软土深开挖致地铁车站基坑及邻近建筑变形特性研究

为了更深入地了解软土深开挖引起地铁车站深基坑工程围护结构及邻近建筑的变形特性,结合深厚软黏土地区某个地铁车站深基坑工程进行了系统性监测及结果分析。结果分析表明:地连墙成槽会引起邻近土体侧向位移,最大土体侧向位移值占基坑开挖期间土体侧向位移值20%左右;土体开挖期间南侧(桩基础建筑一侧)、北侧(浅基础建筑一侧)围护结构邻近土体最大侧向位移平均值分别为0.091%H_e和0.120%H_e;y/H_e值(y为垂直连续墙方向上与连续墙的距离,H_e为开挖深度)小于0.92时,基坑开挖引起土体沉降值及沉降差较大;地表变形与浅基础变形较为接近,桩基础建筑变形值明显小于浅基础建筑变形值且嵌岩桩基础建筑变形值最小;邻近浅基础建筑及桩基础建筑均受到空间效应影响,在x/H_e值(x为平行连续墙方向上与端部的距离)小于1.5时,空间效应较为明显,x/H_e值大于2.0时,邻近建筑及围护结构邻近土体变形接近平面应变状态。     

软土深开挖致地铁车站基坑及邻近建筑变形特性研究

为了更深入的了解软土深开挖引起地铁车站深基坑工程围护结构及邻近建筑的变形特性,结合深厚软黏土地区某个地铁车站深基坑工程进行了系统性监测及结果分析。结果分析表明:地连墙成槽会引起邻近土体侧向位移,最大土体侧向位移值占基坑开挖期间土体侧向位移值20%左右;土体开挖期间南侧(桩基础建筑一侧)、北侧(浅基础建筑一侧)围护结构邻近土体最大侧向位移平均值分别为0.091%H_e和0.120%H_e;y/H_e值(y,垂直连续墙方向上与连续墙的距离,H_e,开挖深度)小于0.92时,基坑开挖引起土体沉降值及沉降差较大;地表变形与浅基础变形较为接近,桩基础建筑变形值明显小于浅基础建筑变形值且嵌岩桩基础建筑变形值最小;邻近浅基础建筑及桩基础建筑均受到“空间效应”影响,在x/H_e值(x,平行连续墙方向上与端部的距离)小于1.5时“空间效应”较为明显,x/H_e值大于2.0时邻近建筑及围护结构邻近土体变形接近平面应变状态。     

软土深开挖致地铁车站基坑及邻近建筑变形特性研究

为了更深入的了解软土深开挖引起地铁车站深基坑工程围护结构及邻近建筑的变形特性,结合深厚软黏土地区某个地铁车站深基坑工程进行了系统性监测及结果分析。结果分析表明:地连墙成槽会引起邻近土体侧向位移,最大土体侧向位移值占基坑开挖期间土体侧向位移值20%左右;土体开挖期间南侧(桩基础建筑一侧)、北侧(浅基础建筑一侧)围护结构邻近土体最大侧向位移平均值分别为0.091%H_e和0.120%H_e;y/H_e值(y,垂直连续墙方向上与连续墙的距离,H_e,开挖深度)小于0.92时,基坑开挖引起土体沉降值及沉降差较大;地表变形与浅基础变形较为接近,桩基础建筑变形值明显小于浅基础建筑变形值且嵌岩桩基础建筑变形值最小;邻近浅基础建筑及桩基础建筑均受到“空间效应”影响,在x/H_e值(x,平行连续墙方向上与端部的距离)小于1.5时“空间效应”较为明显,x/H_e值大于2.0时邻近建筑及围护结构邻近土体变形接近平面应变状态。     

邻近地铁车站基坑开挖位移传递规律数值模拟

上海地铁8号线人民广场站是个平行换乘车站,车站基坑紧邻地铁1号线人民广场站开挖。监测数据说明,随着基坑开挖,地铁车站背向基坑倾斜。通过有限差分法数值模拟,得到了邻近大刚度地铁车站的基坑开挖位移场的位移传递规律,并对其规律进行了分析,结果表明,大刚度地铁车站的存在对基坑开挖的位移场具有很大的影响：（1）对基坑变形的遮拦作用,从而减小了支护结构的变形;（2）隔断了坑周土层的位移传递路径,使得土体位移场发生变化,促使地下建筑物背向基坑方向倾斜。     

广西大学地铁车站深基坑变形监测数据分析

本文以南宁市地铁1号线试验车站广西大学站基坑工程为背景,通过对基坑工程施工动态监测数据进行分析,总结了广西大学站地铁车站深基坑的连续墙变形及周围地表沉降变形特征。监测数据的分析结果表明:广西大学站基坑开挖引起的地表沉降量值比较小,影响范围主要集中于0～2H(H为基坑开挖深度),产生最大沉降值的位置约为墙后0.5～0.7H,沉降变形影响最远延伸至距基坑边缘约为4H处; 并可依此变形特征规律给出圆砾层地区基坑地表沉降预估曲线与环境保护等级的划分。     

地铁二号线杨高路车站上游引水渠道保护

上海地铁２号线车站深大基坑施工采用地下连续墙围护，对邻近的重要地下构筑物保护采取优化内支撑和控制地表沉降的技术，在施工中进行监测和信息反馈。     

宁波轨道交通地下连续墙深基坑工程变形特性及控制研究

由于成因及地域性的差异,宁波软土具有鲜明的特点,深基坑变形特性也有别于其它软土地区。在国内外研究基础上,本文结合宁波轨道交通1号线基坑工程,对13个车站地下连续墙深基坑监测数据进行统计分析。从基坑围护结构水平位移和墙后地表沉降两个方面对基坑变形特性进行了研究,结果表明:宁波地区地下连续墙的最大侧移介于0.18%H和0.80%H之间,平均值为0.39%H,较其它地区大,最大侧移位于开挖面附近,且随软土层厚度的增大而增大;宁波地区Fs取值1.7为宜;地表沉降主要分布于0≤d/H≤2.0范围内,最大值δvm=1.2%H,最小值δvm=0.15%H,平均值δvm=0.69%H,地表沉降较大;围护结构侧移与地表沉降关系为δvm=1.0δhm～1.8δhm。最后,结合分析结果,提出了宁波地区深基坑工程变形控制标准,可以为宁波地区及软土地区深基坑工程提供指导和借鉴作用。     

紧邻地铁枢纽深基坑变形特性离心模型试验研究

对于紧邻地铁枢纽的深基坑工程,其开挖方式对基坑变形特性和施工安全控制有着显著影响。以上海某紧邻地铁隧道的深基坑工程为背景,其设计方案将该基坑工程划分为大、小基坑分别施工,重点研究大、小基坑的开挖方式对于围护结构及地铁隧道变形的影响。针对“先挖大基坑,后挖小基坑”的开挖方案,采用离心模型试验,研究开挖过程中地下连续墙和隧道结构的变形特性。试验结果表明,“先挖大基坑,后挖小基坑”的开挖方案可以有效地控制基坑变形,所得结论对于类似的紧邻地铁隧道深基坑工程设计与施工具有参考价值。     

基坑开挖对近邻运营地铁隧道影响规律研究

对某邻近基坑开挖的地铁隧道的水平位移和沉降的时空分布做了深入分析。由于软土的蠕变效应,应考虑基坑分块开挖的先后顺序造成的时空效应的影响,以及基坑围护体系的水平支撑结构对土体位移的限制作用。基坑开挖对邻近地铁隧道的影响范围为2.5倍开挖深度,而对于远基坑的右线,影响范围更低,甚至低至1.5倍开挖深度。将基坑和隧道的监测数据联系分析,得到比值与水平距离的关系曲线,将基坑监测数据代入拟合公式,对地铁水平和垂直位移进行估算。隧道水平位移与邻近的同深度土体水平位移的比值（?）,其最大累计位移点的? 较多地处在0.60～0.65范围,在底板浇筑都已完成后,稳定在0.60。隧道沉降与邻近地表沉降的比值（?）,其最大累计沉降点的?,较多地处在0.50～0.60间,底板浇筑完成后,稳定在0.52±0.05水平。     

不对称基坑开挖过程中的沉降变形与数值模拟分析

为控制不对称基坑开挖形变、保障基坑稳定性和安全性,开展不对称基坑开挖过程中的沉降变形与数值模拟研究。以西安某地铁坑中不对称开挖工程为例,选取桩体水平位移、桩顶沉降、地表沉降和周围建筑物沉降4个变形指标,对其施工进行监测和Plaxis 3D有限元模拟。研究发现：随着基坑开挖,桩身水平位移不断增加,其最大值为8.23mm;桩顶沉降呈波动趋势,最大值为0.45mm;地表沉降也不断增加,最大沉降值8.81mm,且靠近基坑侧土体沉降较远离侧高15%左右,承载建筑物一侧土体的水平位移较未承载侧高12%;周围建筑物沉降量随着离基坑距离的减小而增加,最大值为9.4mm。通过对比分析发现4个变形指标的实测和模拟结果虽略有差异,但变化趋势基本一致,且4个指标的变形均处于变形控制范围内,不对称开挖过程基坑十分安全和稳定,说明该工程选择的桩-撑联合支护方式能有效控制不对称开挖过程的基坑变形,且在坑中坑不对称开挖工程中使用数值模拟方式能确定基坑开挖方案的安全性。     

A parametric study of wall deflections in deep excavations with the installation of cross walls

Several case studies have revealed that the installation of cross walls in excavations can effectively reduce the amount of wall deflection and ground settlement. However, the behaviour of the diaphragm wall due to the installation of the cross walls is still unclear. This study performed a series of 3D numerical studies of wall deflections for deep excavations with cross walls and studied the effects on the wall deflection of several parameters, including the number of cross walls, the distance to the cross wall, the cross wall interval, the cross wall height and the cross wall embedment. The results presented in this study can be used as a first approximation for cases in which cross walls are designed to reduce the wall deflection induced by deep excavation.     

广州岩溶地区深基坑开挖对周围环境影响的研究

以广州地铁9号线在岩溶地区施工深基坑为例,研究岩溶地层基坑施工对周围环境的影响。该车站基坑长259.7 m,宽18.7 m,深15.8 m。基坑深度范围内包括溶洞和砂层,溶洞地层富水、稳定性差、物理力学性质差,砂层厚0～15 m,有较大的渗透性,基坑施工过程中对地下连续墙的侧向位移和地面沉降进行了监测。监测结果表明,基坑开挖结束时地下连续墙的最大侧向位移为12 mm,地面沉降的最大值为10.1 mm,基坑开挖过程中对周围环境的影响很小。研究成果可为今后类似工程施工提供经验借鉴。     

深软场地地铁狭长深基坑变形特征实测与已有统计结果的对比分析

以上海地区某深软场地地铁狭长深基坑为工程背景,对开挖引起的地表和周边建筑物沉降、地下连续墙侧移、墙顶和立柱竖向位移等的监测数据进行了详细地统计和分析,探讨了深软场地狭长深基坑变形的时空分布特征及其主要诱因。对比分析实测墙体最大侧移?hm和最大地表沉降?vm与已有统计结果和经验预测结果,结果表明深软场地狭长深基坑的变形时空效应非常明显。与已有上海地区深基坑工程实测统计得出的地表沉降预测结果相比,狭长基坑周围地表沉降曲线基本符合已有的经验预测结果,但与已有的实测统计结果相比,实测墙体最大侧移?hm和最大地表沉降?vm与开挖深度的比值平均线明显低于已有的统计结果,主要原因是针对地铁狭长深基坑特点采用的地连墙和多层内支撑的围护结构体系明显区别于一般深基坑的围护结构体系所造成的,表明该围护结构体系能够很好地控制狭长深基坑的变形发展。     

A new approach for estimating the transverse surface settlement curve for twin tunnels in shallow and soft soils

Increasing demand on infrastructures has led to increased attention to shallow soft ground tunneling methods in urbanized areas. Especially in metro tunnel excavations, it is important to control the surface settlements which are observed before and after excavation, which may cause damage to surface structures. Unlike motorway, sewage and other infrastructure tunnels, metro tunnels generally have to be excavated as twin tunnels and must have a larger diameter. Metro tunnels also have shallow depth. Due to their shallow depth, metro tunnels generally have been constructed in weak rocks or weak soils in cities. The construction of twin tunnels will generate ground movements which have the potential to cause damage to existing surface and subsurface structures. To solve this settlement problem, experts have used the Earth pressure balance machine (EPBM) and the slurry balance machine. In such excavations, especially in twin tunnels, the main challenges for constructers are estimating the maximum surface settlement, controlling the interaction of transverse surface settlement and shaping the settlement curve. Incorrect estimation of these parameters can lead to significant problems above the tunnels and in nearby structures. This paper focuses on surface settlement measurements, on the interaction of twin tunnel transverse surface settlement and on the relationship between shield parameters and transverse surface settlement for parallel tunnels using EPBM shields in clay and sand soils in shallow depth. Also, a new equation is proposed for estimating the transverse settlement curve of twin tunnels. The results from this proposed equation are compared with the results of field observations. The transverse settlement curve values obtained from the proposed equation have good agreement with the actual results for the Otogar–Kirazli metro case studies.     

Evaluation of buttress wall shapes to limit movements induced by deep excavation

Three-dimension finite element analyses of deep excavations with buttress walls were performed to evaluate the effect of buttress wall shapes on limiting movements induced by deep excavation. Results showed that a combination of the rectangular and the capital L-letter shapes (RL-shape) yielded the greatest performance in reducing wall deflections and ground surface settlements. The main deformation-control mechanism mainly came from the horizontal and vertical frictional resistances of buttress walls against adjacent soils which were pushed by wall deflections and the soil heave at the excavation bottom, respectively. Besides, the RL-shape buttress walls were successfully verified through a well-documented case history.     

Three‐dimensional inverse analyses of a deep excavation in Chicago clays

Numerical models are commonly used to estimate excavation‐induced ground movements. Two‐dimensional (2D) plain strain assumption is typically used for the simulation of deep excavations which might not be suitable for excavations where three‐dimensional (3D) effects dominate the ground response. This paper adapts an inverse analysis algorithm to learn soil behavior from field measurements using a 3D model representation of an excavation. The paper describes numerical issues related to this development including the generation of the 3D model mesh from laser scan images of the excavation. The inverse analysis to extract the soil behavior in 3D is presented. The model captures the measured wall deflections. Although settlements were not sufficiently measured, the predicted settlements around the excavation site reflected strong 3D effects and were consistent with empirical correlations. Copyright © 2010 John Wiley & Sons, Ltd.     

Test and numerical research on wall deflections induced by pre-excavation dewatering

Numerous studies have been devoted to the performance of excavations and adjacent facilities. In contrast, few studies have focused on retaining wall deflections induced by pre-excavation dewatering. However, considerable inward cantilever deflections were observed for a diaphragm wall in a pre-excavation dewatering test based on a long and narrow metro excavation, and the maximum deflection reached 10 mm (37.6% of the allowable wall deflection for the project). Based on the test results, a three-dimensional soil–fluid coupled finite element model was established and used to study the mechanism of the dewatering-induced diaphragm wall deflections. Numerical results indicated that the diaphragm wall deflection results from three factors: (1) the seepage force around the dewatering well and the soil–wall interaction caused the inward horizontal displacement of the soil inside the excavation; (2) the reduced total earth pressure on the excavated side of the diaphragm wall above approximately 1/2 of the maximum dewatering depth disequilibrated the original earth pressure on both sides of the diaphragm wall; and (3) the different negative friction on the excavated and retained sides of the diaphragm wall led to the rotation of the diaphragm wall into the excavation.     

基于土体小应变本构模型的TRD工法成墙试验数值模拟

等厚度水泥土搅拌墙技术即TRD工法,近年来在深基坑工程中得到了广泛应用。以上海国际金融中心基坑工程开展的0.7 m厚、8 m宽、56.7 m深TRD成墙试验为背景,采用有限元方法,并基于土体小应变本构模型对其成墙过程进行了模拟,得到了土体侧向位移和地表沉降曲线,并与实测数据进行了对比。结果表明,距离墙体5 m处两者的土体侧向位移曲线基本一致,而距离墙体1.4 m处的土体侧向位移在深度大于20 m后的计算结果较实测值偏小;地表沉降在靠近墙体处最大,随着距墙体的距离增大而逐渐减小。最后分析了成墙深度对地表沉降和土体侧向变形的影响,结果表明,深度越深,引起的土体侧向变形和地表沉降也越大。通过不同成墙深度引起的地表沉降归一化曲线可看出,TRD成墙引起的最大地表沉降约为0.05%H（H为成墙深度）,沉降影响区域约为1.8H。     

Investigation of the integrated retaining system to limit deformations induced by deep excavation

A series of three-dimensional finite element analyses of deep excavations with the integrated system between buttress walls and diaphragm walls was conducted to investigate the effect of the buttress wall intervals, treatments, locations, height, and thickness on limiting deformations induced by deep excavation. The integrated retaining system was formed by maintaining buttress walls when soil was excavated. The wall deflection control mechanism of the integrated retaining system mainly came from the combined stiffness between the buttress wall and the diaphragm wall. In addition, the ground settlement control mechanism came from the combined stiffness between the buttress wall and the diaphragm wall, and the frictional resistance between the buttress wall and the surrounding soil. For achieving 50% reduction in the wall deflection and the ground surface settlement, the length and intervals of buttress walls that were applied to the integrated retaining system were at least 4 and 8 m, respectively. When the deflection at the diaphragm wall head was well restrained, for example, by the floor slab, the position of the buttress wall head could be located at a depth the diaphragm wall starts to bulge out. In such a case, the performance between the full height and limited height of buttress walls was quite close. Furthermore, a new well-documented excavation project was analyzed to verify the performance of the integrated retaining system. Results showed that the integrated retaining system worked excellently if the joints between buttress walls and diaphragm walls were constructed properly.