非饱和砂土抗拉强度的试验研究

含水合物土的抗拉强度特性对含水合物地层的稳定评估具有重要意义。以黏质粉土为赋存介质,利用四氢呋喃(THF)合成含水合物土试样,在冷冻库中利用改进后的单轴拉伸装置研究了含水合物土单轴抗拉强度特性。试验结果表明水合物饱和度、试样干密度、细粒含量对含水合物土的抗拉强度存在明显影响。随着水合物饱和度的增加,抗拉强度呈现指数函数的增长趋势。干密度和细粒含量对抗拉强度的影响在不同的水合物饱和度情况下影响不同,在低水合物饱和度情况下,干密度和细粒含量的增加会使抗拉强度增强;而在较高的水合物饱和度情况下,抗拉强度则随着干密度和细粒含量增加而降低。此外,通过分析含水合物土的波速特性,建立抗拉强度与波速之间的经验关系式。这一关系式对采用声波来估算含水合物土试样的抗拉特性具有重要的参考意义。     

Influence of rainfall on the deformation and stability of a slope in overconsolidated clays: a case study

The behaviour of an instrumented unstable slope in a profile of weathered overconsolidated clay has been analysed. Available field investigation data and laboratory tests were integrated in a coupled hydromechanical model of the slope. Particular attention was given to the unsaturated soil conditions above the water table and to the influence of the rainfall record. Recorded pore-water pressures helped to identify the hydrogeological conditions of the slope. The coupled model was used to compute slope deformations and the variation of safety with time. Actual rainfall records were also integrated into the analysis. Comparison of measurements and calculations illustrate the nature of the slope instability and the complex relationships between mechanical and hydraulic factors. Electronic Publication     

On the enhanced confining pressure aproach to the mechanics of reinforced soil

Summary A review is presented of conceptual approaches that are currently in use for interpreting the operation of reinforced soil. The concepts of enhanced confining pressure and of reduced normal tensile strains are found to be closely related to current experimental and theoretical investigations as well as to the design methodologies available at present for reinforced soil applications. Focusing on the enhanced confining pressure concept, analytical expressions are developed that allow the estimation of the value of equivalent confining stress increase when the properties of soil and reinforcement and the state of stresses acting on a cylindrical reinforced soil element are known. The derived expressions can also be utilized for estimating the soil-reinforcement friction angle from the results of triaxial tests on cylindrical samples reinforced with horizontal layers of reinforcement.     

浆固碎石桩成桩注浆影响范围现场试验研究

浆固碎石桩作为一种新型桩基技术,不仅具有一般刚性桩的桩体置换作用,而且能改善桩周土的力学性质,从而可有效地提高复合地基的承载力及减小沉降变形。通过现场进行成桩前后的桩周土性质研究,验证了注浆对桩周土性质的改善作用,得出成桩时注浆影响范围及分布规律。针对黏性土中浆固碎石桩浆液挤密作用,按平面轴对称问题分析了塑性区边界条件及内部单元体的平衡条件,提出浆固碎石桩浆液影响范围的计算公式。理论公式计算结果与原位测试结果较为符合,从而验证了计算方法的合理性,这对浆固碎石桩的注浆加固具有一定的指导意义。     

基于裂缝混凝土的修正氯离子迁移模型研究

通过研究裂缝混凝土内的氯离子运移,建立了混凝土内考虑扩散、结合和电迁移场作用以及裂缝影响的氯离子迁移耦合模型。预测混凝土寿命。模型从已有试验数据中得到了较好验证。在南通盐渍土环境,运用Comsol Multiphysics软件计算混凝土内氯离子随时间和空间的分布;随裂缝宽度、深度及保护层厚度变化的混凝土使用年限变化规律。研究表明：混凝土内氯离子浓度,随时间增加而增加,增速减小;随离子侵入混凝土深度增加而减小,减速趋缓。氯离子从裂缝运移到混凝土孔隙,浓度突降。混凝土使用年限,随保护层厚度增加呈近似线性增加;随裂缝深度增加而减小;随裂缝宽度增加呈指数型函数关系。     

横向土运动作用下群桩的性状研究

以有限元与有限差分相结合,对横向土运动作用下的群桩工作性状,产生群桩效应的临界桩距、桩数及排列、桩顶边界条件等影响因素作出分析;并对沿桩排的应力分布作出初步探讨。     

Field Measurement of Suction, Water Content, and Water Permeability

This paper presents a review of techniques for field measurement of suction, water content, and water hydraulic conductivity (permeability). Main problems in the use of field tensiometers are addressed and hints on how to improve tensiometer performance are given. Advantages and limitations of instruments for indirect measurement of suction including electrical conductivity sensors, thermal conductivity sensors, dielectric permittivity sensors, filter paper, and psychrometer are discussed. Techniques for water content measurement based on dielectric methods are then presented. These include time and amplitude domain reflectometry and capacitance. Finally, a brief overview of methods for measurement of water permeability in the field is presented.     

基于GIS的土壤重金属数据库构建及应用

本文首先探讨了利用GIS技术构建上海市基本农田土壤重金属数据库的方法,该数据库集空间数据、采样点监测数据和元数据于一体,对于土壤重金属信息的管理、应用服务等具有重要的基础作用,是农产品安全生产环境认证和土壤环境长效管理的重要依据;接着,基于数据库进行了重金属元素的描述性统计、动态累积和Kriging插值分析;结果表明,除As外,其余重金属平均含量均高于该区域的背景值含量,尤其是Cd、Hg、Zn、Cu累积指数较高,是上海市农田土壤重金属污染的主要元素。     

An analytical solution for rainfall infiltration into an unsaturated infinite slope and its application to slope stability analysis

Surficial slope failures in residual soils are common in tropical and subtropical regions as a result of rainfall infiltration. This study develops an analytical solution for simulating rainfall infiltration into an infinite unsaturated soil slope. The analytical solution is based on the general partial differential equation for water flow through unsaturated soils. It can accept soil–water characteristic curve and unsaturated permeability function of the exponential form into account. Numerical simulations are conducted to verify the assumptions of the analytical solution and demonstrate that the proposed analytical solution is acceptable for the coarse soils with low air entry values. The pore‐water pressure (pwp) distributions obtained from the analytical solution can be incorporated into a limit equilibrium method to do infinite slope stability analysis for a rain‐induced shallow slip. The analysis method takes into account the influence of the water content change on unit weight and hence on factor of safety. A series of analytical parametric analyses have been performed using the developed model. The analyses indicate that when the residual soil slope, consisting of a completely decomposed granite layer underlain by a less permeable layer, is subjected to a continuous heavy rainfall, the loss of negative pwp and the reduction in factor of safety were found to be most significant for the shallow soil layer and during the first 12 h. The antecedent and subsequent rainfall intensity, depth of a less permeable layer and slope angle all have a significant influence on the pwp response and hence the slope stability. Copyright © 2012 John Wiley & Sons, Ltd.     

scattering and refracting of plane strain wave by a cylindrical inclusion in fluidsaturated soils

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