砂土中隧道施工引起近接隧道位移的试验研究

新建隧道施工对近接隧道的影响,一直是隧道设计和施工中必须考虑的问题,但现阶段对此还没有一致的认识。为了进一步研究新建隧道施工对近接隧道影响机理,设计了能够模拟隧道分步开挖的室内模型试验装置,并用该试验装置进行了砂土地层中新建隧道施工引起近接水平平行隧道位移的试验研究。试验重点研究了两平行隧道间净距、埋深对既有隧道位移的影响。通过对试验结果分析,得到了既有隧道拱顶和靠近新建隧道一侧拱腰部位的位移发展规律。试验结果分析表明,新建隧道开挖会对既有平行隧道结构产生侧向挤压效应,隧道埋深和净距对既有隧道的位移都有影响,但隧道间净距变化对位移量的影响更大。当隧道间净距大于2倍隧道直径时,新建隧道开挖对既有水平平行隧道位移的影响非常小。研究成果可为砂土地层中近距离平行隧道设计和施工提供参考。     

双线隧道开挖对邻近隧道影响的两阶段分析方法

随着我国很多大城市地铁隧道的兴建,大多数隧道设计施工方案都采用双线平行盾构法或暗挖法施工。在地下空间越来越拥挤的城市地区,最重要的研究问题是新建双线平行隧道对既有隧道产生的影响问题。合理预测双线平行隧道施工穿越既有隧道引起的变形是确保既有隧道结构安全和新建双线平行盾构的顺利掘进的关键。考虑新建双线平行隧道施工中对周边土层和既有隧道产生的叠加效应,提出了预测新建隧道引起的邻近隧道纵向变形的两阶段分析方法。首先,考虑新建双线平行隧道引起地层位移的不对称性,计算新建双线平行隧道开挖作用在既有隧道上引起的广义附加荷载。然后,将既有隧道考虑为Pasternak 地基上的Euler-Bernoulli梁,基于 Galerkin 法求解既有隧道纵向变形影响的基本微分方程。通过与工程沉降实测数据进行对比,验证该文提出的预测方法的合理性和结果的准确性。     

Numerical investigation of underlying tunnel heave during a new tunnel construction

This paper presents a case study of protecting existing tunnels during the construction of a new cut-and-cover tunnel above in Nanjing, China. Various construction measures, including sequential excavation, jet grouting, and a pile-slab retaining system were performed to control the heave of existing tunnels. Furthermore, a numerical analysis using a finite difference program, FLAC3D, was conducted to investigate the influence of different construction schemes on the tunnel heave. Finally, a comparison between numerical results and field measurements were carried out to study the influence on the tunnel heave from various factors, such as the ground reinforcement depth, excavation sequence, and the skew angle between new tunnel and existing tunnels. The results show that when the excavation volume is small, the uplift values of existing tunnels increase nonlinearly with the increasing excavation width of each step. The pile-slab retaining system combining with ground treatment method can control the tunnel heave within the required limits. The optimum ground treatment scope is about 1.5 times of the excavation depth in this project. Compared to other construction schemes, the tunnel heave will be the smallest under a staggered segmentation excavation method starting from the sides to the center.     

软土地层并行曲线隧道施工顺序对既有隧道的影响

为了研究并行曲线隧道施工顺序对既有隧道的影响,以横琴杧洲隧道工程为依托,建立了并行曲线隧道三维有限元数值模型。在此基础上,研究了不同施工顺序和曲率半径r(r=500,800 m)下新建曲线盾构隧道开挖对既有隧道变形的影响。结果表明:施工顺序对既有隧道位移影响较小,曲率半径对既有隧道位移影响相对较大; 随着曲率半径(r=500～800 m)的增加,既有隧道位移增加约15%; 既有隧道的位移主要在盾构开挖面前方2D(D为隧道外径)、后方1D范围内产生; 施工顺序对既有隧道内力的影响与曲率半径有关; 隧道曲率半径为500 m时,施工顺序对既有隧道内力变化影响规律相似,即离盾构开挖面最近的既有隧道剖面产生的弯矩最大,且最大弯矩和最小弯矩均出现在靠近新隧道一侧; 内侧隧道先开挖时,既有隧道的弯矩(绝对值)更小,此时对于并行曲线隧道施工,内侧隧道先开挖更安全; 在盾构开挖面前方一定距离内既有隧道产生的轴力最大; 隧道曲率半径为800 m时,双线隧道近似于平行隧道,施工顺序对既有隧道内力变化和大小影响较小。     

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.     

平行隧道开挖引起上方既有隧道的纵向变形研究

城市地铁隧道大多数采用平行双洞的布置形式作为隧道设计施工方案,根据不同的地层条件等因素采用盾构法或暗挖法施工。由于城市地下空间变的越来越拥挤,研究新建平行双洞隧道施工过程中对邻近既有隧道的影响程度问题显得尤为重要。本文基于两阶段分析方法研究预测平行双洞隧道开挖引起上方已建隧道的纵向变形的简化解析方法。首先,采用两高斯曲线叠加,计算新建平行双洞隧道施工引起的作用在既有隧道上的附加荷载。然后,将既有隧道考虑为Winkler 地基上的Timoshenko梁,建立既有隧道纵向变形的基本微分方程,并基于Galerkin 法进行求解。将本文提出的简化解析方法得到的结果与工程沉降实测数据进行对比以验证本文提出的预测方法的合理性。最后,进行了参数敏感性分析,研究了不同隧道相互位置、地层损失率、相对抗弯刚度和地层土性参数等对结果的影响规律。     

新建盾构隧道施工对近接平行隧道的影响分析

针对软土地层中浅埋大直径盾构隧道施工对既有近距离平行隧道的影响,以上海人民路越江隧道工程为背景,采用三维有限差分数值分析方法对南线隧道施工引起北线隧道的变形和洞周土压力的变化规律进行了研究。数值模拟结果表明新建隧道施工会使既有隧道侧向受压,引起既有隧道拱腰部位产生较大的压缩变形,拱顶及仰拱部位产生较大的张拉变形。新建隧道掘进过程中,既有隧道周围土压力经历增加、减小和趋于稳定三个状态。将数值计算结果与现场实测资料进行对比分析,表明计算值与实测值基本一致。此外,数值计算还有效弥补了现场实测在土体位移分布和土体塑性区形成方面的不足,计算结果表明受新建隧道施工影响,既有隧道周围地层位移和塑性区范围都有增加。研究结果可以为浅埋大直径近距离越江盾构隧道的设计和施工提供参考。     

平行盾构开挖离心机模拟试验研究

通过离心模型试验模拟平行盾构隧道近接开挖施工,研究了盾构隧道近接开挖对既有隧道结构内力、管片变形和地表沉降的变化规律。结果表明:1隧道开挖引起地表沉降的大小与开挖的步骤有关,而沉降槽的范围基本不变;2既有隧道靠近新建隧道一侧受拉,这一侧弯矩出现负增量,侧向土压力也有一定的减小,且既有隧道直径水平向变大,而垂向直径基本不受影响;3由于土拱效应,新建隧道已完成开挖部分管片拱顶的土压力随开挖进程先减小后增大;4采用地层结构法可以准确模拟隧道开挖过程的隧道结构力学特性与变形规律。     

Effects of twin tunnels construction beneath existing shield-driven twin tunnels

This paper presents a case of closely spaced twin tunnels excavated beneath other closely spaced existing twin tunnels in Beijing, China. The existing twin tunnels were previously built by the shield method while the new twin tunnels were excavated by the shallow tunnelling method. The settlements of the existing tunnels and the ground surfaces associated with the new tunnels construction were systematically monitored. A superposition method is adopted to describe the settlement profiles of both the existing tunnels and the ground surfaces under the influence of the new twin tunnels construction below. A satisfactory match between the proposed fitting curves and the measured settlement data of both the existing tunnels and the ground surfaces is obtained. As shown in a particular monitoring cross-section, the settlement profile shapes for the existing tunnel and the ground surface are different. The settlement profile of the existing structure displays a “W” shape while the ground surface settlement profile displays a “U” shape. It is also found that due to the flexibility of the segmental lining, the ground losses obtained from the existing tunnel level and the ground surface level in the same monitoring cross-section are nearly the same.     

基坑开挖对旁侧隧道影响及隔断墙作用离心模型试验研究

开展了干砂地层中基坑开挖对旁侧隧道影响及隔断墙保护作用的三维离心模型试验和数值分析,获得了隧道上浮、隧道内力、隧道周围土压力、地表沉降等变化规律以及隧道空间位置和基坑开挖深度的影响。试验结果表明,基坑回弹量与采用Boussinesq解计算的回弹量比较接近;地表沉降量与文献报道的试验结果相近,而明显小于现场实测沉降;靠近基坑一侧的隧道周围土压力有所减小,而远离基坑一侧的隧道周围土压力则有所增加。隔断墙的设置可以一定程度上减小地表沉降、隧道外土压力变化、围护墙水平位移以及隧道上浮和弯矩。数值计算结果表明,隧道上浮量和水平位移随着隧道埋深及其与围护墙距离的增大而减小,而随着基坑开挖深度的增大而增大。     

流变岩体中既有隧道与新建平行隧道相互影响的理论解

在流变岩体中进行隧道施工时,既有隧道与新建隧道的相互作用将使围岩应力、位移分布与单隧道问题有明显不同,且与时间相关。针对黏弹性岩体中深埋双圆形隧洞考虑施工顺序问题,用复变函数方法、Laplace变换、黏弹性叠加关系导出两隧道周边开挖增量位移和应力场的求解方法和理论解答,并与有限元解进行了比对。根据解答分析了既有和新建隧道孔边增量位移与全应力分布特点;隧道周边增量位移随时间的变化;周边位移随隧道间距的变化规律。可用于黏弹性岩体中双圆形隧道顺序开挖的施工分析。相比数值方法,理论解可更方便地进行参数分析和初步设计。     

平行双孔水工隧道相互作用的时效解答

地下工程中常遇到流变岩体中双线近距离隧道施工问题。隧道施工位移的预测和控制,特别是新建隧道的施工对既有隧道产生的影响,是工程中面临的重要问题。针对流变岩体中深埋双圆形水工隧道的问题,笔者采用复变函数方法和Laplace变换技术建立了考虑施工过程时黏弹性应力、位移与弹性复位势之间的关系,然后运用黏弹性叠加原理得到了整个施工过程各个阶段围岩应力和位移全量和增量理论解答,并据此进行新建隧道对既有隧道的影响分析。为验证解答的正确性,对一算例进行了有限元解答和理论解答的比对,两者吻合很好。与数值与实验方法相比,本文解答可以较为便利地对岩体应力、位移进行参数分析,进一步可以指导工程的初步设计。     

新建隧道施工对既有隧道影响的试验研究

通过新宝塔山隧道施工过程对既有宝塔山隧道的影响进行了数值模拟,并实测了新隧道开挖过程中既有隧道衬砌结构的变形和衬砌混凝土的应变变化情况。数值模拟结果和现场实测数据表明,既有隧道衬砌结构的变形和衬砌混凝土的应变变化较小,新隧道施工对既有隧道影响不明显,对后续工程施工有指导意义。     

北京地区浅埋暗挖法下穿施工既有隧道变形特点及预测

 城市地下工程建设中,新建隧道近距离下穿施工对既有隧道造成的扰动不可避免。正确分析及可靠预计既有隧道变形成为目前地下工程建设的热点问题。在预测隧道开挖引起的地表位移的经验法中,Peck公式最简便,应用也最为广泛。搜集北京地区10个近接下穿工程23组数据,对既有隧道实测变形进行拟合,发现绝大多数符合Peck公式分布规律。拟合得到地层损失率为0.116%～1.183%,沉降槽宽度系数为0.93～6.76。讨论新建隧道施工工法、辅助施工方法、新建隧道与既有隧道的埋深、既有隧道刚度、新建隧道双洞间距、变形缝位置等因素对经验参数的影响,给出经验参数的修正公式。将经验参数修正公式与Peck公式相结合,为北京地区受新建隧道下穿施工影响的既有隧道变形提供一个简便、快捷的预测方法,并通过工程实例验证了预测方法的有效性。研究成果可对未来北京同类工程和其他地区近接工程设计和施工提供参考,同时对丰富同类工程数据库具有重要意义。     

Rockburst response in hard rock owing to excavation unloading of twin tunnels at great depth

This study aims to investigate the rockburst characteristics of hard rock during the successive excavation unloading of twin circular tunnels subjected to high active stresses. The entire evolution process of the rockburst phenomena around the tunnels is reproduced. The numerical results indicate that the unloading rates, burial depths, and presence of structural planes between the twin tunnels play important roles in the occurrence and damage degrees of rockbursts. The failure intensity and dynamic responses are aggregated with the increase of the unloading rate of the subsequent adjacent tunnel. The rockburst damage degree is exacerbated with increasing buried depth, and the rock response of the twin tunnels becomes more sensitive to the dynamic disturbance (as compared to a single tunnel at a great depth). The presence of a structural plane between the twin tunnels has both favourable and unfavourable effects on the stability of the surrounding rock. When the structural plane is parallel to the maximum tangential stress, the dynamic disturbance from the adjacent tunnel can be attenuated by the structural plane or rock joints via reflection and scattering, thus reducing the dynamic response between the twin tunnels. However, for those structural planes oblique to the maximum tangential stress, a violent rockburst is more prone to be induced, owing to the integrated response to shearing and sliding along the structural plane, and slabbing from the excavation unloading process. It is also found that the effect of the structural plane on the rockburst response is largely dependent on the burial depth.

     

Numerical analysis of the interaction between twin-tunnels: Influence of the relative position and construction procedure

The development of transportation in large cities requires the construction of twin-tunnels or the construction of new tunnels close to the existing ones. Since, both the relative position of tunnels and the construction procedure affect the soil movement and internal forces in the lining, it is of major interest to study the influence of these factors on the tunnel design. This paper presents analysis of this issue with a particular interest for the optimization of both the relative position of the twin-tunnels and the construction procedure. For this concern, a parametric study is conducted for the investigation of the influence of these two factors on the soil settlement and internal forces resulting from the tunnel construction. The paper presents successively the numerical model and then analyses conducted for three configurations of the twin-tunnels: aligned-horizontally, vertically and inclined. It shows that the construction procedure affects the soil settlement and internal forces. The construction of upper tunnel at first leads to both higher settlement and bending moment. The highest soil settlement is obtained for vertical aligned tunnels, while horizontal aligned tunnels cause the lowest settlement.     

圆形基坑开挖引起下卧隧道三维变形机理研究

深基坑开挖引起的应力变化将不可避免地导致土体位移,进而对邻近隧道产生诸多的不利影响。然而,圆形基坑开挖引起下卧隧道三维变形机理的研究甚少。采用ABAQUS商业软件,开展系统的有限元仿真模拟研究了不同基坑开挖尺寸和隧道埋深比对下卧隧道三维变形机理的影响。研究表明:深基坑开挖引起的隧道横向弯曲应变最大值始终发生在隧道顶部,隧道上拱处的最大纵向弯曲应变是下拱处应变的2倍左右,隧道最大纵向弯曲应变明显小于最大横向弯曲应变。当基坑开挖直径达到7倍开挖深度时,基坑中心线下的隧道隆起和横向弯曲应变达到最大值。若忽视小直径基坑开挖的三维效应,隧道隆起和横向弯曲应变被大大高估。     

双隧道对群桩影响的三维离心模型试验研究

在膨胀土地基中进行了双隧道对群桩影响的三维离心模型试验,目标地层损失比为2%,着重研究引起的地基沉降槽、附加弯矩、轴力的变化规律。试验得出：膨胀土地基中每个隧道开挖形成的地表沉降槽仍符合Peck高斯曲线,双隧道共同作用形成的沉降槽可以看作是每个隧道单独作用形成的沉降槽的叠加;两个隧道开挖引起的前后桩弯矩规律类似,最大附加弯矩均出现在拱冠附近,但存在明显的前桩遮拦效应;随着第一个隧道开挖的临近及远离,前后桩轴力会发生明显不同变化,而第二个隧道影响明显不同,附加轴力最大值约为工作荷载的10%。     

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.     

地铁近距离平行隧道有限元数值模拟

对近距离双孔平行隧道，不同的开挖顺序会有不同的结果，第二孔隙道是在第一孔隧道扰动之后的地层中修建的，地层刚度条件不再对称，第二孔隧道的修建又对已建的第一孔隧道有影响，这一影响又与围岩类别，隧道间的间距，开挖和支护方式等因素有关，应用ANSYS程序对这些因素进行了分析，揭示了这类隧道在开挖之后地表和拱顶下沉的规律。分析表明，第二孔隧道的掘进对已修建的第一孔隧道有较大的影响，这时的分析即不同于单孔隧道，也不同于交错重叠隧道。