Search

There are an increasing number of mega engineering projects of removing the top of hills to fill in the valley for new land creation in the Loess Plateau of China, which significantly changes the hydrological and geological equilibrium state of the site. The formation of a new hydrological equilibrium state is associated with the water movement in the compacted and intact loess layers. Most disasters occurring in the loess area are related to water. The soil-water retention curve (SWRC) is the key to the implementation of unsaturated soil mechanics in engineering practice and is required to numerically model the movement of water in the soil. In this study, the SWRCs and microstructure of intact and compacted specimens from Lanzhou and Yan'an, two typical cities that have new land creation projects, are investigated. The SWRC is obtained using the filter paper method. The mercury intrusion porosimetry (MIP) and scanning electron microscope (SEM) techniques are used to explore the microstructure. The results highlight that the intact loess has a higher air occlusion value (AOV) and a similar slope of SWRC in the transition zone compared with the remolded specimens that compacted at the natural water content. The normalized SWRC (i.e., degree of saturation versus suction/AVO) of the intact specimen is approximately the same as the remolded specimens compacted at the natural water content. The difference in the microstructure between intact and compacted specimens originates from different existing states of the clay particles and further contributes to the variation of the SWRC. • The intact loess has a larger air occlusion value (AOV) and a similar slope of the SWRC compared with compacted specimens. • The normalized SWRCs are approximately the same for the intact and compacted specimens. • The difference between the intact and compacted specimens in the microstructure is attributed to clay particles. [ABSTRACT FROM AUTHOR]

Plowing refers to the phenomenon by which a landslide displaces and pushes the path material forward. Despite its importance in shaping the dynamics of many rapid flow-like loess landslides, the mechanism of plowing is not fully understood. Therefore, this paper presents an improved numerical model based on the material point method (MPM). This model takes into account the interactions between the landslide mass and the path material. The reliability of this model was validated by simulating two granular column collapse experiments involving interaction with an erodible mass. The model was then applied to analyze the plowing dynamics of the Ximiaodian loess landslide in Jingyang County, Shaanxi Province, China. A series of well-designed simulations were conducted to investigate this specific landslide event, contributing to a deeper understanding of the plowing phenomenon in loess landslides. The simulation results show that our model can satisfactorily simulate the plowing process of the Ximiaodian landslide. The plowing process of a rapid-flow loess landslide is proposed to consist of four distinct stages: 1) the collision stage, when the landslide strikes the terrace, resulting in the bending of its strata; 2) the shear failure stage, characterized by significant plastic shear deformation within the bent strata, resulting in the formation of multiple shear failure planes; 3) the steady plowing stage, during which the deformation structure in the affected terrace stabilizes and plowing continues in a steady pattern; and 4) the stopping stage, when the propagation of the disturbed terrace gradually stops. Furthermore, the disturbed terrace zone exhibits three distinct deformation structures. In the rear part, a stable zone develops where the terrace layers are compressed. However, due to the compressive forces exerted by the overlying loess, no significant shear deformation is observed. The middle part is the shear failure zone, characterized by the formation of multiple shear failure planes. The front part is the upheaval zone, where the terrace layers are slightly bent and tilted. • An improved MPM model is proposed to simulate the plowing process of rapid flow-like landslides. • The plowing mechanism of a real loess landslide is analyzed by the MPM model for the first time. • The plowing process of a rapid flow-like loess landslide consists of four stages. • Three distinct deformation structures are formed in the disturbed terrace zone during the plowing process. [ABSTRACT FROM AUTHOR]

This paper presents a case history of the 205 m high intake slope at the Huangjinping (HJP) hydropower station on the Dadu River. Deformation and cracks developed on the cut slope during excavation, and the deformation extended onto the natural slope above the cut, giving rise to serious safety concerns. Research was conducted to study the engineering geological conditions and the deformation characteristics of the slope during excavation. In situ monitoring data and possible causes of cracking were analyzed. The results show that the zone of loosened rock mass extended much deeper into the rock mass than it did at other sites in the region because of the tectonic history of the site and cutting. The empirically designed cable anchors with lengths of 40 m or 45 m were insufficient to stabilize the slope, while the remedial cable anchors as long as 100 m successfully stabilized the slope. The analytic method and procedure used in this paper could be useful to similar projects. [ABSTRACT FROM AUTHOR]

Effective detection of groundwater in landslide areas is crucial for landslide monitoring. The magnetic resonance sounding (MRS) method is a geophysical technique that can directly detect groundwater. However, its application in landslide groundwater monitoring is often hindered by the complex topography of landslides. This paper presents an MRS framework that accounts for the impact of landslide topography on groundwater detection. The framework includes the use of drone photogrammetry to obtain high-precision topography data and real-time kinematic equipment to acquire the coordinates of key points along the MRS coil. A three-dimensional finite element model is then constructed to calculate the alternating magnetic field generated by the MRS coil and the kernel function required for MRS inversion. Two typical landslide topography models—terrace and gully—are constructed and analyzed using numerical simulations. The results indicate that landslide topography significantly impacts the quality of groundwater information retrieved by MRS in both one-dimensional and two-dimensional inversions, affecting the accurate detection and identification of infiltration surfaces, sliding zone water, and bedrock surfaces. If accurate topography data are obtained and appropriate kernel functions are calculated, the accuracy of the inversion can be greatly improved. An example of using the MRS method to detect groundwater in a complex landslide in the Three Gorges Reservoir area of China is then presented. The MRS inversion results that consider landslide topography are confirmed using borehole data, electrical resistivity tomography detection results, and on-site drainage tunnel investigations. The water-content distribution inside the landslide body is obtained, providing information helpful to define sliding zones in multi-level landslides. The proposed landslide MRS detection framework makes it possible to apply MRS methods to the detection of landslide groundwater distribution, analysis of seepage fields, and discrimination of landslide geological structures. • Landslide topography significantly affects the quality of groundwater information retrieved by MRS. • Obtaining accurate topography data and calculating appropriate kernel functions improve MRS inversion results. • MRS field work on a complex landslide is validated by borehole data, ERT, and on-site drainage tunnel investigations. [ABSTRACT FROM AUTHOR]

In reactivated slow-moving landslides, the prediction of velocity and displacement is a crucial issue for understanding landslide kinematics and realizing warning systems. A variety of data-based numerical models have been used to predict landslide displacement; however, kinematics-based models, which consider the shear behaviors of soils within the sliding zone that fundamentally control landslide movement, have been relatively limited. In the present research, the Tangjiao landslide in the Three Gorges Reservoir (TGR) in China was taken as a case study. The monitored ground displacement from March 2007 to September 2016 and deformation signs observed in the field survey show that the Tangjiao landslide experienced slow movement with the ground displacement increasing stepwise in response to seasonal rainfall and periodic fluctuation of the reservoir water level. We performed a rate-stepped continuous ring shear test on two specimens remolded from the sliding zone soil at shear rates ranging from 0.01 to 10 mm/s. The test results show that the residual strengths of both specimens show a nonmonotonic shear rate dependency, i.e., a weak negative shear rate dependency (fitted by an exponential law) followed by a significant positive dependency (fitted by a linear law). The transition from a negative shear rate dependency to a positive shear rate dependency may be attributed to the change in shear mode when the shear rate exceeds a critical value. This complex shear rate-dependent residual behavior regulates the movement of the Tangjiao landslide in the reactivated state. On this basis, a kinematics-based model for predicting landslide velocity and displacement was proposed by taking into account the shear rate-dependent friction of the sliding zone soil. This model can reproduce the velocity and displacement of the Tangjiao landslide from the change in groundwater level (i.e., stress perturbations in this paper). The results suggest that by using this model, the well-investigated material parameters can enhance the prediction reliability and accuracy of landslide behavior. Our proposed approach, with the ability to reliably predict landslide velocity and displacement, such as the Tangjiao landslide in this work, has important implications for predicting movement trends and developing early warning systems for reactivated slow-moving landslides, especially translational landslides under similar geological conditions. • The movement pattern of the Tangjiao landslide in the reactivation stage was analyzed. • The sliding zone soil shows a nonmonotonic shear rate dependency of the residual strength. • A discrepancy between field-scale and laboratory-scale sliding resistances of the sliding zone soil was examined. • A model for predicting landslide velocity and displacement was proposed. [ABSTRACT FROM AUTHOR]

Abstract: In this paper, the large scale China-Mock-up test, intended to study the thermal-hydro-mechanical (THM) behavior of Gaomiaozi (GMZ) bentonite under relevant repository condition, is presented. In accordance with the current disposal concept of High-level Radioactive Waste (HLW) disposal in China, the facility is designed as a vertical cylindrical tank, filled with compacted GMZ-bentonite. A heater, which simulates the HLW canister, is placed inside the compacted bentonite blocks and pellets. The installed hydration system on the exterior surface simulates the supply of groundwater. The operational phase started on 1st April 2011. Based on the current recorded experimental data, several aspects are addressed in the paper, including the observed THM behavior of the compacted bentonite, the displacement of the electrical heater, and also the influence of unexpected interruptions of electric power supply. The saturation process of the compacted bentonite is strongly influenced by the competing mechanisms of drying effect induced by the heater and the wetting effect by water penetration. As a result, the desiccation–saturation process was observed in the zone close to the heater. An upward displacement of the heater was also noticed, which verified the potential influence of buffer material on the stability of canister. The experiment is a valuable step in establishing the viability of the reference concept, and making progress in the understanding of the behavior of buffer material under thermal-hydro-mechanical (THM) coupled condition. [Copyright &y& Elsevier]

Rainfall reservoir-induced landslides in the Zigui Basin, China Three Gorges Reservoir (CTGR) area, exhibit typical step-like deformation characteristics with mutation and creep states. Previous landslide displacement forecasting models yielded low prediction accuracy especially for mutational displacements. Coupled with the lack of monitoring sites and data limitations, it is extremely difficult to obtain accurate and reliable early warnings for landslides. The multi-feature fusion transfer learning (MFTL) method proposed in this paper applies the knowledge and skills obtained from the Baijiabao landslide scenario and sufficient monitoring data to improve the prediction capacity for other landslides, such as the Bazimen and Baishuihe landslides. The model barely relies on the long-time continuous monitoring process, and it can not only fill gaps in data when monitoring is interrupted, but also provide real-time displacement predictions based on accurate weather forecasting and periodic reservoir scheduling. In addition, the non-uniform weight error (NWE) evaluation method is proposed in this paper to focus more on the mutation state prediction accuracy because landslide instability is most likely to occur in this stage. Compared with other intelligent algorithms, the results indicate that the MFTL method owns low prediction error and high reliability, as well as the positive generalization ability in landslide prediction. This study paves the potential way for realizing the real-time, whole-process and accurate landslide forecasting. • An innovative model based on Transfer Learning method is firstly applied in landslide displacement prediction. • The model barely relies on long-time continuous monitoring dataset and it can fill data gaps due to monitoring interruptions. • The model is evaluated by three representative landslides with GPS monitoring datasets in Three Gorges Reservoir area, China. • The model owns low prediction error, high reliability and positive generalization ability in landslide prediction. • This study paves the potential way for realizing the real-time, whole-process and accurate landslide forecasting. [ABSTRACT FROM AUTHOR]

In-situ monitoring system is absolutely necessary for a long-distance linear pipeline infrastructure in permafrost regions due to the complicated interaction between buried pipeline and its harsh permafrost environment. To study this complex problem, a comprehensive in-situ monitoring system has been designed and established along the China–Russia Crude Oil Pipeline (CRCOP), which is one of vital energy channels for importing crude oil from Russia to China. This monitoring system can record the meteorological data, ground temperature and water content within the permafrost foundation, vertical settlement of the oil pipe, ground surface deformation on the pipeline right-of-way (on-ROW), as well as the thaw bulb around the pipeline at four sites with different engineering geological conditions. In this paper, the layout and instrumentation of the whole monitoring system and monitoring methods are described in detail, and then the thermal regime of permafrost on-ROW and off-ROW and cooling performance of the mitigative measures on foundation soils are evaluated. Results show that heat dissipated from the CRCOP lead to the rapid degradation of permafrost on-ROW and produce different sizes of thaw bulb around the oil pipelines. The mitigative measures, including insulation layer, two-phase closed thermosyphon and U-shaped air-ventilated pipes, are effective to minimize permafrost degradation and ensure the thermal stability of permafrost foundation along the CRCOP. Some recommendations are proposed for future research and for the monitoring system to be improved. This monitoring system can provide multi-field data to clarify the interaction between pipeline and permafrost degradation under different geological conditions, and guide the design and maintenance of the buried warm pipeline in permafrost regions. • An in-situ monitoring system is set up along the CRCOP in permafrost regions. • The geological characteristics and layout of instrumentation at four monitoring sites are reported. • The integrated monitoring method for pipeline-permafrost interaction are presented. • Thermal effect of buried warm oil pipe on underlying permafrost is observed. • Cooling performance of the insulation layer, thermosyphon and U-shaped air-ventilated pipes is evaluated. [ABSTRACT FROM AUTHOR]

Abstract A high-fill slope located in Zhenxiong County, Yunnan Province, China, was designed for building placement on its top platform. A reinforcement system consisting of a geogrid, front stability piles (FSPs), retaining sheets, prestressed anchors, and rear deeply buried piles (DBPs) has been used to stabilize the slope. Two typical slope sections were selected to study the high-fill slope stability and retaining mechanism of the reinforcement system. Field measurements of the horizontal displacement and strain in the piles, as well as the anchor working load, were collected and analyzed. In addition, a series of two-dimensional finite element method (FEM) analyses combined with a strength reduction technique was conducted to analyze two selected cross sections. The results show that the retaining structure behavior is closely related to the fill construction process of a high-fill slope. The deflection of the stabilizing pile increases almost linearly with the filling height in the initial stage of fill construction. The variation in the working load of the prestressed anchor shows an offset between prestress loss and increasing fill pressure. The FEM results can provide insight into the pile-soil interaction mechanism and its contribution to fill slope stabilization. The FSPs shift the sliding surface from through the slope toe to through the top of the FSPs. The anchors can reduce the bending moment by supplying additional bearing points. The DBPs can share a portion of the sliding thrust and effectively enhance the safety factor. This paper provides a reference for reinforcement system design for similar engineering projects considering high-fill slopes. Highlights • A case of reinforcement and monitoring for a high-fill slope is presented. • The reinforcement system includes two rows of piles, retaining sheets and anchors. • The behavior of the reinforcement system is investigated through field measurements. • The reinforcement mechanism is analyzed by FEM combined with monitoring. • This study provides a reference for the design of similar high-fill slopes. [ABSTRACT FROM AUTHOR]

Abstract Systems for monitoring the deformation and stress conditions of excavated high rock slopes are usually implemented for safety reasons and to predict the stability of future works. This paper adopts Bayesian methods for updating important geomechanical parameters namely: E (III 1), E (III 2), E (IV 2), E (f 8), c (III 1), c (III 2), c (V 1) and c (f 8) in these types of cases. The proposed method utilizes parametric sensitivity analysis, the BP neural network (back propagation neural network), and Bayesian updating to effectively reduce the number of variables, improve the computational efficiency and gradually update the random variables by using progressive monitoring information. The high rock slope excavation on the left bank at the Lianghekou Hydropower Station in China is illustrated as a detailed case study. Initially, only one type of measurement is first used for Bayesian updating (measured displacements or anchorage forces), and then both types of measurements are used. Compared to using only one type of measurement, the parameter uncertainty is reduced and the model accuracy is improved when both types of measurements are employed. Highlights • A Bayesian updating framework for rock slopes with multiple responses is proposed. • Random variables are gradually updated by using progressive monitoring information. • The effectiveness of three groups of data in Bayesian updating is discussed. • The proposed framework can be used for the prediction of subsequent excavation step. [ABSTRACT FROM AUTHOR]

Abstract High speed railway is an ever-expanding mega project in China, connecting more and more cities of economy importance. This paper presents a theoretical evaluation on vibrations of saturated ground induced by high speed train operating on an elevated bridge. The simply-supported bridge consisting of a slab railway track resting on multiple spans of box girder is treated using the periodic theory. While, the dynamic interaction between the piles and the ground halfspace is solved using the flexible volume method combing with thin layer element method developed by the authors for the saturated soil. Two characteristic frequencies of the superstructure that dominates the ground displacement response have been identified: one is the first natural frequency of girder beam with elastic bearings; the other is the first natural frequency of pier beam supported by the pile foundation. [ABSTRACT FROM AUTHOR]

Abstract Loess is a meta-stable, cemented assemblage of mainly silt and clay-sized particles of low plasticity. When dry it behaves like a brittle material, but when wetted up the fabric rapidly collapses. Unique geomorphological features include extensive surface erosion, soil piping (loess 'karst'), catastrophic landslides, and widespread collapse (hydro-consolidation). The Chinese Loess Plateau is a more or less continuous drape of thick loess covering some 440,000 km2. It is one of China's regions that is most prone to geohazards. This paper reviews advances in the research related to loess geohazards, drawing particular attention to the need to apply research findings to recent, very large (mega-)construction projects in loess terrain such as the Mountain Excavation and City Construction in Yan'an levelling 78 km2 for urban expansion, the Lanzhou New District creating 246 km2 of new level ground for construction, and large engineered interventions in the landscape for gully control and land reclamation such as those in Shaanxi and Gansu generating agricultural land covering an area of some 8000 km2. These projects are in response to increasing pressures to facilitate expansion of urban centres, their interconnecting infrastructures and their agricultural support systems. It is argued that, where proper application of scientific knowledge for engineering control (e.g. densification, drainage) of these new landscapes is absent, these projects could generate a substantial, and costly geohazard legacy for future generations. [ABSTRACT FROM AUTHOR]

Abstract: This paper reports on a study conducted during 1992–1995 on the progressive movement of a slope in Sai Kung, Hong Kong. In spite of the fact that significant downslope movement was triggered during the rainy seasons, the field data show that remarkable rebound in the uphill direction was mobilized during dry season when the groundwater level dropped. This paper focuses on such rebound deformation which is due to the drying of the soils. To investigate the mechanism of the rebound deformation, a two-dimensional finite element model of the slope was established and a series of hydraulic and mechanical analyses were conducted. It is found that the volumetric contractive behaviour caused by the increase in suction within the unsaturated soil zones and the reduction in pore pressure in the submerged soils due to the lowering of groundwater level induced the rebound deformation. Moreover, the water retention properties of the unsaturated soil zones can also strongly influence such deformation. [ABSTRACT FROM AUTHOR]

This paper presents a brief review on land subsidence and its investigation and remedial works made in China. The paper gives a summary on the current status and main features of land subsidence in China. The paper then discusses the research and technology transfer on land subsidence and its remediation in China. The paper discusses some challenge issues in land subsidence currently encountered in Shanghai, China. Based on the review, the paper gives some conclusions and recommendations to address land subsidence in China. [Copyright &y& Elsevier]

The goal of this paper is to evaluate the post-failure behavior of the Hsien-du-shan rock avalanche, which was triggered by Typhoon Morakot in 2009, using a three-dimensional (3D) discrete element program, namely, 3DEC. The 3D slope topography and local joint sets are explicitly considered in the calculations, and the joint sets cut the sliding rock mass into blocks with arbitrary shapes. The modeled blocks exhibit the elastic behavior of the local rocks. The analysis successfully simulates the wedge failure at the initiation of the landslide. Additionally, the 3DEC results clarify the local rock sliding phenomena at the boundaries of the source area. The simulated depositional area correlates well with the actual area affected by the Hsien-du-shan rock avalanche. In addition, the erosion of a ridge by the sliding rock near the southwestern margin of the area at an elevation of 590 m has a significant influence on the shape and size of the impacted area. The interlocking effect between blocks is also considered. [ABSTRACT FROM AUTHOR]

The 2008 Wenchuan earthquake in Sichuan, China triggered numerous landslides in the stricken area. The loose landslide materials retained on mountain slopes and in gullies are prone to reactivation and may transform into debris flows in the rainy season. Nine years after the Wenchuan earthquake, debris flows are still active in Gaojiagou Ravine 16.5 km north of the epicentre. On 14 August 2010, 3 July 2011, 13 July 2013, and 6 July 2016, four large-scale debris flows were triggered by heavy storms in Gaojiagou Ravine. The four debris flows blocked the Minjiang River twice and caused severe damage to nearby villages and reconstruction sites. Several questions arise from these repeated debris flows. Did the level of triggering rainfall change in the four debris flow events? How did the initiation mechanism evolve over time? What are the differences in the runout characteristics in the four events? How did the check dams constructed in 2012 function in the subsequent debris flows? In this paper, we evaluated the loose deposit volumes in Gaojiagou Ravine before and after each of the four debris flows and the runout volumes, and analysed the triggering rainfall intensities, initiation mechanisms and runout characteristics of the four debris flows. The rainfall threshold for the debris flows in Gaojiagou Ravine increased over time, and the initiation mechanisms evolved from landslides to channel-bed failure, and subsequently to channel-bank erosion. The mobility of the debris flows decreased from 2010 to 2016 as the initiation positions moved lower and the particle size of the runout materials became coarser. [ABSTRACT FROM AUTHOR]

Thick loess deposits are considered problematic soils due to their susceptibility to collapse suddenly and in large volumes upon increase of water content. In the past decades, a large number of landslides occurred in the Loess Plateau in Gansu Province, north-western China, triggered by the extensive irrigation. The increase of water content has been identified as a key factor controlling the loess strength. However, the role of long-term saturation and pore fluid chemistry changes has not been investigated systematically. This paper reports on an experimental study on loess samples from Heitai loess terrace (Yongjing, Gansu) carried out through chemical analyses, oedometer and ring shear tests. The natural pore fluid was found to be a concentrated saline solution in unsaturated soil condition. Upon saturation, the pore ion concentration drop can contribute to shear strength loss in the clay component and volume decrease. A prolonged exposure to the irrigation water might facilitate cement dissolution, which could result in further weakening. [ABSTRACT FROM AUTHOR]

Loess collapse is an important factor in earth fissure formation, and earth fissures resulting from loess collapse are widely distributed in loess areas in China. To explore the basic features and formation mechanism of collapsible earth fissures, we conducted an in situ water immersion test in a loess area. This paper describes the genesis of collapsible earth fissures by monitoring the development processes of collapsible settlement and earth fissure formation. This paper demonstrates that the infiltration process can be divided into three stages, and the subsidence curve of the whole test process can be divided into six stages. During the test, the collapsible deformation gradually developed outward, the collapsible settlement decreased with increasing distance from the test pit, and the horizontal influence distance was approximately 18 m. The collapsible earth fissures were parallel to the test pit, and characterised by horizontal tension and vertical dislocation. With the collapsible deformation expanding outwards, the location of the earth fissure developed outwards. The tensile stress and tensile strain caused by the differential collapsible deformation caused the formation of collapsible earth fissures. When the tensile strain or tensile stress was greater than the ultimate tensile strain or tensile strength, the loess experienced tensile failure and formed an earth fissure. • Collapsible subsidence section showed symmetry, forming a "U" shape. • Collapsible earth fissures are characterized by horizontal tension and vertical dislocation. • Tensile stress and tensile strain are main factors for collapsible earth fissures formation. [ABSTRACT FROM AUTHOR]

The upper Minjiang catchment is frequently affected by a significant number of large to giant landslides. In one such massive older landslide, approximately 2 million m3 of sediment was reactivated, threatening the safety of a pylon on the landslide and the safety of the only route that allows high-speed travel from Wenchuan to Maoxian. To trace the deformation evolution history and analyze the current deformation of the new landslide, we examined SAR data since 2007, carried out geological and UAV surveys, and designed and installed real-time monitoring equipment. This paper presents the main spatial and temporal characteristics of the landslide. We found that the landslide has experienced creep deformation in the past five years and its sensitivity to rainfall. The development process of the landslide from the formation of tensile crack at the trailing edge to the gradual pushing forward of the crack propagation was revealed. The innovation of this paper is to reveal the whole process of the spatial-temporal evolution from its beginning to large deformation of a real case of creep landslide, which can provide a very good reference for the analysis and monitoring of such creeping landslide evolution process. This representative case also shows how to combine remote sensing and in situ monitoring methods to carry out continuous monitoring and the establishment of a warning system for potential landslide sites, so as to trace the evolution history, derive activity maps and analyze development trend, which can significantly reduce landslide risk. Additional mitigation procedures can be put into place if continuous monitoring of the Minjiang River Canyon occurs, resulting in a reduction of direct losses. In particular, modeling of the slope deformation and failure, damming process, and prospective flooding can be done in advance. Therefore, it is expected that this report can strengthen the case for the deployment of systematic monitoring of potential landslide sites by integrating earth observation methods and in situ monitoring systems as an approach to reduce risk. • The whole process of the spatial-temporal evolution of a real case of creep landslide is revealed. • This representative case shows how to combine remote sensing and in situ monitoring methods to carry out continuous monitoring. • Ground-based real-time monitoring provides accurate landslide early warning. [ABSTRACT FROM AUTHOR]

Numerous land reclamation projects that utilise dredged fill are currently being executed in the eastern regions of China to cater to the demands of economic development and address the land shortage problem. However, the dredged fill has high water content, low shear strength, and mainly consists of fine-grained particles. A long period is thus normally required for the treatment of dredge fill by vacuum preloading, and clogging always occurs around the prefabricated vertical drains (PVDs), resulting in insufficient consolidation of the soil. To address this issue, combination of vacuum preloading and lime treatment is proposed in this paper. In this method, a certain percentage of hydrated lime (Ca(OH) 2 ) is added into the dredge fill slurry before vacuum preloading, to enhance the engineering properties of the fill, such as the shear strength and permeability. The added hydrated lime would induce cation exchange on the clay surface and flocculation of the fine soil particles. As a result, this method would significantly mitigate the risk of clogging around the PVDs with the enhanced soil permeability, thereby improving the consolidation efficiency. In this study, dredged slurry with a water content of approximately 187% was utilised. Lime modification optimum (LMO) was first determined using the vacuum preloading method, and a comparison test was then conducted to verify the effectiveness of the proposed method. It was found that, compared to the conventional vacuum preloading method, the proposed method significantly increased the vane shear strength of all the soil layers, especially the deep soil layers, and afforded a higher consolidation rate. [ABSTRACT FROM AUTHOR]

The grout curtain in Zhangmatun iron mine, China, suffers from the leakage of water due to the influence of multiple factors including inadequate grouting area, weak rock and mining disturbance. Water seepage through rock mass around the grout curtain further deteriorates the water plugging effect of the grout curtain and poses a potential hazard to workers underground. Thus, a microseismic (MS) monitoring system was established in the Zhangmatun iron mine. In the present paper, a MS monitoring analysis method for assessing a potential seepage channel is proposed. Using the proposed MS monitoring analysis method, the dip, dip angle and center depth of the potential seepage plane across the grout curtain in Zhangmatun iron mine are determined to be 126.1° E, 53.97° and 275 m, respectively. The spatial and temporal behaviors of density distribution, source parameters and cracking type of the seismic source are analyzed to reveal the initiation, propagation, coalescence of seepage channel located at the southwest of the iron mine. Four types of local seepage channel formation processes are summarized by correlating the mechanism of microcracking. Two main weak areas around the grout curtain at the levels of − 230 m and − 318 m are identified and two seepage paths whose water discharge points are localized to the roof of stope 9, 10 and sidewall of stope 10 are determined, respectively. Our study helps to get a better understanding of damage and failure of rock mass around grout curtain and thus provides a basis for taking reinforcement measures to secure the stability of grout curtain in mines. [ABSTRACT FROM AUTHOR]

Large scale landslides are common in the Three Gorges reservoir region due to steep slopes and complex geological conditions, fluctuations of reservoir level, etc. Many phenomena and formation mechanisms related to these landslides are not well understood and need more research. In this study, large scale landslide evolution and formation mechanisms are thoroughly investigated in terms of precedent long-term gravitational deformation (PLTGD). Three large scale landslides in the Three Gorges reservoir region, Huangtupo landslide (HTPL), Huanglashi landslide (HLSL), and Baotaping landslide (BTPL), are taken for example to discuss their phenomena and features of PLTGD, and to investigate the correlation between the PLTGDs and landslide. Many features associated with landslides are caused by slow, downslope gravitational processes before landslide failure, and three criteria for recognition of the PLTGD features are summarized. The investigation results reveal that the PLTGDs play an important role in landslide evolution and formation mechanism. Overall, this paper presents evidences for PLTGDs of large scale landslides and their correlation with landslide evolution, which is helpful to understand the formation mechanism of large scale landslides in the Three Gorges reservoir region. [ABSTRACT FROM AUTHOR]

Rockfall source areas identification of high steep fractured rock slope is a challenging task for hazard mitigation. Considering this difficulty, a new method integrating discontinuity-based threshold slope angle and rockfall trajectory analyses is introduced in this study and applied to a railway bridge in China. First, abundant discontinuity data are collected by means of the modern unmanned aerial vehicle (UAV) digital photogrammetry technique. Then, a threshold slope angle used to delineate rockfall-prone areas is comprehensively determined by probabilistic kinematic and block theory analyses. Next, physically based rockfall trajectory simulation with consideration of mean block size is used to distinguish the hazard level of each release point. Finally, rockfall sources causing moderate and high risks to the train tunnel entrance at the base of high steep fractured rock slope are determined using a semiquantitative risk matrix approach. The final rockfall source map can provide a quantitative reference for hazard mitigation. At the end of this paper, some issues associated with the proposed approach are discussed, such as parameter importance analysis of threshold slope angle, comparison between the two probabilistic approaches and uncertainties in rockfall source areas identification. • A method for rockfall sources identification of jointed rock slope is proposed. • This method integrates threshold slope angle and rockfall trajectory analyses. • Probabilistic approaches are developed to determine a final threshold slope angle. • A multiscanline method is presented to determine the volume of a launched block. • Trajectory dense and sparse areas are used to distinguish different hazard levels. [ABSTRACT FROM AUTHOR]

The special properties of the clay derived alteration developed in the granite intrusive contact zone under the condition of humidity variation have extremely complex effects on engineering. In view of the deformation and destabilization of Yuxi Tunnel in China, detailed geological investigation has found that the deformation and destabilization section is located in the intrusive contact zone of granite and sandstone, in which the clay and marble are developed. The lithofacies and mineral composition test results of the clay show that it is derived from the alteration of hydrothermal fluids and belongs to the altered rock, rather than product of weathering or faulting. Results of laboratory tests show that the clay derived alteration has the properties of strong water absorption and expansion. In addition, its shear strength decreases significantly with the increase of water content. The characteristics of special topography, occurrence conditions, mineral composition and structure of the clay derived alteration are the inherent causes of the deformation and instability of the tunnel. Furthermore, numerical simulation of the response characteristics of the support structure under humidification conditions is realized. The calculation results show that when considering negative effects such as expansion and strength degradation of the surrounding rock, the disturbed range of surrounding rock and the deformation of tunnel vault are greatly increased, and significant stress concentration occurs at tunnel spandrel and arch foot. At the same time, the deformation and stress evolution of the supporting structure show certain accumulation and delay characteristics during the humidification process. The research in this paper not only clarifies the evolution of the displacement and stress of the tunnel support structure with the water content, but also reveals the origin of instability phenomena such as ground fissures, surface collapse, large deformation and collapse in the tunnel. This research methods and results can be used as reference for similar projects. • The deformation and instability characteristics of tunnel crossing altered clay are introduced. • The origin and formation mechanism of Clay in Granite Intrusive Contact Zone is revealed. • The deformation mechanism of tunnel crossing altered clay is revealed. [ABSTRACT FROM AUTHOR]

On July 4, 2013, a substantial disastrous debris flow occurred in the Hou Gully in Shimian County, China. The Hou gully belongs to mine waste debris flow, which seriously threatens a large number of traffic facilities, factories, farmland, and residents located in the accumulation area. This paper took the Hou gully as an example and aimed to describe a typical mine waste debris flow, analyze the formation conditions, calculate the static and dynamic parameters, simulate the movement process, and evaluate the hazard. Distribution characteristics of slag were interpreted using the method of remote sensing and field investigation. FLO-2D model was chosen to simulate the movement process of debris flow in Hou gully under different recurrence period. According to the maximum momentum and maximum accumulation depth obtained by numerical calculation, the classification standard of intensity was established for mine waste debris flow. The occurrence probability and intensity of mine waste debris flow as critical factors to classify the hazard of Hou gully. The study process of this paper are conducive to a better understanding of the formation condition, movement characteristic, and hazard scope of mine waste debris flows induced by intensive rainfall. The hazard assessment map of Hou gully can provide a scientific basis for reconstruction and mitigation projects in the future. • This paper took the Hou gully as an example to describe a typical mine waste debris flow. • Plentiful rainfall, steep terrain, and abundant slag is the critical conditions for debris flow formation. • We simulate the movement process of debris flow in Hou gully under different recurrence period. • The occurrence probability and intensity of mine waste debris flow as critical factors to classify the hazard of Hou gully. [ABSTRACT FROM AUTHOR]

Bed entrainment plays an important role in the run-out process of a flow-like landslide. A limited number of studies have investigated the influence of entraining loose materials on the mechanical properties of a landslide, and some of them have considered bed entrainment either by mechanical or empirical methods. In this paper, a modified finite difference model was used to analyze the propagation process of a typical flow-like landslide with bed entrainment that occurred in the Jingyang loess tableland, China. In this model, the mechanical parameters of the sliding mass were modified according to the local entrainment depth. Triaxial Consolidated Undrained (CU) tests and ring shear tests were conducted to obtain the mechanical parameters needed in the numerical simulation. The triaxial CU tests were conducted on three intact loess samples taken at the back scarp of the landslide, and the ring tests were conducted on gravelly sand samples taken from the first terrace of the Jinghe River, which includes the landslide deposit. The results show that both the simulated run-out distance and final covering area agreed well with the field data. The modified model revealed the propagation process of this landslide. A major contribution of this study is that entraining the saturated gravelly sand contributed to the flow-like movement of the landslide. The case study investigated here is helpful for better an understanding of the flow-like transformation mechanism. In addition, the numerical model adopted in this paper can be effectively used to assess or predict the propagation processes of similar landslides. • The propagation process of a loess flow-like landslide with bed entrainment is analyzed. • The significant shear strength loss of loess contributes to the rapid acceleration of this landslide. • Entraining saturated terrace material contributes to the flow-like transformation of this landslide. [ABSTRACT FROM AUTHOR]

• A new phase-field model is developed for partially saturated porous media. • Tensile and shear cracks are described by using two damage fields. • Effect of pore water pressure on cracking process is considered. • Effects of frictional shear stress and effective normal stress on shear cracks are taken into account. • Rainfall-induced landslides are mainly driven by pore water pressure rise and effective stress change. In this paper, we first present a new phase-field model for modeling the deformation and progressive failure in saturated and unsaturated porous rocks. Two independent damage variables are used to easily capture tensile and shear cracks. The influences of frictional shear stress and normal stress on the evolution of shear cracks are taken into account. The phase-field model is extended to variably saturated porous rocks by including the effect of pore water pressure. The proposed model is implemented in the framework of finite element method for coupled hydro-mechanical and damage problems. The phase field model is able to describe global stress–strain responses and localized cracking patterns in brittle rocks at the laboratory scale. The onset of localized cracks is directly linked to the non-uniform distribution of porosity. The proposed phase-field model is also applied to the analysis of rainfall-induced landslides. The numerical results of cracking scenarios are consistent with the real field observations in the Mayanpo slope in China. The main physical mechanisms involved in the rainfall induced instability of slopes are analyzed. [ABSTRACT FROM AUTHOR]

Suspension bridges have good spanning ability and seismic resistance. They avoid the need for tall piers and reduce the amount of foundation excavation. Therefore, suspension bridges are the first choice when building large-span bridges. Recent expansion of highways in the high mountainous region of western China has led to the widespread construction of large-span suspension bridges. Mountainous areas with deep canyons feature complex topographic and geological conditions, such as constricted construction sites, extensive unloading of rock masses and problematic stability of high and steep slopes, that adversely affect foundation stability and complicate surveys and analyses. In this paper, the Aizhai suspension bridge was used as a case study, and four key issues related to bridge foundation stability were analyzed. The results suggest that a comprehensive geological investigation is needed to develop a full understanding of the geological conditions, particularly unloading and dissolution-related geologic defects, in rock masses. The stability problem in the bridge foundation rock masses occurs primarily in the high and steep slopes on both banks of the canyon. The design load did not cause significant deformation in the rock mass. If proper reinforcement measures are taken to ensure the stability of the slope rock mass, the foundation rock mass will be stable. In addition, no significant interaction was observed between the structures. A tunnel-type anchorage can resist strong pullout forces via the “clamping effect” provided by the surrounding rock. Because tunnel-type anchorages are rarely used, the rock mechanics of the surrounding rocks have not been fully studied. Therefore, the pullout capacity of these anchorages may have been seriously underestimated. [ABSTRACT FROM AUTHOR]

In mountainous areas of Southwestern China, debris flows occur every rainy season in recent years and have become one of the main threats to human life and properties. After a giant debris-flow event on August 13, 2010 in Sichuan province, the need to deploy a real-time monitoring network and early warning system (EWS) in this region with high potential risk became of paramount importance. This paper, therefore, presents a proposal for a 3D WebGIS-based platform combined with wireless sensor network (WSN) for debris-flow monitoring, analysis of rainfall thresholds for potential debris-flow gullies, and preliminary criteria for automatic and continuous monitoring and alert of debris flows. The choice of a WSN environment simplifies data collection, especially for the combination of various monitoring data provided by different sensor terminals. Warning thresholds stored in the database can easily be modified to improve the prediction of debris-flow occurrence, and there is a user-friendly 3D graphical interface which allows an almost real-time solution for decision-makers. The automatic computer-based EWS applied in the case study proves to be useful for debris-flow early warning, and improvements expected from continuation of this study could ultimately reduce the losses caused by such type of natural hazard. [ABSTRACT FROM AUTHOR]

This paper presents an experimental investigation on eleven loess soils retrieved from NW China to explore the influence of grading and age on soil mechanics. There are overall consistent characteristics in stress-strain relationship and stress paths for the loess tested though detailed property depends on the combination of v i and p 0 '. The critical state parameters are quantitatively analyzed against the soil properties. The critic state line (CSL) in p ' − q plane is less variable. The M value of specimens tested varies from 1.15 to 1.41 and the corresponding φ cs ' is between 28.8° and 34.8°, which is not clearly related to the loess grading and plasticity index. In the volumetric plane, the intercept Γ of CSLs varies from 1.63 to 2.17 and the gradient λ of loess fall within a narrow range of λ = 0.08 ± 0.03. The λ linearly increases with the increasing plasticity index I p. The intercept Γ and gradient λ against grading indices has an overall liner trend, i.e., decrease with the increase of D 50 and increase with the increasing C u and C c values. The intact loess usually has a higher I B value, roughly between 0.5 and 0.9, indicating a relatively high liquefaction potential. • The detailed shearing behaviour of loess specimens depends on the combination of v i and p 0 '. • The plasticity index and particle gradation parameters of loess do not appear to significantly affect the M value. • The intercept Γ and gradient λ of CSL against grading indices has an overall liner trend. • The intact loess generally has a higher liquefaction potential. [ABSTRACT FROM AUTHOR]

The paper deals with a development of a new procedure to perform probabilistic block theory analysis using the vector method. The procedure includes the following three main features: (a) the joint orientation is considered as a bivariate distribution including the correlation that exists between the joint dip angle and dip direction angle; (b) the variability of discontinuity shear strength is incorporated in the analysis; (c) it performs deterministic and probabilistic block theory analysis including the mode of failure (MOF), maximum safe slope angle (MSSA), factor of safety (F S ) and the instability probabilities for different cut slope dip angles (CSDA) and different MOFs. A rock slope at a hydropower station in China is used as a case study to illustrate the use of the developed procedure. The slope has six sets of discontinuities. Therefore, both deterministic and probabilistic block theory analyses were conducted for 4-plane, 5-plane, 6-plane and 7-plane blocks to study the stability of the rock slope under different MOFs and CSDA. For most MOFs, the MSSA obtained through deterministic analysis were found to be significantly higher than the CSDA obtained corresponding to zero instability cumulative probability. The differences obtained between the deterministic and probabilistic analyses resulted mainly due to the variability of discontinuity orientation. The case study illustrated the importance and superiority of the probabilistic analysis over the deterministic analysis. For the investigated rock slope by selecting the CSDA of 40° and 50°, the total instability cumulative probability can be limited to less than 5% and 10%, respectively. [ABSTRACT FROM AUTHOR]

The 20 April 2013 Lushan earthquake with a magnitude of M s 7.0 induced widespread landsliding along the southern segment of the Longmen Shan fault zone. This paper presents a preliminary analysis of the characteristics of these co-seismic landslides triggered in an area of 13,323 km 2 . A total of 3810 individual landslide points were identified through an intensive field investigation and from digital aerial photographs taken after the Lushan earthquake. To facilitate the more detailed analysis on the areal frequency of co-seismic landslides as polygons, we selected an area of 732 km 2 around the epicenter that had the highest density of co-seismic landslides. The sizes of the landslides are, in general, much smaller than those that were triggered by the 2008 Wenchuan earthquake. The most common types of landslides in the study area were rock falls and shallow, disrupted landslides from steep slopes, which typically involved the top few meters of weathered bedrock and colluvium. In this study, the relation between the landslide distribution and five main factors was analyzed: fault proximity, epicenter proximity, peak ground acceleration (PGA), slope angle, and lithology. Our study results show that the landslide concentration tends to decrease with distance from the seismogenic fault, and the highest landslide concentration is located within a distance of 5 km. Regarding the distance to the epicenter, the largest landslide density is found at a distance between 5 and 10 km. The landslide concentration also increases with increasing slope angle until a maximum for the slope class 45°–55°. In addition, results show that slopes consisting of deeply weathered and fractured sandstones and mudstones were the most susceptible to co-seismic landslides. In this study, we found that the location of the hanging wall and the footwall of the fault did not seem to have an important effect on the landslide distribution. This is in contradiction to what has been reported in other earthquake areas such as the Wenchuan area. [ABSTRACT FROM AUTHOR]

The loose deposits of red beds located in southwestern China are vulnerable to the occurrence of landslides. In this paper, a shallow progressive landslide developed in loose deposits of red beds was selected as a case study, and the physical and mechanical properties of the main slip zone were analyzed in detail. It was observed that the main slip zone of the progressive landslide is composed of fine-grained soils with substantial amounts of expansive clay particles (interlayered illite/smectite and interlayered chlorite–smectite). The one-dimensional consolidation test of the residual soils shows that the soils are overconsolidated. The shear stress versus shear displacement curves reveal that the slip zone soil has exhibited a strain softening behavior. The residual friction angle of the undisturbed slip zone soil determined by the ring shear tests is 7.2°, indicating that the residual strength of the soil is very low when in a saturated state. The microstructure of the slip zone was investigated using a combination of images captured by means of polarising microscopy (PM) and scanning electron microscope (SEM) techniques. It was found that the slip zone possessed generally softer structure with higher relative porosities than its confining materials. The microstructure of the slip zone is generally characterized by its softer structure and higher degree of alignment of fine silts, suggesting that the slip zone underwent two deformation processes (i.e. dilatancy and particle rearrangement). The global mechanical behavior of the investigated slip zone may be conceptualized as an overconsolidated clayey soil under drained conditions. [ABSTRACT FROM AUTHOR]

Undrained shear behavior of loess after the K 0 consolidation was investigated through laboratory experiments. Both the monotonic and cyclic triaxial tests were performed on the intact loess samples retrieved from a construction site in Yan'an city, China. It was found that the coefficient of lateral earth pressure at rest (K 0) of the intact loess is stress-dependent, and it varies between 0.46 and 0.85. Under the monotonic loading condition, the peak q in the undrained shear test is higher for the samples under the K 0 consolidation than those under the isotropic consolidation. Besides, the cyclic loading tests were conducted on the loess samples subjected to different magnitudes of the initial deviatoric stress, including the K 0 stress state. The test results revealed that different initial stress conditions cause distinctly different failure patterns. It includes the cyclic mobility with progressive development of the axial strain, and limited deformation followed by an abrupt gain of the axial strain with no precursor. In accordance to the build-up of the excess pore water pressure during the tests, each failure pattern of loess was interpreted in the q - p ' diagram alongside the undrained instability state (UIS) line. The outcomes of this paper suggest a pressing need to thoroughly consider the K 0 values of the intact loess with variations of the initial stress state. • K 0 value of intact loess samples is stress dependent. • Shear strength of loess is underestimated if K 0 stress state is not properly considered. • At no stress reversal condition, an abrupt failure of loess sample can take place. [ABSTRACT FROM AUTHOR]

More than 257 sizable landslide dams were induced by the 2008 Wenchuan earthquake, which required timely risk mitigation measures. This paper aims to summarize the engineering measures taken to mitigate the landslide-dam risks; provide a method for optimal design of spillways to minimize the risks; and quantitatively evaluate practical options for spillway design with a physically-based dam breach model. The engineering measures taken to mitigate the risks of 37 highly hazardous landslide dams induced by the Wenchuan earthquake are summarized. An optimization method is proposed and applied to the spillway design for the Tangjiashan landslide dam, which is the largest one caused by the Wenchuan earthquake. It is found that the peak outflow rate could be reduced from the recorded 6500 m 3 /s to 2900 m 3 /s using the optimal design. A spillway with a shallow and broad cross section is suitable for low-erodibility dams, while a spillway with a deep and narrow cross section is suitable for high-erodibility dams. A spillway with a large longitudinal gradient is beneficial for high-erodibility dams with large dam widths and gentle downstream dam slopes. A spillway close to one bank can reduce the peak outflow rate if the bank is erosion resistant. [ABSTRACT FROM AUTHOR]

Abstract: Numerous landslides were triggered by the 12 May 2008 Wenchuan earthquake in China, particularly near the epicenter. During the rainy season in 2010 after the earthquake, much of the landslide debris was reactivated, causing a large number of fatalities. The earthquake has a significant impact on the subsequent rain-induced landslides. Based on interpretation of satellite images taken in 2008 and 2010, combined with yearly field investigations, this paper attempts to (1) map the earthquake-induced landslides near the epicenter; (2) present the distribution of the landslides occurring during a subsequent extreme storm in the same area; and (3) compare the distribution characteristics of the earthquake-induced landslides and the rain-induced landslides. Through this study, the following findings were obtained: (1) the internal relief of the landslides in the study area is much higher than that in other affected regions of the Wenchuan earthquake zone; (2) the landslide area in hard rocks (i.e. the granite and diorite zones) is much larger than that in alluvium; (3) the volume of hill-slope loose deposits decreased while the volume of channel deposits increased during the process of mass transportation caused by rainfall after the earthquake; (4) during the rainy seasons after the earthquake, the density of landslides increased while the area of landslides decreased significantly and the type of landslides transformed from debris slides to debris flows; and (5) the rain-induced landslides are less steeper than the earthquake-induced landslides. [Copyright &y& Elsevier]

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 3200m, 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. [Copyright &y& Elsevier]

Abstract: Stabilizing piles are used worldwide to stabilize unstable slopes. However to date, there is little coverage in the scientific literature on the effects of the pore water pressure and the shear strength of the slip zone on the lateral force acting on the piles. This paper presents and compares two methods to estimate the lateral force acting on the stabilizing piles. These are the limit equilibrium method (LEM), and the finite element shear strength reduction method (FE-SRM). For both methods, the COMSOL software was used to model the infiltration of reservoir water and rainfall into the sliding mass. The distribution of lateral force was then simulated by the normal stress distribution on the piles with FE-SRM in PLAXIS 8.2 software. The effect of shear strength of the slip zone on the lateral force and its distribution were also studied. The lower Ercengyan landslide in the Three Gorges Reservoir was used as study area, with four different hydrological scenarios based on the reservoir water level fluctuations and rainfall amounts. The results show that the lateral force with the LEM method is slightly greater than with the FE-SRM method. The lateral force reaches a peak when the level of the reservoir rises to 175m combined with high rainfall amount, and decreases linearly as the effective shear strength of the slip zone increases. The distribution of the lateral force is parabolic, and varies with the shear strength parameters of the slip zone. In conclusion, the LEM and FE-SRM methods can be used to calculate the lateral force acting on the stabilizing piles, and estimate the lateral force distribution. This technique effectively analyzes the behavior of stabilizing piles for landslides. It can be applied in the routine practical design of stabilizing piles in the Three Gorges Reservoir as well as other similar areas. [Copyright &y& Elsevier]

Abstract: A type of clayey diatomaceous earth of Pliocene Mangbang Formation (N2 m) was encountered in highway projects in the Tengchong region of Yunnan Province, Southwest China. The Tengchong clayey diatomaceous earth is characterized using multiple test methods, such as granulometric analysis, chemical analysis, X-ray diffraction (XRD) and scanning electron microscopy (SEM) analysis, shrinkage and swelling tests, unconfined or uniaxial compression test, triaxial test and direct shear tests. The chemical and mineralogical compositions, physical and hydraulic properties and engineering properties of the clayey diatomaceous earth are presented in this paper. It is revealed that the Tengchong clayey diatomaceous earth is an unusual soil or rock which has characteristics of both typical diatomaceous earth and swelling clayey soil or soft clay rock. The diatoms in the earth enhance the connection between micro-structures, and improve the mechanical properties of diatomaceous earth. However, due to the existence of a significant amount of swelling clay minerals, the Tengchong clayey diatomaceous earth becomes swelling soft rock, and is prone to engineering problems or geohazards. Based on the test results, a number of issues regarding classification, discrimination and geohazard control related with the clayey diatomaceous earth are discussed to provide both some basic understanding and new insight into the characteristics of the clayey diatomaceous earth deposits. [Copyright &y& Elsevier]

This paper compares the performance of five popular machine learning methods, namely, particle swarm optimization–extreme learning machine (PSO–ELM), particle swarm optimization–kernel extreme learning machine (PSO–KELM), particle swarm optimization–support vector machine (PSO–SVM), particle swarm optimization–least squares support vector machine (PSO–LSSVM), and long short-term memory neural network (LSTM), in the prediction of reservoir landslide displacement. The Baishuihe, Shuping, and Baijiabao landslides in the Three Gorges reservoir area of China were used for case studies. Cumulative displacement was decomposed into trend displacement and periodic displacement by the Hodrick–Prescott filter. The double exponential smoothing method and the five machine learning methods were used to predict the trend and periodic displacement, respectively. The five machine learning methods are compared in three aspects: highest single prediction accuracy, mean prediction accuracy, and prediction stability. The results show that no method performed the best for all three aspects in the three landslide cases. LSTM and PSO–ELM achieved better single prediction accuracy, but worse mean prediction accuracy and stability. PSO–KELM, PSO–LSSVM, and PSO–SVM always yielded consistent predictions with slight variations. On the whole, PSO–KELM and PSO–LSSVM are recommended for their superior mean prediction accuracy and prediction stability. • The performances of machine learning methods depend on the selected evaluation index and reservoir landslide case. • Using single prediction accuracy for evaluating the superiority of machine learning methods may be unreliable. • PSO-KELM and PSO-LSSVM are recommended for their superior mean prediction accuracy and prediction stability. [ABSTRACT FROM AUTHOR]

Understanding the spatial distribution regularity of coseismic landslides is important for mitigation in future earthquakes. Unveiling the controlling factors of the distribution of coseismic landslides is a long-standing unsolved problem. On 3 August 2014, a Mw 6.1 earthquake occurred in Ludian County, Yunnan Province, China, and resulted in a great number of landslides and substantial losses. The coseismic landslide distribution in this earthquake, which was triggered by an unmapped fault, shows a different pattern. This paper conducted a spatial analysis to reveal the controlling factors in the Ludian earthquake. A spatial database of landslides has been built by interpreting the ZY-3 pre-earthquake, unmanned aerial vehicle (UAV), GeoEye-1 and GF-1 post-earthquake. A total of 1414 landslides were identified after a combination of image interpretation and field investigation in an area of 704.7 km2. The geological setting of the study area, including the tectonics and lithology, has been mapped in detail. The digital elevation model (DEM) of the study area with a resolution of 30 m × 30 m was presented to address the topographic characteristics. A geographic information system (GIS) was used to analyse the spatial characterization of the landslides. Correlations between the occurrences of landslides and factors, i.e., slope gradient, elevation, slope aspect, intensity, distance to coseismic fault, distance to the epicentre, lithology, distance to non-coseismic faults, distance to rivers and distance to road, were characterized with a spatial analysis in GIS. It can be concluded that the slope gradient and the distance to the coseismic fault are the two most important factors for determining the spatial distribution of coseismic disasters. Some other factors play a role by influencing the slope gradient to a certain extent, and the movement of the coseismic fault is the prone direction of coseismic landslides. Slope cutting fractures the rock mass, increases the slope gradient, and significantly increases the occurrence of coseismic landslides. A statistics analysis indicates that the landslide concentration (LC) generally has an obvious exponential decrease with an increasing distance to the coseismic fault, while it has a good Weibull cumulative distribution with the slope gradient. • A complete coseismic landslide inventory were documented in 2004 Mw 6.1 Ludian struck area of 704.7 km2. • Correlations between landslide occurrences and nine factors including geographical and geological setting were investigated. • The relationships among factors influencing the spatial distribution of coseismic landslides are disclosed. • Slope gradient and the distance to the coseismic fault or epicentre are the two determinants for LC of coseismic landslides. [ABSTRACT FROM AUTHOR]

Abstract: This paper focuses on the piezocone (CPTU) test results and the related interpretation procedures to predict ultimate pile load capacities of driven and jacked piles for the Jiangsu soft soil deposits in China. The pile foundation data including pile load tests on twenty six piles from several field sites are compiled and presented. A comparison was made to explain the advantages and fallacies of various CPT based interpretation methods. A modified CPTU-based method has been proposed, which was used to predict the ultimate capacity from effective cone tip resistance and excess pore water pressure. Comparison of the calculated pile capacities to the measured pile capacities showed that the modified CPTU method''s predictions showed a better agreement with the ultimate load capacities determined from static loading tests. Also, there was less scatter in this method''s predictions than other CPTU methods for deep foundations of soft clay deposits, indicating a higher reliability in the proposed methodology. [Copyright &y& Elsevier]

Abstract: Particle breakage is an important phenomenon that is observed in high rockfill dams as the dam material is subjected to both weathering and stresses. This paper presents a study of the particle breakage of an argillaceous siltstone used in a rockfill dam in southwest China that is 261.5m in height. The region is characterized by abundant rainfall and a wide variation in temperature (10–60°C). A series of oedometer tests were performed with specimens subjected to different types of weathering. The study aims to examine the development of particle breakage of an argillaceous siltstone and the manner in which the particle size distribution of the weathered material changes over time. The results highlight that the combined effect of water and thermal weathering is a major factor controlling the disintegration of soft rocks. Particle breakage is characterized by three mechanisms: angular fracture, particle cracking and particle breakup. The weathering rate, defined as the rate of particle breakage over a weathering cycle, declines as the number of cycles increases. The ultimate particle breakage induced by weathering approaches a constant despite different axial stresses. [Copyright &y& Elsevier]

Abstract: Completely decomposed granite (CDG) is abundant in Hong Kong. It has been used extensively as fill materials in various applications, such as back-filling materials for retaining structures and pavements. In this paper, results of a series of triaxial tests, including isotropic and anisotropic compression, and drained and undrained shearing tests, on a medium-fine-grained re-compacted CDG with overconsolidation ratio ranged between 1 and 8 are reported. The tests aim to understand the mechanical behavior of the soil in its saturated state under various initial states, stress paths and drainage conditions. It is found that the material is highly compressible during virgin isotropic and anisotropic compression. Moreover, the virgin compression lines are uniquely associated with their stress ratios and they appear to parallel to each other in an e-lnp′ plane. All specimens exhibit strain-hardening type response during drained shearing. In undrained shear, normally consolidated specimens reveal contractive response until the ultimate states are reached. Overconsolidated specimens, however, show complex stress paths and volumetric tendency. Dilatancy responses of the soil during a constant stress ratio compression and deviatoric shear are discussed respectively. Unique isotropic compression line (ICL) and critical state line (CSL) are reported for the studied soil. [Copyright &y& Elsevier]

Abstract: Suzhou is located at the lower reaches of the Yangtze River in southeastern Jiangsu, China. It is part of the Su-Xi-Chang area including Suzhou, Wuxi and Changzhou. As one of the most developed areas in China, this region has suffered from severe land subsidence caused by extensive groundwater exploitation since 1980s. The land subsidence was controlled by prohibition of groundwater exploration in the past several years. However, the surface water pollution prompted a new task of how to sustainably utilize the groundwater resource, especially to satisfy the emergency demands of water supply. In this paper, we took Suzhou as a representative case to discuss how to develop groundwater resources while controlling the land subsidence. The relationship between the deformation and the groundwater level was analyzed, with focus on the deformation features after the period of groundwater exploitation ban. The results confirmed the conclusion by Shi et al. (2007, 2008a): even in the period of rising groundwater level, same units may manifest different deformation characteristics, such as elasticity, elasto-plasticity, and visco-elasto-plasticity, at different locations of the cone of depression. A land subsidence model that couples a 3-D groundwater model and a 1-D deformation model was developed to simulate the groundwater level and deformation. A high-resolution local grid (child model) for Suzhou was built based on the regional land subsidence model of Su-Xi-Chang area by Wu et al. (2009). The model was used for a number of predictive scenarios up to the year of 2012 to examine how to develop sustainable use of groundwater resources under the conditions of land subsidence control. Our results indicated that about 3.08×107 m3/a groundwater could be provided as emergency and standby water source while meeting the land subsidence control target of 10mm/a. [Copyright &y& Elsevier]

Abstract: The analysis of site response to earthquake is of great importance for seismic design of structure. Although it has long been recognized that the ground is simultaneously subjected to both horizontal and vertical motions during a real earthquake, the effect of vertical motion is usually ignored in most site response analyses. Moreover, some studies show that there are significant differences in site responses for saturated and unsaturated soil deposits, and site response is influenced by variation of groundwater table. Therefore, these factors should be considerably considered in the dynamic site response analysis. Based on the results of geological investigation as well as laboratory and field tests conducted in Shanghai, a deep geotechnical profile with a depth of 280m is analyzed in this paper. By using a verified, fully coupled and inelastic finite element procedure, a series of numerical analyses is carried out for a deep soft soil profile subjected to multidirectional earthquake loadings. Parameters of the model in the procedure are calibrated by field and laboratory tests. Numerical results demonstrate that the behavior of vertical amplification is quite different from the horizontal counterpart. Furthermore, the use of a single horizontal component as seismic input in site response analysis, neglecting the other horizontal component and the vertical one, may result in considerable underestimation of site response. Variation of groundwater table brings about a profound effect on both vertical and horizontal motions, its ratio, the response spectra at ground surface, and excess pore water pressure ratio. The analysis can capture a more complete and fundamental aspects of ground response for preliminary seismic assessment. [Copyright &y& Elsevier]

Abstract: Geotechnical engineers worldwide practice a variety of in-situ techniques to classify soils in order to obtain their physical and engineering properties. An electric piezocone, which is an advanced version of the cone penetrometer, is capable of measuring cone resistance, sleeve friction and pore pressure. The piezocone testing data not only provide valuable information on soil types but are also useful in deriving correlations with the engineering properties of soil for the purposes of analysis and design of foundations. In a view to establish a region-specific correlation between piezocone penetration resistance and soil properties, piezocone penetration tests (PCPT or CPTu), borings, and other in situ tests were carried out at seven locations in Jiangsu Province, China. PCPT data were first used for classifying soil; thus the data were fully analyzed and validated for providing a reasonable soil classification. Several available CPT based classification charts are used to determine soil types; these results are further validated with the soil classification determined from the field samples and basic soil test results. This paper summarizes these analysis results, including description of the available charts and their performance in soil classification. [Copyright &y& Elsevier]

Abstract: In the urban area of Shanghai, the dewatering of groundwater was controlled strictly and the engineering–environment effect of the high-rise building group became to be the main cause of land subsidence in Shanghai. Based on the high-rise building group in the soft soil area in Shanghai, the mechanism of land subsidence was studied in this paper by the centrifuge model test. The central area of the building group has larger subsidence and the subsidence superimposition effect is obvious. It can exceed the allowance and cause land subsidence hazard. The land subsidence affected by the different building distances was also studied. For smaller building distances, the subsidence superimposition effect is more obvious. The engineering characteristics of soils are controlled by the state of pore structure of soils to a great extent. The parameter of specific subsidence was put forward as a tie to analyze the relationship between land subsidence and pore structure of soils. The pore structure of each soil layer was studied by the mercury intrusion porosimetry test (MIP) and the pore distribution of each soil layer was studied by the fractal theory. There are mainly macropores in silty clay of layer no. 4, clayey soil of layer no. 8, silty sand of layer no. 7 and layer no. 9 in Shanghai. The ink-bottle effect exists in the intrusion stage in the MIP test. There are four different fractal dimensions in silty clay of layer no. 4 and clayey soil of layer no. 8 and three different fractal dimensions in silty sand of layer no. 7 and layer no. 9. [Copyright &y& Elsevier]

Abstract: A fractal study method of the number of geological mass fractures is introduced in detail in this paper. Three main aspects of the problem were studied: (1) The random distribution of fractures in a geological mass was in good agreement with the fractal law. The size scale of the studied geological mass ranged from 2400m to 1mm for the length of each side, and the geological mass samples were taken from 13 coal areas in China. (2) The geological mass fractures were evidently directional and anisotropic, having originated from tectonic movement. Observation and statistics for the data from the Xuangang, Fenxi and Dongshan coal areas in Shanxi, China, demonstrated that the fracture distribution of each group, classified by the strike of the strata, still follow the fractal law, even though the fractal dimension varies to a certain extent with different strikes. (3) The sedimentary strata containing the coal seams, as a geological mass, underwent almost similar tectonic movements in their geological history. The mechanical experiments on geological mass samples from Fenxi and Jiexiu in Shanxi demonstrated that the fractal dimension of the number of fractures in the same strata is in good power function with the product of strength and elastic modulus. The larger the product of the strength of the elastic modulus is, the larger is the fractal dimension, and vice versa. [Copyright &y& Elsevier]

Abstract: For the Xiashu loess–palaeosol sequence in Nanjing, China, further to our work on the cyclic variability in its chemical composition and swelling-shrinkage properties [Xia, J., Huang, G.L., Liu, Z. T., Chen, X.M., 2007. Cyclic variability in chemical composition and swelling–shrinkage properties of the Xiashu loess stratum near Nanjing, China. Pedosphere 17 (5), 666–672.], this paper studies the cyclic variability in its microstructure and physico-mechanical properties and the corresponding influence on its engineering behaviour for geotechnical and geological practices. In addition, the cyclic variability in the soil''s grain-size distribution and geochemical characteristics is compared with that of the loess–palaeosol sequences at two other sites in China, indicating a geographical pattern of cyclic variation of the sequences. [Copyright &y& Elsevier]