2021-11-23 10:11

2.4 Special Topics A :Slope Stability

In mine development, there are many situations where soil mechanics can be applied to the design of structures and to mining activities .They include the following:

1.Structureal stability

2.Founndations,retaining walls,dams

3.Slope stability




2.4.1Principles of Soil Mechanics

Soil mechanics is the study of the properties of soils and their behavior in relation to the design, construction, and performance of engineering works. It is applicable, however, to man made materials such as fills, wastes, tailings dumps, stockpiles, bins as well as to soils, which broadens its utility in mine engineering. Soil mechanics is a companion field to rock mechanics, and the two share much in common in the analysis and design of geotechnical structures.

Soil properties are usually grouped in two categories Index properties are identification properties used to classify soils. Mechanical properties are physical properties which describe soil behavior. We shall discuss some examples of each.

The most important soil index property is grain size Grain size distribution is measured in the laboratory by sieving, sedimentation, or a commercial particle size analyzer. Once determined, the size distribution is plotted either as a frequency graph or as cumulative-undersize graph. Since a log-probability graph paper, and a straight-line plot has obvious interpretative advantages, this means is frequently employed to present a soil grain size distribution.

Once determined, the size distribution is used to name and classify the soil. The usual basis for classifying the Public Roads Administration system .It considers three prominent size fractions of the soil, considering of very fine ,fine, and coarse .A fourth category is sometimes employed for the very coarse fraction. The upper divisions occur at 2mu;m for silt, and 2mm for sand. Once the fractions are read from the size distribution graph, they are plotted on the PRA chart and the soil name read.

The use of piles to stabilize active landslides, and as a preventive measure in stable slopes ,has become one of the important innovative slope reinforcement techniques in recent years. Some of the successful applications of such techniques have been reported by De Beer et al.1970. The piles used in slope stabilization are usually subjected to lateral force by horizontal movements of the surrounding soil and hence they ate considered as passive piles. Driven timber piles have been used to reinforce the slope stability of very soft clays in Sweden, while cast–in-place reinforce concrete piles as large as 1.5m diameter have been used in Europe and the United States to stabilize active landslides in stiff clays.

A number of techniques have been developed to evaluate lateral pressures acting against piles which are used as reinforcement in slopes. Reese et al.(1992) have presented a “p-y” approach for assessing the improvement in slope stability which arises from using piles .Rowe and Poulos developed a two-dimensional finite element approach that allowed for the three dimensional effect of soil flowing through rows of piles .A three dimensional elastic finite element approach has been developed by Oakland and Chameau usually not suitable for routine practical design purposes. Some of the basic failure mechanisms associated with the use o piles to stabilize slope have been suggested and discussed by Viggiani. These failure mechanisms provide better insight into the pile-slope stability interaction problem. To have incorporated a plastic extrusion deformation model to compute the lateral pressures action on a row of passive piles In limit equilibrium solutions for slope stability. Although this approach appears useful, the model is derived for rigid piles with infinite length. These piles may not represent the actual piles in the field since the latter have finite length and also are unlikely to be frigid. Also it may provide doubtful solutions when the piles are closely spaced.

An alternative approach is presented here in which a modified boundary element method is employed to study the response of a row of passive piles incorporated n limit equilibrium, or as a set of springs, with nonuniform variation of stiffness and strength with depth. The solution incorporates a nonlinear piles-soil interface element with the ability to represent a hardening or softening response prior to reaching an ultimate state .The slope stability analysis is performed using Bishoprsquo;s simplified slip circle approach. A microcomputer-based program has been developed based on the above analysis. Theoretical solutions have been obtained by this approach in order to study the most effective means of using piles for stabilizing slopes.

2.4.2 Method of Analysis

The analysis is formulated using an uncoupled approach in which the pile response and slope stability are considered separately. Pile Response

The sliding soil mass above the failure surface is assumed to be strengthened by the discretely placed piles to form a barrier that resists soil movements and transfers loads to the more stable underlaying layers. The portion of the piles embedded in the sliding slope is subjected to large lateral soil movements .The vertical soil movements are ignored here. The pile shear forces and bending moments developed at the sliding surface by the external soil movements are evaluated using a modified boundary element method as described by Hull et al., and employed by Lee et al.

An incremental approach has been developed in which the analysis can be carried out with defined soil deformation up to the limiting pile-soil pressure .A restriction to complete mobilization of pile-soil interface element strength is the basic requirement that equilibrium must be maintained. When the piles yield ,it


2.4 专题A:边坡稳定性 2

2.4.1 土力学原理 2

2.4.2 分析方法 3 桩响应 3 边坡稳定性 3 参数解决方案 4

2.4.3 结论 5

2.5 专题B:露天开采境界优化 6

2.4 专题A:边坡稳定性








2.4.1 土力学原理





利用桩稳定活性滑坡,作为稳定边坡的预防措施,已成为近年来边坡加固的重要创新技术之一。De Beer等人在1970年报道了这种技术的一些成功应用。用于边坡稳定的桩基通常受周围土体水平运动的侧向力作用,因此被认为是被动桩。瑞典采用打木桩加固非常软粘土的边坡稳定性,欧洲和美国采用直径1.5m的现浇混凝土桩加固硬土中活跃的滑坡。



2.4.2 分析方法

分析采用非耦合方法,分别考虑桩的响应和边坡的稳定性。 桩响应


本文提出了一种增量法,该方法可以在极限桩土压力下进行确定的土体变形分析。限制桩土界面单元强度的完全活动作用是保持平衡的基本要求。当桩屈服时,假定桩的最大弯矩与桩的屈服弯矩相等。假定土体是弹性的,但在分析中加入非线性效应,允许桩土界面在达到规定的桩土极限压力时发生屈服。同一受荷群桩的相互作用效应也可以包括不同的桩头和基桩,可以模拟不同桩顶和基桩的相互作用效果。在粘土中,杨氏模量Es和桩土极限压力py 分别与不排水抗剪强度Cu与系数KE与Kpy的乘积相关。KE和Kpy的典型值分别是250-1000和3-12。通过增量分析,解决了桩土相互作用问题,使土体侧向运动达到或超过了全桩土界面强度的状态。 边坡稳定性

采用传统的毕晓普简化滑移圈分析方法,确定了临界滑移面、阻力矩Mrs 和覆盖力矩Mo。桩产生的抗弯弯矩Mrp 由桩的剪力和弯矩在滑移面深度处分析得到,如前一节所述。因此,坡桩的最终的总安全系数为Fps 可决定如下:


利用该非耦合公式编制了基于微机的计算机程序,对上述桩坡稳定性问题进行了分析。 参数解决方案

本文对均匀土和双土坡上的一排假定现浇钢筋混凝土桩进行了理论求解。分析的均匀土边坡问题如图2所示。坡度10米高,地面以下10米为寒冷的地基。这斜坡与地面成20度角倾斜。假定土体为均匀软粘土,不排水抗剪强度为30kN/m2且不排水泊松比为0.5,土壤密度为18.5 KN/m3。分别取土体的杨氏模量和桩土极限压力是未排水抗剪强度的500倍和9倍。混凝土桩的直径为lm,以3m的中心距离分散放置。



其中Fp =桩坡安全系数的最小值,Fs =无桩边坡稳定问题的最小安全系数,选取该问题中各参数的值,使 Fs对于均匀的土体坡度约为1.00。


图3(缺图)显示了沿着边坡桩的位置对改进比 Nps 的影响。最有效的桩位接近边坡的顶部和底部,此时桩坡的改进比大约为1.08,当桩靠近边坡的中间位置时,边坡改进比变为1.0,这表明桩的存在对稳定性有很大的影响。这是因为临界滑移面靠近桩顶。由于滑动面与桩头不接近,因此对旋转固定桩头的稳定性影响不大。






图7显示了嵌在两层土坡中的假想桩。对于情形A,上面的软层被硬层所覆盖。假定土的扬子模量和极限桩土压力乘数与均质土边坡相同。对于情形B,下软层被硬层覆盖。例A和B的 Fs值分别约为1.03和1.18。







2.4.3 结论


2.5 专题B:露天开采境界优化












从寻找重叠圆锥之间的相互支持的角度来看,由于需要大量的计算工作,移动圆锥方法具有很大的局限性(Barnes, 1982)。实际上,大多数移动锥算法的实现通常不需要确定重叠锥之间的相互支持。该方法通常在对所有

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