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.     

基于物理模型试验的滑坡-抗滑桩位移场变化特征

滑坡-抗滑桩体系演化机理是滑坡灾害防治的重要理论基础,其中桩土相互作用是滑坡-抗滑桩体系中的关键,而位移场是相互作用的重要表征之一,因此,对滑坡-抗滑桩体系位移场的研究具有十分重要的工程意义。以物理模型试验为手段,基于三峡库区堆积层滑坡工程地质特征,建立大型物理试验模型,通过逐级施加荷载来模拟滑坡后缘推力,采用高速摄像机及粒子图像测速技术等获取滑坡坡表与桩顶位移数据,定量分析了体系位移场变化特征。试验结果显示:在滑坡-抗滑桩体系演化过程中,坡表位移场变化呈现出很好的规律性,这为桩土相互作用研究机理起到了一定的推动作用。      

土压力滑楔理论的统一解

基于滑楔理论计算土压力的基本原理,运用考虑中间主应力效应的统一强度理论,对传统的土压力公式不能反映土体材料强度的中间主应力效应的公式进行了改进,推导了基于滑楔理论的土压力统一解公式,Coulomb和Rankine土压力公式为其特例.通过变换统一强度参数,可获得一系列的解.在工程运用中可根据土质和工程的实际情况,适当选择统一强度参数和应力状态来确定土压力的大小.     

Improved plane layout of stabilizing piles based on the piecewise function expression of the irregular driving force

The paper presents an improved plane layout for stabilizing piles based on a proposed piecewise function expression for the irregular driving force. Based on the specific morphological characteristics of a highway landslide, the piecewise function is used to calculate the irregular driving force by dividing the landslide into several sub-areas. Furthermore, the reasonable layout range and pile spacing can be obtained based on the piecewise function expression of the irregular driving force and on relevant research results of the plane layout for stabilizing piles. Therefore, an improved plane layout of stabilizing piles is presented in consideration of a piecewise function expression of the irregular driving force. A highway landslide located in eastern Guizhou Province, China, is analyzed as a case study using the proposed method. The results demonstrate that the theory presented in this paper provides improved economic benefits and can reduce the required number of stabilizing piles by 28.6% compared with the conventional plane layout scheme.     

Active earth pressure acting on retaining wall considering anisotropic seepage effect

This paper presents a general solution for active earth pressure acting on a vertical retaining wall with a drainage system along the soil-structure interface. The backfill has a horizontal surface and is composed of cohesionless and fully saturated sand with anisotropic permeability along the vertical and horizontal directions. The extremely unfavourable seepage flow on the back of the retaining wall due to heavy rainfall or other causes will dramatically increase the active earth pressure acting on the retaining walls, increasing the probability of instability. In this paper, an analytical solution to the Laplace differential governing equation is presented for seepage problems considering anisotropic permeability based on Fourier series expansion method. A good correlation is observed between this and the seepage forces along a planar surface generated via finite element analysis. The active earth pressure is calculated using Coulomb’s earth pressure theory based on the calculated pore water pressures. The obtained solutions can be degenerated into Coulomb’s formula when no seepage exists in the backfill. A parametric study on the influence of the degree of anisotropy in seepage flow on the distribution of active earth pressure behind the wall is conducted by varying ratios of permeability coefficients in the vertical and horizontal directions, showing that anisotropic seepage flow has a prominent impact on active earth pressure distribution. Other factors such as effective internal friction angle of soils and soil/wall friction conditions are also considered.     

上硬下软地层中h型桩与滑坡相互作用机理模型试验研究

组合式抗滑桩是加固大型滑坡的有效防护措施,但上硬下软等复合地层中h型抗滑桩的加固机理仍有待深入研究。基于一套自主研发的上硬下软地层滑坡-h型抗滑桩物理模型试验装置,综合应力应变监测、激光测距仪、高速相机与粒子图像测速(PIV)技术研究了上硬下软地层滑坡中h型桩的位移、内力响应规律与滑体变形破坏特征,揭示了上硬下软地层条件下h型桩与滑坡相互作用机理。研究结果表明,在坡顶荷载逐渐增加的条件下,h型桩加固的上硬下软地层滑坡的演化阶段可划分为蠕变阶段、匀速变形阶段、加速变形阶段和破坏阶段4个阶段。受连系梁影响,前排桩与后排桩桩顶位移较小,应变最大值出现在靠近滑面深度处;后排桩弯矩呈“S”型分布,前排桩弯矩呈三角形分布,负弯矩最大值位于连系梁下方20 cm处。随着硬岩体积分数(φ_B)增加,桩顶位移逐渐减小,前、后排桩最大弯矩值也逐渐减小,但硬岩体积分数超过60%后最大弯矩值变化幅度较小。当φ_B=20%和40%时,后排桩土压力总体呈抛物线形式;当φ_B=60%和80%时,土压力总体呈反“S”型,且滑面附近出现第二个土压力峰值;前排桩土...     

外基坑宽度对坑中坑条件下被动土压力的影响

工程实践表明, 外基坑宽度和坑中坑会影响基坑坑底滑裂面的形成方式, 因此, 经典朗肯土压力理论的假设建立在半无限空间土体的基础上不再适用。基于极限平衡理论和微分体受力平衡方法, 考虑土体黏聚力和围护结构与滑动土体摩阻力, 推导了宽基坑和窄基坑坑中坑的被动土压力理论计算公式。通过具体算例对比了宽基坑与窄基坑在坑中坑条件下被动土压力大小的变化趋势。结果表明, 考虑摩擦力条件下的被动土压力大于未考虑摩擦力的被动土压力; 无论宽基坑还是窄基坑, 有内坑的被动土压力小于无内坑时的被动土压力; 无内坑时, 外基坑宽度的增加导致被动土压力减小, 而在有内坑的情况下, 外基坑宽度的增加, 反而增大被动土压力; 在窄基坑中, 随着内坑位置的移动, 土压力先变小后增大, 且内坑平面尺寸的增大导致土压力逐渐减小。因此, 内坑的存在将降低坑中坑基坑的外坑被动土压力, 工程中应注意内坑的存在。      

Time history of seismic earth pressure response from gravity retaining wall based on energy dissipation

The seismic design of gravity retaining walls is based mostly on the pseudo static method.The seismic earth pressure is assumed to be a constant without conside...     

基于断裂力学的煤层气井破裂压力计算方法

为了提高煤层气井破裂压力预测精度,运用断裂力学理论推导裂缝性地层破裂压力计算公式,结合分形岩石力学理论建立裂缝性地层破裂压力解析模型,提出一种实用的破裂压力计算方法.结果表明:在非均匀地应力下,煤岩井壁更易沿最大水平主应力方向起裂,解析模型与传统模型在表达形式上具有统一性和更广泛的适用性.煤岩裂缝具有分形特征,分形效应提高岩石阻碍裂缝扩展的能力,当分形维数越大、相似比越小时破裂压力越大.在不同裂缝状态下,缝长对破裂压力的影响规律不同,当裂缝长度较小时破裂压力随裂缝长度增加而迅速减小;当裂缝长度增加到一定数值后,闭合裂缝破裂压力随缝长增加而增大,开启裂缝破裂压力随缝长增加而减小并趋于定值.郑庄地区5口煤层气井实例计算表明:该计算方法预测的破裂压力误差在10%以内,破裂压力对缝长变化特别敏感,合理确定裂缝长度对准确预测破裂压力尤为重要.     

Estimation of earth pressure against retaining walls with different limited displacement modes based on elastic theory

The earth pressure acting on retaining walls due to creep and consolidation is under limited equilibrium conditions (limited displacement).Linear elastic consti...     

Finite element analysis on impact of foundation treatment in bridgehead transition section upon bridge piles

In order to decrease relative settlement, foundation treatment plays an extremely important role in bridgehead transition section, especially, the situation of building the bridge piles firstly, and th...     

Research on method of pressure grouting piling of driven tube

The pressure grouting pile of driven tube can improve the load bearing capacity of the single pile from the mechanism of pressure grouting pile of driven tube. On the basis of analyzing the mechanism, the authors designed the machines and tools of pressure grouting, determined the operating manufacture and technology parameter on the pressure grouting secondly. The result shows that the pressure grouting pile of driven tube not only changes the pile type but also reduce the length of the pile and its engineering cost, it enhances the load bearing capacity of single pile an the same time.     

Research on method of pressure grouting piling of driven tube

The pressure grouting pile of driven tube can improve the load bearing capacity of the single pile from the mechanism of pressure grouting pile of driven tube.On the basis of analyzing the mechanism,the authors designed the machines and tools of pressure grouting,determined the operating manufacture and technology parameter on the pressure grouting secondly.The result shows that the pressure grouting pile of driven tube not only changes the pile type but also reduce the length of the pile and its engineering cost,it enhances the load bearing capacity of single pile an the same time.     

Improvement of pseudo-static method for slope stability analysis

traditional In this paper, two drawbacks pseudo-static method （vertical of the slice method） in the slope stability evaluation have been studied. First, the sliding mass is divided into vertical slices according to this method, which is irrational to some extent in the seismic design of slope. Second, only peak ground acceleration （PGA） is considered, and the effects of shaking frequency and duration on slope stability are neglected. And then, based on the theory of elastic wave and the summarized geological model, this paper put forwards an improved method of pseudo-method by using the theory of elastic wave and Hilbert-Huang transform. The improved pseudostatic method gives reasonable considerations to the time-frequency effects of seismic wave and its rationality has been verified by the shaking table test. This method can evaluate the safety of a slope, the happening time and the scale of landslides. At the same time, this method also can improve the high accuracy of the evaluation of the safety of the slope.     

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.     

基于Fisher判别分析法的岩溶塌陷预测

为了更准确地预测岩溶塌陷,基于Fisher判别分析法,首先选择内聚力、内摩擦角、覆盖层厚度、覆盖层厚度减高水位埋深、覆盖层厚度减低水位埋深5个最主要的影响因素作为判别因子;接着以桂林市20组岩溶塌陷案例为学习样本进行计算,建立相应的Fisher线性判别函数;然后利用回代估计法对上述20组样本的预测结果进行逐一检验,其正确率为100%;随后将上述预测结果与前人运用逐步判别、神经网络判别等方法得到的结果进行比较分析,认为Fisher判别分析法具有不需进行模型和参数的选择以及不受人为因素的影响等优点;最后将建立的Fisher线性判别函数用于另外的10组实际案例进行预测分析,预测结果与实际情况完全吻合。结果表明:用Fisher判别分析法进行岩溶塌陷预测,简易方便,正确率高,实用性好;该方法是岩溶塌陷预测的一种新方法。     

Reliability analysis method applied in slope stability: slope prediction and forecast on stability analysis

Landslide is one kind of geologic hazards that often happens all over the world. It brings huge losses to human life and property; therefore, it is very important to research it. This study focused in combination between single and regional landslide, traditional slope stability analysis method and reliability analysis method. Meanwhile, methods of prediction of slopes and reliability analysis were discussed.     

Reliability analysis method applied in slope stability： slope prediction and forecast on stability analysis

Landslide is one kind of geologic hazards that often happens all over the world.It brings huge losses to human life and property;therefore,it is very important to research it.This study focused in combination between single and regional landslide,traditional slope stability analysis method and reliability analysis method.Meanwhile,methods of prediction of slopes and reliability analysis were discussed.     

基于粗糙集理论与响应面法的老黏土膨胀敏感性分析方法

评价老黏土膨胀性等级时出现的误差主要源于多因素在参数统计上的不确定性,对此提出老黏土膨胀敏感性分析方法。结合粗糙集理论分析各因素的敏感性并确立主导因素,进而构建老黏土膨胀性等级的多因素定量评价模型,随后通过响应面法,分析主导因素间参数不确定性的交互作用对评价结果的影响。襄阳城区老黏土研究表明,自由膨胀率和体缩率为影响评价结果的主导与次主导因素,二者参数变化产生的交互作用对膨胀性评价等级影响较显著。当体缩率统计值较大时,随着自由膨胀率的上升,膨胀性评价等级变幅较大,偏大的自由膨胀率将高估老黏土的膨胀性,致使评价过于保守,偏小的自由膨胀率则会对其低估,导致结果较不可信;而当体缩率统计值较小时,评价等级随自由膨胀率的上升变化不大,因此评价结果较为准确。所得结论可为老黏土膨胀性评价与分类工作提供参考。