高填方加筋黄土路堤稳定性的有限元分析

采用有限元法对国内最高(62 m)的山西北张沟加筋黄土高填路堤稳定性进行了数值模拟,对其最大主应力、最小主应力、剪应力和塑性破坏区及其变形进行了计算,然后将其计算结果与未加筋路堤相比较,得出高填方加筋黄土路堤及地基变形特性和应力特性的变化规律。结果表明,由于加筋的作用,降低了黄土高路堤的变形,提高了其稳定性。这与现场沉降观测结果基本一致。     

中仑昆山北坡黄土特征及其环境

根据野外调查和实验分析资料,阐述和分析中昆仑山北坡黄土的形成时代、物质成分和结构及沉积条件,认为黄土属晚第四纪风积物质,现代黄土堆积持续进行,物质主要来源于塔克拉玛沙漠。在干旱气候背景上,7000—5000a.B.P.为明显相对湿润时期。     

延安Q2黄土统计损伤本构模型研究

中国黄土的物理力学性质改变具有明显的地域性,是一种特殊土体。以延安Q2黄土在不同围压和含水量下进行常规三轴试验获得的数据为基础,运用岩石统计损伤理论对延安Q2黄土的损伤本构模型进行研究。在考虑损伤门槛值对延安Q2黄土损伤变量的影响下,建立了延安Q2黄土在三轴压缩条件下的统计损伤本构模型,统计损伤本构方程中的参数通过对试验结果进行线性回归求得。试验和分析表明:在半对数坐标下,延安Q2黄土初始损伤点为三轴应力应变曲线的峰值拐点,对应的应力值为损伤应力门槛值。当施加的应力低于损伤门槛值时,应力应变曲线为线弹性关系,延安Q2黄土不发生损伤; 而当施加的应力超过损伤门槛值时,延安Q2黄土发生损伤,并且随着施加的应力增大,损伤不断扩大。将统计损伤理论曲线与试验曲线进行对比,发现二者基本吻合,表明考虑损伤门槛值的延安Q2黄土统计损伤本构模型能较好的反映该地区黄土的变形破坏特征,对该区黄土地区岩土工程设计具有参考和借鉴作用。     

波浪作用下砂质海床瞬态液化判别准则分析探讨

波浪会引起松砂和中等密实度的砂质海床发生液化,海床液化直接影响着海洋构筑物的安全。目前文献中常用的液化判别公式主要基于有效应力和超孔压的概念提出。在对当前文献中的4种主要液化判别准则的物理意义进行分析的基础上,基于波浪作用下海床应力和孔压的解析解,对不同计算参数条件下4种液化判别准则得到的液化区分布特征进行了对比,分析了4种液化判别准则的适用性,主要结论为：基于海床平均有效应力的液化判别准则b,在海床饱和度不小于0.99,且海床计算厚度不大于0.4倍波长时不适用;基于海床竖向超孔隙水压力和海床平均上覆有效自重应力的液化准则d,其所得海床液化深度较多情况下超出海床的塑性区深度,且其物理意义不明确,因此不建议使用该液化判别准则;基于海床竖向有效应力的液化准则a,与基于海床竖向超孔隙水压力和海床上覆竖向有效自重应力的液化准则c,其适用性较好,推荐应用该2个液化准则。     

Blake极性事件与古土壤层S1的沉积环境

对黄土高原定边、西峰、渭南三个剖面中古土壤层S1的定向连续古地磁样品作了详细的岩石磁学和古地磁学研究,均未发现Blake极性事件．在对其成因进行了分析研究后,提出如下看法：（1）六盘山以东黄土高原北部边缘的风成沉积可能存在局部的不连续性,因而没有记录Blake极性事件;（2）黄土沉积物的主要载磁矿物力磁铁矿,次生磁性矿物对剩磁的贡献可能大于原生磁铁矿,故在六盘山以东黄土高原北部边缘没有发现Blake极性事件;（3）六盘山以东黄土高原中部和南部地区,强烈的成土作用掩盖了持续时间较短的Blake极性事件;（4）六盘山以西的黄土高原具高速稳定沉积的特点,且成土作用弱,可记录Blake极性事件．     

New OSL dating of UK loess: indications of two phases of Late Glacial dust accretion in SE England and climate implications

Windblown dust deposits or loess, locally known in the UK as brickearth, blanket many parts of southern England outside the limits of the British and Irish Ice Sheet. The best‐studied loess exposures occur in Kent, southeast England, where the deposits are believed to be Late Glacial in age. New sedimentological evidence is presented for phases of accretion with two distinct units, a calcareous brickearth exhibiting periglacial cryoturbation and a non‐calcareous, massive brickearth. Optically stimulated luminescence (OSL) dating has been applied to chemically isolated modal quartz silts to derive a chronology for sediment accretion and to better understand the palaeoclimatic significance of these deposits. © British Geological Survey/Natural Environment Research Council copyright 2007. Reproduced with the permission of BGS/NERC. Published by John Wiley & Sons, Ltd.     

Support vector machines‐based modelling of seismic liquefaction potential

This paper investigates the potential of support vector machines (SVM)‐based classification approach to assess the liquefaction potential from actual standard penetration test (SPT) and cone penetration test (CPT) field data. SVMs are based on statistical learning theory and found to work well in comparison to neural networks in several other applications. Both CPT and SPT field data sets is used with SVMs for predicting the occurrence and non‐occurrence of liquefaction based on different input parameter combination. With SPT and CPT test data sets, highest accuracy of 96 and 97%, respectively, was achieved with SVMs. This suggests that SVMs can effectively be used to model the complex relationship between different soil parameter and the liquefaction potential. Several other combinations of input variable were used to assess the influence of different input parameters on liquefaction potential. Proposed approach suggest that neither normalized cone resistance value with CPT data nor the calculation of standardized SPT value is required with SPT data. Further, SVMs required few user‐defined parameters and provide better performance in comparison to neural network approach. Copyright © 2006 John Wiley & Sons, Ltd.     

Three‐dimensional analysis of the seismic behaviour of micropiles used in the reinforcement of saturated soil

This paper includes a numerical study of the behaviour of micropiles used for the reinforcement of saturated soil. Analysis is carried out using the (u–p) formulation (displacement for the solid phase and pore‐pressure for the fluid phase) implemented in a three‐dimensional finite element program. The soil behaviour is described by means of a cyclic elastoplastic constitutive relation which was developed within the framework of the bounding surface concept. The paper is composed of three parts. The first one is concerned with a presentation of the numerical model; the second includes analysis of the seismic behaviour of a single micropile; the last part deals with the group effect under seismic loading. Copyright © 2001 John Wiley & Sons, Ltd.