深基坑开挖对邻近地埋管线影响分析

 为建立深基坑开挖对邻近地埋管线影响的评估方法,采用FLAC3D分析基坑开挖对邻近不同管径管线的影响。计算结果表明,管径大小对管、土相互作用影响很大;当管径约小于400 mm时,管线基本与土体具有相同的位移;管径大于400 mm时,应考虑管–土相互作用;此外,管线最大曲率、转角、最大应力和弯矩均发生在基坑端角部20%开挖长度的范围内。在数值分析的基础上,给出小管径管线变形受力计算的简化分析方法。     

工程荷载对地埋管线纵向响应影响的模型试验

隧道开挖和地面堆载以土体不均匀沉降的形式作用于管线,使管线产生纵向应力和变形。以物理模型试验手段研究了两种荷载形式下管土相互作用的差别、接头刚度对纵向响应的影响以及隧道开挖下的管土脱开现象。通过修正Gaussian曲线拟合自由土体位移场,对实测弯矩进行归一化处理发现,隧道开挖会引起管线周围相对土体模量下降,而地面堆载则会引起土体模量相对增大。非连续接头管线通过增大转角及变形来降低最大弯矩值,改善了管线的受力状态。当土层损失比增大到一定程度以后,管线下方将出现空洞,并随着损失比的增加而逐渐扩大,最终达到稳定。     

类矩形盾构隧道施工对邻近地下管线的影响研究

简化地下管线的三维力学计算模型,利用随机介质理论推导的土体沉降计算公式,得到类矩形盾构隧道施工对垂直交叉地下管线变形、弯矩、应力和应变的计算公式,通过算例分析土质条件、管线埋深和管线直径以及管壁对管线所受极限弯矩的影响。研究结果表明:管线极限弯矩受土质条件的影响较大,砂土中管线所受的最大极限弯矩大于黏土,但黏土中极限弯矩的影响范围更广;随着管线埋深的增加,管隧间距变小,隧道施工对管线的影响变大,管线所受的极限弯矩随之变大;管径和管壁的改变对管线所受极限弯矩有较大影响,管径的缩小造成管线的抗弯刚度减小,导致管线极限弯矩减小。     

承压水作用下基坑三维有限差分模型分析

隔水层土体采用应变相关修正剑桥模型,建立考虑承压水、土体、支护结构、水平支撑体系和竖向支承系统共同作用的三维有限差分耦合模型,考虑连续墙和土体之间的接触,采用FLAC3D实现基坑分步开挖过程。分析了承压水作用下深基坑开挖变形性状,包括坑底隆起变形、围护结构侧移、墙后地表沉降和侧移、深层土体沉降和侧移等,最后分析不同承压水头对基坑变形的影响。结果表明:初始承压水头较大时,坑底隆起变形受初始承压水头影响较大,特定点隆起变形随初始承压水头变化规律与室内试验结果较为吻合;不同初始承压水头下水平支撑以下的连续墙侧移差异较大;随初始承压水头增大隔水层中墙体和承压含水层中墙体的侧移表现出不同的变化形态;初始承压水头对墙后土体变形影响较小;在理想隔水层条件下,承压水头对基坑开挖过程中的变形影响较小。     

盾构双隧道不同开挖顺序及不同布置形式对管线的影响研究

在离心模型试验中同时考虑隧道开挖所致地层损失效应和质量损失效应,研究不同开挖顺序及不同布置形式下双隧道开挖对管线的影响规律。同时采用基于地层损失比的位移控制有限单元法对离心模型试验及其他4组拓展工况进行分析,其中土体本构模型采用考虑土体小应变特性的HP(Hypoplasticity model)模型,并将试验结果与已有的解析方法进行对比。研究结果表明,双隧道不同开挖顺序及不同布置形式对地表沉降、管线沉降、管线弯曲应变的影响显著;管线存在所产生的"遮拦"效应对管线正上方地表沉降的影响程度随着自由场最大地表沉降的增加而逐渐加剧;双隧道开挖所致管线沉降的主要影响区域为-1.2D_T~1.2D_T;实际工程中应加强浅埋后继隧道开挖时管线工作性状的监测工作,且不应简单采用叠加原理对不同施工工序及不同布置形式的双隧道开挖所致地表沉降、管线沉降及管线弯曲应变进行预测,应合理考虑后继隧道开挖所致土体的累计剪切应变及上覆隧道的遮拦效应对管–土相对刚度的影响。     

桩-锚支护深基坑开挖的有限元分析

为研究深基坑开挖对基坑及周围土体的位移影响,采用有限元软件ABAQUS模拟基坑开挖过程,对基坑内部、支护结构及临近土体位移进行研究。研究表明开挖初期,基坑后侧土体沉降最大处位于开挖深度1～2倍距离范围;开挖深度增大,基坑后侧土体沉降出现两个极值,分别发生锚杆自由段与锚杆尾部处;开挖深度较大时,在靠近支护桩位置出现大于基坑中心位置隆起量的凸起。支护结构最大侧移点位于坑底以上2～3m处。增加锚杆预应力或支护结构刚度,结构最大侧移、支护桩附近回弹凸起、坑后锚杆自由段处沉降量均减小,刚度增加前期的侧移控制效果更为显著。增加锚杆预应力,支护结构最大侧移点下降至坑底以下,排桩变形由"大肚子"状逐渐变为"S"形。     

砂土中隧道施工条件下管土相互作用的室内模型试验研究

为分析砂土中隧道施工条件下管线与土体相互作用的机理,利用室内模型试验,自制模型箱,以江砂为填料,选取高密度聚乙烯管材进行试验。结果表明:在砂土中,与穿既有管线轴线相垂直的下穿隧道施工过程中,管线中间部位主要受下拉效应影响,而上拱效应则支配着管线两侧的变形;管线的存在对土层位移的影响范围约为水平向距管线轴线3倍的直径;随着地层损失量的增大,管线与土层的变形曲率比值逐渐减小,管线的弯矩与应变相应增大;隧道施工条件下管线上覆荷载有增大的趋势,管线中间部位管底土压力逐渐趋于零,管线与土层分离区宽度随着地层损失量的增大逐渐增大并趋于一恒定值;通过对管土相互作用机理的探讨,明确了沉降槽宽度系数i、中心最大沉降量smax以及管线埋深与管径比值H/D等因素对管土相对刚度的影响,基于室内模型试验结果提出了管土相对刚度的计算式。     

某地铁深基坑顺逆结合开挖变形性状的实测分析

目前对于软土地区采用顺逆结合法开挖的深基坑变形性状研究还较少。研究了杭州某34.5m深的地铁基坑在顺逆结合开挖方法下的变形性状,分析了基坑开挖对一倍开挖深度距离内邻近地铁隧道附近土体的影响。研究结果表明:(1)逆作板加强了围护结构体系的刚度,有效地限制了地下连续墙的侧移、墙后地表沉降和立柱隆起,进而限制了邻近隧道附近土体的位移;(2)合理的土体开挖顺序能有效地限制基坑中间处的墙体侧移,使得该截面的墙体侧移并非是沿基坑长边所有截面中墙体侧移最大的;(3)隧道与附近土体相互作用明显,附近土体在隧道埋深处都随刚度相对较大的隧道向基坑内呈现一定程度的水平移动,而上部土体的水平移动随着空间位置的不同而表现各异。相关结论对软土地区类似深基坑工程的变形控制具有一定的参考意义。     

地铁车站洞桩法施工引起的地表沉降和邻近柔性接头管道变形研究

在城市复杂建设环境下,地铁车站施工对地层和邻近管道的影响问题备受关注。依托北京地铁10号线黄庄站工程,基于地表和管道沉降的实测数据,建立"车站结构-地层-管道"三维耦合有限元模型,研究车站洞桩法施工对地层和管道的影响。采用主从接触面有限滑移方法模拟管道与土体相互作用,并利用两节点连接单元约束模型模拟柔性接头管道的接头变形,获得车站洞桩法施工对地表沉降和邻近柔性接头管道沉降、变形、应变、接头转角和脱开的影响规律。结果表明,"导洞开挖支护"和"中跨扣拱及拱部土体开挖支护"两个施工阶段是车站洞桩法施工中引起地表沉降的重要工序;管道变形与其相对于隧道的位置关系密切,管道正下方土体开挖过程对管道的影响最为显著;柔性接头管道的变形主要由管道接头承担,可采用接头转角和脱开作为管道变形的控制指标;管道接头转角的变化经历初始变化、凸曲率、凹曲率和稳定等四个阶段,而管道接头脱开经历初始变化、快速增长和稳定等三个阶段。     

上海地区板式支护体系基坑变形预测简化计算方法

基坑变形预测是分析基坑开挖对环境影响的核心内容之一。收集了上海地区65个常见的板式支护体系基坑工程案例,并对其进行了分类。对不同类型的板式支护体系基坑建立不同的基于土体HS-Small模型的平面应变有限元模型进行分析。根据室内土工试验结果与基于实测数据的参数反演分析,确定了上海软土地区典型土层土体的HS-Small模型计算参数。通过对108个有限元计算结果的分析及归一化,推导了能够综合考虑基坑系统刚度、基坑深度和基坑宽度的上海地区板式支护体系基坑围护结构最大侧移和地表最大沉降的简化计算公式,并且提出了基坑围护结构侧移曲线和地表沉降曲线,同时也给出了上海地区板式支护体系基坑变形的预测流程。采用本文给出的简化方法预测了上海地区的7个工程的变形并与实测结果进行了比较,结果表明该方法能较好地预测上海地区的板式支护体系基坑的变形。     

地下管道破损诱发沉降的预测模型及试验验证

设计了一套富水砂层中管道破损诱发地面沉降的试验系统,对骨架粒径d90=1.45~8.45 mm的11种土样,在6种渗透比降和管道满流流速下,土体渗流侵蚀诱发地面沉降的规律进行了研究。在此基础上,提出了地下管道破损诱发地面沉降的预测模型。研究表明:(1)富水砂层中管道破损是否会诱发沉降,主要由土体骨架粒径d90、破损口直径D和厚跨比hs/D决定;发生沉降的土体骨架粒径d90最大值,需同时满足破损口直径D和厚跨比hs/D两个条件,并取两者中的较小值;(2)富水砂层中管道破损诱发沉降的区域平面上呈圆形、剖面上呈倒置三角形,坡面角与土体饱和内摩擦角接近;沉降区顶面半径和沉降深度随满流流速u和渗透比降hw/hs的增加而增大,随厚跨比hs/D的增大而减小;(3)在曼宁公式基础上推导出的沉降半径、沉降深度预测公式,规律上与试验结果一致,数值上与试验结果接近,可用于富水砂层中管道破损诱发地面沉降的预测。     

Environmental risk management for a cross interchange subway station construction in China

Ground surface settlement induced by urban subway construction using shallow tunnelling method is inevitable and it may cause a series of negative impact to existing nearby structures and utilities. In order to guarantee environmental safety, a risk management methodology which aims at process control for ground settlement and existing nearby structures is proposed. It includes 5-stage technology-based steps: survey of existing conditions, designing control standards for key risk factors, analyzing environmental response under tunnel construction and designing process control standards, monitoring and taking proper process control measures during construction, and risk reassessment after construction. This methodology was put into practice in the Huangzhuang subway station construction which is the largest cross interchange subway station construction using shallow tunnelling method in China. According to site survey, nearby pipelines and existing buildings were determined to be the key risk factors. The risk control standards for nearby pipelines and existing buildings were made according to available standards in China and related literatures. Design of process control standards for ground surface settlement was assisted by numerical simulation, which aimed at controlling the key risk factors. During construction, monitoring was adopted for the nearby pipelines, existing buildings and ground surface. After the four drifts excavation of the double-deck part of Line 4, a series of risk control measures, which included treatment of the unfavorable geological bodies, installation of roof pipes, compensation grouting, full-face grouting and some other control measures, were taken. Due to these risk control measures, ground surface settlements, except at two measuring points of Line 4, were successfully controlled under the given process control standards for both Line 4 and Line 10. All the pipelines and buildings were under their normal service state during tunnel construction. The maximum deflection for the 6 pipelines above the station was controlled to be within 2 mm/m and the maximum settlement of all the monitoring points for the pipelines was less than 30 mm. For the four important existing buildings in close vicinity, the maximum deflection was less than 1 mm/m; the maximum settlement value was 6.8 mm and the maximum uplift value was 3.0 mm. The risk control system was shown to be effective in ensuring environment safety, structure safety and construction safety. These safety control methods, the methodology of designing these control standards and the measures taken in the construction can serve as a practical reference for other similar projects.     

隧道降水施工地表沉降的渗流-应力耦合分析

根据有效应力分析方法,建立了弹塑性渗流–应力耦合分析理论模型;采用流体体积方法方法来跟踪非稳定渗流场的动态自由水面,开发相应的数值模拟分析程序;并对某地铁隧道工程的动态降水过程和开挖过程进行仿真模拟,对降水和开挖过程中的地表沉降进行重点分析,得出动态变化的地表沉降曲线,通过将地表沉降计算值与现场量测值比较分析,两者数据吻合较好。研究结果表明,降水的影响半径约为30m,降水所引起的地表最大沉降值约为23mm,左右隧道施工完时地表最大沉降值约为43mm,施工期间周围建筑物和地下管线均无安全隐患。而通常采用30mm的控制标准,说明城市地铁工程的沉降控制基准要视具体的工程环境条件而定,这为该工程和类似工程施工提供了依据和参考作用。     

地基沉降作用下埋地聚乙烯管强度失效的数值模拟

对聚乙烯(PE)管进行不同应变率下的拉伸试验,并采用率相关本构模型获得PE管的材料参数.利用Abaqus软件模拟了埋地PE管在地基沉降作用下的应力-应变行为,分析了PE管应力随沉降位移的变化情况,探讨了过渡段长度对PE管屈服应力的影响.结果表明:PE管的最大Mises应力随沉降位移的增加而增大,危险段发生在过渡段与沉降区或非沉降区的交界处;随着过渡段长度的增加,PE管屈服的沉降位移逐渐增大,在同等沉降位移条件下,长过渡段埋地PE管比短过渡段埋地PE管更安全.     

类矩形盾构施工对地下管线影响的模型试验研究

类矩形盾构隧道开挖使土体以不均匀沉降形式作用于地下管线,导致管线产生纵向变形、破坏。针对类矩形盾构隧道施工,采用室内缩尺寸模型试验,综合考虑管隧相对位置、管线埋深及土体损失率3个影响因素,研究类矩形盾构隧道在砂土地层中施工,地下管线沉降、变形及地表沉降的规律变化。研究结果表明:管隧垂直工况时,管线竖向位移曲线呈高斯分布,竖线位移反弯点出现在隧道轴线附近处,管线弯矩呈"M"型分布,最大竖向位移及弯矩位于隧道轴线正上方;管隧斜交工况所受影响比管隧垂直工况影响更大;管线埋深越大,管线受影响程度越深;管线竖向位移随土体损失率减小相应降低,隧道轴线正上方管线竖向位移与管线最大正弯矩及两个较大负弯矩减小幅度较大,管线两端受影响程度较小;地表沉降受土体损失影响较大,沉降值比管线大。     

Application of the arctangent function model in the prediction of ground mining subsidence deformation: a case study from Fushun City,Liaoning Province,China

Ground subsidence disasters are characterized by wide distribution, long duration, and high-intensity damage, which can cause serious damages to surface buildings, underground pipelines, aquifers, and so on. Therefore, research on the stability evaluation of ground subsidence and subsidence deformation prediction is of great significance. This paper takes ground subsidence in Fushun City, Liaoning Province, China, as a case study. Combined with data from 60 monitoring points in the subsidence areas, the final settlement deformation values of all monitoring points were obtained through an arctangent function model using non-linear curve fitting with monitoring data. The proposed model could enable the prediction of settlement deformation trends of the monitoring points. Correlation coefficients are all above 0.937, indicating the strong reliability of the prediction model. By processing the final settlement deformation predictive values of the 60 monitoring points, a final settlement contour map was drawn with the help of the Kriging interpolation method. This map could forecast the whole distribution characteristics of ground settlement deformation in the research area. Then, risk zoning can be obtained by combining the settlement rate and residual settlement deformation in the study area. The research results could provide a basis for future city construction and regional planning in Fushun City.     

软土地区深基坑施工对周边环境影响监测分析

对软土地区某深基坑施工期间周边环境影响开展监测研究工作。监测内容包括地下管线变形、周边地表沉降、周边建(构)筑物变形等。监测分析表明:周边管线变形呈现逐步下沉趋势,累计沉降量逐渐增大,距离基坑越近的管线变形越大;东侧深桩基建筑物,未出现较大的变形;南侧三航小区自行车简易房西侧部分沉降较为明显,东侧沉降不明显;三航小区4号居民楼,北侧房屋监测点沉降较为显著,南侧房屋监测点沉降较小;基坑周边地面变形均为距离基坑较近的监测点变形大。     

城市浅埋大跨连拱隧道非对称开挖地表沉降偏态性研究及其对策

 大量实测资料及试验表明,地表下沉曲线以及拱顶沉降、中墙应力、围岩塑性区分布具有明显的非对称性,即具有偏态性。对于此偏态问题,国内外学者以Weibull分布作为影响函数建立预计方法,利用地表移动的最终结果拟合,给出了偏态下沉预计的经验公式,但对偏态形成的原因却没有深入分析。结合城市浅埋大跨连拱隧道工程实例,针对已成功应用的CD,CRD工法等非对称开挖方法,根据现场监测数据进行反分析,采用数值模拟方法,对开挖沉降曲线的偏态性及其内在机制进行了深入研究。在此基础上,提出采取压浆弥补地层损失,设置隔水帷幕限制偏态沉降范围,非等参支护调节时空效应等具体防范对策;监控量测中,应耦合建构筑物的健全度,评估施工环境影响风险阀值,拟定控制标准,保证地下管线和地面建构筑物的安全。     

Effect of surrounding soil on stress–strain response of buried pipelines under ground loads

In order to determine the stress–strain response of buried pipelines under the ground load, the pipeline–soil coupling finite element model was established. The mechanical behaviours of buried pipelines in the soil stratum and the rock stratum, as well as the effects of surrounding soil's elasticity modulus, Poisson's ratio and cohesion on stress and strain of buried pipelines were investigated. The results show that the maximum von Mises stress, high stress area, axial strain and plastic strain increase with the increasing ground load. Buried pipeline in the soil stratum is more prone to failure than in the rock stratum under the same ground load. The maximum axial compressive strain appears at the bottom of buried pipelines when there is no buckling, and the maximum tensile strain appears on the two sides. High stress area, the axial strain, the plastic strain and the plastic area decrease with the increase of the soil's elasticity modulus and cohesion. But the surrounding soil's Poisson's ratio has a small effect on the stress and strain of buried pipelines under the ground load. The results can provide a theoretical basis and reference for safety evaluation, repair and maintenance of buried pipelines.