Numerical simulation of dynamic response of operating metro tunnel induced by ground explosion

To evaluate the effects of possible ground explosion on a shallow-buried metro tunnel, this paper attempts to analyze the dynamic responses of the operating metro tunnel in soft soil, using a widely applied explicit dynamic nonlinear finite element software ANSYS/LS-DYNA. The blast induced wave propagation in the soil and the tunnel, and the von Mises effective stress and acceleration of the tunnel lining were presented, and the safety of the tunnel lining was evaluated based on the failure criterion. Besides, the parametric study of the soil was also carried out. The numerical results indicate that the upper part of the tunnel lining cross-section with directions ranging from 0° to 22.5° and horizontal distances 0 to 7 m away from the explosive center are the vulnerable areas, and the metro tunnel might be safe when tunnel depth is more than 7 m and TNT charge on the ground is no more than 500 kg, and the selection of soil parameters should be paid more attentions to conduct a more precise analysis.

Strata consolidation subsidence induced by metro tunneling in saturated soft clay strata

To choose the optimum construction method of metro tunneling, we conducted research with numerical simulation on strata consolidation subsidence by dewatering, dynamic dewatering, and non-dewatering construction method, taking the integrated effects of fluid-solid coupling and tunneling mechanics into account. We obtained the curved surfaces of ground surface subsidence and strata consolidation subsidence. The results show that the quantity of ground surface subsidence is 31 mm for the non-dewatering method, 39 mm for the dynamic dewatering method, and 105 mm for the dewatering method. Their ratio is 1：1.3：3.4; and the percentages of strata consolidation subsidence to whole ground surface subsidence of each construction method is 27% （no-dewatering）, 50% （dynamic dewatering）, and 79% （dewatering）. It is obvious that the non-dewatering construction method is the most effective method to control the strata consolidation subsidence induced by metro tunneling in saturated soft clay strata, and it has been successfully applied to the construction of the Shenzben metro line 1.

Deformation characteristics and safety assessment of a high-speed railway induced by undercutting metro tunnel excavation

Stratum deformation(settlement) is a challenging issue in tunnel engineering, especially when construction of metro tunnels has to undercut high-speed railway. For this purpose, we used the FLAC30 software to analyze the stratum settlement characteristics of high-speed railway at different crossing angles intersected by metro tunnel, in terms of ground settlement trough, stratum slip line and irregularity of ballastless tracks. According to the evolution of the stratum settlement at different angle regions, an optimized angle is proposed for the actual project design. In order to reduce the influence of stratum settlement on the safety of high-speed railway, an approach of safety assessment is proposed for the shield engineering undercutting high-speed railway, as per Chinese specifications using numerical results and on-site conditions. A case study is conducted for the shield tunnel section crossing the Wuhan-Guangzhou High-speed Railway between the Guangzhou North Railway Station and the Huacheng Road Station, which represents the first metro tunnel project passing below a high-speed railway in China. A series of measures is taken to ensure the safe excavation of the shield tunnel and the operation of the high-speed railway. The results can provide a technical support for performing a safety evaluation between high-speed railways and metro tunnels.

Mechanical responses of underground carriageway structures due to construction of metro tunnels beneath the existing structure:A case study

To understand the mechanical response pattern of the existing structure and ground due to the construction of metro tunnels underneath,the finite difference method is adopted to study the torsional deformation and stress variation of the existing structure and the effect of underground carriageway structures on the surface subsidence.The curves of the maximum differential subsidence,torsion angle,and distortion of the cross-section of the existing structure show two peaks in succession during traversing of two metro tunnels beneath it.The torsion angle of the existing structure changes when the two tunnels traverse beneath it in opposite directions.The first traversing of the shield tunnel mainly induces the magnitude variation in torsional deformation of the existing structure,but the second traversing of the subsurface tunnel may cause a dynamic change in the magnitude and form of torsional deformation in the existing structure.The shielding effect can reduce the surface subsidence caused by metro tunnel excavation to a certain extent,and the development trend of subsidence becomes slower as the excavation continues.

Influence of extreme shallow jacked box tunnelling on underlying metro tunnels:A case study

The application of jacked box tunnelling for underground passages has grown rapidly in recent years in China.In this study,the design of an extreme shallow jacked box tunnel traversing the underlying metro tunnels was introduced.An innovative additional soil filling above the ground surface was carried out to overcome the overlying-soil-carrying effect of the extreme shallow jacked box tunnelling.The structural safety of metro tunnels during the jacking process was analyzed through in-situ monitoring.It indicated that the overlying-soil-carrying effect was successfully alleviated.The metro tunnels generally showed horizontal displacement towards the receiving shaft,uplift and horizontal stretch during the jacking process.The stop of jacking machine in front of obstacles generally contributed to the decrease of horizontal displacement,uplift and horizontal stretch of metro tunnels.The largest horizontal displacement(1.3–1.6 mm),uplift(1.5 mm)and horizontal convergence(1.6–1.8 mm)generally occurred when the reception of jacking machine was completed,and they all met the requirement of 2 mm for this project.The design and construction of this shallow jacked box tunnel project could provide references for future similar projects.

Deformation analysis and safety assessment of existing metro tunnels affected by excavation of a foundation pit

The excavation of a foundation pit considerably affects the adjacent structures and underground pipelines owing to the change in the stress state of the surrounding soil,resulting in deformation.The study of an actual engineering case was conducted to examine the influence of excavation on the deformation of adjacent subway tunnels.The finite element analysis software PLAXIS 3D was used to simulate the entire excavation process.The structural design of the foundation pit was optimized based on the simulation results to ensure the stability of the foundation pit and the safety of the existing subway tunnel structure.Finally,the safety evaluation of the excavation of the foundation pit that caused the deformation of the adjacent subway tunnel was performed.The influence of the excavation and unloading of the foundation pit on the subway tunnel is closely related to the distance between the subway and the foundation pit,the amount of earthwork excavated at one time,and the engineering geological conditions.The results of this paper can provide useful reference for the design optimization and safety assessment of similar projects.

Evaluation of train-induced settlement for metro tunnel in saturated clay based on an elastoplastic constitutive model

In this study,a two-dimensional(2D)soil–water coupling dynamicfinite element(FE)analysis is conducted to investigate the effect of repeated train vibrations on the long-term settlement of a metro tunnel in saturated clay.Particular attention is paid to the leakage prob-lem of the metro tunnel by assuming different permeability conditions,namely fully permeable,fully impermeable,and partially perme-able,on the periphery of the tunnel for simplicity.The train vibration load isfirst evaluated using a rail–fastener–tunnel–subgrade model and averaged over a characteristic length for 2D numerical analysis.Cyclic Mobility model is used to simulate the mechanical behaviors of saturated soft clay in the FE analysis.Excess pore water pressure(EPWP)and associated tunnel settlement in trial operation and normal operation are calculated using the FE code DBLEAVES for different permeability conditions.It is found that a very low EPWP is generated in the trial operation,which then increases rapidly to peak values at the early days of normal operation.Afterward,the EPWP diminishes gradually as the train vibration continues.The permeability of the tunnel lining plays a significant role in the distri-bution of EPWP around the tunnel but produces a minor influence on the development of tunnel settlement.The train-induced tunnel settlement is mainly caused by the static settlement resulting from the EPWP dissipation during train interval,while the dynamic settle-ment arising from dynamic consolidation in each train vibration only accounts for a small portion.According to the 2D dynamic FE analysis,thefinal train-induced settlement of the metro tunnel in saturated clay is estimated to reach 160 mm while the peak EPWP value can reach 26.55 kPa.The settlement discrepancies between the numerical method and empirical method are discussed in detail.

3D reconstruction and automatic leakage defect quantification of metro tunnel based on SfM-Deep learning method

Various structural defects deteriorate tunnel operation status and threaten public safety.Current tunnel inspection methods face problems of low efficiency,high equipment expense,and difficult data management.Combining the deep learning model and the 3D reconstruction method based on structure from motion(SfM),this paper proposes a novel SfM-Deep learning method for tunnel inspection.The high-quality 3D tunnel model is constructed by using images taken every 1 m along the longitudinal direction.The instance segmentation of leakage in longitudinal images is realized using the mask region-based convolutional neural network deep learning model.The SfM-Deep learning method projects the texture of the images after defect recognition to the 3D model and realizes the visualization of leakage defects.By projecting the model to the design cylindrical surface and expanding it,the tunnel leakage area is quantified.Through its practical application in a Shanghai metro shield tunnel,the reliability of the proposed method was verified.The novel SfM-Deep learning method can help engineers efficiently carry out intelligent tunnel detection.

Novel SfM-DLT method for metro tunnel 3D reconstruction and Visualization

Metro tunnels play a crucial role in urban transportation.However,with growing tunnel operation periods,defects,and large deformations appearing,these are influencing tunnel structural performance and threatening public safety.Three-dimensional(3D)tunnel reconstruction is an effective way to highlight tunnel conditions and provide a basis for engineering management and maintenance.However,the current methods of tunnel 3D reconstruction do not sufficiently combine the qualitative and quantitative characteristics of tunnel states.In this study,a novel method for metro tunnel 3D reconstruction based on structure from motion(SfM)and direct linear transformation(DLT)is proposed.The dimensionless 3D reconstruction point cloud acquired through the SfM method showcases the qualitative characteristics(such as leakage and pipelines)of the tunnel state.The close-range photogrammetry DLT method provides scale information missing from the SfM method and quantitative characteristics(such as profile deformation)of the tunnel state.The SfM-DLT method was tested in a Shanghai metro tunnel,and proved to be feasible and promising for future tunnel inspections.

Tunnelling performance prediction of cantilever boring machine in sedimentary hard-rock tunnel using deep belief network

Evaluating the adaptability of cantilever boring machine(CBM) through in-depth excavation and analysis of tunnel excavation data and rock mass parameters is the premise of mechanical design and efficient excavation in the field of underground space engineering.This paper presented a case study of tunnelling performance prediction method of CBM in sedimentary hard-rock tunnel of Karst landform type by using tunneling data and surrounding rock parameters.The uniaxial compressive strength(UCS),rock integrity factor(Kv),basic quality index([BQ]),rock quality index RQD,brazilian tensile strength(BTS) and brittleness index(BI) were introduced to construct a performance prediction database based on the hard-rock tunnel of Guiyang Metro Line 1 and Line 3,and then established the performance prediction model of cantilever boring machine.Then the deep belief network(DBN) was introduced into the performance prediction model,and the reliability of performance prediction model was verified by combining with engineering data.The study showed that the influence degree of surrounding rock parameters on the tunneling performance of the cantilever boring machine is UCS > [BQ] > BTS >RQD > Kv > BI.The performance prediction model shows that the instantaneous cutting rate(ICR) has a good correlation with the surrounding rock parameters,and the predicting model accuracy is related to the reliability of construction data.The prediction of limestone and dolomite sections of Line 3 based on the DBN performance prediction model shows that the measured ICR and predicted ICR is consistent and the built performance prediction model is reliable.The research results have theoretical reference significance for the applicability analysis and mechanical selection of cantilever boring machine for hard rock tunnel.

Risk identification and risk mitigation during metro station construction by enlarging shield tunnel combined with cut-and-cover method

Constructing a metro station by enlarging shield tunnels combined with a mining/cut-and-cover method provides a new method to solve the contradictions of construction time limits of shield tunnels and stations. As a new-style construction method, there are several specific risks involved in the construction process. Based on the test section of Sanyuanqiao station on Beijing metro line 10, and combined with the existing methods of risk identification at present, including a review of world-wide operational experience of similar projects, the study of generic guidance on hazards associated with the type of work being undertaken, and discussions with qualified and experienced staff from the project team, etc., the specific risks during the construction process of the metro station constructed by enlarging shield tunnels combined with the cut-and-cover method are identified. The results show that the specific risks mainly come from three construction processes which include constructing upper enclosure structures, excavating the soil between shield tunnels and demolishing shield segments. Then relevant risk mitigation measures are put forward. The results can provide references for scheme improvement and a comprehensive risk assessment of the new-style construction method.

隧道轮廓激光雷达点云线特征共面约束标定方法

地铁隧道断面轮廓参数测量过程中,需要对高速激光雷达点云进行高精度系统标定。特别是大场景隧道环境,对标定模板要求高,标定过程复杂,检测精度影响大。针对此问题,本论文提出了一种新颖的适用于地铁隧道轮廓点云的标定方法,并基于双激光雷达测量系统,进行了算法研究。本方法设计了专用的手推行便携式标定系统,利用由点云数据提取的标定板线特征,建立目标函数,通过混合了遗传算法和Levenberg-Marquardt算法的非线性优化方法,寻找全局最优解从而实现对激光雷达的标定。实验结果表明:本方法对于两侧钢轨顶轨的标定误差在±1.5 mm以内;静态测量精度X误差在±1 mm内、Y误差在±4 mm内;当采集系统以5 km/h的速度进行数据采集时,动态测量精度X误差在±4 mm内、Y误差在±6 mm内。本方法能够实现激光雷达的高精度标定,算法鲁棒性强,具有易操作、环境适应性强的特点。

成都地区卵石地层深基坑开挖的土压力计算方法

[目的]现有土压力理论计算方法未考虑卵石地层孔隙度大、结构松散等离散性特点,计算结果与实际土压力有所偏差,需要研究适用于成都地区卵石地层的土压力计算方法。[方法]以成都轨道交通7号线为依托,分析卵石地层深基坑土压力与朗肯土压力理论值的差别,并建立深基坑开挖土压力计算方法。采用离散元数值模拟和数据统计分析,获取围护结构平动、围护结构绕墙顶转动和围护结构绕墙底转动三种基本变位模式下静止土压力、被动土压力和主动土压力的分布特征。与朗肯土压力理论计算结果进行比较,得到不同变位模式下三种土压力的修正系数,并建立深基坑土压力修正计算方法。进一步与现场实测数据比较,对比验证所提出的土压力计算方法。[结果及结论]主动土压力和被动土压力分布形式具有强烈的非线性,可采用双折线进行描述,交点分别位于埋深8 m和9 m处。静止土压力修正系数分布在0.91~0.96之间,在使用时不需要修正;主动土压力修正系数分布在0.33~0.78之间,被动土压力修正系数分布在0.52~0.91之间,在使用时应予以修正。所提出的卵石地层深基坑土压力计算结果与现场实测结果吻合较好,可为类似轨道交通工程提供参考。

3D打印隧道衬砌-围岩界面力学性能研究

[目的]3D打印技术在工程结构施工的研究和应用已逐渐深入,应用3D打印建造地铁隧道开拓了一种新的思路和方法,而3D打印施工过程中,衬砌与隧道围岩的共构效果和协同工作性能的保障是构建隧道衬砌结构体系的关键,需对其进行深入研究。[方法]通过试验模拟不同围岩条件下的界面特性,深入研究了3D打印隧道施工中衬砌和围岩之间的粘结力学性能及其影响因素。[结果及结论]围岩表面的粗糙度对3D打印衬砌混凝土的粘结效果有显著影响,而表面涂覆涂层能够有效改善衬砌-围岩界面的粘结性能,通过填补衬砌-围岩界面的微观不平整有利于提高3D打印衬砌施工质量。

大跨度人防隧道工程下穿施工对既有地铁隧道区间结构稳定性的影响

[目的]为分析新建大跨度人防隧道工程小净距下穿既有地铁线路施工时对地铁隧道区间结构稳定性的影响,需对人防隧道下穿施工过程进行模拟研究。[方法]依托青岛某扁平大断面人防隧道下穿既有地铁区间隧道工程,建立了三维有限元模型,模拟人防隧道开挖的全过程。重点分析了人防隧道设置的中隔墙在开挖过程中的力学响应及变形规律,以及整个施工过程对既有地铁车站及其区间隧道的影响情况。[结果及结论]人防隧道中隔墙在先行洞和后行洞施工过程中呈现出明显的偏压趋势;人防隧道初期支护结构受既有地铁隧道的上部拱顶效应与中隔墙的双重作用,呈现出罕见的前大后小的“四象限”分布规律,且右侧沉降值大于左侧沉降值;既有地铁车站及其区间结构受人防隧道开挖空间效应的影响明显,其变形趋势均表现为向开挖侧移动,但其变形值均小于规范规定的预警值。

高铁列车荷载作用下桩-土复合地基及近接地铁隧道的动力响应模拟研究

[目的]作为典型的振动荷载,高铁列车运行引起的振动荷载会诱发桩-土地基及附近结构产生动力响应,有必要对桩-土复合地基及近接隧道的动力响应特性进行研究。[方法]基于西安地铁14号线下穿大西高速铁路特大桥工程,采用模型试验和数值模拟相结合的方法,以峰值振动加速度、峰值振动速度和峰值振动位移作为动力响应评价指标,研究了列车移动荷载作用下桩-土复合地基及近接隧道的动力响应特性。[结果及结论]研究结果表明,当施加列车荷载时,地基内部的动力响应指标均随着埋深的增加而衰减,但存在近接隧道时,动力响应指标值显著增加,且在隧道埋深处衰减明显。随着距桩基中心距离的增加,隧道埋深处的桩-隧之间地基的各动力响应指标从“波浪形”分布变为单调递减分布。根据峰值振动速度的控制阈值,近接隧道埋深处距桩基础中心水平3.6 m范围内的地基处于危险影响区,必须采用减振措施;3.6~11.4 m范围内的地基处于强影响区,建议采取减振措施;11.4 m以外的地基处于弱影响区,视结构的重要性决定是否需要采取减振措施。

隧道开挖对上覆既有管线影响的简化解析计算方法

[目的]当盾构隧道下穿既有管线时,会引起既有管线发生沉降变形,因此有必要通过理论计算对隧道开挖引起的上覆既有管线受力变形进行研究。[方法]基于两阶段法提出一种可预测隧道开挖对上覆既有管线变形响应影响的简化计算方法,先采用Loganathan公式获得隧道开挖引起的周围土体自由竖向位移,并把土体自由竖向位移附加在既有管线轴线上,再将既有管线简化为无限长梁搁置于Vlazov地基模型,考虑管线侧向土体的影响,利用有限差分法获得管线纵向变形的解析解。[结果及结论]将所提简化计算方法与既有文献中的实际工程监测数据进行对比,验证了所提简化计算方法的合理性;将所提简化计算方法同退化的Vlazov地基模型及Winkler地基模型计算结果进行对比,验证了所提简化计算方法更贴近实测数据。地层损失率、隧道开挖半径的增大会引起既有管线沉降及弯矩的增大;增大新建隧道与既有管线的夹角能够减小管线沉降,但会造成管线弯矩的增大。

富水砂层地铁盾构隧道渣土混合改良的流塑性与渗透性

[目的]盾构在富水砂层中掘进时,易产生刀盘扭矩过高、磨损严重以及螺旋运输机喷涌等问题。为了保证施工的安全性,需对渣土进行改良。[方法]以西安地铁16号线某盾构区间工程为依托,根据砂土地层自稳性差、摩擦性高、渗透率高的特点选取渣土改良剂。通过渣土坍落度试验、渗透试验、现场试验相结合的方式,采用泡沫单独改良、泡沫及膨润土泥浆混合改良两种方案开展富水砂层渣土改良试验研究。[结果及结论]实际盾构掘进施工中,在考虑安全、高效、经济的前提下,结合室内试验所得数据,确定采用膨润土泥浆、泡沫混合改良的方案。当膨润土与水质量比为1/8,发泡液质量分数为3%时,改良剂性能满足施工要求;泡沫单独改良渣土受含水率影响大,含水率越高,泡沫最佳注入率越小。中砂的最佳改良方案是BIR(膨润土泥浆注入比)为10%,FIR(泡沫注入率)为20%~25%;砾砂的最佳改良方案是BIR为10%,FIR为35%~40%。工程实践表明,渣土混合改良效果良好,盾构掘进参数平稳。

时速120 km地铁快线空气动力学试验研究

为探明设计时速120 km快速地铁列车在多区段桥隧衔接线路运行时的气动效应和气密性能,采用实车试验的方法,在武汉某多区段桥隧衔接地铁快线对某4车编组的新研A型密封性地铁列车开展空气动力学测试。实验测试系统采用LL-250-15A型Kulite压力传感器,通过测量列车外部和内部的瞬态压力变化,分析全线路车外压力波动特性,对比沿列车长度方向不同测点位置的压力变化幅值,并分析不同空调状态下的车内压力舒适性。经过3次实验测试分析,该实验的结果具有可重复性。研究结果表明:全线路运行时,列车在隧道段内加减速导致车外压力变化幅值明显大于高架段,气动效应最恶劣的位置为地下段人防门变截面处,列车上行通过该处时车外任意3 s内压力变化幅值为1 071 Pa,下行通过该处时车外任意3 s内压力变化幅值为905 Pa;相对于下行线全线路,上行线车外任意3 s内压力变化幅值大18.3%;列车正线运营时压力波保护阀会在压力变化剧烈区段进行动作响应,列车上行时,空调开启、压力波保护阀正常启用状态下,车内任意3 s内压力变化幅值相对于压力波保护阀打开未启用时减少了16%,下行时,减少了28%,空调压力波保护阀能够有效降低车外压力波动对车内气压变化的影响。本文研究成果可为快速地铁线路设计、地铁列车运营及地铁气密性优化提供参考依据。