Selected aspects of the stability assessment of slopes with the assumption of cylindrical slip surfaces

A comprehensive analysis of maintaining stability by model homogeneous and stratified slopes, with possible surcharge loading, is carried out within the article. Calculations are performed by the Swedish method of Fellenius under the assumption of a cylindrical slip surface passing through the slope foot. Proposals for searching for the reach of the break-off wedge of a potential slip surface are put forward. An analysis of the effect of surcharge load location on general slope stability is also made, providing the capability to determine the safe distance of positioning of an excavator on the surcharge of a non-encased excavation.     

Seismic stability of retaining walls with surcharge

The use of pseudo-static methods for the computation of soil thrust acting on retaining walls under seismic condition is well established in the design of such structures. Although different methods, based on the limited displacement concept, have been developed in the last 20 years, the most common design method is still the method derived from the theory developed by Mononobe and Okabe. However, the Mononobe–Okabe method presents a basic shortcoming: the solution is based on the limit equilibrium of the soil wedge without taking into account the presence of the wall. In the paper a new solution based on the pseudo-static equilibrium of the soil–wall system is presented. The developed solution takes into account the effect of the presence of the wall and it is applied to soil–wall systems with surcharged backfills. Formulas are provided to calculate directly the yield acceleration and the inclination of the failure surface. The effect of the intensity of the surcharge and of its distance from the wall is investigated and the results are compared to those obtained in the case of soil–wall systems without surcharge.     

Response of heterogeneous slopes to increased surcharge load

Slope stability analysis generally considers a homogeneous slope composed of either soil or rock. There is no definitive criterion to distinguish homogeneous and heterogeneous slopes. This paper presents five model tests on two-layered slopes with different interface subjected to surcharge load. Numerical simulations were performed to capture the behaviors observed. Given the satisfactory reproduction of the model tests, a parametric study was then conducted to investigate the impact of the interface, slope angle and strength parameters. Finally, a set of criteria based on the relative cohesion ratio was proposed to characterize a distinct change in the nature of the slope.     

单向压缩状态下上海地区软土的蠕变变形与次固结特 性研究

基于上海地区原状软土的一维固结试验,讨论了在不同加荷比、加荷速率及超载预压情况下软土的蠕变变形特性和次固结特性。试验结果表明:蠕变变形随应力水平、加荷速率的增大而增大。相同应力水平下,加荷比较大的土样蠕变变形较小。蠕变变形为非线性,随着应力水平的增加,蠕变变形从粘弹性到粘塑性转变,加荷比较大时,这种转变更明显。对试验结果进行曲线拟和,确定Metchell一维经验模型参数,拟和曲线与试验结果吻合较好。通过对次固结阶段试验数据的线性拟合可知,对于正常固结土,次固结系数Ca值受应力水平和加荷比的影响不大,而与加荷速率密切相关,加荷速率较大时,Ca值随荷载的增大急剧增大后略有降低。超载预压可有效减小次固结系数,从而有利于减小工后次固结沉降。     

Effect of Surcharge on the Stability of Anchored Rock Slope with Water Filled Tension Crack under Seismic Loading Condition

In this paper, an analytical expression is derived for the factor of safety of the rock slope incorporating most of the practically occurring destabilizing forces as well as the external stabilizing force through an anchoring system. The slope stability is analyzed as a two-dimensional problem, considering a slice of unit thickness through the slope and assuming negligible resistance to sliding at the lateral boundaries of the sliding block. A detailed parametric study is presented to investigate the effect of surcharge on the stability of the rock slope for practical ranges of governing parameters such as inclination of the slope face, inclination of the failure plane, depth of tension crack, depth of water in tension crack, shear strength parameters of the material at the failure plane, unit weight of rock, stabilizing force and its inclination, and seismic load. For the range of parameters considered in the present study, it is found that the factor of safety of the rock slope decreases with increase in surcharge; the rate of decrease being relatively higher for lower values of surcharge. It is also observed that for a specific surcharge, the factor of safety depends significantly on all other parameters, except for unit weight of rock and higher values of inclination of stabilizing force to the normal at the failure plane. For any combination of these variables, the surcharge plays a vital role in the stability. A perfectly stable slope at relatively low surcharge can become unsafe with the increase in surcharge. The deterioration in the stability can be quite rapid, depending on the combination of the factors under consideration. The analysis and the general expression proposed herein can be used to carry out a quantitative assessment of the stability of the rock slopes.     

Improvement of estuarine marine clays for coastal reclamation using vacuum-applied consolidation method

Consolidation occurs in estuarine marine clays for coastal reclamation by dissipation of the excess pore pressure, which is induced by increasing the total overburden stress during conventional mechanical surcharging. The excess pore pressure can be decreased usually by the use of several construction methods such as sand drain and paper drain. Besides the drain methods, vacuum can also be used in the soil mass to consolidate the estuarine marine clays by decreasing the pore pressure as well as increasing the effective stress.The study on vacuum consolidation is devoted so far mainly for laboratory model tests or numerical analysis in Korea. Recently, an instrumentation system was applied to manage the vacuum-applied consolidation on a field, in which a sewage disposal plant was constructed. While vacuum was applied, the behaviors of estuarine marine clays such as the settlement, lateral deformation and pore water pressure have been investigated precisely. The behavior of estuarine marine clays during vacuum-applied consolidation shows some difference from the behavior of estuarine marine clays in the case of conventional preloading. A principal difference is that the lateral deformation corresponding to settlement is smaller than before vacuum application even though the surcharge height has been increased.     

砂井排水堆载预压软基处理的工程实践

对厚度10.5~13.8m、埋深2~17m、高含水量、高压缩性、低强度及欠固结的不能满足公路工程建设工后沉降量要求的软基路段进行了砂井排水堆载预压法地基处理;采用分层综合法等理论方法,通过对地基处理前后地基沉降量的计算和预压处理工程中地层固结度的计算,并与预压过程中分层沉降量观测成果进行对比分析,预压处理后的地基工后沉降量可满足规范要求,达到了预期目的。     

排水固结法加固软基变形简化计算分析

插板和砂井堆载预压是处理软基有效方法之一,现有的沉降变形计算方法大部分采用轴对称理论的解析解和以太 沙基或比奥固结理论为基础的数值解,仍较为复杂。根据软基排水固结机理,采用固结度等效原理,对渗透系数进行调整,把 砂井(插板)地基简化为均质成层地基。运用有限元对某软土路基处理工程进行简化计算,并和监测结果进行对比分析,对简 化计算方法进行验证。发现具有较好的准确性,为实际软基处理工程的沉降变形分析提供了一种简单实用的方法。     

平板载荷试验确定桩端承载力的方法

以广西南宁地区进行的平板载荷试验为例,介绍了非超载和未加载至破坏两种情况下确定桩端承载力的方法,该法对处理载荷试验数据、积累地区性经验等方面具有实用价值.     

L'inclinométrie,un nouvel outil pour le suivi temporel des aquifères ?

This study explores the sensitivity of tilt measurements to hydrogeologic phenomena in order to use them to characterise aquifers and explain the signals observed on the instruments. The challenge is to separate the hydrogeological contribution from other phenomena that affect this type of measurements. First, we applied the theory propounded by Farell (1972) and Pagiatakis (1990) to simple hydrogeological cases. Then a simulation of the tiltmeter signal obtained in the Seine valley reveals that the order of magnitude is significant: the signal of a load with hydrologic origin therefore represents a significant part of any tiltmeter signal. Moreover, it can be interpreted in hydrogeological terms: it depends directly on the load gradient through a convolution formalism. Consequently, it is possible to imagine a use of the tiltmeter in hydrogeology to characterise, to a certain extent, mass transfer of water in the ground. To cite this article: T. Rerolle et al., C. R. Geoscience 338 (2006).