A general method to calculate passive earth pressure on rigid retaining wall for all displacement modes

A general analytical method to calculate the passive rigid retaining wall pressure was deduced considering all displacement modes. First, the general displacement mode function was setup, then the hypotheses were made that the lateral passive pressure is linear to the corresponding horizontal displacement and the soil behind retaining wall is composed of a set of springs and ideal rigid plasticity body, the general analytical method was proposed to calculate the passive rigid retaining wall pressure based on Coulomb theory. The analytical results show that the resultant forces of the passive earth pressure are equal to those of Coulomb＇s theory, but the distribution of the passive pressure and the position of the resultant force depend on the passive displacement mode parameter, and the former is a parabolic function of the soil depth. The analytical results are also in good agreement with the experimental ones.

A modified logarithmic spiral method for determining passive earth pressure

In this study, a modified logarithmic spiral method is proposed to determine the passive earth pressure and failure surface of cohesionless sloping backfill, with presence of wallesoil interface friction. The proposed method is based on a limit equilibrium analysis wherein the assumed profile of the backfill failure surface is a composite of logarithmic spiral and its tangent. If the wallesoil interface is smooth, a straight line does not need to be assumed for the failure surface. The geometry of the failure surface is determined using the Mohr circle analysis of the soil. The resultant passive earth thrust is computed considering equilibrium of moments. The passive earth pressure coefficients are calculated with varied values of soil internal friction angle and cohesion, wall friction angle and inclination angle, and sloping backfill angle. This method is verified with the finite element method(FEM) by comparing the horizontal passive earth pressure and failure surface. The results agree well with other solutions, particularly with those obtained by the FEM. The implementation of the present method is efficient. The logarithmic spiral theory is rigorous and self-explanatory for the geotechnical engineer.

Limit state analysis of rigid retaining structures against seismically induced passive failure in heterogeneous soils

Soils are not necessarily uniform and may present linearly varied or layered characteristics,for example the backfilled soils behind rigid retaining walls.In the presence of large lateral thrust imposed by arch bridge,passive soil failure is possible.A reliable prediction of passive earth pressure for the design of such wall is challenging in complicated soil strata,when adopting the conventional limit analysis method.In order to overcome the challenge for generating a kinematically admissible velocity field and a statically allowable stress field,finite element method is incorporated into limit analysis,forming finiteelement upper-bound(FEUB)and finite-element lower-bound(FELB)methods.Pseudo-static,original and modified pseudo-dynamic approaches are adopted to represent seismic acceleration inputs.After generating feasible velocity and stress fields within discretized elements based on specific criteria,FEUB and FELB formulations of seismic passive earth pressure(coefficient K_(P))can be derived from work rate balance equation and stress equilibrium.Resorting to an interior point algorithm,optimal upper and lower bound solutions are obtained.The proposed FEUB and FELB procedures are well validated by limit equilibrium as well as lower-bound and kinematic analyses.Parametric studies are carried out to investigate the effects of influential factors on seismic K_(P).Notably,true solution of K_(P) is well estimated based on less than 5%difference between FEUB and FELB solutions under such complex scenarios.

Calculation of passive earth pressure of cohesive soil based on Culmann's method

Based on the sliding plane hypothesis of Coulumb earth pressure theory, a new method for calculation of the passive earth pressure of cohesive soil was constructed with Culmann＇s graphical construction. The influences of the cohesive force, adhesive force, and the fill surface form were considered in this method. In order to obtain the passive earth pressure and sliding plane angle, a program based on the sliding surface assumption was developed with the VB.NET programming language. The calculated results from this method were basically the same as those from the Rankine theory and Coulumb theory formulas. This method is conceptually clear, and the corresponding formulas given in this paper are simple and convenient for application when the fill surface form is complex.

Lateral Earth Pressure Coefficient and Lateral Earth Pressure against Retaining Walls

According the Coulomb earth pressure theory,it is obtained that,for normally consolidated soils,the lateral pressure coefficient of a soil at rest is equal to 1,and it is independent of the soil type,either granular or cohesive;or that the material is in a loose or compact state;hard or a soft cohesive soil.Also,a methodology to calculate the earth pressure for intermediate states between at rest condition and the active pressure is presented.In addition,a methodology to calculate the earth pressure for intermediate states between at rest condition and the passive pressure is presented.Two practical examples are presented:one for a frictionless wall;and another for a coarse wall.Practical recommendations are given for the use of the lateral earth pressure coefficient for different applications.

矿区采动区框架桥紧邻有限空间土体侧土压力试验研究

为揭示矿区采动区框架桥侧墙紧邻土体为有限宽度时侧土压力的分布规律,开展了墙体绕墙底转动(RB模式)下松砂非极限土压力试验。研究结果表明:RB模式下,加载墙体和被动受压墙体的侧土压力均呈凸曲线分布,且均随墙体深度的增加先增大后减小。墙体深度相同的条件下,侧土压力、侧土压力合力均随相对挤压位移的增大而增大。加载墙体和被动受压墙体的侧土压力三维分布均为凸曲面分布,但是侧土压力极值出现区域不同。在相对挤压位移相同的条件下,加载墙体的侧土压力合力大于受压墙体,侧土压力合力作用点高于受压墙体。

墙后填土倾斜时二次抛物线准则下粘土压力计算新解

在计算挡土墙土压力时,挡土墙后填土面往往具有一定的倾角,倾角的存在及其大小会显著影响挡土墙土压力的研究计算。本文基于粘土的二次抛物线型强度准则,对墙后填土的极限平衡状态进行分析,进而推导出墙后填土倾斜时粘土的主动土压力以及被动土压力计算新解。研究结果表明,墙后填土倾斜时粘土的土压力呈非线性分布。随着其抗拉强度的增大,墙后填土的主动土压力减小,被动土压力增大;随着墙后填土倾角的增大,其主动土压力减小,被动土压力减小。

采空区下沉盆地防积水淹没框架桥“桥上建桥”力学特性研究

为防止采空区下沉盆地框架桥被积水淹没,提出2种治理方案,采用ANSYS建立其有限元模型,研究不同土压力作用下框架桥“桥上建桥”的可行性。研究结果表明,①采空区下沉盆地压缩区原有框架桥随着侧土压力的增大,其合位移随之增大;②采空区下沉盆地压缩区原有框架桥随着侧土压力的增大,其第一主应力也随之增大;③极限被动土压力作用下,原有框架桥可采用加大截面法进行加固,但加大截面尺寸较大,不经济;④通过松动框架桥两侧土体,减小框架桥侧土压力,然后在其上续建新框架桥,形成组合框架桥,可以节省混凝土,更为经济。

考虑基坑坑内有限土体被动土压力研究

通过数据分析,定量研究了坑内是否考虑有限土体对基坑支护结构位移和弯矩等的影响,并根据极限平衡理论推导了坑内有限土体被动土压力的计算表达式,分析了土体黏聚力、土体内摩擦角、支护与土体间外摩擦角以及有限土体坡脚变化时坑内有限土体被动土压力的变化情况。研究结果表明:坑内有限土体在实际工程中不能仅作为安全储备,应充分考虑其有利作用;被动土压力会随着黏聚力、内摩擦角、外摩擦角和坡脚的增大而增大,土体的破裂角会随着内摩擦角、外摩擦角、坡脚的增大而减小;在黏聚力值相同的条件下,当坑内有限土体宽度与高度比值逐渐增大时,破裂角也逐渐增大;当坑内有限土体宽度与高度比值相同时,黏聚力越大,对应的破裂角也越大;当坑内有限土体宽度与高度比值>1.0后,随着比值的增大,黏聚力值越小,破裂角的增幅越大;当坑内有限土体宽度与高度比值>1.2时,可以将坑内有限土体视为无限土体,可按照经典土压力理论进行求解。

Vane Shear Footing-Integrated Rational Approach for Seismic Bearing Capacity of Foundations &Seismic Pressure

Structural buildings are subjected to huge cyclic powers during earthquakes. The structural failures during seismic events notably impact a variety of facets of buildings within tolerable levels like sustainable strength and stable energy dissipation capability to sustain inter-story drifts and overall structural damages. The major structural elements such as columns, beams and soil shearing capacities are majorly affected during seismic events. Buildings situated in the earthquake prone zone are exposed to most concerns in the structural design. Boreholes are also one of the main factors responsible for seismic waves and soil shearing. Shear strength is a term used in soil mechanics to describe the magnitude of the shear stress that soil can sustain, especially selected BC soil. The shear resistance of soil is a result of friction and interlocking of particles, and possibly cementation or bonding at particle contacts. Soils consist of individual particles that can slide and roll relative to one another. Shear strength of a soil is equal to the maximum value of shear stress that can be mobilized within a soil mass without failure taking place. In many parts of the world to avoid or control these consequences, buildings have been constructed as steel-composite structures. However, in India, buildings are being constructed as RCC framed structures. Here a novel combination of VANE shear footing and BRB method has been introduced. In this article, the effects of boreholes increase seismic bearing capacity of foundation, and load bearing capacity to balance seismic pressure.

土体呈梯形分布的光滑直立型挡土墙土压力理论

尝试性地建立梯形土体的土压力理论(包括主、被动土压力),挡土墙被简化为光滑直立型.通过算例的数值分析发现,梯形土体的土压力理论给出的主、被动土压力均小于等于经典土压力理论Rankine公式和Coulomb公式的主、被动土压力,其差值在地表附近为0,当深度有一定增加时会出现,并随深度的增加而变大,且该差值在被动土压力中表现得更明显.结果表明,与新建立的关于梯形土体的土压力理论相比,Rankine土压力理论和Coulomb土压力理论会在一定程度上高估梯形土体的主、被动土压力.

基坑开挖及桩基施工对围护结构变形的影响分析

以北京通州某深基坑工程为例,分析基坑开挖卸荷、基坑锚杆施工、基底CFG桩和抗拔桩施工对基坑围护结构和周边环境的影响。结果表明:基坑围护结构及基坑周边地表随着基坑的开挖、围护锚索和基坑内工程桩的施工出现典型的先上浮后沉降的趋势,应力重新分布现象明显。具体表现为基坑开挖卸荷初期引发围护结构及基坑周边地表上浮,随着基坑开挖深度的增加,在基坑侧向位移和基坑锚索竖向分力作用下,围护结构及基坑周边地表开始下沉;在基坑槽底施工CFG桩和抗拔桩削弱了护坡桩嵌固区被动土压力,基坑降水导致土体有效应力增加,产生附加固结沉降,在基坑地下水渗流的联合作用下,围护结构及基坑周边地表呈现二次加速下沉;基坑开挖和基础桩施工对桩顶水平位移和锚索轴力影响较小。根据分析结果,建议类似基坑增加嵌固深度、调整被动土压力区打桩顺序,将有利于围护结构及基坑周边环境变形控制。

水囊土压力计研制与试验验证研究

针对土压力盒易发生应力集中的问题,研制了水囊土压力计,即通过透明的PU空压软管将感压水囊与电子压力表进行连接,其中感压水囊的厚度可控制在5~10 mm,在使用时电子压力表的高度位置进行固定。将水囊土压力计与振弦式土压力盒埋设在不同压缩模量的土体中进行了对比试验,结果分析表明,由于感压水囊比土压力盒薄,虽然实测土压力偏大问题不可避免,但相对土压力盒测试结果而言,采用水囊土压力计测试地层中的土压力时应力集中问题显著改善;从测试结果可知,由测试元件厚度所导致的土压力偏大幅值为非线性,这与测试元件周围的土体颗粒变形调整有关。将水囊土压力计用于盾构隧道响应模型试验研究中,从测试结果可知,水囊土压力计与土压力盒的测试结果具有明显的不同;从测试结果的变化趋势分析来看,水囊土压力计的测试结果可信,且有必要采用水囊土压力计直接贴在模型盾构隧道外壁测试其周围土压力。水囊土压力计的测试原理简单,且成本低、精度高,因其为柔性构造,可根据测试需求选用感压水囊用于结构物表面为非平面的土压力测试。

软土地区临河基坑围护设计实践

以杭州某临河软土基坑为例,对基坑两侧土压力不平衡问题,采用增强围护体系整体刚度、坑底内加固及搅拌桩封堵墙软分坑等常规措施。临河侧坑外土压力采用主动土压力向被动土压力转化的计算方法,对回填土宽度确定进行了优化设计,取得了良好效果,可为后续临河基坑设计、施工提供参考依据。

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。

有限宽度砂土刚性挡墙被动土压力的离散元模拟及简化计算方法

为考虑砂土的应变软化效应及其有限宽度情况下墙后被动土压力计算,首先提出一种实用的砂土应变软化模型;在此基础上,采用极限平衡法简化求解了墙后有限填土被动土压力,并与离散元法(DEM)数值结果对比验证了该方法的有效性,还探讨了填土宽度和墙体位移对墙后有限填土被动土压力的影响。分析结果表明,有限砂土被动土压力计算中应考虑应变软化效应,尤其对于密实砂土;随着墙体位移和墙后填土宽度增加,被动土压力会减少。

基于双剪统一强度理论的挡土墙土压力计算

在工程实践中采用未考虑中间主应力对强度影响的经典的朗肯土压力理论来对挡土墙进行支护设计时往往存在误差较大的问题。文章基于双剪统一强度理论,将平面应变条件下的强度准则引入挡土墙土压力计算中,推导了基于双剪统一强度理论的挡土墙主动以及被动土压力计算新解。分析结果表明:中间主应力系数b对挡土墙的主动以及被动土压力值均有较大的影响,随着b值的增大,挡土墙主动土压力减小,墙后填土拉张区开裂深度增大,挡土墙被动土压力增大。因此,在工程应用中若能合理地考虑中间主应力对挡土墙土压力的影响,则会产生一定的经济效益。

论主动静止土压力、被动静止土压力与朗肯土压力计算公式的优化

通过对朗肯土压力理论和库仑土压力理论中的主动土压力、被动土压力与静止土压力之间的关系分析,指出现今的静止土压力并不是主动土压力与被动土压力之间的平衡土压力点。假设土层在各个方向都呈相同各向异性的前提下,分析主动土压力与被动土压力的定义,提出将挡土墙水平向不发生向外移动的最大水平向作用压力定义为主动静止土压力,填土竖直向不发生向上移动的最小水平向作用压力定义为被动静止土压力,挡土墙水平向不发生移动同时填土竖直向不发生移动的水平向作用压力定义为绝对静止土压力,并优化了二维应力状态下主动状态、被动状态与静止状态的应力圆。依据莫尔应力圆土体极限平衡理论优化了朗肯主动土压力与被动土压力计算公式,解决了朗肯土压力计算值与现实不相符的难题。通过举例计算主动土压力、被动土压力与主动静止土压力、被动静止土压力之间的关系,验证了作者优化的朗肯土压力计算公式的正确性。希望对理论土力学的发展有一定的推动作用。

刚性挡墙被动土压力模型试验研究

为了研究刚性挡墙被动土压力的形成机理 ,介绍了一个试验模型的制作 ,通过模型试验对砂土在不同变位情况 ,即墙体的平移 (T模式 )、绕墙顶上某点转动 (RTT模式 )和绕墙底下某点转动 (RBT模式 ) ,得出刚性挡墙被动土压力的试验结果 ,最后分析了不同变位条件下被动土压力的变化规律。

刚性挡土墙被动土压力数值分析

采用有限单元法对作用于刚性挡土墙上的被动土压力进行数值分析,土体采用弹塑性的Mohr-Coulomb本构模型,在土与结构接触面间引入无厚度的Goodman接触单元,接触面上剪应力和剪切位移采用弹塑性的本构模型,研究了不同的挡土墙的变位模式、不同墙面摩擦特性以及土体变形特性等因素对土压力大小和分布的影响。