Energy-based probabilistic evaluation of soil liquefaction

This paper presents a seismic wave energy-based method with back-propagation neural networks to assess the liquefaction probability. An empirical equation and Fourier spectrum of acceleration are employed, respectively, to calculate the seismic wave energy. Discriminant analysis is used to determine the equation of the boundary curve separating the data points with and without liquefaction. The proposed method shows capability in evaluating the probability of soil liquefaction based on the boundary curve and a logarithm normal distribution.     

Mapping the liquefaction induced soil moisture changes using remote sensing technique: an attempt to map the earthquake induced liquefaction around Bhuj, Gujarat, India

The Bhuj earthquake (Mw = 7.9) occurred in the western part of India on 26th January 2001 and resulted in the loss of 20,000 lives and caused extensive damage to property. Soil liquefaction related ground failures such as lateral spreading caused significant damage to bridges, dams and other civil engineering structures in entire Kachchh peninsula. The Bhuj area is a part of large sedimentary basin filled with Jurassic, Tertiary and Quaternary deposits. This work pertains to mapping the areas that showed sudden increase in soil moisture after the seismic event, using remote sensing technique. Multi-spectral, spatial and temporal data sets from Indian Remote Sensing Satellite are used to derive the Liquefaction Sensitivity Index (LSeI). The basic concept behind LSeI is that the near infrared and shortwave infrared regions of electromagnetic spectrum are highly absorbed by soil moisture. Thus, the LSeI is herein used to identify the areas with increase in soil moisture after the seismic event. The LSeI map of Bhuj is then correlated with field-based observation on Cyclic Stress Ratio (CSR) and Cyclic Resistance Ratio (CRR), depth to water table, soil density and Liquefaction Severity Index (LSI). The derived LSeI values are in agreement with liquefaction susceptible criteria and observed LSI (R ² = 0.97). The results of the study indicate that the LSeI after calibration with LSI can be used as a quick tool to map the liquefied areas. On the basis of LSeI, LSI, CRR, CSR and saturation, the unconsolidated sediments of the Bhuj area are classified into three susceptibility classes.     

胶新铁路砂土液化区路基沉降规律研究

地震液化常给人们带来巨大损失,而剪切振动和循环荷载作用下的动力学效应常被认为是地震液化的主要原因,人们对剪切荷载作用下饱和砂土的液化问题进行了较多的研究,而对循环荷载作用下砂土液化的动力学效应研究较少。胶新铁路在DK39+000开始为高地震烈度区,DK283+550~DK283+770分布有地震可液化层,工程修建后列车动荷载的影响将会有诱发砂土液化的可能性。为了研究通车前自然沉降特征和通车后循环荷载作用下的路基沉降变形规律,本文在具体分析了砂土液化的概念和准则判别的基础上,重点分析了砂土液化区路基沉降特征,包括测试断面竖向分层沉降变形特征分析和路基水平位移特征分析。最后在试验的基础上,从理论上给出了循环荷载下砂土的本构关系。     

模糊识别模式在粉土液化判别中的应用

基于模糊数学的基本原理和方法,分析了粉土液化的影响因素,选取粉土的平均粒径,相对密度,标准贯入击数和上覆有效压力作为评价指标,构造粉土液化的模糊识别模式。验证和应用结果表明,模糊识别模式具有很好的映射能力,是粉土液化势预测的有效手段。     

Three-Dimensional Interpolation and Lithofacies Analysis of Granular Composition Data for Earthquake-Engineering Characterization of Shallow Soil

In Japan, many major cities are located on tectonic basins which are surrounded by faults and underlain by soft alluvial materials. Because these areas are subject to earthquake damages, it is important to determine their seismic engineering characteristics. Geotechnical databases which contain many borehole logs are useful information sources for this type of analysis. Each datum stored in the database has a value or an attribute, and its location is irregular in both horizontal and vertical directions. A new interpolation method based on the optimization principle is proposed here to deal with such three-dimensionally distributed data. Susceptibility of unconsolidated ground to liquefaction is known to be related to the content of loose and saturated sand. The mixture ratio of several soil types in a deposit, i.e., granular composition, is strongly influenced by the sedimentary environment. There are two numerical methods: the optimization principle method (OPM) used to determine three-dimensional distribution of granular composition and the model used to evaluate liquefaction. The application of the proposed methods to two locations in Japan indicated that the zones with high susceptibility to liquefaction were indeed those that had suffered from liquefaction during past earthquakes.     

Study on Liquefying Simulation Test of Retaining Structure Ground of Kobe Port

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未来上海地区海平面上升激化土层液化的探讨

未来上海地区海平面上升引起地下水位抬升,将会激化土层液化,本文就土层液化问题从理论上进行了分析探讨,并对未来工作提出了设想。     

Stress-strain transformations and liquefaction of sands

Presented in this paper are the results of the laboratory tests of sands performed for the purpose of defining the characteristics of the dynamic shear stress-shear strain relationships. For this purpose, the transformation of the initial stress-strain characteristics of undrained saturated sands was investigated separately. These transformations take place under conditions of an increase in pore pressure under the effect of sufficiently intensive dynamic excitations. The process of occurrence and development of liquefaction was investigated simultaneously. The obtained results show that the transformation of the stress-strain relationships leads to intensive reduction in the initial dynamic characteristics of sands. At the moment of occurrence of initial liquefaction, for the selected strain, shear moduli are considerably reduced in respect to their initial values. These parameters tend to be further reduced in the phase of post-initial liquefaction. It is concluded that the process of liquefaction of sands can be completely defined through the transformation of the stress-strain relationships.     

地震振动液化形变的研究

多种地质作用可造成年青的松散沉积物发生变形。为了判别沉积形变中的地震振动液化形变形迹,着重讨论了振动液化形成机制、形变几何形态特征以及它们与融冻变形和准同生变形构造的区别。认为振动液化形变形迹可以作为鉴别古地震标志之一。     

水平动载下饱和砂土地基液化区扩展

对一侧受沿深度分布的水平振动载荷时 ,半无限饱和砂土地基液化区域的扩展进行了数值分析。结果表明 :在水平振动载荷作用下 ,砂土地基液化区域从载荷端由近到远逐渐发展 ;随载荷强度和频率的增加 ,以及土体模量的减小 ,液化发展逐渐加快。在考虑的频率范围内 ,随着载荷频率的增加 ,土体表面的变形和土中的孔隙压力上升速度增加。