盾构掘进速度及非正常停机对地面沉降的影响

软土中盾构隧道施工不可避免地扰动周围地层,进而引起地面沉降,沉降过大时将危及邻近建（构）筑物的正常使用和结构安全。全面理解盾构隧道施工引起的地面沉降的影响因素及对沉降的准确预测,对于减少施工环境危害十分重要。考虑盾构压重后,引入Mindlin解计算盾构下卧土层中的附加应力,采用单向压缩分层总和法计算盾构下卧土层的总固结沉降,由盾构掘进速度及停机时间确定附加应力作用时间后,应用太沙基一维固结理论计算在该作用时间内的固结沉降,应用Peck公式建立了盾构下卧土层沉降与地面沉降的关系,并以杭州庆春路过江隧道地面沉降的实测验数据对上述理论进行了验证。分析表明,考虑盾构掘进速度及停机时间的地面沉降计算理论基本合理;盾构掘进速度及停机时间会对隧道施工引起的地面沉降产生显著影响;在其他施工条件相同的前提下,提高盾构掘进速度和减少停机时间有利于减少地面沉降。     

一种盾构掘进引起地表沉降的实用预测方法

盾构隧道施工中,提前预知盾构影响范围内的地表沉降情况对减少施工对既有建筑物的危害是有帮助的。Peck法公式用于描述隧道掘进引起地表沉降分布曲线已经被工程界广为接受,但地层损失一般从工程经验中获得,导致该理论在实践中应用受限。基于实测沉降数据,用最小二乘法求解地层损失,并且对Peck法公式进行了拓展,建立了一种用于预测盾构影响范围内地表沉降情况的实用方法。并编制了可视化的电算程序,工程实例表明,该方法行之有效。     

Mechanized tunneling induced ground movement and its dependency on the tunnel volume loss and soil properties

This study investigates the ground movements due to mechanized tunnel excavation by applying two-dimensional finite element analyses. To assess the contribution of the compressibility and plasticity of the soil on the ground movements, different constitutive models are employed to describe the soil behavior. The influence of volume loss around the tunnel on the surface volume loss is investigated, and a quadratic correlation between them is proposed. Consequently, the empirical Gaussian distribution curve, which is generally used to determine the tunneling induced settlement trough, is improved by applying the proposed quadratic correlation between surface volume loss and tunnel volume loss. Furthermore, the settlement trough width parameter has been derived by a linear function of tunnel volume loss as well. The proposed equations are validated via a case study of centrifuge tests from the literature. The results show that the proposed modification enhances the empirical solution by having better knowledge on the model parameters. Additionally, tunnel overburden and coefficient of lateral earth pressure at rest (K₀) are taken into account to study their influence on the tunneling induced surface settlements. Finally, global sensitivity analysis is applied to evaluate the relative importance of corresponding model parameters in terms of their influence on the ground movements.     

Analytical stress and displacement due to twin tunneling in an elastic semi‐infinite ground subjected to surcharge loads

The construction of twin tunnels at shallow depth has become increasingly common in urban areas. In general, twin tunnels are usually near each other, in which the interaction between tunnels is too significant to be ignored on their stability. The equivalent arbitrarily distributed loads imposed on ground surface were considered in this study, and a new analytical approach was provided to efficiently predict the elastic stresses and displacements around the twin tunnels. The interaction between 2 tunnels of different radii with various arrangements was taken into account in the analysis. We used the Schwartz alternating method in this study to reduce the twin‐tunnel problem to a series of problems where only 1 tunnel was contained in half‐plane. The convergent and highly accurate analytical solutions were achieved by superposing the solutions of the reduced single‐tunnel problems. The analytical solutions were then verified by the good agreement between analytical and numerical results. Furthermore, by the comparison on initial plastic zone and surface settlement between analytical solution and numerical/measured results of elastoplastic cases, it was proven that the analytical solution can accurately predict the initial plastic zone and its propagation direction and can qualitatively provide the reliable ground settlements. A parametric study was finally performed to investigate the influence of locations of surcharge load and the tunnel arrangement on the ground stresses and displacements. The new solution proposed in this study provides an insight into the interaction of shallow twin tunnels under surcharge loads, and it can be used as an alternative approach for the preliminary design of future shallow tunnels excavated in rock or medium/stiff clay.     

A case study on the behavior of shield tunneling in sandy cobble ground

This study investigates the behavior of shield tunneling based on a complete case record of an excavation in sandy cobble ground. Both numerical and analytical analyses were conducted to estimate the surface displacement along the tunnel axis and the surface-zone affected by the shield tunneling. This paper presents the performance of the Peck method in forecasting the transversal surface settlement trough caused by the shield tunneling in a sandy cobble layer. In particular, this study has made a comparison with the vertical surface displacement monitored during the advancing excavation to the settlements estimated by using the Peck method and by conducting a three-dimensional finite element analysis. The effective measures to provide the necessary face support pressure and to reduce the formation of sinkholes and ground settlements in sandy cobble ground were also investigated and discussed.     

考虑涂抹区压缩及渗透系数变化的堆载预压固结解

为评估涂抹区土体压缩和渗透系数变化对含竖向排水体地基固结的影响,采用等体积应变假设,考虑涂抹区土体的压缩变形及其水平向渗透系数沿径向分别呈线性和抛物线分布,并考虑井阻作用以及地基附加球应力沿深度任意分布,推导了随时间线性堆载预压条件下固结微分方程的显式解析解答,分析了涂抹区半径、水平向渗透系数的分布模式、以及体积压缩系数对地基整体平均固结度的影响。结果表明,涂抹区土体采用均匀折减的水平向渗透系数明显低估了地基的固结速率,而当涂抹区半径较大时,不考虑涂抹区土体的压缩变形将会高估地基的固结速率。在含竖向排水体地基固结问题的分析中,这些影响不可忽视。     

Lateral soil–pipeline interaction in sand backfill: Effect of trench dimensions

Current analytical methodologies for the evaluation of soil pressures on laterally displaced pipelines, as in the case of differential (e.g. fault-induced) permanent ground movements, allow the use of sand fill material properties under the condition that the size of the trench is adequate so that the failure surface develops fully within the sand fill (i.e. “free field” response). The accuracy of this assumption is investigated in this paper by means of numerical analyses, which employ a number of advanced features, such as pipe-backfill interface elements, large strain formulation and mesh rezoning. Following verification against well-documented experimental data, the analyses investigate: (a) the shape and size of the failure mechanism, as well as, (b) the potential trench effects on soil pressures and pipeline strains in the case of a strike-slip fault rupture. It is shown that for small embedment depths soil failure extends to the ground surface, in the form of a general shear failure mechanism, while for larger depths it becomes progressively localized and surrounds the pipeline. It is also shown that, for most cases of pipeline diameter and embedment depth, common trench dimensions cannot contain the “free field” failure surface dimensions. Finally, analyses for limited trench dimensions, reveal that the ultimate soil pressure increases exponentially with decreasing trench width, leading to high bending strains in pipelines subjected to differential lateral ground displacements.     

考虑椭圆化地层变形影响的浅埋隧道弹性解

研究了浅埋隧道周围地层最终变形的计算问题,提出了考虑椭圆化变形影响的计算模型和浅埋隧道位移边界条件,并利用Airy应力函数得到了该问题弹性解析解。在此基础上,通过算例分析了椭圆化变形对竖向位移和水平位移的影响。结果表明,椭圆化变形对水平位移的影响远大于竖向位移。     

软土虹吸排水完整井非稳定流模型及解析解

软土地基的处理一直是工程界的难题,大多数处理方式采用排出软土中水的措施。虹吸排水免动力,且操作简单,可以降低地下水。根据该技术的这些优点,可以将其应用于软土地基处理领域。为了得到虹吸排水作用下土体内部的水位及虹吸管内流量的变化,针对软土中地下水运动进行理论分析。基于Theis理论,针对潜水含水层完整井的轴对称井流微分方程,采用Boltzmann变换,推求得到虹吸过程中软土地基中的水位和流量的显式解析解,并进行室内物理模拟试验验证。结果表明,解析解与试验数据较吻合。与前人经典解析解进行对比,表明相对误差绝对值范围为0～15%,误差较小。推导得到的解析解相比经典解析解而言,计算更简单,更有利于工程应用。     

双圆盾构隧道施工引起的地面沉降预测

将随机介质理论应用于双圆盾构隧道施工引起的地面沉降计算,假定开挖后土体移动模式为不均匀收敛,推导了土体损失引起的地面沉降计算公式。算例分析结果表明：预测结果与实测值比较吻合;双圆叠加模型计算结果明显偏大,原因是没有考虑双圆盾构重叠部分减少的土体开挖面积,仍按两个单圆的土体开挖面积来计算,导致土体损失量比实际大;将双圆叠加模型计算结果按实际土体开挖面积相应折减,发现其计算结果仍比实测值大,表明双圆盾构隧道不能简单地采用两个单圆叠加得到。对双圆叠加模型进行修正,提出修正系数取值,修正后的双圆叠加模型计算值与实测值较吻合。     

A Simple Method for Analysis of Point Anchored Rockbolts in Circular Tunnels in Elastic Ground

Summary. A simple analytical method for the analysis of point anchored rockbolts is presented in this paper. The solution has been derived for elastic ground and rockbolts, for plane strain conditions, and for tunnels with circular cross section. The method provides accurate results for the rockbolts’ loads and displacements and explicitly includes the connection of the rockbolts to the surrounding ground. The addition of such details to a Finite Element numerical model is critical; otherwise the solution obtained may be dependent on the discretization used and on the stiffness of rockbolts and ground. As an alternative to including details of the rockbolt head and anchor point in the numerical model, which could be computationally very expensive, an equivalent spring constant is proposed. The spring constant is obtained by matching numerical with analytical results for a simple case, but keeping the geometry, material properties, and discretization unchanged.     

A new closed‐form solution for analysis of unlined pressure tunnels under seepage forces

In this study, a simplified analytical closed‐form solution, considering plane strain and axial symmetry conditions, for analysis of a circular pressure tunnel excavated underwater table, is developed. The method accounts for the seepage forces with the steady‐state flow and is based on the generalized effective stress law. To examine the effect of pore pressure variations and also the boundary conditions at the ground surface, the formulations are derived for different directions around the tunnel. The proposed method can be applied for analysis and design of pressure tunnels. Illustrative examples are given to demonstrate the performance of the proposed solution and also to examine the effect of seepage forces on the stability of tunnels. The simplified analytical solution derived in this study is compared with numerical analyses. It is concluded that the classic solutions (Lame's thick‐walled solution), considering the internal pressure as a mechanical load applied to the tunnel surface, are not applicable to pervious media and can result in an unsafe design. Copyright © 2012 John Wiley & Sons, Ltd.     

环形单圈管冻结稳态温度场解析解

人工地层冻结技术被广泛应用于地下工程施工中。冻结温度场的计算是人工冻结法理论研究的基础,也是冻结施工设计的重要依据。人工地层冻结施工常使用环形单圈冻结管冻结,而至今尚无关于其温度场的解析解。基于水-热异类相似原理,根据传热过程与地下水流动相似的特点,利用保角映射、汇源反映和势函数叠加原理,类比推导了环形单圈冻结管稳态温度场解析解,并用热学数值模拟方法加以验证,同时提出了简化的解析公式。结果表明,解析解计算结果与数值模拟结果较吻合,其简化公式得到的结果与原解析公式基本一致。在解析公式的基础上,经过简化,反推得到外部冻结壁厚度公式。解析解、简化公式以及厚度公式可为环形单圈冻结施工与设计提供理论的依据与指导。     

Calculation of surface settlements caused by EPBM tunneling using artificial neural network, SVM, and Gaussian processes

Increasing demand on infrastructures increases attention to shallow soft ground tunneling methods in urbanized areas. Especially in metro tunnel excavations, due to their large diameters, it is important to control the surface settlements observed before and after excavation, which may cause damage to surface structures. In order to solve this problem, earth pressure balance machines (EPBM) and slurry balance machines have been widely used throughout the world. There are numerous empirical, analytical, and numerical analysis methods that can be used to predict surface settlements. But substantially fewer approaches have been developed for artificial neural network-based prediction methods especially in EPBM tunneling. In this study, 18 different parameters have been collected by municipal authorities from field studies pertaining to EPBM operation factors, tunnel geometric properties, and ground properties. The data source has a preprocess phase for the selection of the most effective parameters for surface settlement prediction. This paper focuses on surface settlement prediction using three different methods: artificial neural network (ANN), support vector machines (SVM), and Gaussian processes (GP). The success of the study has decreased the error rate to 13, 12.8, and 9, respectively, which is relatively better than contemporary research.     

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。     

运动荷载附近有限层厚软土地基的振动研究

基于Biot多孔弹性介质的波动理论,研究了运动荷载附近软土地基的振动问题。假设一条形均布荷载作用在地基表面,则该模型可视为平面应变问题进行分析。通过引入4个势函数和Helmholtz原理,并利用Fourier变换及逆变换技术,获得了运动荷载作用下软土地基的应力、位移和孔隙水压力的解答。利用离散Fourier逆变换得到数值计算结果,分析了荷载速度,频率以及软土的渗透系数及多孔弹性参数对运动荷载作用下地表竖向位移及土体中任一点孔隙水压力分布的影响。     

Analytical solution to one-dimensional consolidation in unsaturated soils under loading varying exponentially with time

This note presents an analytical solution to one-dimensional consolidation in unsaturated soils with a finite thickness under confinement in the lateral direction and vertical loading varying exponentially with time. The boundary conditions are that the top surface is permeable to water and air and the bottom is impermeable to water and air. The transfer relationship between the state vectors at the top surface and any depth is gained by applying the Laplace transform and Cayley-Hamilton mathematical methods to the governing equations of water and air, Darcy’s law and Fick’s law. The excess pore-air and pore-water pressures and settlement in the Laplace-transformed domain are obtained by using the Laplace transform with the initial and boundary conditions. By performing the inverse Laplace transforms, the analytical solutions of the excess pore-air and pore-water pressures at any depth and settlement are obtained in the time domain.     

Prediction of settlement trough induced by tunneling in cohesive ground

Surface settlements of soil due to tunneling are caused by stress relief and subsidence due to movement of support by excavation. There are significant discrepancies between empirical solutions to predict surface settlement trough because of different interpretations and database collection by different authors. In this paper, the shape of settlement trough caused by tunneling in cohesive ground is investigated by different approaches, namely analytical solutions, empirical solutions, and numerical solutions by the finite element method. The width of settlement trough was obtained by the finite element method through establishing the change in the slope of the computed settlement profile. The finite element elastic-plastic analysis gives better predictions than the linear elastic model with satisfactory estimate for the displacement magnitude and slightly overestimated width of the surface settlement trough. The finite element method overpredicted the settlement trough width i compared with the results of Peck for soft and stiff clay, but there is an excellent agreement with Rankin’s estimation. The results show that there is a good agreement between the complex variable analysis for Z/D = 1.5, while using Z/D = 2 and 3, the curve diverges in the region faraway from the center of the tunnel.     

二维饱和地基中空沟主动隔振分析

根据饱和土Biot理论,在频域内提出了一种适用于弹性波波动问题的有限元-无限元解法,其中有限单元用于近场介质的模拟,而形函数基于一维解析解答的无限单元则被用于人工边界,它可反映波传递到无限远处的特性;应用该法计算算例,以证明其有效性与正确性。在此基础上,对饱和地基中空沟主动隔振效果进行了详细的数值分析,结果表明,空沟深度是影响隔振效果的主要因素,一般沟深越大,隔振效果越好;当沟深一定时,空沟到振源的距离不宜超过1.5倍饱和土剪切波长;空沟的宽度对隔振效果的影响相对较小。     

劈裂注浆复合土体三维等效弹性模型理论研究

劈裂注浆可以有效改善土体的变形参数,大大降低土体在受力状态改变时的变形量,对劈裂注浆后复合土体的等效变形参数进行研究十分重要。在综合分析劈裂注浆扩散机制和工程应用实际的基础上,基于均质化理论提出了劈裂注浆后复合土体的三维单元体几何模型,按等效原则给出了浆-土体积及受力分配关系模型图;接着基于横向各向同性本构关系推导了模型的等效弹性模量和等效泊松比的解析解。然后采用有限元方法取得了模型特定条件下的等效弹性模量和等效泊松比,并与解析结果进行对比分析。最后把模型和相应的解析结果引入Flac3D岩土工程专业分析软件,结合一个热力隧道工程实例对隧道劈裂注浆后关键位置的沉降进行预测分析,并与实测值进行了对比。研究表明：对所提出的计算模型,解析计算与有限元方法计算结果吻合度较高,说明了解析结果的正确性;基于该模型及其解析结果得到的隧道开挖后的沉降预测值与实测值具有良好的一致性,说明所提出的模型和相应的解析计算方法具有一定的可靠性和实用性。