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.

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.

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.

Analytical solution for evaluating deformation response of existing metro tunnel due to excavation of adjacent foundation pit

The excavation of foundation pit generates soil deformation around existing metro tunnel with shield driving method,which may lead to the deformation of tunnel lining.It is a challenge to evaluate the deformation of shield tunnel accurately and take measures to reduce the tunnel upward displacement as much as possible for geotechnical engineers.A new simplified analytical method is proposed to predict the longitudinal deformation of existing metro tunnel due to excavation unloading of adjacent foundation pit in this paper.Firstly,the additional stress of soils under vertical axisymmetric load in layered soil is obtained by using elastic multi-layer theory.Secondly,the metro tunnel is regarded as a Timoshenko beam supported by Winkler foundation so that the shear effect of tunnels can be taken into account.The additional stress acting on the tunnel due to excavation unloading in layered soil are compared with that in homogeneous soil.Additionally,the effectiveness of the analytical solution is verified via two actual cases.Moreover,parametric analysis is conducted to investigate the responses of the metro tunnel by considering such factors as the variation of subgrade coefficient,offset distance from the excavation center to tunnel longitudinal axis as well as equivalent shear stiffness.The proposed method can be used to provide theoretical basis for similar engineering project.

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.

Development of a new type of foam concrete and its application on stability analysis of large-span soft rock tunnel

The long-term stability of large-span soft rock tunnel is influenced greatly by the creep effect of surrounding rock.The development of a new type of foam concrete which has the property of high compressibility and low ductility was introduced.And it was made as filling material of reserved deformation layer between the first lining and the second lining used in large-span soft rock tunnel.The effect of the new type of foam concrete was simulated as filling material of reserved deformation layer using numerical simulation.Through the comparison with the common large-span soft rock tunnel,the vault settlement and surrounding convergence are reduced by about 61% and 45%,respectively,after creep of 100 a.And in the second lining,the plastic zone reduces apparently and the maximum equivalent plastic strain decreases relatively.So,it can be found that the application of the new type of foam concrete as the filling material of reserved deformation layer can relieve the excessive force in second lining induced by rock creep,reduce its deformation and improve the stability of tunnel.

In Situ Experiments on Supporting Load Effect of Large-span Deep Tunnels in Hard Rock

A section of the Nanliang high speed railway tunnel on Shijiazhuang-Taiyuan high-speed passenger railway line in China was instrumented and studied for its mechanical properties and performances. The cross section for the tunnel was300 m2and is classified as the largest cross section for railway tunnels in China. Through in situ experimental studies, mechanistic properties of the tunnel were identified, including the surrounding rock pressure, convergences along tunnel perimeter and safety of primary support and lining structure.Based on the field measured data, the surrounding rock pressure demand for large-span deep tunnel in hard rock is recommended as double peak type in the vertical direction and fold line type was recommended for horizontal pressure. The results suggested that Promojiyfakonov's theory was most close to the monitored value. Specific recommendations were also generated for the use of bolts in tunnel structures.Numerical simulation was used to evaluate the safety of the tunnel and it confirmed that the current design can satisfy the requirement of the current code.

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.

The Use of Underground Metro Stations and Tunnels as Protective Structures in Case of Nuclear Emergencies

This paper discusses the use of Underground Metro stations and tunnels as protective structures in case of nuclear emergencies. Six lines are taken as a case study to investigate the use of their underground stations and tunnels. The research explains the structural design of Underground Metro and the necessary needs for hidden people inside Underground Metro used as shelters. The research investigates the calculations of the number of hidden persons inside Underground Metro used as shelters. A field study has been conducted to an Underground Metro station to detemaine the peaceful use and the emergency use of all basements of the station. Also, the field study aims to determine the existing spaces and the needed spaces of the Underground Metro station to dual--used as a nuclear shelter. Three Underground Metro stations have been selected and a field study has been conducted to determine the usages of these basements, the planning, general and design features for each one of them, and whether they can be used as protective structures for citizens in emergencies. These basements were compared for their protective factors. Also, their capacities for sheltering were calculated.

Research on Construction Control Technology of Large-Span and Small Clear Distance Underpass High-Voltage Line Tunnel

Hanping tunnel is a control project of national highway 310 Dahejia to Qingshui highway project.It needs to cross a 330kV high-voltage transmission line under the condition of small clear distance,which requires high construction requirements.In view of the difficulties such as shallow buried depth of tunnel and small clear distance between tunnel and tower of high-voltage line,multiple excavation blasting method is adopted,and smooth blasting,charge quantity control and damping hole setting are comprehensively used to reduce the impact on the tower and structure of high-voltage line.In order to ensure the smooth progress of the project,the large-scale finite element analysis software is used to simulate the whole excavation project.The influence of the full-section method and the middle partition wall method(CD method)on the surrounding rock and the high-voltage electric tower is compared.It is found that the CD method can effectively control the displacement of the surrounding rock and the tower on it and the uneven settlement.

Distribution characteristics and the evolution law of excavation damage zone in the large-span transition section of high-speed railway tunnel based on microseismic monitoring

Purpose–The microseismic monitoring technique has great advantages on identifying the location,extent and the mechanism of damage process occurring in rock mass.This study aims to analyze distribution characteristics and the evolution law of excavation damage zone of surrounding rock based on microseismic monitoring data.Design/methodology/approach–In situ test using microseismic monitoring technique is carried out in the large-span transition tunnel of Badaling Great Wall Station of Beijing-Zhangjiakou high-speed railway.An intelligent microseismic monitoring system is built with symmetry monitoring point layout both on the mountain surface and inside the tunnel to achieve three-dimensional and all-round monitoring results.Findings–Microseismic events can be divided into high density area,medium density area and low density area according to the density distribution of microseismic events.The positions where the cumulative distribution frequencies of microseismic events are 60 and 80%are identified as the boundaries between high and medium density areas and between medium and low density areas,respectively.The high density area of microseismic events is regarded as the high excavation damage zone of surrounding rock,which is affected by the grade of surrounding rock and the span of tunnel.The prediction formulas for the depth of high excavation damage zone of surrounding rock at different tunnel positions are given considering these two parameters.The scale of the average moment magnitude parameters of microseismic events is adopted to describe the damage degree of surrounding rock.The strong positive correlation and multistage characteristics between the depth of excavation damage zone and deformation of surrounding rock are revealed.Based on the depth of high excavation damage zone of surrounding rock,the prestressed anchor cable(rod)is designed,and the safety of anchor cable(rod)design parameters is verified by the deformation results of surrounding rock.Originality/value–The research provides a new method to predict the surrounding rock damage zone of large-span tunnel and also provides a reference basis for design parameters of prestressed anchor cable(rod).

Experimental Study of Tunnel Fire with Natural Ventilation

The 1/15 reduced-scale experiments using Froude scaling were designed to study the effect on the smoke control efficiency for subway tunnel fires with natural ventilation mode.The propane gas fires with heat release rate 11.48 kW was used,which corresponds to the heat release rate 10 MW in the full-scale tunnel.The temperature distributions under the ceiling were measured by K-type thermocouples to investigate smoke movement,and the velocity of smoke in shafts was measured by hot-wire anemometer to obtain the smoke extract amount of ventilation shafts.The results show that the smoke temperature under the ceiling varies with the longitudinal different distance from fire source.The results also show that the smoke temperature distributions and the smoke control efficiency in tunnel vary with the space between ventilation shafts and vary with the area and the height of ventilation shaft.

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.

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。

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。

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。

不同基坑开挖卸荷方案对既有地铁隧道结构的影响研究

随着城市建设不断推进,地下工程进入快速发展时期,基坑工程对下方既有结构的影响不可忽略。基于此,文章以某换乘地铁站项目上方基坑开挖为例,通过FLAC3D数值模拟软件,分析既有隧道结构上方基坑在一次性开挖、分区开挖、跳挖方案下隧道洞顶结构的变形状态。分析结果表明,无论是否考虑反压作用,3种方案下洞顶结构竖向最大变形排序均为:一次性开挖方案>分区开挖方案>跳挖方案,跳挖方案相较于一次性开挖方案和分区开挖方案隧道洞顶最大位移分别减少了48.6%、38.3%,可有效降低基坑开挖变形量。相关研究可为此类工程施工方案选择提供参考和借鉴。

有变形缝工况下地铁左右线盾构并行下穿对既有明挖公路隧道变形及应力的影响

[目的]为确保有变形缝工况下地铁盾构隧道并行下穿既有明挖公路隧道工程的顺利实施,须对该工况下既有明挖公路隧道的变形情况及应力特征进行分析。[方法]建立了济南济泺路下穿黄河隧道工程中市域轨道交通S2线左右线盾构隧道并行下穿既有明挖公路隧道的精细化模型,分析了既有明挖公路隧道车道结构底板的z向(竖向)沉降、x向(水平向)位移及车道结构底板的应力变化情况。选取有无变形缝2种工况,对2个施工步完成后测线的x向位移和z向沉降变化情况进行对比。进一步选取工程中的2号变形缝,分析施工过程中2号变形缝两侧的结构沉降差和变形缝的应力状态发展历程。[结果及结论]与无变形缝工况相比,有变形缝工况降低了既有明挖公路隧道结构的整体性,改变了其变形及受力特征;变形缝始终受到拉应力及剪应力的影响;有变形缝工况下,变形缝两侧沉降随地铁盾构掘进呈现出明显的变化,地铁盾构掘进至该变形缝正下方时,沉降达到最大值。

基于Pathfinder的地铁盾构隧道疏散平台优化研究

为探究地铁盾构隧道疏散平台应对火灾、水灾以及列车区间故障等不同场景人员疏散的合理方案,以疏散地铁6辆B型车定员1460人为目标,建立Pathfinder疏散仿真模型开展研究。先对4种不同疏散平台布置方案的最快疏散时间、疏散完成时间和车厢内人员撤离规律进行研究;再以最优的“四向通行”方案为例,对7种疏散平台宽度的最快疏散时间、疏散完成时间和车厢内人员撤离规律进行研究。研究结果表明:1)车厢内人员撤离分为快速撤离、缓慢撤离和人员清空3个不同特征阶段。从车厢撤离乘客是脱困最重要的环节,时间占整个疏散时间的比例大,需做好乘客撤离车厢的组织引导工作。2)在联络通道处采用“四向通行”结构,可实现疏散平台与道床连通且不中断疏散平台的最优方案。该方案可实现利用道床面在烟气底层疏散以应对火灾工况、疏散平台纵向连通并在高处疏散以应对水灾工况的双重功能。3)疏散平台宽度增加会大幅缩短乘客撤离车厢的时间,对最快疏散的时间影响小,宽度未加宽到1100 mm时对疏散时间无显著影响。4)需做好在联络通道、道床、人防门、防淹门、道岔区疏散平台的顺畅性设计。

公铁合建双层盾构隧道设计关键技术

为解决公铁合建双层盾构隧道面临的总体布置、结构设计、汽车与地铁车辆联合振动以及通风排烟等技术难题,以武汉长江公铁隧道和济南黄河济泺路隧道工程实践为基础,采用方案综合比选、2.5维数值计算等方法,对公铁合建双层盾构隧道设计关键技术进行系统研究。结果表明:1)通过对隧道平面、纵断面和横断面的合理优化布置,并在废水泵房段、疏散楼梯段采取特殊布置方案,可减少公铁合建盾构隧道地下空间占用,并提高断面利用率,减小盾构隧道外径;2)采用半预制半现浇的管片+非封闭内衬结构型式,能充分发挥内部结构与管片衬砌的联合承载作用,显著减小河床冲淤作用;3)汽车与地铁联合振动作用对隧道影响较小,隧道基底饱和粉细砂地层不会发生液化;4)地铁隧道采用分段纵向烟道,可解决地铁长大区间无风井条件下的排烟难题,同时提高疏散便捷性,并大幅降低建设难度;5)公铁合建隧道在运营管理上不可避免地会出现交叉和影响,建议在管理界面划分和投资分劈上提前研究,便于决策。