分区施工基坑对邻近隧道变形影响的三维有限元分析

上海世博片区绿谷一期深大基坑工程紧邻越江双线盾构隧道,基坑环境保护要求高,基坑采用分区方案实施。以PLAXIS3D有限元软件建立基坑与邻近隧道的三维有限元模型,土体采用HS-Small小应变本构模型,对基坑分区开挖的过程进行了动态模拟。计算结果与实测结果对比表明,采用HS-Small小应变土体本构模型的三维有限元分析能较好地模拟基坑的变形以及基坑开挖对邻近隧道的影响;分区施工方案通过减小单个基坑的规模,充分利用了基坑的时空效应,起到了很好的变形控制作用。     

基坑开挖对周边环境影响的三维数值分析

基坑开挖会对邻近既有隧道及土体变形特性产生重要影响。基于Midas GTS420研究基坑开挖对周边土体、支护结构及邻近双向水平隧道的变形特性影响。数值模拟结果表明:周边土体沉降主要发生在开挖基坑长边中部及拐角部位,最大沉降位置位于围护结构外约1/3基坑宽度处;围护结构的最大水平位移位于基坑长短边拐角处,当基坑开挖深度接近于临界深度时,水平位移迅速增大;隧道的横向位移存在一个临界埋置深度,其深度约9m。     

大型基坑分区开挖对邻近地铁的影响

本文通过现场实测数据分析了大型基坑分区开挖对临近地铁车站以及车站两端盾构隧道竖向和水平向变形的影响。分析结果表明:受邻近基坑开挖卸荷的影响,在竖直方向车站产生了隆起变形,盾构隧道受地质条件差异和施工参数的影响,既有沉降也有隆起;在水平方向车站和隧道均朝向基坑移动;流变对车站和隧道竖向变形影响较大,因流变而产生的竖向变形可占总变形的50%;分区开挖由于可以充分利用中隔墙对基坑变形的约束,以及时空效应对变形的影响,因此可以有效地减小基坑开挖对邻近地铁变形的影响。     

深基坑开挖对邻近软土隧道的影响分析

随着地下空间综合利用的迅速发展,越来越多基坑工程紧邻隧道进行建设,基坑开挖将必然会对邻近隧道产生一定的影响。因此,在保证既有隧道安全的前提下建设新的基坑工程已成为众多学者关注的重要课题。以某邻近既有隧道的基坑工程为背景,采用有限元软件MIDAS建立三维数值模型,分析基坑开挖对邻近软土隧道的影响。研究表明,基坑开挖会引起邻近隧道发生一定的水平位移和竖向位移,其中竖向位移为主要位移。在设计和施工中,应考虑减少基坑开挖卸荷对周边土体的影响。研究成果可为类似工程的设计和施工提供一定的参考和借鉴。     

基坑开挖对邻近地铁区间影响的数值模拟分析

临近基坑的地铁轨道会因为基坑的开挖而产生位移和变形,这将影响到轨道交通的运营安全。以长沙某深基坑工程为背景,通过划分不同的施工阶段,用PLAXIS软件模拟分析了在该项目的基坑开挖过程中,邻近地铁区间的土体位移和管片变形的发展规律。结果表明:随着开挖的进行,地层最大竖向位移发生在基坑底部,最大水平位移发生在基坑顶部,地铁隧道处的地层位移变化较小;地铁管片离基坑越近,变形越大。     

深基坑开挖对邻近地铁隧道影响数值计算分析

基于招商银行深圳分行大厦深基坑开挖工程,考虑隧道衬砌与土的相互作用,采用ABAQUS数值模拟研究了基坑开挖对邻近地铁隧道的影响。计算分析结果表明：基坑开挖对邻近地铁盾构区间产生一定影响,但影响程度较小,沉降与位移值均在规范要求范围之内;地表沉降、隧道衬砌位移随基坑开挖深度加深逐渐变大,在内支撑间距离较大时,沉降与位移增加速率较大;考虑衬砌与土的相互作用,隧道的水平位移值明显低于支护桩,基坑开挖对大直径管道影响计算分析中,应考虑管-土的相互作用。     

近接地铁隧道的基坑开挖土体扰动影响测试研究

近接地铁隧道的软土基坑开挖会对周边土体产生扰动,其应力状态和力学性质将发生变化,进而影响邻近隧道的变形和稳定。为此,本文在现有施工扰动评价方法的基础上,以近接宁波轨道交通3号线某区间盾构隧道的JD08地块基坑工程为例,采用现场原位测试方法,研究了基坑开挖前、开挖后周边土体的变形、水土压力和静力触探指标变化,分析了基坑开挖对周边土体的扰动作用以及扰动度分布规律,结果表明：近基坑侧的测点的锥尖阻力衰减(扰动度)主要分布在20%～40%之间;邻近地铁隧道侧的测点的锥尖阻力衰减总体上小于20%,基坑开挖卸荷影响较小。本基坑所采用的地连墙支护有效减小了基坑开挖对周边地层的扰动,确保了邻近地铁隧道的安全和稳定。     

复杂条件下基坑开挖对周边环境的影响研究

为了研究复杂条件下的基坑开挖对周围环境产生的影响,使用Midas GTS NX有限元软件建立三维数值模型,分析常州历史文化街区一基坑开挖对土体、围护结构及临近地铁隧道的影响。结果表明：基坑开挖存在明显的空间效应,阴角利于基坑稳定;开挖后坑内土体隆起,坑外土体沉降;地铁隧道在竖向主要表现为隆起,水平向主要表现为朝向基坑方向发生位移;隧道竖向位移和水平位移均与基坑范围存在明显对应关系,在基坑范围内的隧道变形最大;隧道整体在竖向表现为收缩变形,水平向表现为扩张变形。     

浅析深基坑开挖对邻近盾构隧道的影响

以上海某隧道在运营期间受到邻近车站基坑开挖的影响为例,运用连续介质模型分析了基坑开挖前、后盾构隧道内力变化和变形趋势,分析中通过选取合理的本构模型,控制隧道的变形增量在20~30mm之间[1],观察内力增加量,并给出相应的设计施工措施加以控制。分析指出基坑开挖一般会引起隧道向基坑方向侧移并使隧道断面呈横椭圆形状变形[3]。本文研究成果对认识基坑开挖导致邻近隧道影响的规律和制定隧道保护标准具有指导意义。     

基于HSS模型的基坑开挖对近邻地铁影响数值分析

随着城市轨道交通网络的不断扩大,城市深基坑工程大多邻近地铁区域.基坑开挖将导致周围土体产生附加位移,当土体位移过大时,就会对邻近结构物产生不利影响,因此开展基坑开挖对邻近地铁隧道区域和车站安全性影响的分析研究具有重要的现实意义.以天津某地铁车站明挖基坑工程为例,运用有限元软件Plaxis 3D分析基坑开挖对邻近隧道区间...     

敏感环境下深大基坑开挖实测分析及数值模拟

邻近已有地铁隧道的深大基坑的开挖是一项非常复杂的工程,开挖工程中如何能够安全地控制地铁隧道的变形尤其重要。对某邻近地铁区间隧道的深基坑施工进行全过程跟踪监测,及时反映不同工况下基坑围护结构变形、立柱回弹的变化特征;分析基坑施工对周边环境,特别是对邻近地铁隧道的影响,同时应用三维有限元分析手段,对地铁隧道在基坑施工过程中所产生的影响进行弹塑性分析。分析结果与工程实测数据比较吻合,表明整体有限元方法可以较好地模拟此类工程问题,从而为实际工程的设计施工提供一定的理论和计算依据。     

Investigation of response of metro tunnels due to adjacent large excavation and protective measures in soft soils

The inevitable influence of large excavation in soft soils on nearby tunnels is of great concern in practice. In this paper, the influence of a nearby large excavation on existing metro tunnels of the Ningbo Metro Line 1 in sensitive soft soils is investigated and presented. Considerable displacement in the left tunnel closer to the excavation induced by the nearby excavation was revealed by field monitoring. Visible cracks and leakages were observed in left tunnel linings. Three dimensional numerical simulations are conducted to investigate the responses of the ground and left tunnel due to the adjacent excavation. The development of bending moment and displacement of the left tunnel during different construction stages of the nearby excavation is obtained. Then the interaction mechanism between the nearby excavation, surrounding soils and existing twin tunnels is investigated, which is of significance to the interpretation of the influence of the nearby excavation on the existing twin tunnels. Several protective measures for alleviating the influence of adjacent excavation on left tunnel are studied, including divided excavation, soil improvement and a cut-off wall. It is found that the left tunnel is influenced to varying degrees during different construction stages and the time effect is distinct for this large excavation in soft soils, which would be suggestive to engineers to pay more attention to the protection of adjacent tunnel during the crucial construction stages. The bending moment and displacement of the left tunnel is strongly related to the unloading effects and displacement of surrounding soils, which can be alleviated by means of proper improvement of excavation sequence. Comparatively, longitudinally divided excavation is more effective in protecting the left tunnel than soil improvement or a cut-off wall. This study is of certain reference value for protecting metro tunnels adjacent excavation in soft soils.     

环形结构支撑体系在基坑工程中的应用

通过广州珠江新城B1-7项目基坑支护工程,讨论在场地狭窄的闹市区并且附近有运营的地铁隧道的情况下,进行基坑支护和土方开挖时产生的问题。考虑地质条件、主体结构形式、施工场地和地铁隧道等因素,提出采用环形结构支撑体系作为基坑支护结构,有效地解决了场地狭窄、阻碍主体结构施工的内支撑等问题。采用理正深基坑支护F-SPW 5.41和MIDAS/GTS两个软件进行计算,分析基坑开挖对地铁隧道、周边建筑物的影响。计算结果和监测数据显示,采用环形结构支撑体系有效地保证了地铁及周边建筑物的安全。     

膨胀土条件下隧道下穿既有地铁车站CRD开挖工法优化

为保证膨胀土条件下新建隧道施工和既有结构的安全,以合肥地铁5号线下穿既有地铁车站工程为依托,考虑膨胀土胀缩性及裂隙性等不良特性,对其采用了袖阀管注浆加固方法.基于CRD工法的开挖工序和循环步距提出了不同优化方案,并通过PLAXIS3D岩土有限元软件,模拟了计算隧道及周边地层的受力和变形,选择出了最优方案.该研究表明:不...     

深基坑开挖对既有地铁车站影响的计算模式分析

城市地铁沿线建设不可避免地会遇到深基坑工程问题。针对深基坑开挖对邻近既有地铁车站的影响 ,提出一种弹性地基上的板壳有限元计算模型 ,并通过对即有车站板下结构土体整体变位和单独考虑底板下土压力方案的对比分析 ,对模型中土压力的作用方式进行了分析。     

Prediction of tunnel displacement induced by adjacent excavation in soft soil

Deep excavation may have impact on the adjacent tunnels. The interaction between new excavations and existing tunnels has been increasingly serious with the rapid development of underground space and metro system in urban area. It hence creates a high necessity to predict tunnel displacement induced by nearby excavation to ensure the safety of tunnel. In this paper, a semi-analytical method to evaluate the heave of underlying tunnel induced by adjacent excavation is presented and verified by field measurement results. The influence of excavation and the resistance of tunnel are obtained based on Boussinesq’s and Mindlin’s solutions, respectively. Then the soil–tunnel interaction behavior is analyzed based on the displacement coupling condition by assuming the tunnel as an elastic beam. A visco-elastoplastic model (VEP model) is employed to simulate the rheologic deformation of soil. The behavior of the tunnel underneath excavation is studied by the new method to discuss the influence of different factors, including excavation area, relative distance and construction procedure. Results of case studies show a good agreement between prediction and measurements.     

Ground Behavior Due to Tunnel Excavation with Existing Foundation

Two-dimensional (2D) and three-dimensional (3D) model tests of tunnel excavation with nearby existing foundation are carried out to investigate the influence of the existing foundation due to the interaction between ground and the existing structures. Three types of foundations: flat foundation, group-pile foundation and piled raft are considered. 2D and 3D finite element analyses using subloading t_ij model are also conducted. The deformation mechanism and distribution of earth pressure during tunnel excavation in the ground with nearby foundation are found to be different from those of green field condition. Surface settlement trough due to tunnel excavation in the ground with existing foundation does not follow the usual pattern of a Gaussian distributive curve, which can be observed in the case of green field. Especially, in the case of pile foundation, D_p, the distance between pile tip and tunnel is an important factor for the ground deformation and surface settlement. For a short distance D_p, although the length of pile is long, the ground deformation is concentrated at a place near the front pile and the rotation of foundation becomes larger. The maximum surface settlement in the case of existing foundation is also larger than those in the case of green field. Due to the existing foundation, unsymmetrical distributions of earth pressure occurred at the bottom of the ground due to tunnel excavation, both in model tests and numerical analyses. The earth pressure at the crown of tunnel in the case of existing foundation is almost the same as those in the case of green field. The arching at the shoulder of tunnel in the case of existing foundation, however, is much larger than those in the case of green field due to the dead load exerted on the foundation. The numerical results agree well with the results of the model tests.     

Effects of lateral unloading on the mechanical and deformation performance of shield tunnel segment joints

Unloading during lateral excavation widely occurs in existing subway shield tunnels. Previous studies have focused on the overall stress and deformation of existing tunnels caused by nearby unloading. However, the stress and deformation state of tunnel segment joints have yet to be considered. This study considered the non-continuity of the shield tunnel lining and the interactions among tunnel segment, surrounding rocks and ballast bed. A hybrid model of a shield tunnel was established based on 3D nonlinear contact theory. The mechanical and deformation properties of the segments and joints of an existing shield tunnel under the influence of lateral excavation of the foundation pits were studied. Unloading during lateral excavation caused the cross section of the shield tunnel to generate vertical convergence and shift horizontally towards the foundation pit. An opening and dislocation in the joint, which caused the waterproof ability of the joint to decrease sharply, were observed. Meanwhile, stress at the segment joint increased sharply and caused local cracks in the segment lining. Axial and shearing force on the joint bolt also increased significantly. Based on existing subway regulations, the calculation results were combined to establish a deformation control standard for existing shield tunnels under lateral excavation. The rate of vertical convergence of the lining should be less than 3.68‰, and the rate of horizontal shift of the axis should be less than 0.53‰.     

深厚淤泥土深长基坑开挖对邻近建筑的影响

沿海区域存在大量淤泥土层,其通常表现出高压缩性、流变性及触变性等不良工程地质性质。因此,深厚淤泥土深长基坑开挖面临着极高施工风险,对周边环境的影响显著。为进一步阐明深厚淤泥土深长基坑开挖施工力学效应,依托某深基坑工程,通过有限元三维数值模拟,揭示了淤泥土深长基坑开挖对邻近建筑的影响规律。结果表明:深厚淤泥土层的存在使基坑开挖影响区的水平影响区域明显增大,竖向影响区域所受影响较小,在水平距离150 m、深度85 m范围内土体皆受基坑开挖影响;基坑以及建筑轮廓凹凸部出现应力集中,在淤泥土层,地连墙以及既有隧道墙板应力集中处的水平位移存在明显突变;既有隧道水平位移和沉降曲线呈“中间大,两头小”的特征;大桥变形随开挖深度增加而变大,桥桩在淤泥土层的水平位移明显增大,最大水平位移达5.33 mm,最大沉降达9.92 mm。     

台北市软弱地基改良后之深开挖分析

为降低于软弱黏土层开挖可能引起挡土壁及地表沉陷过大之问题,常搭配辅助性之挡土措施。其中地基改良方法,实务上大都简化假设改良之复合土壤平均强度来进行分析。为求能更进一步探讨台北市软弱黏土层地基改良后之深开挖行为,本研究系以台北市内湖重划区已开挖完成案例,再利用二维有限元法程序PLAXIS来进行分析,并与现地监测数据比较分析,藉以探讨软弱黏土层地基改良后之深开挖特性。