaction are minor factors shoal development is greatly influenced by reef distribution sea level changes level of carbonate productivity and duration of shoal deposition subsidence compaction and sediment redistribution are also factors modeling of parameters affecting reef and shoal development associated with pre jurassic paleohighs in combination with 3 d seismic reflection studies increases the chances of drilling a successful exploration well

experimental study on the effect of water gushing on loess metro tunnel in the construction of metro tunnels water gushing accidents caused by the rupture of underground pipeline often occur and in loess area the collapsibility of loess makes this problem more complex and difficult to investigate the damage of metro tunnel caused by collapsible loess under the action of local dynamic water gushing water a model experiment was conducted based on the pipeline water gushing accident happened in the construction of metro tunnel located in loess area through the study of similar materials of loess and tunnel lining the test materials and apparatus were prepared according to similarity criterion by simulating water gushing environment in the loess stratum this paper analyzed mechanical characteristics of tunnel water pressure of surrounding rock contact pressure and internal force of tunnel lining and deformation of surrounding rock and tunnel furthermore combining with the process of local collapse of loess in the model experiment it is concluded that the formation of water transport channel is the main reason for the difference of tunnel structural response when water gushing occurs at different locations finally a three dimensional spatial model of water transport channel in loess stratum under the environment of local water gushing was established to study the rule of water transport

influence of topography and volume on mobility of loess slides within different slip surfaces mobility of loess slides has been evaluated using an empirical approach based on a detailed field investigation and remote sensing image interpretation for all the loess slides the affected area increases with increasing loess slides volume from the statistical analysis it is seen that the travel distance has an increasing trend while the coefficient of friction has a decreasing trend with the increase in landslide volume landslide volume determine its travel distance and coefficient of friction that can be shown with a regression equation having simple power law form which indicates that the mobility of loess slides increases with increasing volumes by analogy the greater the energy of the sliding loess mass the stronger is the mobility of loess slide a plot of the travel distance of loess slide versus fall height shows a significant positive power law correlation indicating the increase in mobility of loess slide with fall height the negative power law correlation observed between the travel distance and slope inclination implies that the mobility decreases with the increase of slope inclination three datasets of loess slides characterized by different slip surfaces were distinguished the red clay contact landslides have the strong mobility than landslides in loess and bedrock contact

landslides triggered by excavation in the loess plateau of china a case study of middle pleistocene loess slopes abstract the frequent occurrence of catastrophic landslides caused by excavation in a loess slope is one of the commonly encountered engineering problems in the loess plateau middle pleistocene loess slopes were selected as a case study for current research the distribution of excavation induced loess landslides was studied by field investigation on the basis of centrifuge model tests the deformation features and failure mechanism of a homogeneous loess slope and a double paleosol interlayer loess slope under different excavation slope angles were analyzed and compared it was shown that the response of horizontal earth pressures in the lateral region of the excavation zone has a close relationship with the failure of the slope displacement measurements showed that the deformation stages of loess slopes due to excavation are independent of the paleosol interlayer the excavation slope inclinations and soil properties significantly affected the failure process and division of the slope the characteristics that excavation induced loess landslides always occur in hysteresis and abruptness were interpreted by the analysis of the failure process the influence of blade penetration during the excavation performed was quantitatively estimated finally based on the result of stress path tests an improved unloading constitutive model was proposed to simulate the deformation of soils in the lateral and bottom of the excavation area

geochemistry of organic contaminants in narragansett bay sediments abstract organic contaminants from several different chemical classes were analyzed in surface sediments along a transect from the head to the mouth of narragansett bay the chemical classes included total hydrocarbons polycyclic aromatic hydrocarbons substituted benzotriazoles and phthalic acid esters sediment concentrations of all compounds were highest in the providence river and decreased with distance downbay the observed decreases were approximately exponential for all compounds however the distances at which the concentrations decreased to one half of their initial concentrations half distances were different the depth distributions of these compounds in sediment cores from three locations were also investigated a sediment core collected near the head of the bay conimicut point showed a well defined historical record of contaminant input to the bay at a mid bay location north jamestown however the record was smeared because of extensive bioturbation a sediment core collected near the mouth of the bay rhode island sound showed a subsurface increase for all of the measured compounds the results of detailed analyses suggest that this horizon may have been influenced by dredge spoil material originally from the head of the bay

late quaternary landscape evolution in a small catchment on the chinese loess plateau abstract late quaternary landscape evolution was analysed with reference to a small 0 08 km 2 drainage basin system in southeastern gansu province southwestern chinese loess plateau in this region v shaped valleys with broad valley floors are prominent landscape features whose basic shape already existed prior to mis 2 during mis 2 the valley bottoms were infilled with fluvially reworked loess today forming accumulation terraces infrared optically stimulated luminescence irsl dating of these loess like deposits assigned them to the time span ranging from 22 5 to 17 7 ka bp during the late holocene valley fills were partly eroded and the receiving stream channel was deepened by at least 25 m close to the confluence of the study site s channels these alternating erosion and accumulation phases were triggered by climatic factors or human impact in the most recent past the high landscape sensitivity of the chinese loess plateau has led to increasing soil conservation measures that have effectively confined surface erosion however the lack of drainage on the artificial terraces induces piping processes

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

engineering properties and zoning of loess and loess like soils in china the widely distributed loessic soils of china are described concentrating on the collapsible soils of the upper strata of the loessic series a general trend of gradual steady reduction in the tendency to collapse on wetting is found going in the direction from northwest to southeast cases of damage and flooding tests of pits are cited for illustration results of electron microscope studies of structural features of loess specimens from different locations are compared with the engineering behavior especially the susceptibility to self subsidence and degree of collapsibility in view of this trend and the differences between loessic soils of different regions a preliminary zoning of the loessic soils was made resulting in seven zones as shown on a schematic map

prediction of rainfall induced shallow landslides in the loess plateau yan an china using the trigrs model in this work a transient rainfall infiltration and grid based regional slope stability model trigrs was implemented in a case study of yan an city northwest china in this area widespread shallow landslides were triggered by the 12 july 2013 exceptional rainstorm event a high resolution dem soil parameters from in situ and laboratory measurements water table depths the maximum depth of precipitation infiltration and rain gauge corrected precipitation of the event were used as inputs in the trigrs model shallow landslides triggered on the same day were used to evaluate the modeling results the summarized results are as follows i the characteristics and distribution of thirty five shallow landslides triggered by the 12 july 2013 rainfall event were identified in the study area and all were classified as shallow landslides with the maximum depth area and volume less than 3 m 200 m2 and 1000 m3 respectively ii four intermediate factor of safety fs maps were generated using the trigrs model to represent the scenarios 6 12 18 and 24 hours after the storm event the area with fs 1 increased with the rainfall duration the percentage of the area with fs 1 was 0 2 3 3 3 8 and 5 1 for the four stages respectively twenty four hours after the rainstorm trigrs predicted that 1255 grid cells failed which is consistent with the field data iii trigrs generated more satisfactory results at a given precipitation threshold than sinmap which is ideal for landslide hazard zoning for land use planning at the regional scale comparison results showed that trigrs is more useful for landslide prediction for a certain precipitation threshold also in the regional scale iv analysis of the responses of loess slope prone to slope failure after different precipitation scenarios revealed that loess slopes are particularly sensitive to extended periods of heavy precipitation copyright 2016 john wiley sons ltd

thickness trends and sequence stratigraphy of the middle devonian marcellus formation appalachian basin implications for acadian foreland basin evolution analysis of more than 900 wireline logs indicates that the middle devonian marcellus formation encompasses two third order transgressive regressive t r sequences mss1 and mss2 in ascending order compositional elements of the marcellus formation crucial to the successful development of this emerging shale gas play including quartz clay carbonate pyrite and organic carbon vary predictably within the proposed sequence stratigraphic framework thickness trends of marcellus t r sequences and lithostratigraphic units reflect the interplay of acadian thrust load induced subsidence short term base level fluctuations and recurrent basement structures rapid thickening of both t r sequences especially mss2 toward the northeastern region of the basin preserves a record of greater accommodation space and proximity to clastic sources early in the acadian orogeny however local variations in t r sequence thickness in the western more distal area of the basin may reflect the reactivation of inherited eocambrian basement structures including the rome trough and northwest striking cross structural discontinuities induced by acadian plate convergence episodes of block displacement locally warped the basin into northeast southwest trending regions of starved sedimentation and or erosion adjacent to depocenters in which regressive systems tract deposits were ponded block movement appears to have initiated in late early devonian time resulting first in thinning and local erosion of the oriskany sandstone in northwest pennsylvania this study in addition to providing the basis for a predictive sequence stratigraphic model that can be used to further marcellus exploration tells of a foreland basin more tectonically complex than accounted for by simple flexural models

dynamics characteristic of red clay in a deep seated landslide northwest china an experiment study abstract the red mudstone sediments are widely encountered in earthquake region northwestern china which is vulnerable to the occurrence of landslides previous studies focused on rain induced shallow landslides some deep seated landslides in red clay with a gentle inclination are still not well understood a fatal landslide named as zhengjiamo landslide located in tianshui china was investigated the aim of this study was to study mechanism of shear surface development under earthquake using a series of cyclic triaxial tests the test results of the red clay from the zhengjiamo landslide revealed that the undrained shear strength and excess pore pressure increase with increasing confining stresses 3 and ocr it is also observed that those stress strain behaviors on the deviatoric stress axial strain and pore water pressure subsequent to the initial contractive response the saturated clay exhibited dilation upon continued shearing the dilated tendency of the clay becomes more prevalent with increasing confining stresses 3 and ocr during the dynamic response the reduction of shear strength of the red clay is substantially caused by the increasing number of cycles n under earthquakes the sliding zone may behave in a brittle ductile pattern

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

influence of environmental factors on the wetting front depth a case study in the loess plateau abstract reliable information on the wetting front depth and variation of water contents within the zone of wetting is required for addressing geotechnical problems in loess deposits such as estimation of the collapse deformation and assessment of the slope stability for this reason a field test was conducted at a site in the loess plateau of china to obtain data on soil water contents and temperatures at different depths for a period of one year the variation of water contents was interpreted from the influence of environmental factors and soil temperature and used to determine the maximum wetting front depth in the loess soils in the study region in addition a commercial software vadose w was used to simulate the flow behaviour in unsaturated loess taking account of the influence of environmental factors a reasonable agreement was found between the results of field investigations and numerical simulations the study results are useful as they provide valuable information about the wetting front depth and water content variation in unsaturated loess in response to environmental factors the field investigations and numerical simulations summarized in this paper can serve as a reference for future studies on other soils