邻近地铁隧道的深基坑变形控制分析

结合具体工程实例,利用有限元分析方法对邻近地铁隧道的基坑围护变形控制要求进行研究。分析结果表明:针对不同的围护结构变形控制标准,地铁隧道结构的位移量亦随之发生变化。当围护结构位移值达到40mm时,隧道结构的位移将达到甚至超过地铁隧道的变形控制限值;当围护结构的变形值达到20mm时,隧道结构的位移相对较小,可更为有效地保护隧道结构的安全。     

隧道纵向变形曲线与围岩特征曲线耦合分析

目前,多数关于开挖面空间效应的研究仅采用弹性与理想弹塑性模型进行分析。然而,具有不同地质强度指标（GSI）的岩体呈现不同的峰后破坏模式,应采用合适的力学模型计算表征空间效应的隧道纵向变形曲线。同时,可将相同模型下围岩特征曲线与之进行耦合,从而指导隧道支护设计。提出了一种简便的基于有限差分法的分析方法,该法可计算Hoek-Brown与Mohr-Column屈服准则下,采用理想弹塑性、弹脆塑性、应变软化模型的隧道纵向变形曲线与围岩特征曲线。利用已有研究成果,验证了方法的合理性,并比较了不同GSI范围与不同力学模型下开挖面后部某一位置处的虚拟支撑力。结果表明：GSI越大,3种模型下对应的虚拟支撑力差别越大,更应如实考虑岩体峰后力学行为;GSI中等或较高时,离开挖面距离小于约0.8倍洞径时,理想弹塑性模型设计偏于保守,但大于此距离时情况相反。     

Deep learning-based evaluation of factor of safety with confidence interval for tunnel deformation in spatially variable soil

The random finite difference method (RFDM) is a popular approach to quantitatively evaluate the influence of inherent spatial variability of soil on the deformation of embedded tunnels. However, the high computational cost is an ongoing challenge for its application in complex scenarios. To address this limitation, a deep learning-based method for efficient prediction of tunnel deformation in spatially variable soil is proposed. The proposed method uses one-dimensional convolutional neural network (CNN) to identify the pattern between random field input and factor of safety of tunnel deformation output. The mean squared error and correlation coefficient of the CNN model applied to the newly untrained dataset was less than 0.02 and larger than 0.96, respectively. It means that the trained CNN model can replace RFDM analysis for Monte Carlo simulations with a small but sufficient number of random field samples (about 40 samples for each case in this study). It is well known that the machine learning or deep learning model has a common limitation that the confidence of predicted result is unknown and only a deterministic outcome is given. This calls for an approach to gauge the model's confidence interval. It is achieved by applying dropout to all layers of the original model to retrain the model and using the dropout technique when performing inference. The excellent agreement between the CNN model prediction and the RFDM calculated results demonstrated that the proposed deep learning-based method has potential for tunnel performance analysis in spatially variable soils.     

Computational method of large deformation and its application in deep mining tunnel

The characteristics of deep rock mass, such as the elastic resilience, creep, stress release, expansion, dilation and the long-term strength, are of great importance to the rock mass deformation and failure mechanism. However, there is not yet a constitutive model which can describe all these properties of the deep rock mass. The proposed dynamic failure constitutive model in this paper analyzes the elastic resilience and the dilation deformation of the surrounding rock mass during the unloading process, and the pre-peak (elastic and internal frictional hardening stages) and the post-peak(softening and residual failure stages) stages are also taken into account. A computational software has been coded based on the dynamic explicit finite element method. The constitutive model has also been implemented into this software. The complete stress–strain relation using the new model in numerical unloading test was obtained. The sensitivity of the parameters of the dynamic failure constitutive model has also been analyzed. Based on the long-term monitored data for Zhuji coal mine, the parameter inversion of the two different sections of the piebald mudstone has been conducted with the nonlinear least square method. Further, the whole process simulation of the deformation of Zhuji coal mine has been performed with the inversed parameters. A high degree of agreement on the deformation has been achieved by the comparison between the calculated and the measured data in actual engineering project.     

地表堆载对既有盾构隧道纵向变形影响

临时基坑开挖弃土和建筑垃圾引起的地表堆载将对盾构隧道产生不利影响,威胁盾构隧道运营安全,因此有必要评估地表堆载作用下盾构隧道的变形。利用非线性Pasternak地基模型,考虑地基非线性变形特点,通过接头非连续盾构隧道计算模型反映盾构隧道环间接头的影响,利用两阶段法,推导得到地表堆载作用下盾构隧道纵向变形简化计算方法。首先,通过Boussineq解求得地表堆载下盾构隧道所受附加荷载; 其次,将附加荷载作用于盾构隧道,结合接头非连续盾构隧道模型推导得到盾构隧道在地表堆载作用下的纵向变形方程,并使用有限差分法对方程进行求解,最后结合2个工程案例验证了所提方法的合理性。结果表明:增加盾构隧道环间接头的转动刚度对减小隧道沉降的作用较小,但可以有效减小接头张开量; 增加堆载长度会同时增大盾构隧道沉降量和沉降范围,而增加堆载宽度只会导致隧道沉降量缓慢增加,但不会引起隧道沉降范围增大; 增大堆载边界线到隧道轴线的距离会有效减少堆载引起的沉降量。     

Analysis of shearing effect on tunnel induced by load transfer along longitudinal direction

In order to analyze the behavior of load transfer mechanism of shield-constructed tunnel in longitudinal direction, tunnel is modeled as the cylindrical shell within elastic foundation (CSEF). By applying the theory of elastic cylindrical shell (ECS) with considering shear deformation and assumed displacement functions of trigonometric series, the distribution of stress and deformation in tunnel lining is obtained. In the solution, the stiffness of tunnel lining is decomposed into two components of circumferential and radial stiffness. The effects of both components on the behavior of deformation and internal forces of tunnel lining are discussed in details. By using the proposed solution, more reasonable results on the behavior of tunnel lining are obtained, e.g bending moment in tunnel cross section becomes smaller with the increase of the circumferential shear stiffness. The analytical results are verified by the results of 3D FEM analysis and field measured data. In accordance with the proposed analytical method, the tunnel lining in soft ground should be designed via considering the following aspects: (i) three dimensional effect of tunnel lining; (ii) relatively weaker shear stiffness in radial direction, and (iii) increase the circumferential shear resistance between rings.     

Physical model simulation of rock-support interaction for the tunnel in squeezing ground

The existence of squeezing ground conditions can lead to significant challenges in designing an adequate support system for tunnels.Numerous empirical,observational and analytical methods have been suggested over the years to design support systems in squeezing ground conditions,but all of them have some limitations.In this study,a novel experimental setup having physical model for simulating the tunnel boring machine(TBM)excavation and support installation process in squeezing clay-rich rocks is developed.The observations are made to understand better the interaction between the support and the squeezing ground.The physical model included a large true-triaxial cell,a miniature TBM,laboratoryprepared synthetic test specimen with properties similar to natural mudstone,and an instrumented cylindrical aluminum support system.Experiments were conducted at realistic in situ stress levels to study the time-dependent three-dimensional tunnel support convergence.The tunnel was excavated using the miniature TBM in the cubical rock specimen loaded in the true-triaxial cell,after which the support was installed.The confining stress was then increased in stages to values greater than the rock’s unconfined compressive strength.A model for the time-dependent longitudinal displacement profile(LDP)for the supported tunnel was proposed using the tunnel convergence measurements at different times and stress levels.The LDP formulation was then compared with the unsupported model to calculate the squeezing amount carried by the support.The increase in thrust in the support was backcalculated from an analytical solution with the assumption of linear elastic support.Based on the test results and case studies,a recommendation to optimize the support requirement for tunnels in squeezing ground is proposed.     

盾构法施工隧道纵向地层移动与变形预计

将盾构法施工隧道开挖引起的地表下沉以及盾构挤压引起的地表隆起均视为随机过程,应用随机介质理论,对隧道施工所引起的纵向地层移动与变形进行了分析,推导了相应的计算公式。工程实例分析表明,该方法效果良好。     

浅埋铁路隧道CRD法施工对地表变形影响的数值分析

针对龙厦铁路石桥头隧道工程围岩软弱,埋深浅的特点,应用数值分析手段,分析了浅埋铁路隧道在CRD法下施工,对地表沉降变形的影响。结果表明:CRD法下隧道各部施工对地表沉降均有影响,掌子面上部开挖产生的地表沉降明显大于下部,纵向地表沉降随隧道开挖过程分为三个阶段。结合分析结果,文章指出了施工过程中应采取的相应措施。     

深埋隧道排水系统非对称堵塞后渗流场的解析研究

 基于目前未见对隧道排水系统非对称堵塞渗流场进行解析研究,通过对研究区域进行简化假设,求解代表渗流场的Laplace方程。对研究区域内未知边界条件,采用PDE工具进行数值解后,得到近似的非齐次边界条件。基于此,再运用复平面内的保角变换、坐标变换、微分方程定解问题的分解等方法,将边界条件齐次化,在Hilbert空间中将最后唯一的非齐次边界条件表达为正交函数族的级数和,从而得到了此情况下的隧道周边渗流场解析级数,其后考查了级数项的多少对计算结果的影响。研究结果表明：(1) 隧道排水系统非对称堵塞后渗流场可以表达为解析后级数,可简化将来针对这一情况下渗流场的求解难度;(2) 隧道排水系统非对称堵塞后渗流场大致呈漏斗状,但在堵塞侧水头较高;(3) 求和项数对计算精度的影响至多到100项,多数情况下只需50项;(4) 考查了隧道可能受到的水压力分布和渗流量,分别与相同条件下的数值模拟结果进行对比,两者相差仅4.28%和4.05%。     

Studies on buoyancy driven two-directional smoke flow layering length with combination of point extraction and longitudinal ventilation in tunnel fires

This paper investigates the buoyancy-driven smoke flow layering length (both upstream and downstream) beneath the ceiling with combination of point extraction and longitudinal ventilation in tunnel fires. A theoretical model is developed based on previous back-laying model with only longitudinal ventilation, with modified actual heat release rate, as well as modified upstream and downstream opposing longitudinal air flow velocities by the induced flow velocity due to point extraction. Experiments are carried out in a reduced scale model tunnel with dimensionless of 72 m×1.5 m×1.3 m. A LPG porous gas burner is used as fire source. The smoke flow layering length both upstream and downstream are identified based on temperature profiles measured along the ceiling, for different experiment conditions. CFD simulations with FDS are also performed for the same scenarios. Results show that with combination of point extraction and longitudinal ventilation, the smoke flow layering length is not symmetric where it is longer downstream than that upstream. The upstream smoke layering length decreases, while the downstream layering length increases with increase in longitudinal ventilation velocity; and they both decrease with increase in point extraction velocity. The predictions by the proposed theoretical model agree well with the measurements and simulation results.     

Smoke spreading characteristics during a fire in a shallow urban road tunnel with roof openings under a longitudinal external wind blowing

A series of fire experiments was conducted using a 1:12 scale model of a shallow urban road tunnel with roof openings to clarify the flow structure of smoke and fresh air during a fire with a longitudinal external wind blowing above the roof openings. The model tunnel consisted of two road tubes separated by a pillar-type median structure. Five fire test cases were conducted by changing the heat release rate as the experimental parameter. When the smoke produced by a fire in the tunnel tube was exhausted by natural ventilation through the roof openings of the tunnel tube, fresh air was sucked in from the roof openings of the opposite tunnel tube. The flow of exhausted smoke and sucked-in fresh air created a complex three-dimensional flow structure inside the tunnel tubes. Stratified smoke that had formed under the ceiling of the tunnel tube was disturbed by the flow of sucked-in fresh air and was diffused on the upstream side of the fire. Compared to the condition without a longitudinal external wind, when a longitudinal external wind blew over the tunnel with the pillar median structure, the smoke spreading distance on the upstream side was longer than that without the external wind due to the diffusion of smoke. On the other hand, the smoke spreading distance on the downstream side of the fire was shorter than that without the external wind due to the improved smoke extraction performance by the Venturi effect of the longitudinal external wind. Furthermore, the smoke spreading distance on the downstream side was nearly constant and independent of the heat release rate of the fire, within the scope of our experimental conditions.     

地表堆载下盾构隧道纵向非线性变形简化解析解

既有盾构隧道在地表堆载下将会导致纵向不均匀沉降,威胁地铁列车的安全。目前地表堆载下盾构隧道的沉降预测方法没考虑到土体变形非线性的特点。基于所提的非线性地基模型,推导得到在地表堆载影响下盾构隧道纵向非线性变形简化解析解。地表堆载引起的隧道附加荷载通过Boussinesq解估算,通过连续梁模拟隧道的变形,推导得到在地表附加荷载下盾构隧道沉降的微分方程,引入有限差分法与Newton迭代法相互结合数值求解方法。通过三维有限元结果验证了其正确性,可以为在地表堆载下盾构隧道的沉降变形预测提供理论支持。     

软土隧道盾构法施工引起的纵向地面变形预测

假定土体不排水,利用弹性力学的Mindlin解,推导了正面附加推力和盾壳与土体之间的摩擦力引起的纵向地面变形计算公式,结合土体损失引起的地面变形计算公式,得到盾构施工引起的总的纵向地面变形计算公式,该方法适用于施工阶段。与两个工程实例进行了对比,本文方法计算得到的结果与实测数据较吻合。算例分析表明,正面附加推力引起开挖面前方地面隆起,后方地面沉降,以开挖面为轴线呈反对称分布,在正常施工时产生的地面变形较小;盾壳与土体之间的摩擦力引起的地面变形较大,分布规律与正面附加推力相似,但轴线位于盾构中间部位;土质参数对地面变形影响较大。     

考虑隧道剪切效应的基坑开挖对邻近隧道纵向变形分析

 基坑施工将打破周围地层已平衡的应力场,引起应力释放,对既有下卧地铁隧道产生不利的影响。针对既有研究的不足,提出考虑隧道剪切效应的基坑开挖对下卧隧道影响的解析解。既有隧道简化为搁置于Winkler地基上的Timoshenko梁。通过两阶段分析法,考虑基坑卸荷作用下已建隧道的响应。首先基于Timoshenko梁理论,建立考虑隧道剪切效应的隧道纵向变形微分方程,然后将由Mindlin弹性解计算得到附加荷载施加于既有隧道上,最后通过有限差分法得到在附加荷载作用下隧道的纵向变形解答。收集3个已发表工程实例的实测数据,并与本文方法及Euler-Bernoulli梁法的计算结果进行对比分析,发现实测结果与2种方法得计算结果有较好的一致性。然而,在内力分析上,相对比于本文方法,Euler-Bernoulli梁法明显高估基坑卸荷引起的隧道弯矩与剪力。由于本文方法可有效模拟既有隧道剪切效应,因而可进一步给出1在卸荷作用下隧道管片间错台量。研究成果可为合理预测邻近基坑施工对既有隧道的影响提供一定的理论支持。     

Numerical modeling of large deformation and nonlinear frictional contact of excavation boundary of deep soft rock tunnel

Roadways excavated in soft rocks at great depth are difficult to be maintained due to large deformation of surrounding rocks, which greatly influences the safety and efficiency of deep resources exploitation. During the excavation process of a deep soft rock tunnel, the rock wall may be compacted due to large deformation. In this paper, the technique to address this problem by a two-dimensional (2D) finite element software, large deformation engineering analyses software (LDEAS 1.0), is provided. By using the Lagrange multiplier method, the kinematic constraint of non-penetrating condition and static constraint of Coulomb friction are introduced to the governing equations in the form of incremental displacement. The numerical example demonstrates the efficiency of this technology. Deformations of a transportation tunnel in inclined soft rock strata at the depth of 1 000 m in Qishan coal mine and a tunnel excavated to three different depths are analyzed by two models, i.e. the additive decomposition model and polar decomposition model. It can be found that the deformation of the transportation tunnel is asymmetrical due to the inclination of rock strata. For extremely soft rock, large deformation can converge only for the additive decomposition model. The deformation of surrounding rocks increases with the increase in the tunnel depth for both models. At the same depth, the deformation calculated by the additive decomposition model is smaller than that by the polar decomposition model.     

一类盾构管片接头破坏历程的解析解

为研究一类采用斜直螺栓、不设传力衬垫构造形式的盾构管片接头在高荷载水平下的破坏力学性态,在引入一定假设基础上,提出了可用于分析管片接头破坏历程的简化解析模型,并对简化模型在线性转动、接头张开、接头屈服等不同阶段的接头截面应力分布和转动情况进行了分析和推导。并通过弯矩-转角关系曲线和接头极限弯矩两个方面对本文简化力学模型的解析解与管片接头足尺试验结果进行了比较和验证,比较结果表明,该方法所得结果与试验结果基本一致,是可行的。     

An elastic stress–displacement solution for a lined tunnel at great depth

By using the complex potential theory proposed by Muskhelishvili, an elastic plane strain solution for stresses and displacements around a lined tunnel under in situ stresses is presented. The tunnel is assumed to be driven in a homogeneous and isotropic geomaterial, and the tunnel construction sequence is properly taken into consideration. Numerical analyses indicate that, in order to simultaneously meet the needs of structural strength and rigidity, the relative rigidity and thickness of liner should be in an appropriate range. Either too high or low values for these parameters are unfavorable for the structural stability. The variations of stresses in the geomaterial intensively rely on the relative rigidity and thickness of liner when the ratio between the distance of the point under investigation to the tunnel axis and the outer radius of the liner is in the range from 1 to 2. In addition, the present solutions contain previously known results as the special cases.     

Performance validation of a hybrid ventilation strategy comprising longitudinal and point ventilation by a fire experiment using a model-scale tunnel

We examined the exhaust performance of a hybrid ventilation strategy for maintaining a safe evacuation environment for tunnel users in a tunnel fire. The hybrid ventilation strategy combines the longitudinal ventilation strategy with the point ventilation strategy which is a type of transverse ventilation strategy. The model tunnel developed by this study was scaled to 1/5 the size of a full-scale tunnel. The model-scale experiment was performed taking into consideration Froude's law of similarity. Measurement items were the distribution of temperature and concentration of smoke inside the tunnel, longitudinal wind velocity, mass flow of smoke in the point ventilation duct, and the heat release rate of the fire source. The following main conclusions were obtained. The smoke height was constant even when varying the extraction rate of smoke from the ceiling vent. The backlayering length and critical velocity of the smoke flow in the hybrid strategy could be predicted by the methodology developed by using the longitudinal strategy. The hybrid strategy maintained a safe evacuation environment on both sides of the tunnel fire.