A simple prediction model for wall deflection caused by braced excavation in clays

Deep excavations particularly in deep deposits of soft clay can cause excessive ground movements and result in damage to adjacent buildings. Extensive plane strain finite element analyses considering the small strain effect have been carried out to examine the wall deflections for excavations in soft clay deposits supported by retaining walls and bracing. The excavation geometry, soil strength and stiffness properties, and the wall stiffness were varied to study the wall deflection behavior. Based on these results, a simple Polynomial Regression (PR) model was developed for estimating the maximum wall deflection. Wall deflections computed by this method compare favorably with a number of field and published records.     

A simple estimation model for 3D braced excavation wall deflection

A series of two-dimensional (2D) and three-dimensional (3D) finite element analyses using the Hardening Soil (HS) model were carried out to investigate the influences of soil properties, wall stiffness, excavation length, excavation depth, clay thickness at the base of the excavation and wall embedment depth, on the maximum wall deflection induced by braced-excavation. The results show that the 3D maximum wall deflections are generally much smaller than those for 2D. Comparisons were also made with other commonly used semi-empirical charts. Based on the finite element results in this study, a simple wall deflection equation was developed for estimating the maximum wall deflection that takes the 3D effects into consideration through different ratios of excavation length over excavation width.     

软土地区深基坑连续墙最大变形简易计算方法

采用有限单元法研究了影响软土地区地下连续墙最大侧向变形的主要参数。针对基坑开挖深度H、基坑开挖宽度B、单位宽度地下连续墙系统刚度S、支撑结构的轴向刚度 及黏土归一化的不排水抗剪强度 为不排水抗剪强度, 为有效垂直应力）5个参数进行分析研究,通过回归分析研究结果,给出地下连续墙最大侧向变形的简易计算方法。利用简易计算方法,计算实际工程中基坑案例的地下连续墙最大侧向变形,并与现场监测结果进行对比,验证了计算方法的准确性,可为以后预估地下连续墙最大侧向变形及检查设计提供参考。     

内撑式支护的软土基坑开挖抗隆起稳定性分析

采用强度折减法有限元方法（SSRFEM）,分析了不排水条件下软土地基中内撑式排桩支护基坑开挖的抗隆起稳定性,并研究了软土不排水抗剪强度、支护结构条件、基坑尺寸对基底抗隆起的影响。研究表明,以往通常采用的极限平衡公式,对基坑开挖基底抗隆起稳定分析不能完全考虑支护结构的影响,也不能考虑基坑侧壁位移的影响,在一些条件下误差较大,而SSRFEM分析方法是求解基坑极限状态实际而自然的破坏形式,可很好地分析基底隆起稳定性。     

An efficient probabilistic back-analysis method for braced excavations using wall deflection data at multiple points

This paper presents an efficient Bayesian back-analysis procedure for braced excavations using wall deflection data at multiple points. Response surfaces obtained from finite element analyses are adopted to efficiently evaluate the wall responses. Deflection data for 49 wall sections from 11 case histories are collected to characterize the model error of the finite element method for evaluating the deflections at various points. A braced excavation project in Hang Zhou, China is chosen to illustrate the effectiveness of the proposed procedure. The results indicate that the soil parameters could be updated more significantly for the updating that uses the deflection data at multiple points than that only uses the maximum deflection data. The predicted deflections from the updated parameters agree fairly well with the field observations. The main significance of the proposed procedure is that it improves the updating efficiency of the soil parameters without adding monitoring effort compared with the traditional method that uses the maximum deflection data.     

Numerical analysis of lateral movements and strut forces in deep cement mixing walls with top-down construction in soft clay

This article presents the observed and simulated lateral movements and strut forces induced in deep cement mixing walls under deep excavation using top-down construction techniques in soft Bangkok clay. The walls are supported laterally by permanent concrete slabs and temporary struts. A three-dimensional numerical model is first calibrated with observed data from a case study. Then, a parametric study is performed to compare this construction method with the bottom-up method and investigate the influence of the DCM wall thickness on lateral movements and strut forces of the wall.     

非均质软土基坑抗隆起稳定性的极限分析方法

考虑到实际工程中土体非均质以及软土地区基坑开挖过程中土体稳定性的特点,将极限分析上限方法应用于非均质软土基坑抗隆起稳定分析计算中,讨论了极限分析方法的适用性问题。选用Prandtl机构建立了非均质软土地区基坑抗隆起稳定分析的运动许可速度场,根据速度场推导了极限分析上限方法的计算公式。讨论了该方法中土体强度、基坑宽度、支护墙体入土深度、基岩埋置深度等因素对坑底抗隆起稳定的影响。通过几个工程的计算与对比,验证了该方法的适用性和优越性。     

核废料处置概念库开挖及封闭后近场热-水-应力耦合数值分析

考虑了缓冲层中温度梯度水分扩散、水蒸汽扩散对水连续性及能量守恒的影响,进一步完善了饱和-非饱和介质中热-水-应力耦合现象的控制方程。应用缓冲材料的实验资料,对核废料处置概念库开挖及封闭后近场的热-水-应力耦合过程进行了数值模拟,以考察围岩中的位移、塑性区、主应力、孔隙水压力和温度的分布及变化。认为开挖是引起洞室围岩中的变形及应力重新分布的主要原因,但坑道封闭后的热-水-应力耦合过程对变形及应力状态也产生了明显的影响。     

Probability of serviceability failure in a braced excavation in a spatially random field: Fuzzy finite element approach

A simplified framework is proposed for evaluating the probability of “serviceability failure” in a braced excavation in a spatially random field. Here, the “serviceability failure” is said to occur when the excavation-induced wall or ground movement exceeds specified limiting values. Knowledge of this probability can aid in engineering decision-making to prevent damage to adjacent infrastructures. The proposed framework consists of five elements: (1) finite element method (FEM) for analyzing wall and ground responses in a braced excavation, (2) fuzzy set modeling of parameter uncertainty, (3) spatial averaging technique for handling spatial variability, (4) vertex method for processing fuzzy input through FEM model, and (5) interpretation of fuzzy output. The proposed framework is demonstrated through a well-documented case history. The results show the proposed framework is simple and effective for assessing the probability of serviceability failure in a braced excavation in a spatially random field. To focus on the proposed fuzzy FEM approach, the scope of this paper is limited to one-dimensional modeling of spatial variability with an assumed exponential autocorrelation function.     

地下隧洞开挖和支护的三维数值分析计算

根据地下工程锚固支护原理,采用隐含锚杆柱单元的三维有限元和混凝土喷锚支护的三维数值计算方法,对复杂的地下泄洪隧洞的开挖和支护进行了分析计算。该方法不仅能够有效地反映锚杆的长度、密度、倾角对洞室开挖的影响,而且能够较好地模拟钢拱架和锚杆的时间施加效应。由于隐含锚杆柱单元和喷层单元是隐含在岩体单元中的,所以锚杆和喷层单元不受岩体单元划分的影响,能够有效地模拟各种支护方案,加快计算速度,合理反映锚固支护所作用的位置和时间影响。通过对构皮滩泄洪洞施工开挖和锚固支护的模拟计算,论证了施工开挖的稳定性和锚杆、喷层、钢拱架的支护作用,提出了洞室结构的加固措施,为工程施工开挖提供了有效的设计依据。     

非均质与各向异性黏土基坑抗隆起稳定分析

经典的Prandtl 机构不能很好地反映支护结构入土深度的影响,也不能反映土体强度非均质和各向异性的影响。根据塑性极限分析上限定理,基于修正的Prandtl机构,推导了既可以合理反映支护结构入土深度影响,又可以反映土体强度非均质和各向异性特性的基坑抗隆起稳定的上限解公式,同时基于商业化程序的二次开发,建立了可以考虑土体强度非均质和各向异性影响的强度折减弹塑性有限元方法。通过提出的修正Prandtl机构上限解与强度折减有限元方法以及多块体上限解的对比,验证了修正机构上限解以及强度折减有限元法的合理性和可行性,最后讨论了非均质系数、各向异性系数、支护机构入土深度等因素对基坑抗隆起稳定性的影响,并通过了实例的验证,相关结论可供工程参考。     

填筑和开挖边坡的稳定性分析

在有限元应力应变分析的基础上,采用以剪应力定义的安全系数和模式搜索的方法确定边坡的安全系数及最危险滑动面。在平面应变条件下,对土层均质的填筑和开挖边坡的稳定性进行了较为全面的研究,并同天然边坡的安全系数和破坏面进行比较,计算结果表明,这3类边坡滑动面的形状基本一致,天然边坡安全系数要高于填筑和开挖边坡;同时比较了采用有限元稳定评价方法和采用极限平衡方法计算结果的差别;最后分析研究了计算参数变化对填筑和开挖边坡稳定性的影响。     

基坑开挖对下卧运营地铁隧道影响的数值分析与变形控制研究

以紧邻已运营天津地铁1号线既有隧道箱体上方的西青道下沉隧道基坑工程为背景,结合现场实测数据,采用ABAQUS软件对基坑的实际施工过程进行动态模拟。在此基础上分析既有隧道箱体两侧的土体加固、浇筑底板与抗浮桩形成“保护箍”以及堆载回压等措施对既有箱体轨道的影响及其有效性,指出有针对性地综合采用上述保护措施,能够及时有效地控制既有箱体轨道上抬,保证地铁的安全运营,并进一步研究了不同加固参数对既有箱体轨道变形的影响规律,结果表明：提高各加固参数能减小箱体轨道上抬及变形缝处的箱体间差异变形,但其加固效果却随着参数的增加而减弱,存在着一个合理的参数范围,为施工设计的优化提供依据。     

A continuum mechanics‐based framework for boundary and finite element mesh optimization in two dimensions for application in excavation analysis

The determination of the optimum excavation sequences in mining and civil engineering using numerical stress analysis procedures requires repeated solution of large models. Often such models contain much more complexity and geometric detail than required to arrive at an accurate stress analysis solution, especially considering our limited knowledge of rock mass properties. This paper develops an automated framework for estimating the effects of excavations at a region of interest, and optimizing the geometry used for stress analysis. It eliminates or simplifies the excavations in a model while maintaining the accuracy of analysis results. The framework can equally be applied to two‐dimensional boundary and finite element models. The framework will have the largest impact for non‐linear finite element analysis. It can significantly reduce computational times for such analysis by simplifying models. Error estimators are used in the framework to assess accuracy. The advantages of applying the framework are demonstrated on an excavation‐sequencing scenario. Copyright © 2005 John Wiley & Sons, Ltd.     

核废料处置概念库近场热-水-应力耦合模型及数值分析

特别考虑了缓冲层中温度梯度水分扩散、水蒸汽扩散对水连续性及能量守恒的影响,进一步完善了所建立的分析饱和-非饱和介质中热-水-应力耦合现象的控制方程,并针对试验资料,使用所开发的有限元程序对一个核废料处置概念库近场的热-水-应力耦合过程进行了数值模拟,考察了缓冲层及岩体中若干点的温度、饱和度、孔隙水压力及主应力的变化、分布情况,并将部分结果与国外类似软件的计算数据作了对比,结果显示,在定性和定量上二者的规律有某种一致性,从而得出了一定的认识。     

上覆流沙层隧道开挖面稳定性分析与数值试验研究

为解决上覆流沙层隧道开挖面极易发生坍塌破坏的技术难题,以典型该地质条件下的青岛地铁M2号线啤苗区间（啤酒城站至苗岭路站）为研究对象,基于开挖面的实际破坏特征建立了开挖面失稳破坏力学模型,从功能转化平衡角度,进行了隧道开挖面稳定性上限分析,并利用强度折减与重力加载两种方式,提出了隧道开挖面安全系数,得到了不同开挖面土体黏聚力、摩擦角、重度、隔水层厚度及隧道开挖高度下的临界土体破裂范围及破裂模式。理论研究表明：随着开挖面土体黏聚力、摩擦角、隔水层厚度等参数的增加,开挖面安全系数不断增大,稳定性不断提高;随着土体重度、隧道开挖高度增加,开挖面安全系数不断减小,稳定性不断降低。通过建立不同工况的数值模型验证了理论研究的正确性,得到了上覆流沙层地质条件下开挖面的典型破坏模式和临界参数,并提出了相应工程建议。研究成果为青岛地铁M2号线的顺利贯通及该类地质条件下的隧道施工提供了理论指导和科学对策。     

Three-dimensional numerical analysis of the keying of vertically installed plate anchors in clay

Plate anchors, such as suction embedded plate anchors and vertically driven plate anchors, offer economically attractive anchoring solutions for deep/ultra-deep water offshore developments. The rotation/keying processes of plate anchors will cause embedment losses, which lead to decreases of the uplift resistances of the anchors in normally consolidated soil. In the present paper, the keying processes of vertically installed strip and square plate anchors are simulated using the 3-D large deformation finite element method. The effects of loading eccentricity and pullout angle on the embedment loss during keying are investigated. Both the development of the uplift resistance and the soil flow mechanisms are presented. The numerical results show that the loading eccentricity e/B has a much larger effect on the embedment loss than the pullout angle does. The anchor shape has a minimal effect on the loss in anchor embedment. The shape factors (square/strip) are 1.05–1.09 for loss of embedment and 1.10–1.19 for capacity.     

天津某深基坑工程施工监测及数值模拟分析

本文介绍了天津铜锣湾广场深基坑工程开挖实例.通过对开挖过程中的支护结构内力、坑周土体水平位移等的现场监测和数值模拟分析,讨论了基坑开挖过程中支护结构受力的特点及其对周围环境的影响,得到了基坑周边土体水平位移的变化规律,为考虑施工因素的支护结构设计提供了依据.     

Performance of geosynthetic-reinforced granular piles in soft clays: Model tests and numerical analysis

The laboratory model tests and numerical analyses have been performed on reinforced granular piles installed in very soft clay. The granular piles were reinforced with geosynthetic in the form of vertical encasement, horizontal strips and combined vertical-horizontal reinforcement. The short term-displacement control model tests were carried out either only a granular pile loaded or with an entire area loaded. The laboratory results in the form of vertical load intensity-settlement behaviour were compared with that obtained from FEM software, PLAXIS 3D. The results indicated significant improvement in ultimate load intensity and stiffness of treated ground due to inclusion of geosynthetic.     

基坑开挖对下卧运营地铁既有箱体影响的实测及分析

天津西站交通枢纽西青道下沉隧道工程上跨于已运营天津地铁1号线区间既有箱体,其上跨段隧道底板距既有箱体顶板仅0.3 m,需对其可能引起的既有隧道变形进行严格控制。设计中对运营线路有针对性地提出地基加固、分段开挖、及时堆载回压等施工方案及措施。通过对西青道下沉隧道下邻近既有地铁隧道的抗浮桩、三轴水泥搅拌桩施工和基坑开挖阶段的监测数据进行分析,研究了不同施工阶段的地铁箱体及轨道变形规律及特点。实测结果表明,在邻近既有地铁隧道处施工钻孔灌注桩可引起既有隧道下沉,基坑开挖可引起既有隧道上浮。分块开挖、分段压载并结合信息化施工可有效控制因开挖卸荷引起的既有隧道竖向位移及隧道箱体之间的差异变形。