Lateral Bearing Capacity of Modified Suction Caissons Determined by Using the Limit Equilibrium Method

The modified suction caisson(MSC) adds a short-skirted structure around the regular suction caissons to increase the lateral bearing capacity and limit the deflection. The MSC is suitable for acting as the offshore wind turbine foundation subjected to larger lateral loads compared with the imposed vertical loads. Determination of the lateral bearing capacity is a key issue for the MSC design. The formula estimating the lateral bearing capacity of the MSC was proposed in terms of the limit equilibrium method and was verified by the test results. Parametric studies on the lateral bearing capacity were also carried out. It was found that the lateral bearing capacity of the MSC increases with the increasing length and radius of the external skirt, and the lateral bearing capacity increases linearly with the increasing coefficient of subgrade reaction. The maximum lateral bearing capacity of the MSC is attained when the ratio of the radii of the internal compartment to the external skirt equals 0.82 and the ratio of the lengths of the external skirt to the internal compartment equals 0.48, provided that the steel usage of the MSC is kept constant.

A Generalized Limit Equilibrium Method for the Solution of Active Earth Pressure on a Retaining Wall

In this paper, a generalized limit equilibrium method of solving the active earth pressure problem behind a retaining wall is proposed.Differing from other limit equilibrium methods, an arbitrary slip surface shape without any assumptions of pre-defined shapes is needed in the current framework, which is verified to find the most probable failure slip surface. Based on the current computational framework, numerical comparisons with experiment, discrete element method and other methods are carried out. In addition, the influences of the inclination of the wall, the soil cohesion, the angle of the internal friction of the soil, the slope inclination of the backfill soil on the critical pressure coefficient of the soil, the point of application of the resultant earth pressure and the shape of the slip surface are also carefully investigated. The results demonstrate that limit equilibrium solution from predefined slip plane assumption, including Coulomb solution, is a special case of current computational framework. It is well illustrated that the current method is feasible to evaluate the characteristics of earth pressure problem.

Overhanging rock slope by design:An integrated approach using rock mass strength characterisation,large-scale numerical modelling and limit equilibrium methods

Overhanging rock slopes(steeper than 90°) are typically avoided in rock engineering design, particularly where the scale of the slope exceeds the scale of fracturing present in the rock mass. This paper highlights an integrated approach of designing overhanging rock slopes where the relative dimensions of the slope exceed the scale of fracturing and the rock mass failure needs to be considered rather than kinematic release of individual blocks. The key to the method is a simplified limit equilibrium(LE) tool that was used for the support design and analysis of a multi-faceted overhanging rock slope. The overhanging slopes required complex geometries with constantly changing orientations. The overhanging rock varied in height from 30 m to 66 m. Geomechanical modelling combined with discrete fracture network(DFN)representation of the rock mass was used to validate the rock mass strength assumptions and the failure mechanism assumed in the LE model. The advantage of the simplified LE method is that buttress and support design iterations(along with sensitivity analysis of design parameters) can be completed for various cross-sections along the proposed overhanging rock sections in an efficient manner, compared to the more time-intensive, sophisticated methods that were used for the initial validation. The method described presents the development of this design tool and assumptions made for a specific overhanging rock slope design. Other locations will have different geological conditions that can control the potential behaviour of rock slopes, however, the approach presented can be applied as a general guiding design principle for overhanging rock cut slope.

Comprehensive analysis of slope stability and determination of stable slopes in the Chador-Malu iron ore mine using numerical and limit equilibrium methods

One of the critical aspects in mine design is slope stability analysis and the determination of stable slopes. In the Chador- Malu iron ore mine, one of the most important iron ore mines in central Iran, it was considered vital to perform a comprehensive slope stability analysis. At first, we divided the existing rock hosting pit into six zones and a geotechnical map was prepared. Then, the value of MRMR (Mining Rock Mass Rating) was determined for each zone. Owing to the fact that the Chador-Malu iron ore mine is located in a highly tectonic area and the rock mass completely crushed, the Hoek–Brown failure criterion was found suitable to estimate geo-mechanical parameters. After that, the value of cohesion (c) and friction angle (φ) were calculated for different geotechnical zones and relative graphs and equations were derived as a function of slope height. The stability analyses using numerical and limit equilibrium methods showed that some instability problems might occur by increasing the slope height. Therefore, stable slopes for each geotechnical zone and prepared sections were calculated and presented as a function of slope height.

Probabilistic Analysis of Slope Using Finite Element Approach and Limit Equilibrium Approach around Amalpata Landslide of West Central, Nepal

The stability study of the ongoing and recurring Amalpata landslide in Baglung in Nepal’s Gandaki Province is presented in this research. The impacted slope is around 200 meters high, with two terraces that have different slope inclinations. The lower bench, located above the basement, consistently fails and sets others up for failure. The fluctuating water level of the slope, which travels down the slope masses, exacerbates the slide problem. The majority of these rocks are Amalpata landslide area experiences several structural disruptions. The area’s stability must be evaluated in order to prevent and control more harm from occurring to the nearby agricultural land and people living along the slope. The slopes’ failures increase the damages of house existing in nearby area and the erosion of the slope. Two modeling techniques the finite element approach and the limit equilibrium method were used to simulate the slope. The findings show that, in every case, the terrace above the basement is where the majority of the stress is concentrated, with a safety factor of near unity. Using probabilistic slope stability analysis, the failure probability was predicted to be between 98.90% and 100%.

A Method Combining Numerical Analysis and Limit Equilibrium Theory to Determine Potential Slip Surfaces in Soil Slopes

This paper describes a precise method combining numerical analysis and limit equilibrium theory to determine potential slip surfaces in soil slopes. In this method, the direction of the critical slip surface at any point in a slope is determined using the Coulomb’s strength principle and the extremum principle based on the ratio of the shear strength to the shear stress at that point. The ratio, which is considered as an analysis index, can be computed once the stress field of the soil slope is obtained. The critical slip direction at any point in the slope must be the tangential direction of a potential slip surface passing through the point. Therefore, starting from a point on the top of the slope surface or on the horizontal segment outside the slope toe, the increment with a small distance into the slope is used to choose another point and the corresponding slip direction at the point is computed. Connecting all the points used in the computation forms a potential slip surface exiting at the starting point. Then the factor of safety for any potential slip surface can be computed using limit equilibrium method like Spencer method. After factors of safety for all the potential slip surfaces are obtained, the minimum one is the factor of safety for the slope and the corresponding potential slip surface is the critical slip surface of the slope. The proposed method does not need to pre-assume the shape of potential slip surfaces. Thus it is suitable for any shape of slip surfaces. Moreover the method is very simple to be applied. Examples are presented in this paper to illustrate the feasibility of the proposed method programmed in ANSYS software by macro commands.

LOWER BOUND LIMIT ANALYSIS OF THREE-DIMENSIONAL ELASTOPLASTIC STRUCTURES BY BOUNDARY ELEMENT METHOD

Based on the lower bound theorem of limit analysis, a solution procedure for limit analysis of three_dimensional elastoplastic structures was established using conventional boundary element method (BEM). The elastic stress field for lower bound limit analysis was computed directly by three_dimensional boundary element method (3_D BEM). The self_equilibrium stress field was constructed by the linear combination of several self_equilibrium “basis vectors” which can be computed by elastic_plastic incremental iteration of 3_D BEM analysis. The lower bound limit analysis problem was finally reduced to a series of nonlinear programming sub_problems with relatively few optimal variables. The complex method was used to solve the nonlinear programming sub_problems. The numerical results show that the present solution procedure has good accuracy and high efficiency.

基于极限平衡法的危岩倾覆稳定性三维计算方法

目前危岩防治工作中,危岩稳定性评价主要以简化后的二维剖面作为计算模型。由于自然界中的危岩形态极不规则,采用二维剖面计算模型并不能真实反映危岩受力情况。为了研究危岩稳定性三维计算方法,在前人研究基础上,基于极限平衡理论,提出了由后缘裂缝抗拉强度控制的危岩倾覆稳定性三维计算公式,采用数值积分和空间几何方法给出了在危岩单体三维模型基础上求解危岩后缘岩体抗拉力、水压力及其力矩计算公式和实现流程。以三峡库区瞿塘峡吊嘴危岩为实例开展了应用,并通过数值分析进行了验证。通过不同形态危岩的三维稳定性分析,讨论了三维与二维稳定性计算结果的关系,对比发现危岩形态对稳定性计算结果有明显影响,三维计算较二维计算更准确和实用。

广义对数螺旋型滑面模型的构建与验证

临界滑动面的合理确定是边坡稳定性分析的关键问题之一。传统的边坡滑动面假设方法构造生成的潜在滑动面形式单一,且无法考虑复杂边坡中土层强度参数变化对临界滑动面形状的影响,从而降低了边坡稳定性分析结果的可靠性。基于此,提出一种新的广义对数螺旋型滑面模型,该模型可生成包含传统圆弧滑动面和对数螺旋滑动面在内的多种形式的潜在滑动面;并针对非均质边坡中各土层抗剪强度不同的特点,采用多中心分段构造策略,将该滑面模型应用于非均质边坡稳定性分析中。基于极限平衡理论计算滑动面安全系数并搜索临界滑动面,对边坡进行稳定性评估。选取多个均质边坡及多种型式的非均质边坡(水平分层、倾斜分层和斜折线分层)经典算例与现有研究成果以及数值模拟软件获得的结果进行对比分析,验证该滑面模型的合理性与优势性。研究结果表明:文中方法计算所得安全系数与其他方法相比更小,相对误差在5%以内。能够得到传统滑动面假设方法下难以搜索到的临界滑动面,并与数值模拟结果吻合度较好,稳定性分析结果更接近实际情况。由此说明,此方法用于均质边坡及非均质边坡稳定性分析是合理可行的,有望为工程实践提供更优的临界滑动面解决方案。

石灰石露天矿高陡边坡稳定性计算分析

以西南某石灰石矿高陡边坡为研究对象,根据矿山边坡现状、边坡岩体结构和结构面发育特征因素对“现状边坡”和“终了边坡”进行地质分区,通过岩石室内物理力学试验获得坡体岩石物理力学参数,采用GSI法计算边坡岩体内摩擦角、粘聚力、变形模量和泊松比等参数,评估边坡地质强度特性,采用Morgenstern-Price极限平衡法分三种荷载工况分别计算“现状边坡”和“终了边坡”各分区稳定性系数。经分析,该石灰石矿各地质分区“现状边坡”和“终了边坡”稳定性好,采场边坡参数设计合理,可为矿山扩产安全设施设计和安全生产提供参考。

非线性M-C强度准则下预应力锚索加固边坡时效稳定性分析M-P法

拓展传统极限平衡方法在复杂条件下边坡稳定性分析中的适用性一直是岩土工程界的研究热点。众所周知,边坡岩土体剪切失效一般服从于非线性强度准则,而传统极限平衡方法仅适用于线性强度准则下边坡稳定性分析。此外,预应力锚索作为一种主动防护措施,可极大地即时提高边坡稳定性而被广泛应用于中、大型边坡工程加固。然而,在应力松弛、蠕变效应以及腐蚀环境影响下预应力锚索加固边坡稳定性时效特征往往被忽视。由此,基于Morgenstern-Price(M-P)法,嵌入非线性Mohr-Coulomb(M-C)强度准则,并融入应力松弛与蠕变效应下锚索预应力损失模型以及腐蚀环境下锚索性能劣化模型,从而,建立非线性强度准则下预应力锚索加固边坡安全系数时程表达式。进一步,为了解决非线性强度准则下隐式嵌套公式难以求解的问题,归零化条间法向力初始值,并应用迭代循环求解策略,在引入循环终止允许误差判别条件后,可实现边坡稳定性理论真实结果的逼近求解。经过后续算例对比分析,验证了所提方法的可行性和合理性,与此同时,还研究了不同预应力损失速率和不同锈蚀环境下预应力锚索加固边坡稳定性的时效变化规律。

降雨条件下层状土坡三维边坡稳定性分析

降雨是诱发滑坡的重要因素之一,在降雨型滑坡的研究中,关于土壤水分剖面形状动态变化对三维边坡稳定性的影响有待进一步考虑。鉴于此,在前人工作的基础上,本文采用含修正形状系数的形状曲线描述土壤水分剖面的变化,结合非饱和土的水力特性,计算等效渗透系数,推导出改进入渗模型并拓展至双层土体入渗。利用GRASS GIS建立三维边坡模型,选取椭球面作为三维滑动面,通过蒙特卡洛法模拟椭球面参数,确定试算滑动面,采用Hovland三维极限平衡法计算考虑雨水入渗影响的三维边坡安全系数。根据湿润锋面、土层间界面和潜在滑动面三者的相对位置关系,将栅格单元柱分为5种情况考虑。通过算例分析验证所提出的降雨条件下三维边坡稳定性分析方法的可行性,结果表明:蒙特卡洛模拟试算样本数的最佳取值可定为2500次;最小三维边坡安全系数随着降雨历时的增加而减小,减小幅度为0.055~0.126。

爆破振动荷载作用下填埋场稳定性计算分析

针对爆破振动荷载作用下填埋场稳定系数分析,建立数学坐标系确定两种形状填埋场每个点的坐标位置,分别采用质心法和积分法计算爆破振动惯性力;考虑渗滤液对填埋体、衬垫界面物理力学参数的影响,建立填埋场沿垃圾坝背和坝底破坏时的三楔体分析模型,列楔体极限平衡方程;借助MATLAB求解爆破振动荷载下任意时刻填埋场沿底部复合衬垫界面滑移的安全系数,通过算例验证楔体极限平衡方程的正确性。结果表明:质心法计算的安全系数时程曲线开始发生变化的时间落后于积分法,且与积分法相比,波动幅度更大,最小安全系数更小,实际安全系数应在两种方法之间。当爆源位于垃圾坝底内边缘下方区域或填埋体底部中点左右区域的下方时,安全系数最小,发生失稳的概率最大。爆破振动频率对填埋场安全系数的影响,积分法得出随着振动频率变大,安全系数总体变化趋势增大,且增加幅度逐渐减小。渗滤液水位显著影响填埋场的稳定性。研究结果对评估填埋场在隧道下穿时的稳定性、优化隧道爆破开挖设计、确保施工安全具有重要意义。

聚丙烯纤维加固膨胀土边坡稳定性分析

为提高膨胀土边坡稳定性,改善膨胀土力学性能,使用聚丙烯纤维对膨胀土进行改性。通过直剪试验计算出不同围压、不同聚丙烯纤维掺量改性膨胀土边坡的抗剪强度变化规律,并应用Geostudio软件中的极限平衡法对不同聚丙烯纤维掺量的膨胀土边坡进行分析。研究发现,聚丙烯纤维含量在一定范围内可有效提高膨胀土边坡抗剪强度,掺量0.14%的纤维土在直剪试验中表现出较好的抗剪性能,Geostudio极限平衡法分析结果显示,0.14%纤维土边坡稳定系数为2.431,较素膨胀土边坡稳定性系数提高0.591。建议采用掺量0.14%的纤维土加固膨胀土边坡。

基于荷载扰动深度的矿山采动场地稳定性分析

荷载扰动下的安全临界深度作为判别矿山采动场地稳定性的关键指标,对矿山地质安全与变形控制具有重要指导意义。采用极限平衡法分析壁式开采采空区破裂岩体自然平衡应力拱结构特征,利用角点法计算矩形均布荷载作用下地基中附加应力影响深度,推导了地下开采工作面与上方荷载扰动下的临界深度计算公式。以山东省济宁市某矿山采动场地稳定性评价为工程实例的研究结果表明:顾及上覆荷载附加应力的采空区活化的临界深度为159.5m,与采用开采条件判别法和地表移动变形判别法得到的场地稳定性评价结果一致。研究成果可为相似地质采矿条件下采空区破裂岩体结构特征分析与矿山安全地质危险性评价提供理论指导。

黄河茨哈峡导流洞进口边坡稳定性综合评价及处置优化

复杂地质条件下边坡稳定性受结构面、岩体性质等因素影响明显,其准确评价对边坡施工安全至关重要。依托黄河茨哈峡导流洞进口边坡施工工程,提出了一套综合赤平投影理论、二维极限平衡法与三维极限平衡法的边坡稳定性综合评价方法。首先基于赤平投影理论定性地描述了具有复杂结构面的导流洞进口边坡4#倾倒体失稳块体;随后分别采用二维极限平衡法与三维极限平衡法对施工期逐层开挖过程诱发边坡失稳风险进行了分析;最后根据“少开挖+强支护”的设计原则,从多方法综合评价和循环优化的角度,提出将原破碎体全部挖除的大开挖方案优化为保留部分破碎体的小开挖方案,并从安全性与经济性的角度对优化方案进行了评价。计算结果表明大开挖方案边坡稳定性安全系数约为1.17~1.19,小开挖方案安全系数约为1.078,大开挖方案边坡安全性高于小开挖方案;在对小开挖方案进行支护优化后边坡稳定性安全系数提高至1.159~1.183,边坡稳定性由临界稳定变为稳定,支护优化效果显著。综合边坡开挖安全性与经济性评价结果可见,所提“少开挖+强支护”边坡开挖方案符合相关规范安全控制标准,具有较好的经济效益与工程价值,可为相关工程提供参考。

大型高拱坝嵌深对坝肩块体稳定性的影响分析

结合古学拱坝坝肩不同嵌深设计方案,利用刚体和有限元极限平衡法,对坝肩块体进行稳定性分析,研究了高拱坝嵌深变化对坝肩块体稳定性的影响规律。结果表明,拱坝嵌深的增加会产生块体体积、滑面面积减小和拱推力增加两种效应,分别增加和降低块体稳定性,因此坝肩块体抗滑稳定安全系数随嵌深增加呈现出持续增大、持续减小、先增后减、先减后增4类变化趋势。经比选,推荐古学拱坝采用左岸嵌深36.5m、右岸嵌深40.5m的中嵌深方案。

Seismic passive earth resistance using modified pseudo-dynamic method

In earthquake prone areas, understanding of the seismic passive earth resistance is very important for the design of different geotechnical earth retaining structures. In this study, the limit equilibrium method is used for estimation of critical seismic passive earth resistance for an inclined wall supporting horizontal cohesionless backfill. A composite failure surface is considered in the present analysis. Seismic forces are computed assuming the backfill soil as a viscoelastic material overlying a rigid stratum and the rigid stratum is subjected to a harmonic shaking. The present method satisfies the boundary conditions. The amplification of acceleration depends on the properties of the backfill soil and on the characteristics of the input motion. The acceleration distribution along the depth of the backfill is found to be nonlinear in nature. The present study shows that the horizontal and vertical acceleration distribution in the backfill soil is not always in-phase for the critical value of the seismic passive earth pressure coefficient. The effect of different parameters on the seismic passive earth pressure is studied in detail. A comparison of the present method with other theories is also presented, which shows the merits of the present study.

石头梅一号露天煤矿南排土场扩容方案及稳定性研究

为了减少露天煤矿外排运输距离和减少土地占用,以石头梅一号露天煤矿南外排土场为工程背景,通过理论分析和数值模拟的方法对外排土场的扩容方案和稳定性就行了研究。通过理论分析基底极限承载能力,采用普朗特尔-赖斯公式计算出排土场最大高度为134 m;采用Bishop法分析分析排土场边坡的稳定性,得出排土场边坡稳定系数随单台阶高度的增加逐渐降低,优化后的单台阶高度为30 m;排土场稳定系数随着帮坡角的增加急剧降低,优化后的帮坡角为21°。

里底水电站库区巴迪滑坡蓄水前后稳定性评价

针对澜沧江上游里底水电站库区右岸的巴迪滑坡,分析其成因机制为倾倒型蠕滑变形,利用极限平衡法计算水库蓄水前后滑坡稳定性。结果表明:水库蓄水前,滑坡整体各工况下均处于稳定状态;蓄水后,滑坡在天然及暴雨工况下整体仍为稳定状态,但暴雨及地震工况下滑坡体前缘稳定性较差。对该滑坡蓄水后进行设备监测得滑坡体地下水位上升、变形速率最大时段为水库蓄水后10个月里,此后呈蠕变状态。滑坡体破坏形式为前缘陡坡地段(高程1885.00~1900.00 m)片状塌岸,前缘部位整体下滑的可能性很小。