利用 FLAC 3D 对基坑支护数值模拟分析

FLAC 3D 是岩土工程中广泛应用的软件。本文以某地区基坑为背景,进行土钉墙支护设计,并利用 FLAC 3D 软件对土钉墙支护前后进行数值模拟。在基坑开挖完成后,边墙位移一般为 20 ～ 40 cm,最大位移为 45 cm。采用土钉墙支护后,边墙的位移为 2 ～ 4 cm,最大位移为 6 cm。对比表明,土钉墙支护能够有效的阻止基坑的变形,维持基坑的稳定。同时,根据土钉的轴力分布特征,分析基坑在不采取支护措施的情况下将发生滑移破坏。     

Modelling of the mechanical interaction between anchored wire meshes and granular soils

In this paper a theoretical and numerical analysis of the mechanical interaction between an anchored deformable facing structure and the underlying granular soil is presented. The reinforcement system is mainly composed of wire meshes, geosynthetics, bars/ties, and spike steel plates. This is usually employed for stabilising potentially unstable slopes. The punching process that can occur locally is described by considering the complex interaction mechanisms arising among the different system elements and the soil. For the sake of simplicity, the soil stratum and the anchor are assumed to be horizontal and vertical, respectively. A simplified displacement-based approach is introduced with the main goal of evaluating both the maximum force that can be applied on the anchor and the correlated penetration of the spike plate within the soil. The approach is validated by means of experimental laboratory test results already available in the literature. Finally, in order to stress the role of the spike plates' spacing and the soil stiffness in influencing the mechanical response of the system, the numerical results of parametric analyses are discussed.     

Modelling the behaviour of a retaining wall in residual soils for a cut and cover construction of a deep station in Metro do Porto

This paper presents a re-appreciation of the ground characterisation and the criteria to select the most representative geomechanical parameters to consider in a numerical model to predict the behaviour of a retaining wall of a deep excavation in highly weathered granite rock masses and residual soils. This study was focused in the construction of a deep station of Metro do Porto, which involved a cut and cover solution, with unusual proportions (in plant and in depth), built in the typical Oporto's granite weathered profiles, being the excavation conducted with retaining walls consisting of multi-anchored concrete piles. Specific sections were carefully instrumented, due to the presence of historic buildings in the vicinity. The definition of representative model parameters was based on precise laboratory tests over high quality soil samples, including oedometer and high-precision triaxial tests. Geotechnical and geological characterisation of all the area for the original design, was initially based on in situ tests, such as SPT and rock masses classification, and on the local experience on this type of ground. After this construction, the assumptions of parameterisation, using a constitutive modelling based on new laboratory tests over high quality block samples, allowed a reanalysis of the assumptions on the design phase. A back-analysis of monitored displacements and forces during the construction was made, assuming the designed structural solutions, which were in fact implemented in construction, but considering the new approaches on the definition of the geomechanical parameters for the prevailing weathered rock masses, necessary for the numerical simulation based on the commercial software Plaxis®, using the Mohr-Coulomb and “Hardening-Soil” models. Some specific changes of the constructive sequence during the excavation and activation of supporting system were attained, by looking at the information found during the construction. The results of this parametrical re-approach and analysis of the singularities of highly weathered granite and corresponding residual soils masses for modelling of retaining walls of large excavations are discussed.     

System reliability-based analysis of cantilever retaining walls embedded in granular soils

Reliability-based analysis of cantilever retaining walls requires consideration of different failure mechanisms. In this paper, the reliability of soil-wall system is assessed considering two failure modes: rotational and structural stability, and the system reliability is assumed as a series system. The methodology is based on Monte Carlo Simulation (MCS), and it deals with the variability of the design parameters in the limit equilibrium analysis of a wall embedded in granular soil. Results of the MCS indicate that the reliability of the failure components increases exponentially by increasing the variability of design parameters. The results of the system reliability indicate how the system reliability is different from the component reliabilities. The strength of the weakest component influences the reliability of the system. The system reliability index increases with the wall section gradually. However it remains constant for the rotational failure mode.     

墙土体参数对地下连续墙基础沉降数值模拟的影响

考虑到墙周土体及接触的非线性,借助Mar软件建立了空间三维有限元模型,通过与工程实测比较,证明模型合理;在此基础上分析了土体变形模量、泊松比及墙土接触的摩擦对地下连续墙基础沉降的影响,结果表明:土体变形模量对基础沉降的影响相当大,泊松比取其经验值对基础基本无影响,墙土间摩擦系数的提高对基础沉降的减小有一定的作用。     

北京某深基坑复合土钉墙支护受力监测及分析

通过对某深基坑开挖及支护过程中土钉钢筋受力、锚索轴力及坡顶水平位移情况进行监测,并通过对土钉拉筋受力特征、锚索轴力特征、坡顶水平位移监测值特征及其相互关系进行系统分析,将其与传统的受力模型进行对比,解析了该基坑在此方面的普遍性与特殊性,为今后类似工程提供借鉴。     

Geotechnical problems on freezing ground soil and experimental investigation in Kazakhstan

Frost susceptibility should be considered in the design and construction of foundations and retaining-wall structures in regions with the seasonally freezing-soil ground condition. When planning construction that goes deep into this soil, one has to understand the impact of horizontal forces to an underground wall and realize the potential effect of frost heaving upon, deep foundations. This article presents a few soil tests for frost heaving and the results of those tests show dangerous data for retaining structures under the soil conditions in Kazakhstan. The main parameters of the soil include frost penetration and heaving rate and amount. So, in designing underground structures, one must understand and consider that frost heaving occurs in various directions; this factor is very important for predicting on the restriction of deformations of structures in the seasonally freezing-soil ground condition.     

Pile group response to liquefaction-induced lateral spreading: E-Defense large shake table test

This paper presents the results of a large-scale shake table test at E-Defense facility on a pile group located adjacent to a gravity-type quay wall and were subjected to liquefaction-induced large ground displacements. Extensive liquefaction-induced large ground lateral spreading displaced the quay wall about 2.2 m and damaged the pile foundation. The pile foundation consisted of a six-pile group which supported a footing and a superstructure model. Large lateral soil displacements were measured by several sensors such as inclinometers and the results favorably agreed with the directly observed deformations. Soil lateral displacement decreased as the distance from the quay wall increased landward. The piles were densely instrumented and the measured bending strain records were able to explain the damage to the piles. Lateral pressures of the liquefied soil exerted on the piles were measured using earth pressure (EP) sensors. The application of two design guidelines (JRA [1] and JSWA [2]) for estimation of liquefaction-induced lateral pressure on piles is discussed and their advantages and shortcomings are addressed. Furthermore, two simplified methods (Shamoto et al. [3] and Valsamis et al. [4]) are employed to predict the extent of liquefaction-induced large ground displacements and they are compared to the measured deformations. Finally, their accuracy for predicting the liquefaction-induced lateral displacements is evaluated and practical recommendations are made.     

摩擦型阻尼填充墙单元的设计及性能试验研究

基于阻尼填充墙的构造与原理,设计一种以低强度薄层砂浆为阻尼层的摩擦型阻尼填充墙单元(FDIWU)构造方案.通过对三榀砌块类型不同的FDIWU试件进行拟静力试验,研究FDIWU的力学性能.试验结果表明:(1)以低强度薄层砂浆为阻尼层的FDIWU的构造和原理是可行的,能成功实现“砌体单元平动,不破坏”的预期机制和设计目标.(2)以低强度薄层砂浆为阻尼层的FDIWU具有较大的初始刚度;起滑后,刚度明显降低.(3)以低强度薄层砂浆为阻尼层的FDIWU耗能机理明确,耗能能力强.(4)用不同类型砌块砌筑的FDIWU的承载力、刚度、强度退化及变形特性基本相同,耗能性能有差别.用表面较为粗糙的砌块砌筑的FDIWU的耗能能力较强.     

芦山7.O级地震中钢筋混凝土框架结构震害分析

2013年4月20日四川芦山7.0级地震给震区建筑结构造成了严重破坏.本文选择不同烈度区典型震害的钢筋混凝土框架结构,介绍了结构梁柱、填充墙、其他附属构件及地基等的破坏特点,分析了各类震害特征与破坏机理.结果显示,钢筋混凝土框架结构在本次地震中表现出了良好的抗震性能,除了极震区个别建筑框架柱发生了结构性破坏外,地震区绝大部分均为非结构性破坏,如填充墙及其他附属构件破坏,且大部分破坏不影响结构框架承重体系继续使用.最后针对该次地震中钢筋混凝土框架结构存在的主要问题,给出了一些钢筋混凝土框架结构设计与建设改进建议.