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Engineering Geology
Elsevier Science B.V.
Engineering Geology

Elsevier Science B.V.

0013-7952

Engineering Geology/Journal Engineering GeologySCIISTPEIAHCI
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    A slow and complex landslide under static and seismic action

    Pinyol N.M.Alonso E.E.Di Carluccio G.
    17页
    查看更多>>摘要：A dam construction project for the heightening of a dam is threatened by a large landslide located in the Spanish Southern Pyrenees. A marked syncline structure, folding a flysch formation overlying a marl substratum, is the main geological feature of the unstable valley slope. The landslide is characterized by two main and superimposed slip surfaces which follow the bedding layers. The motion observed is very slow and its acceleration can be related to rainfall regimes and changes in loading condition due to excavations. The paper provides an insight into the complexities associated with stability and kinematic evolution of a landslide under static and dynamic actions. Simplified procedures are proposed to predict the complex landslide behaviour. A comprehensive hydrogeological model is developed to relate rainfall history and water pressure which incorporates available data about the anisotropic permeability of flysch and the natural drainage obtained from pumping test and insitu measurements. The stability analysis of the slope focuses on the discussion of safety factors and their practical implication not only in terms of static limit equilibrium, but also on creeping velocity. The latter was evaluated under the simplified assumption of planar landslide and invoking the strain-rate effects on residual strength. A derived analytical expression provides a relationship between Safety Factor and creeping velocity. Under such hypothesis, the increment of the strength required to avoid predicting unrealistic landslide acceleration should be imposed for a lower range of shear velocity than the usual value imposed in the laboratory shearing tests. The seismic response of the landslide is also analysed. A Newmark's approach and a stress-strain finite element (FE) analysis are compared, with special emphasis on the effect of the superimposed slip surfaces on the dynamic landslide response. To do that, the Newmark's analysis has been extended to two overlaying sliding surfaces with independent strength properties and pore water pressure. It is concluded that assuming a single deeper sliding surfaces may underestimate the co-seismic permanent displacement. The comparison of two-block Newmark's analysis with two-dimensional elastoplastic FE approach highlights the effect of geometry in the landslide motion.
      原文链接:
    • NSTL
    • Elsevier

    Unraveling the effect of a two-layer system on the mobility of rapid gravitational flows

    Zheng Y.Li Y.Xu Q.Huang R....
    11页
    查看更多>>摘要：Rapid gravitational flows such as debris avalanches and debris flows may entrain significant amounts of in situ material along their tracks, increasing their volume. Interactions between rapid gravitational flows and bed material are complicated. Especially, the physical mechanism of the fluidization has remained a mystery up to now. To gain a better understanding of the fluidization mechanism and influencing factors, we conducted flume experiments simulating the process of a flow overriding saturated bed material. Results showed that the overriding flow fluidized the bed material into a viscous state rather than liquefying saturated bed material. We also carried out a rheometer test on the saturated bed material. It revealed shear-thinning of the bed material. We deduced that shear thinning, and not liquefaction, was the principal mechanism for bed-material fluidization. Based on these results, a two-layer flow model was proposed using the classical depth-integrated approximation and the Saint Venant equation. It was assumed that both the dry rock avalanche and the impacted saturated bed material behaved as visco-plastic flows with different apparent viscosities. The model's two viscosity parameters were calibrated using the experimental run-out times and distances. We conclude from comparison of the tests and simulations, that our model well simulates the entrainment process.
      原文链接:
    • NSTL
    • Elsevier

    Subsidence monitoring and influencing factor analysis of mountain excavation and valley infilling on the Chinese Loess Plateau: A case study of Yan'an New District

    Yang Y.Zhang H.Zeng R.Zhang Y....
    18页
    查看更多>>摘要：With the significant expansion of the urban population on the Chinese Loess Plateau, large-scale land infilling and excavation projects have been implemented to alleviate the shortage of construction land. However, loess collapsibility associated with engineering disturbances can often lead to geological hazards, such as land subsidence. The Yan'an New District (YND) is the largest area of mountain excavation and valley infilling on the Loess Plateau. Post-construction subsidence is likely to threaten future infrastructure; therefore, the monitoring and analysis of the settlement are essential. The temporal and spatial distribution of settlement in the YND was investigated, and the key influencing factors, such as filling, construction, and precipitation, were analysed in this study. Integrated with remote sensing methods, such as SBAS-InSAR technology, shadow altimetry, and uncrewed aerial photogrammetry, were used, which have seldom been applied to regional analysis. The results revealed that the rate of deformation in the YND from 2015 to 2019 was ?73 to 18 mm/yr, and in the fill area, the maximum cumulative subsidence was 256 mm, while in the excavation area, the maximum cumulative uplift was 35 mm. We obtained a linear regression model for the fill area, which indicated that settlement was positively correlated with the fill thickness and negatively correlated with the building height. In the excavation area, there was no clear relationship between the excavation thickness or building height on deformation. In the fill area, no obvious collapsible settlement was observed during the rainy season, and uplift occurred in the excavation area, with a maximum uplift of 17 mm.
      原文链接:
    • NSTL
    • Elsevier

    Flow amplification from cascading landslide dam failures: Insights from flume experiments

    Hu W.Li Y.Fan Y.Xiong M....
    13页
    查看更多>>摘要：The 2008 Wenchuan Earthquake triggered numerous co-seismic landslides, and formed many landslide dams. Debris flows or floods during intense rainfall can cause the sequential collapse of those landslide dams. There is an amplification effect of the cascading landslide dam failures, which increases the magnitudes of debris flows or floods. Runs of flume experiments with different initial conditions were conducted to study the scale amplification effect. Among them, a large-scale flume experiment was performed to reduce the size effect of the miniaturized physical experiments to some extent. Experimental data such as the flow discharge, pore pressures, and microseismic and acoustic signals were used to investigate the dam failure processes and to quantify the amplification scale. The experimental results show that channel gradients and dam-failure patterns have significantly influences on the amplification effect. The intrinsic mechanism of the amplification effect can be interpreted from the perspective of energy, which is a progressive storage of potential energy and subsequent rapid release of the energy. Steep channel gradients imply greater potential energy and lower stability of the landslide dam. The sudden dam collapse related to internal pore pressure evolution will lead to rapid release of the accumulated potential energy to downstream, and cause a maximum instantaneous dam-break discharge. Experimental results show that the peak dam-break discharge caused by sudden failure can be 2–3 times that of overtopping, which should be fully considered to avoid underestimating the scale of the potential catastrophe.
      原文链接:
    • NSTL
    • Elsevier

    Integrated bedrock model combining airborne geophysics and sparse drillings based on an artificial neural network

    Lysdahl A.K.Christensen C.W.Pfaffhuber A.A.Voge M....
    14页
    查看更多>>摘要：Cost overruns caused by unforeseen geological challenges are commonplace for large infrastructure projects. Thorough ground investigations can reduce this risk, but geotechnical drillings and laboratory test are expensive and time consuming. Airborne electromagnetics (AEM) is a low-cost geophysical method being increasingly used for geotechnical ground investigations. However, extracting engineering parameters from these complex data is challenging. We present a novel approach of extracting depth to bedrock from AEM data using artificial neural networks (ANN) and sparse drillings. Using synthetic models, we test its theoretical performance and analyse sources of error. We find that geological complexity is the main limitation on performance. We also test the algorithm on real field data from a complex geological setting. Results show that ANNs produce bedrock models that rival the accuracy of manual interpretations by experts and that are markedly more accurate than existing automated resistivity model interpretation methods. Using ANN based bedrock interpretation, one needs 2 to 3.5 times fewer geotechnical drillings (i.e., a reduction of 50–70%) in the early phases of a project compared to ground investigations using only borehole data. Further improvements may be possible with strategic planning of drilling campaigns and careful data pre-processing.
      原文链接:
    • NSTL
    • Elsevier

    Site-scale liquefaction potential analysis using a sectional random field model

    Gholampour A.
    18页
    查看更多>>摘要：This paper presents a new random field modeling to assess the site-scale spatial variability of soil properties applied in liquefaction mapping. In this procedure, the initial random fields are primarily generated, based on in-situ measured data. These initial fields are considered as the virtual known values to construct interior random fields, section-by-section and around a central axis. Assembling these sections results in a three-dimensional random field model. Through this approach, more accurate vertical semivariogram models can be available, in addition to a higher number of measured data involved in the generation of random fields. Based on a verification procedure, computational cost reduction and a more appropriate prediction of the layering characteristics are the two most important beneficial points of changing the modeling strategy from planar to sectional. The proposed approach is implemented in a case study in Oceano, California and the spatial distribution of liquefaction probability is estimated. It is concluded that the sectional random field can efficiently locate the liquefiable zone through the soil volume, based on liquefaction evidence. In addition to performing the liquefaction severity assessment, it is also illustrated that the hazard assessments based on liquefaction severity alone cannot provide the comprehensive prediction of liquefaction potential and may lead to unconservative engineering judgments.
      原文链接:
    • NSTL
    • Elsevier

    Physics-based large-deformation analysis of coseismic landslides: A multiscale 3D SEM-MPM framework with application to the Hongshiyan landslide

    Wang G.Chen Z.Huang D.Jin F....
    16页
    查看更多>>摘要：A multiscale framework is developed based on the spectral element method (SEM) and material point method (MPM) for the large-deformation analysis of coseismic landslides. At a regional scale, SEM is used to model elastic wave propagation from a seismic source to a local site with complex topography. At a local scale, the coseismic landslide process and large deformation behavior are simulated by a nonlinear MPM model. Therefore, the proposed SEM-MPM model is able to reproduce the entire coseismic landslide process, including triggering, sliding and deposition. In this study, the coupled SEM-MPM method is used to simulate the massive Hongshiyan landslide triggered by the 2014 Ms6.5 Ludian earthquake in China. The study shows that the domain reduction method is able to reproduce the complex wave field across the SEM and MPM platforms, especially the strong topographic amplification of ground motion on the mountain ridge, which triggered the catastropic failure of the Hongshiyan landslide. The simulated volume of the sliding mass, sliding velocity, and final deposition profile are comparable with the field data and previous numerical studies, showing that the SEM-MPM method is a promising physics-based numerical tool for an integrated study of coseismic landslides.
      原文链接:
    • NSTL
    • Elsevier

    Characteristics and causes of crest cracking on a high core-wall rockfill dam: A case study

    Zhang H.Jing Y.Chen J.Xu Y....
    15页
    查看更多>>摘要：Avoiding and controlling dam crest cracking is one of the most difficult problems facing high core rockfill dams of more than 100 m. However, few studies have been conducted on the characteristics and causes of dam crest cracking based on long-term measurement data. In this study, a real case of a dam suffering cracking at the crest was studied. The dam has a maximum height of 186 m and has been in service for 10 years. The spatiotemporal characteristics of the dam crest cracking were determined based on monitoring data obtained using crack monitoring instruments, radar detection, seismic refraction tomography, and pit exploration. The causes of dam cracking were analyzed based on the deformation inclination and strain index. The factors controlling the cracking (such as the dam structure, geological structure, and materials' properties) were investigated. The results show the following. 1) The cracks mainly occurred at the interface between the core wall and the downstream dam shell. 2) The cracks mainly developed during the impoundment and operation periods with high water levels, and there was no convergence trend within the 10 years of operation. 3) Uneven settlement and uneven horizontal displacement were the main reasons for the crack formation. 4) The factors influencing the cracking include dam zoning, the geological structure, wetting, and the rheological properties of the rockfill materials, and the reservoir level. The results of this study provide an important engineering reference for the prevention and control of dam crest cracking in high rockfill dams.
      原文链接:
    • NSTL
    • Elsevier

    Mechanical behaviour of bimodal kaolin clay with aggregates

    Kuhn V.D.O.Lopes B.D.C.F.L.Caicedo B.Cordao-Neto M.P....
    12页
    查看更多>>摘要：Soil structure has been recognised as a key feature in the understanding of soil's mechanical behaviour, and research efforts have been made trying to relate them. However, the main difficulties encountered are that numerous factors can simultaneously affect the mechanical behaviour of soils. Among these factors, the presence of aggregates is decisive for the fabric configuration of bimodal soils. The aim of this paper is to evaluate the effect of aggregates on the mechanical behaviour of bimodal soils with no mineralogical variability. For this purpose, aggregates of Kaolin Clay were obtained by compaction at high stresses and bimodal samples with different aggregates content were produced. All samples were subjected to unidimensional consolidation and direct shear tests. Results showed that the increase in aggregates content and the presence of macro-pores affected compressibility, decreasing pre-consolidation stresses and altering compressibility coefficients. The increase in interaction between aggregates generated an increase in friction angles in samples with aggregates, which also impacted their volumetric behaviour during shearing. Thus, the present work contributes to a better understanding of the mechanical behaviour of bimodal soils influenced exclusively by the presence of aggregates.
      原文链接:
    • NSTL
    • Elsevier

    On compression behavior and particle breakage of carbonate silty sands

    Tong C.-X.Dong Z.-L.Zhang S.Sun Q....
    14页
    查看更多>>摘要：Carbonate soils are high in compressibility and low in particle strength, and therefore need special treatment for many geotechnical applications. This paper presents comprehensive one-dimensional compression tests to investigate the compression behavior and particle breakage of carbonate soils with various initial particle size distributions (PSDs) and a wide range of initial void ratios at a high effective vertical stress of 32 MPa. A clear shape transition in terms of the void ratio against effective vertical stress was observed with varying silt fraction and void ratio. The deformation mechanism for the samples with less silt fraction and higher void ratio is mainly dominated by the particle-breakage-induced unlocking effect. Samples with more silt fraction and lower void ratio will experience less particle breakage and their deformation mechanism is mainly attributed to interparticle locking effect. A ‘transitional’ mode of behavior without a unique normal compression line was identified for the samples with silt fraction ranging from 1.6% to 33%. It was also found that carbonate soil samples with both ‘transitional’ and ‘non-transitional’ modes of compression behavior may both experience considerable amount of particle breakage and show different trends in the evolution of particle shape.
      原文链接:
    • NSTL
    • Elsevier