Spannungs‐ und Porenwasserdruckentwicklung infolge Schlitzwand‐Herstellung in weichen bindigen Böden

Stress and pore water pressure development during the construction process of dipahragm walls in soft clay. The influence of a diaphragm wall construction on the stress field in a soft clayey soil is investigated by the use of a three‐dimensional FE‐model of seven adjacent wall panels. The installation procedure comprises the excavation and the subsequent pouring of each panel taking into account the increasing stiffness of the placed fresh concrete. The soft clay deposit is described by a visco‐hypoplastic constitutive model considering the rheological properties and the small‐strain stiffness of the soil. The construction process considerably affects the effective earth and pore water pressures adjacent to the wall. Due to concreting, a high excess pore water pressure arises, which dissipates during the following construction steps. The earth pressure finally shows an oscillating, distinct three‐dimensional distribution along the retaining wall which depends on the installation sequence of the panels and the difference between the fresh concrete pressure and the total horizontal earth pressure at rest. In comparison to FE‐calculations adopting the earth pressure at rest as initial condition, greater wall deflections and surface ground settlements during the subsequent pit excavation can be expected, as the average stress level especially in the upper half of the wall is increased by the construction procedure of the retaining structure.     

Gebrauchstauglichkeitsbetrachtung von Streifengründungen während der Herstellung einer benachbarten Schlitzwand in weichem Boden

On the deformation behaviour of strip footings during the construction process of an adjacent diaphragm wall in soft clayey ground. The installation of diaphragm walls in soft clayey soil deposits itself can produce considerable deformations of the adjacent ground affecting the serviceability of nearby structures. This article highlights the influnce of the stepwise construction process on the development of settlements of neighbouring strip footings. Therefore, a three‐dimensional finite element model of a plain diaphragm wall section and an adjacent footing is adopted. The stress‐strain behaviour of the ground is described by an advanced constitutive model, which especially takes into account the rheological properties of the soft clay, like creep, relaxation and a rate‐dependent stiffness. Numerous calculations are performed considering the impact of the panel geometry and the installation sequence of the diaphragm wall. Furthermore, the loading as well as the bending stiffness of the strip footing is varied. With respect to the serviceability of the footing, recommendations are finally drawn aiming at a prevention oriented construction technique.     

上海东方金融广场深基坑施工监测分析与信息化施工

以上海东方金融广场为例,对土方开挖及支撑形成全过程地下连续墙深层水平位移监测数据进行分析和探讨,利用时空效应原理及Rankine土压力理论解释地下连续墙水平位移变形机理,并通过对监测数据变化规律的分析及时调整施工作业流程,最终确保了基坑开挖全过程围护结构自身及周边环境的安全。     

倾斜面墙加筋挡墙施工过程仿真与潜在破裂面分析

在现场监测的基础上,利用FLAC3D对湖南湘潭至衡阳西线高速公路K124＋300路段的倾斜面墙加筋土挡墙进行了施工过程仿真,研究了施工过程中墙内竖向土压力、侧向土压力、侧向变形以及筋带应变的发展过程和挡墙潜在破裂面形态。结果表明,对加筋土挡墙进行施工过程仿真分析可以再现施工过程中挡墙内部的应力应变发展过程;加筋土挡墙的...     

弹性索理论在加筋土挡墙结构设计中的应用研究

在差异沉降现象下,现阶段关于加筋土挡墙面板与筋材连接处的结点应力及筋材的变形情况的研究尚少。例如软土地区地基较软处加筋土挡墙易发生差异沉降,其相关理论的不完善也导致了加筋土挡墙的区域适用性降低。为完善加筋土挡墙的设计理论,运用弹性索理论为理论基础,以加筋土挡墙面板与筋材的连接处为研究对象,结合现有的加筋土挡墙变形及其土压力计算理论,提出了一套差异沉降下加筋土挡墙筋材应力分布及其变形曲线的计算方法。通过理论分析,并结合室内模型试验数据验证了该方法的可行性和准确性。该方法具有计算简便,适用广泛等特点,能够较好地解释面板与筋材连接处的破坏形式,对完善加筋土挡墙的设计理论,特别是沉降控制设计方面具有一定的意义。     

坭洲水道桥圆形地连墙支护体系监测与分析

对虎门二桥坭洲水道桥直径90 m、深29 m东锚碇工程进行了监测,实测得到开挖过程中地连墙墙后土压力、墙体径向位移、竖向弯矩等。同时,设计并实施了地连墙槽段接缝的单元体试验,探讨了圆形地连墙环向刚度折减系数的取值方法,并结合轴对称弹性地基梁法对监测数据进行了对比分析。计算与实测分析结果表明,圆形地连墙支护体系墙体最大位移值为开挖深度的0.018%,远小于工程预警值,说明其可有效控制基坑变形;施工过程中土体开挖及内衬施工对地连墙应力影响最大,是相应深度地连墙应力达到峰值的主要原因,其影响范围为上下两倍当层开挖深度;圆形地连墙墙后土体具有空间效应,实测土压力值小于主动土压力理论计算值;由计算对比可知,考虑环向效应及环向刚度折减的弹性地基梁法可较好地反映圆形地连墙支护体系的受力变形特性。     

地下连续墙深基坑开挖综合特性研究

本文在前人研究成果及笔者近年来工作的基础上,对软土地基地下连续墙作挡墙的深开挖理论进行了较为详细的研究,包括基坑周围地层变位机理研究、地表沉降与墙体侧移的预估、稳定性与地表沉降的关系、支撑轴力的预测、改善基坑受力及变形特性的具体施工措施和现场实测结论等等。本成果可供软土地区深基坑开挖的性态分析作参考。     

软土地基上新型加筋土挡土墙的应用

结合工程实例,简要介绍了在软土地基上设置新型加筋土挡土墙设计的内容和方法,并提出了设计和施工过程中应该注意的几个问题,以推广加筋土挡土墙在工程实践中的广泛应用。     

预应力返包式加筋土挡墙的动力响应分析

在地震作用下,返包式加筋土挡墙作为一种柔性结构常因侧向变形较大或局部产生破坏而影响其正常使用。为解决该问题,提出了预应力返包式加筋土挡墙结构。为完善预应力返包式加筋土挡墙的设计理论,运用拟动力法和附加应力法理论,以预应力返包式加筋土挡墙作为研究对象,结合现有的加筋土挡墙侧向动土压力和侧向位移计算理论,提出了一套用于计算预应力返包式加筋土挡墙侧向动土压力和侧向位移的理论公式。结合室内振动台模型试验验证了所提理论方法的可行性和合理性。该方法计算简洁,适用性广,能够较好地计算预应力返包式加筋土挡墙的侧向动土压力和侧向位移,对完善预应力返包式加筋土挡墙的设计理论具有一定的指导和借鉴意义。     

软粘土地基中齿坎抗滑效应的研究

通过位于软弱地基中的无齿挡墙和齿坎式挡土结构物的现场抗滑试验，研究了齿坎对挡土结构物所起的抗滑作用，还用非线性有限元方法对现场试验成果进行分析，通过研究得出结论：尽管齿坎较短，但对挡土结构物的抗滑作用颇大，在试验齿长范围内，抗滑力与齿长成正比，当挡土结构物处于极限破坏状态时，齿前土压力达到‘被动’土压力值，而齿后主动土压力甚小，有限元分析与现场试验成果具有很好的一致性，最后用有限单元法研究了齿坎的临界长度。     

邻近地层损失对地下挡土结构土压力与地表沉降影响试验研究

城市浅层空间隧道往往从一侧或两侧地下挡土结构物之间穿过,多数情况下会引起地层损失.目前城市地下开挖引起塌陷事故呈现逐年增多的趋势,当地层损失产生后,周边已建或在建基坑挡土结构的土压力和地层沉降发展规律是决定是否需要进行加固或处理的依据.为了获取地层损失的扰动影响规律,开发了模型试验装置与钢棒相似土技术,采用活动门下沉模...     

三向应力作用下的Rankine被动土压力公式

基于Mohr-Coulomb理论推导的Rankine被动土压力计算公式,只考虑大小主应力的影响,没有考虑中间主应力的影响,而三向应力作用的双剪强度理论克服了Mohr-Coulomb屈服准则的不足,使被动土压力公式在三向应力作用下推导出来,更加符合实际,实例演算表明三向应力状态下的被动土压力值大于经典Rankine被动土压力值,计算结果用于设计更偏于安全。     

Modellversuche zum Erd‐ und Auflastdruck auf Winkelstützwände

Model tests on earth pressure and load pressure on cantilever retaining walls. Design‐ing the sections of cantilever retaining walls, it is required to know the earth pressure acting directly on the wall stem and the load pressure acting directly on the wall heel. Large scale model tests are presented, which aim to determine the development of the contact pressures due to dead load of the backfill as well as due to uniform surface loads. The model tests simulate the construction as well as the backfilling process. Wall geometry and subsoil flexibility are varied. The principal behaviour of cantilever retaining walls is presented. The test results are used to derive basic properties of the earth pressure and the load pressure.     

某钢厂热轧带钢漩流池圆形基坑监测分析

根据某钢厂一个圆形深基坑工程的监测实例,对圆形基坑开挖过程中地下连续墙侧向位移、土压力、孔隙水压力、地下连续墙钢筋应力、底板钢筋应力等的变化规律进行了分析.本工程中地下连续墙实测变形呈悬臂结构变形特征,与工程设计中常用的弹性地基梁比拟法所得结果存在较大差异.从设计方法中对圆形围护结构"拱效应"的模拟,内衬作用的发挥以及地下连续墙槽段接头泥浆的影响等方面对此进行了深入分析,可为同类工程的设计、施工和监测提供借鉴.     

悬锚式挡土墙墙后土压力特征有限元分析

为了研究拉杆和锚定板对挡墙土压力的影响,利用有限元软件对悬锚式挡土墙进行计算,分析挡墙的土压力分布和水平位移的变化情况。结果表明墙后土压力在挡墙底部有减小趋势,随挡墙高度大致线性增加,锚定板和拉杆的布置越多,水平位移控制的越好。计算结果可为后续施工提供理论基础。     

临近地下室外墙的挡土墙主动土压力研究

关于考虑土拱效应的临近地下室外墙影响下的挡土墙主动土压力的研究目前已经取得了很多成果,但对考虑地表附加应力影响时的研究还有较多的不足。研究发现,考虑地表附加应力时挡土墙后破裂土体的平均竖向应力σ_v的求解公式与地表到墙后土体破裂面的最短距离H₁和张拉裂缝的深度zc的正负以及两者之间的关系有关,以此为基础将该问题分为4种情况进行研究,推导出了各情况下相应的σ_v的求解公式,并得得到了其相应的主动土压力计算公式;同时,通过对主动土压力积分推导出了各情况下相应的主动土压力合力和倾覆力矩的计算公式,由此可以计算合力作用点的高度。算例表明,地表附加应力的存在会对主动土压力的分布以及合力作用点的位置有较大的影响,证明了本文研究的必要性。     

温度应力对环形地连墙围护结构受力变形的影响分析

温度场对深基坑围护结构受力变形的影响不仅是温度场与应力场的热力耦合问题,同时也是水、土、围护结构共同作用问题。通过对日本东京新丰洲变电所深基坑工程实测结果的反分析,确定了温度场对环形深基坑围护结构受力变形影响的分析方法,获得了温度场变化引起的围护结构受力变形模式,并将研究成果应用于上海世博变深基坑围护结构受力变形分析。分析结果表明：基坑开挖后,围护结构的内侧面暴露在大气中,受大气温度变化的影响,地连墙内外侧存在温度差,且不同位置、不同施工阶段,地连墙的温度场不同;开挖面以上的地连墙没有坑内土体的约束作用,其环向应力的大小主要取决于坑外水、土压力的作用,温度下降时,地连墙向坑内收缩变形;开挖面以下及开挖面附近的墙体,墙体收缩变形受到坑内土体的约束,温度下降时,地连墙的环向应力减小。     

Influences of 3D Effects,Wall Deflection Process and Wall Deflection Mode in Retaining Wall Problems

Two-dimensional (2D) and three-dimensional (3D) model tests and the corresponding elastoplastic finite element analyses were carried out to investigate the influences of 3D effects, wall deflection process and wall deflection mode on the earth pressures and the ground movements in retaining wall problems. Aluminum rod mass were used in 2D model tests, and alumina balls were used in 3D model tests. The stress-strain behavior of these materials is similar to that of dense sands with positive dilatancy. In the finite element analyses, a recently developed elastoplastic constitutive model, named subloading t_ij model, were used. This model can describe typical stress deformation and strength characteristics of soils such as the influence of intermediate principal stress, the stress path dependency of plastic flow and the influence of density and/or confining pressure properly. The test results show that the earth pressures on the retaining wall in 3D condition are much smaller than those in 2D condition, and these distributions of earth pressure are more influenced by the wall deflection process than by the wall deflection mode. Observed surface settlements at the backfill just behind the wall in 3D condition are larger than those in 2D condition, but 3D surface settlements occur more locally. These 2D and 3D surface settlements are influenced by the wall deflection process more than the wall deflection mode. However, at the same wall deflection process and the same wall deflection mode, there is not much difference in the shapes of the earth pressure distributions and the surface settlement troughs between 2D and 3D conditions. These differences and similarities of the earth pressures and the surface settlements are simulated not only qualitatively but also quantitatively in the analyses using the above constitutive model.     

软土地基基坑挡墙土压力变化的动态分析

以软土地基为背景 ,区别于常规基坑挡墙土压力的计算模式 ,以挡墙与土体共同变形为条件 ,提出了基坑挡墙随基坑不断开挖 ,土体在开挖侧的不断卸载 ,土与围护结构体系不断达到动态平衡的土压力动态分析方法 ,计算结果与一般实测土压力分布规律吻合。     

土工格栅加筋土挡墙现场试验分析

通过埋设水平土压力盒、柔性位移计,对模块式土工格栅加筋土挡土墙墙后的水平土压力和格栅水平变形进行了系统监测,采用加筋组合法对加筋土挡墙的土压力进行了计算,与实测、交系数法所得数据对比分析,得出采用该方法计算的土压力更能合理地解释工作状态下加筋土挡墙的土压力分布规律;对比分析了施工阶段和竣工后格栅的应变,得出拉筋应变主要发生在施工阶段,工后应变较小,并结合试验结果,提出了关于施工控制的相关建议.