基于内外功率比的非直线坡面型边坡的稳定系数研究

在边坡稳定性上极限分析中, 由于考虑了材料的理想弹塑性本构关系与相关流动法则, 相比极限平衡法更符合岩土材料的特征。在以往的二维边坡极限分析上限法中, 要求坡面形态为规则的直线, 而无论是天然边坡还是人工边坡, 边坡的坡面形态往往并非规则的直线。此外, 以往的边坡极限上限分析中得到的稳定数N_s=c/γH主要针对土坡的临界高度计算, 且未考虑孔压等外力对边坡施加的外功率。不同于传统极限平衡法采用静力学的平衡条件, 本研究针对非直线型坡面边坡稳定性问题, 假定滑动面为对数螺旋线, 基于极限分析上限定理和虚功原理, 提出了一种边坡发生旋转破坏时旋转中心的确定方法, 推导出了非直线型坡面边坡的重力虚功功率和能量平衡方程的解析解, 并提出了基于内、外功率之比的稳定系数K用以评价边坡的稳定性。通过算例比较了不同形态天然边坡的稳定性和人工削坡对边坡稳定性的影响, 并分析了边坡的坡度(β)、土体的内摩擦角(φ)、黏聚力(c)以及孔压系数(r_u)对稳定系数K的影响规律。对于坡度较大的边坡, 通过削坡改变坡面形态提高了边坡的稳定系数K。稳定系数K随黏聚力的增加而非线性增大, 随孔压系数的增加而降低。当黏聚力相对于孔压系数对边坡稳定性影响更大时, 稳定系数K随内摩擦角的增加而增大; 反之, 稳定系数K则随内摩擦角的增加而减小。以上结果符合对边坡稳定性分析的普遍认知, 验证了模型的合理性。另外, 通过将该方法与传统的Bishop法的计算结果进行对比, 发现安全系数F_s=1与稳定系数K=0的临界状态物理意义相同, 稳定系数K随黏聚力非线性增加, 更符合边坡的渐进破坏过程。      

极限平衡方法在夏日哈木镍钴矿山拟建露天采场边坡角优化中的应用

夏日哈木镍钴矿为大型镍钴硫化物矿床,现拟建大型露天采场,边坡采用分台阶式高边坡,最高边坡高度超过600m。该工程具有开挖成本高,边坡一但失稳后果严重的特点。为此需要选择一个即节约经济成本又保障整体边坡稳定的最佳边坡角。本文采取Geostudio软件中的Slope模块极限平衡方法对拟建露天采场假设开挖边坡角的整体边坡稳定性进行分析,提出最佳设计边坡角。　本次边坡角优化的思路：首先根据场地工程地质条件和拟建边坡的高度等因素将拟建边坡划分为5个区,选择典型边坡工程地质剖面并进行工程地质岩体分段,然后通过岩石强度指标折减计算（本文采用费辛柯法、M.Georgi法和经验法）给各分段的岩体赋予凝聚力、内摩擦角等计算参数,采用极限平衡方法（Geostudio软件中的Slope模块法）对不同角度下对各分区边坡的破坏形式及安全系数进行计算,最后提出了各分区边坡的最佳设计边坡角。     

基于最短折减路径法的边坡安全系数研究

使用双参数折减方法分析边坡稳定性的研究较多, 如何把两个折减系数定义为单一的综合安全系数是目前研究的一项重要内容。Isakov提出的最短折减路径法能够保证在不同工况下得到最小安全系数, 但是该方法的缺点在于计算复杂, 不适合工程应用。通过有限元数值模拟, 利用最短折减路径方法计算不同强度黏土构成的不同坡度均质土坡的最小安全系数和对应的折减系数, 探索了最小安全系数与土的初始黏聚力、内摩擦角以及边坡坡度的关系, 分析了初始强度对折减系数的影响。结果表明, 相同坡度下不同强度的黏土边坡在失稳时, 最小安全系数对应的临界破坏强度相同。临界破坏强度与坡度近似成线性正相关关系。由此基于最短折减路径法提出了一种新的计算最小安全系数的方法, 该方法得到的安全系数与目前常用的极限平衡方法所得结果相近, 并且计算简单, 因此可以用于边坡稳定性分析。      

平面剪切岩质边坡滑裂面的确定及稳定性分析

由于传统搜索方法对岩质边坡滑裂面的确定无法兼顾效率与精度, 如何迅速准确确定潜在滑裂面仍然是个难题。极限平衡法在岩质边坡稳定性分析中备受认可, 采用岩质边坡平面剪切滑动模型, 以滑裂面的倾角来表征潜在滑裂面的位置; 基于极值法, 推导了极限平衡条件下平面剪切破坏型岩质边坡潜在滑裂面的解析解, 并结合香港秀茂坪路边坡对其准确性进行了验证, 进一步对四川宜宾打营盘山公路多级边坡进行了整体稳定性分析。结果表明: 香港秀茂坪边坡采用本文方法确定的边坡潜在滑裂面倾角与实际滑坡倾角基本一致。实际工程应用中, 采用Slide软件中布谷鸟搜索法和模拟退火法两种搜索方法得到的滑裂面倾角分别为38.0°和37.0°, 本解析法所得倾角为34.8°; 选用Janbu法、Morgenstern-Price法和Sarma法分别计算对应的稳定系数, 结果均为1.04左右, 本文所得稳定系数为1.15, 可见本文方法所得结果基本准确。通过参数敏感性分析发现, 随着黏聚力的增加, 边坡滑裂面倾角越来越小, 稳定系数也随之增加; 而当内摩擦角增大时, 边坡滑裂面倾角和稳定系数也随之增大。      

京广铁路K1219路基土质边坡深层滑移失稳机制与整治对策

为研究土质边坡深层滑移失稳机制, 以京广铁路下行线K1219+000处路基边坡失稳为例, 通过现场调查测绘、工程地质钻探、原位试验和室内试验、深部位移监测和数值模拟等手段, 详细研究了该土质边坡变形破坏特征、地质力学过程和失稳模式。结果表明: 路基边坡表面裂缝宽度及深度呈坡顶至坡脚逐渐变浅变窄, 变形具有一定的旋转性, 牵引式特征明显, 属于深层滑移拉裂式失稳; 土质边坡经历了因坡脚开挖、抽水引起的应力场和渗流场重新分布阶段、雨水入渗软化导致下滑力不断增大而滑面逐渐迁移扩大加深阶段以及支挡结构抗力失效阶段3个地质力学过程, 其失稳模式包括浅层滑移、浅层滑面向深层迁移、动荷载触发深层滑移失稳3个阶段。在此基础上, 综合确定了滑面位置, 并通过反演方法确定了滑面力学参数。研究采用了刚架式双排抗滑桩的整治方案, 通过理论计算和数值分析, 边坡变形与抗滑桩变形基本一致, 且与监测结果整体吻合, 这表明土质边坡深层失稳理论分析准确且计算的力学参数科学, 整治对策稳妥、可靠。      

三维坐标变换算法的比较

通过模拟数据,从计算精度、稳定性、计算效率、左右手坐标系之间变换的适用性等4个方面比较三维坐标变换的迭代法和解析法。结果表明,迭代法中的正交矩阵形式计算精度最高,各种算法对退化到平面上的对应点集均具有适应性,解析法中的单位四元数法计算效率最高,迭代法中的正交矩阵形式以及解析法中的SVD分解法和正交矩阵解法都能够用于左右手坐标系之间的变换。     

基于灰色关联分析法的边坡敏感性分析

综合考虑边坡坡高、角度、岩土体黏聚力、摩擦角和容重等因素对边坡稳定性的影响,通过有限单元应力法建立数值模
型,进行应力分析,最后计算得到边坡安全系数,这一方法将数值分析和极限平衡方法有机地融合在一起,达到优势互补的效果;
然后基于灰色关联分析法对有限单元应力法得到的数据建立数学模型,对各影响因素与安全系数进行关联分析,最后得到各影响
因素对边坡稳定性影响的敏感性。结果表明:影响边坡稳定性的因素敏感性依次为黏聚力、容重、摩擦角、边坡角度和坡高。利用
敏感性分析结果,可对边坡加固位置提出设计改进,将有限的加固措施加于敏感性较高的位置,能够更有效地提高边坡的稳定性。      

西安白鹿塬北缘黄土边坡稳定的可靠度分析

在西安白鹿塬北缘实测了14个黄土自然边坡断面,建立了地质模型,通过采样测试并收集已有的测试资料,获得了各时代黄土地层的物理力学参数,将Morgenstern-Price法稳定性计算公式作为极限状态方程,分别采用Monte-Carlo法和Duncan法进行了边坡稳定的可靠度分析。结果表明:采用Monte-Carlo法和Duncan法得到的14个边坡稳定系数分别为1.11～1.41和1.09～1.33,显示这些边坡处于基本稳定—稳定状态;采用上述两种方法得到的边坡可靠指标分别为0.56～1.79和0.39～1.60,得到的失效概率分别为3.4%～29.0%和5.5%～34.8%,并且共有75%的边坡失效概率大于10%,失效可能性较大。统计结果表明:白鹿塬区边坡的坡高和坡度存在负相关性。低而陡的边坡潜在最危险滑面剪出口较高,失效概率较小;坡高达到50m及以上时,边坡高而缓,剪出口较低,失效概率较大,其中河流下切深,有N2泥岩出露的极高边坡,稳定性最差。Duncan法求解的稳定系数略小于Monte-Carlo法求得的结果,而前者求解的失效概率略大于后者,两种方法计算结果较为接近。由于Duncan法理论简单,计算量小,更宜于在实际工程中应用。     

一种考虑波动效应的拟动力地震边坡稳定性分析方法

考虑地震波在坡体内的传播特征,基于拟动力法,结合传统静力边坡稳定性分析极限平衡法(瑞典条分法),推导了边坡地震力公式和地震边坡稳定性安全系数公式。在此基础上,借助MATLAB软件开发了最危险滑面搜索和安全系数求解程序,实现了一种考虑波动效应的拟动力地震边坡稳定性分析方法。通过探讨地震动特性对地震边坡稳定性的影响,得到了地震边坡稳定性安全系数随地震动参数的变化规律。对于既定边坡,其安全系数随地震波初始相位呈现周期性波动变化,存在最小安全系数;并且此安全系数随地震系数和地震波波长与边坡坡高比的增大而减小。此外,从波动理论角度揭示了拟动力法与拟静力法的区别与联系,给出了两类方法的适用范围:当地震波波长与边坡坡高比大于10时,两类方法所得结果基本一致,均适用;而当地震波波长与边坡坡高比小于10时,拟静力法所得结果较拟动力法相对保守,仅拟动力法适用。     

物质点强度折减法边坡失稳判据选择方法

用物质点强度折减法求解边坡安全系数时, 需要选择一定的失稳判据, 而采用不同的失稳判据获得的安全系数通常存在一定差异。为此, 采用物质点强度折减法对两个边坡算例进行了稳定性分析, 对比研究了文献中常用的4种边坡失稳判据(计算不收敛、特征点位移突变、塑性应变贯通及界限值判据)在计算边坡安全系数时的合理性及适用性。同时, 将Spencer极限平衡法获得的安全系数作为参考, 进一步验证了结果的合理性与准确性。结果表明: ①数值计算的收敛性不能作为边坡失稳判据; ②将特征点位移突变视为边坡失稳判据时, 获得的安全系数与极限平衡法获得的结果基本一致, 故特征点位移突变可以作为边坡失稳判据; ③塑性应变贯通和边坡最大位移随迭代时间步趋于稳定的界限值不宜单独作为边坡失稳判据。      

A new method for the stability analysis of geosynthetic-reinforced slopes

This paper is concerned with the stability analysis of reinforced slopes. A new approach based on the limit equilibrium principle is proposed to evaluate the stability of the reinforced slopes. The effect of reinforcement is modeled as an equivalent restoring force acting the bottom of the slice and added into the general limit equilibrium (GLE) method. The equations of force and moment equilibrium of the slice are derived and corresponding iterative solution methods are provided. The new method can satisfy both the force and the moment equilibrium and be applicable to the critical failure surface of arbitrary form. Furthermore, the results predicted by the proposed method are compared with the calculation examples of other researchers and the centrifuge model test results to validate its correctness and effectiveness.     

Seismic stability analysis of slopes with pre-existing slip surfaces

In analyzing seismic stability of a slope with upper bound limit analysis method, the slip surface is often assumed as a log-spiral or plane slip surface. However, due to the presence of a weak layer and unfavorable geological structural surface or a bedrock interface with overlying soft strata, the preexisting slip surface of the slope may be irregular and composed of a series of planes rather than strictly log-spiral or plane shape. A computational model is developed for analyzing the seismic stability of slopes with pre-existing slip surfaces. This model is based on the upper bound limit analysis method and can consider the effect of anchor bolts. The soil or rock is deemed to follow the Mohr-Coulomb yield criterion. The slope is divided into multiple block elements along the slip surface. According to the displacement compatibility and the associated flow rule, a kinematic velocity field of the slope can be obtained computationally. The proposed model allows not only calculation of the rate of external work owing to the combined effect of self-weight and seismic loading, but also that of the energy dissipation rate caused by the slip surface, interfaces of block elements and anchorage effect of the anchors. Considering a direct relationship between the rate of external work and the energy dissipation rate, the expressions of yield acceleration and permanent displacement of anchored slopes can be derived. Finally, the validity of this proposed model is illustrated by analysis on three typical slopes. The results showed that the proposed model is more easily formulated and does not need to solve complex equations or time consuming iterations compared with previous methods based on the conditions of force equilibrium.     

Stability of submarine slopes in the northern South China Sea: a numerical approach

Submarine landslides occur frequently on most continental margins. They are effective mechanisms of sediment transfer but also a geological hazard to seafloor installations. In this paper, submarine slope stability is evaluated using a 2D limit equilibrium method. Considerations of slope, sediment, and triggering force on the factor of safety (FOS) were calculated in drained and undrained (Φ=0) cases. Results show that submarine slopes are stable when the slope is <16° under static conditions and without a weak interlayer. With a weak interlayer, slopes are stable at <18° in the drained case and at <9° in the undrained case. Earthquake loading can drastically reduce the shear strength of sediment with increased pore water pressure. The slope became unstable at >13° with earthquake peak ground acceleration (PGA) of 0.5 g; whereas with a weak layer, a PGA of 0.2 g could trigger instability at slopes >10°, and >3° for PGA of 0.5 g. The northern slope of the South China Sea is geomorphologically stable under static conditions. However, because of the possibility of high PGA at the eastern margin of the South China Sea, submarine slides are likely on the Taiwan Bank slope and eastern part of the Dongsha slope. Therefore, submarine slides recognized in seismic profiles on the Taiwan Bank slope would be triggered by an earthquake, the most important factor for triggering submarine slides on the northern slope of the South China Sea. Considering the distribution of PGA, we consider the northern slope of the South China Sea to be stable, excluding the Taiwan Bank slope, which is tectonically active.     

High slope stability of diversion power system intake of Jinchuan hydropower station

The excavated height of the left bank slope of the diversion power system intake in Jinchuan hydropower station is about 16o m. The stability and safety of the slope during construction and its operation/utilization become one of the most important geological engineering problems. At the same time, it is also crucial to select a safe and economic excavation gradient for the construction. We studied the problem of how to select a safe and economic slope ratio by analyzing the geological condition of the high slope, including the lithology, slope structure, structural surface and their combinations, rock weathering and unloading, hydrology, and the natural gradient. The study results showed that the use of an excavation gradient larger than the gradient observed during site investigation and the gradient recommended in standards and field practice manuals is feasible. Then, we used the finite element method and rigid limit equilibrium method to evaluate the stability of the excavation slope under natural, rainstorm and earthquake conditions. The calculated results showed that the excavated slope only has limited failure, but its stability is greatly satisfactory. The research findings can be useful in excavation and slope stabilization projects.     

ADI BAROTROPIC OCEAN MODEL FOR SIMULATON OF KUROSHIO INTRUSION INTO CHINA SOUTHEASTERN WATERS

In this numerical model for simulating the Kuroshio intrusion into the East and South China Seas,vertically averaged marine hydrodynamic equations governing ocean currents and long-period waves areapproximated by a set of two-time-level semi-implicit finite difference equations. The major terms in-cluding the local acceleration, sea-surface slope, Coriolis force and the bottom friction are approxi-mated with the Crank-Nicholson scheme, which is of second order accuracy. The advection terms are app-roximated with the Leith scheme. The difference equations are split into two sets of alternating directionimplicit quations, each of which has a tridiagonal matrix and can be easily solved. The model reproduces a major Kuroshio intrusion north of Luzon Island, one north of Taiwan Island, andone west of the Tokara Strait. The model shows a current system running from the Luzon Strait to the coastof Vietnam and Hainan Island, through the Taiwan Strait and then into the Tsushima Strait. The summerand winter monso     

ADI barotropic ocean model for simulation of Kuroshio intrusion into China southeastern waters

In this numerical model for simulating the Kuroshio intrusion into the East and South China Seas, vertically averaged marine hydrodynamic equations governing ocean currents and long-period waves are approximated by a set of two-time-level semi-implicit fimite difference equations. The major terms including the local acoeleration, sea-surface slope, Coriolis force and the bottom friction are approximated with the Crank-Nicholson scheme, which is of second order accuracy. The advection terms are approximated with the Leith scheme. The difference equations are split into two sets of alternating direction implicit equations, each of which has a tridiagonal matrix and can be easily solved. The model reproduces a major Kuroshio intrusion north of Luzon Island, one north of Taiwan Island, and one west of the Tokara Strait. The model shows a current system running from the Luzon Strait to the coast of Vietnam and Hainan Island, through the Taiwan Strait and then into the Tsushima Strait. The summer and winter monsoons generate several eddies in the South China Sea. Project supported by the National Natural Science Foundation of China.     

A force transfer mechanism for triggering landslides during rainfall infiltration

Shallow slope failures induced by rainfall infiltration occur frequently, and the relevant triggering mechanisms have been widely studied.Rainfall-induced landslides are widely recognized to be caused by increases in soil weight, seepage force and pore water pressure or decreases in soil mechanical properties. However, even when all these factors are considered, some landslides still cannot be explained well. The increased pore water pressure in a slope reduces the effective stress of the soil and may trigger slope failure. Similarly, the pore gas pressure in a slope also reduces the effective stress of the soil but has been neglected in previous studies. As the viscosity of air is nearly negligible when compared with that of water, the pore gas pressure spreads faster, and its influence is wider, which is harmful for the stability of the slope. In this paper, the effects of pore gas pressure are considered in a shallow slope stability analysis, and a self-designed experiment is conducted to validate the force transfer mechanism.Numerical simulation results show that the pore gas pressure in the slope increases sharply at different locations under heavy rainfall conditions and that the pore gas pressure causes a rapid decrease in the slope safety factor. Laboratory experimental results show that the pore gas pressure throughout the whole unsaturated zone has the same value, which indicates that the gas pressure could spread quickly to the whole sample.     

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岩质边坡非饱和带水汽运移机制及其生态学意义

岩质边坡非饱和带水分对于边坡植物生长具有重要的生态学意义.目前对岩质边坡非饱和带水汽运移的系统性研究还很少,现有研究大部分集中在大气与岩体的接触面和凝结水能否生成的定性层面,而未将边坡非饱和带作为一个系统整体来研究.为了阐明岩质边坡非饱和带的水汽运移机制及其与边坡植物生长之间的关系,运用热力学和系统科学的理论,开展边坡温湿度监测试验,进行了详细的水汽运移机制的研究.研究发现,岩质边坡非饱和带内的水汽运移驱动力为水汽分压梯度,水汽从水汽分压大的位置向水汽分压小的位置运移.冬季时,水汽从边坡深部向浅部运移,夏季时,水汽从大气向边坡深部运移.岩质边坡非饱和带内存在水汽饱和带,夏季范围较大,冬季范围收缩.同时,通过对岩质边坡复绿植物的成活率进行监测分析,论述了岩质边坡非饱和带内的水汽内循环机制及其生态学意义.本文对于研究岩体非饱和带水文学、探索植物水分来源、指导岩质边坡复绿乃至干旱半干旱带的生态修复都有极为重要的理论和现实意义.