Required unfactored strength of geosynthetics in reinforced 3D slopes

The design of reinforced earth structures uses idealized two-dimensional (2D) geometry – classifying as a plane-strain analysis. This 2D idealization greatly simplifies design by ignoring stabilizing effects posed by three-dimensional (3D) characteristics. While the outcome of this 2D idealization is conservative in terms of required reinforcement strength, ignoring 3D end effects in back-calculations of experimental and field data may overestimate the contribution of the reinforcement to stability thus possibly leading to unconservative learned lessons related to design. The objective of this study is to explore 3D effects on the required strength of reinforcement in geosynthetic-reinforced earth structures (GRESs) using a modified 3D limit equilibrium (LE) slope stability analysis. To determine the stability of GRESs, a rotational, 3D failure mechanism, derived from variational LE analysis, is applied using a log-spiral surface generalized to 3D conditions. In order to determine the long-term strength of geosynthetics required to ensure sufficient internal stability, the moment equilibrium approach is applied and its respective equations solved. In order to conveniently assess the end effects on the required total strength of reinforcement and the volume of failing mass considering the feasible length of potential failure, a series of design charts are presented. These charts can also be useful in forensic studies when back-calculating the in-situ mobilized strength of the geosynthetic for 3D failures. The impact of seismicity and the assumed function of forces distributed amongst the reinforcement layers were investigated to highlight their importance. To keep this study focused on 3D end effects, this study is limited to a simple 3D GRES problem; however, extending the present framework to deal with complex homogenous problems is straightforward.     

Pore pressure and consolidation of saturated silty clay induced by progressively heating/cooling

The thermal pore pressure and consolidation of a saturated silty clay are experimentally studied. The specimen was heated progressively from the room temperature of 25 °C to 85 °C (T = 25 °C → 35 °C → 45 °C … → 85 °C), and then cooled from 85 °C to 25 °C (T = 85 °C → 75 °C → 65 °C … → 25 °C), with (case 1) or without (case 2) drainage between temperature stages at four confining pressures (50, 100, 150 and 200 kPa, respectively). It shows that during the undrained heating/cooling, the pore pressure reaches a peak at the time when the specimen is heated to the required temperature and then decreases slightly, and it declines to a minimum at the time when the specimen is cooled to the required temperature and then increases slightly. Such phenomenon can be attributed to the adjustment of soil structure induced by the interaction of solid grains with pore water. On the other hand, during the drained heating/cooling, the maximum pore pressure increases with the increase of temperature stages, and the normalized negative pore pressures show a decreasing trend with the decrease of temperature stages. This appears to be especially obvious as the applied confining pressures decrease. It is also observed that consolidation volumetric strains during the isothermal drainage increase significantly with the increase of temperature stage, and the reduction in the volumetric strains due to absorption after cooling shows a decreasing trend with the decrease of temperature stage.     

Effects of silica fume on the geotechnical properties of fine-grained soils exposed to freeze and thaw

Both the landfill liner and cover systems are the most important parts on a waste disposal landfill site. These systems are generally constructed using compacted fine-grained soils. It is known that the strength and permeability are particularly affected by freezing and thawing cycles in the cold regions. The aim of this study is to reduce the effects of freezing and thawing cycles on the strength and permeability. To modify the fine-grained soils, silica fume generated during silicon metal production as very fine dust of silica from a blast furnace and historically considered a waste product has been used as a stabilizer. The natural fine-grained soils and soil–silica fume mixtures have been compacted at the optimum moisture content and subjected to the laboratory tests. The test results show that the stabilized fine-grained soil samples containing silica fume exhibit high resistance to the freezing and thawing effects as compared to natural fine-grained soil samples. The silica fume decreases the effects of freezing and thawing cycles on the unconfined compressive strength and permeability. We have concluded that silica fume can be successfully used to reduce the effects of freezing and thawing cycles on the strength and permeability in landfill liner and cover systems constructed from compacted fine-grained soils.     

砂土液化研究概述

在查阅大量资料的基础上，叙述了砂土的液化机理、影响因素以及液化的分析、判别方法及常用的地基处理方法，并指出液化土的加固处理是抗震工程的重要组成部分，应引起重视。     

灰土和土挤密桩在湿陷性黄土地基中的设计与应用

通过灰土和土挤密桩在湿陷性黄土地基的作用原理，结合工程实际情况，分析了灰土和土挤密桩复合地基的设计和检测情况，提出了土挤密桩成孔时施工方法及技术应用，阐述土挤密桩在处理厚度较大的湿，陷性黄土地基的优势。     

Measurement of unsaturated shear strength parameters of silty sand and its correlation with unconfined compressive strength

Compressive strength and direct shear testing parameters on unsaturated soil are often used in analysis and design of several geotechnical infrastructures. Rarely, any attempt has been made to quantify shear strength of unsaturated soil under different net normal stress conditions. The objectives of this study are to quantify shear strength parameters of unsaturated silty sand and to establish a simple correlation of it with unconfined compressive strength. Consolidated drained direct shear tests and unconfined compressive strength tests were performed to determine shear strength of unsaturated completely decomposed granite (CDG) soil. To interpret this, a series of typical soil water characteristic curves (SWCC) of CDG soil under different net normal stresses were also measured. Experimental results show that the unsaturated shear strength significantly increases with increase in net normal stress and matric suction. A new model for prediction of unconfined compression strength of unsaturated soil from shear strength and initial suction was proposed. The predictions from newly proposed model were found to be consistent with the measured unconfined compressive strength. This correlation can be useful in economical and rapid design/analysis of geotechnical infrastructure.     

基于原位十字板强度的沿海地区软黏土超固结比分析

超固结比OCR是评价软黏土变形和强度特性的重要参数。基于天津、上海、连云港、深圳、中山和珠海这6个沿海地区软黏土的原位十字板强度,系统地分析这些地区软黏土的固结状态,并探讨其形成机制。研究结果表明:(1)基于原位十字板强度得到的OCR要明显大于室内一维压缩试验的结果,室内压缩试验会显著低估沿海软黏土的OCR;(2)6个地区的OCR随深度的变化规律较为一致,OCR随深度增加,逐渐减小至某一稳定值,浅层均表现出一定的超固结现象,而深层的固结状态则表现出一定的复杂性;(3)现有模型能够解释我国沿海软黏土超固结的成因以及变化规律,浅部的超固结现象源于以风化胶结为主的"表层作用",而深部的超固结则源于次压缩。考虑到软黏土突出的取土扰动问题,这种基于原位十字板强度的软黏土OCR评价及成因分析方法值得在我国沿海地区推广。     

现浇型生态混凝土护岸抗水力冲刷性能试验研究

目前,现浇型生态混凝土等新型的生态型护坡逐渐取代传统混凝土护坡,得到了越来越广泛的应用。但作为一种新兴的护坡方式,现浇型生态混凝土抗水力冲刷性能缺少实验数据的支撑。根据实际工程中的应用情况,制作了三种不同厚度的现浇生态混凝土样本,采用专用的实验仪器研究其在高速明渠流作用下的抗水力冲刷性能。结果表明:边界效应对生态混凝土的抗冲刷性能影响很大。在处理好边界效应的情况下,现浇型生态混凝土护岸在高速明渠流的作用下,水力淘刷现象不明显,下覆土体表面基本保存平整,土体高程下降微小(0.1 mm)。因此,现浇型生态混凝土护岸有着很好的抵抗高速水流(本研究最大流速达到6.11 m/s)冲刷的能力,在水利护岸工程中可以代替传统护岸和预制生态混凝土护岸进行应用。     

谈改良土填筑施工作业

根据技术规范,在总结多年施工经验的基础上,从材料、施工工艺、安全、环保措施等各方面分析了改良土填筑施工作业的技术要点,以达到指导实践的目的。     

锁口钢管桩围护仿真分析

以某深基坑开挖支护为工程背景,建立锁口钢管桩围护三维有限元模型。基于盾恩法确定了钢管桩嵌入深度,采用库仑经典土压力公式计算坑外主动土压力,应用＂m＂法计算坑底被动土压力。通过仿真计算得出各控制工况最大应力、变形的数值及发生位置,确定整个施工阶段的控制技术指标及参考值。