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Experimental investigation of face instability for tunnels in sandy cobble strata

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Underground Space 2023年第3期10卷 199-216页

作者： Qiguang Di Pengfei Li mingju zhang Xiaopu Cui Key Laboratory of Urban Security and Disaster Engineering Ministry of EducationBeijing University of TechnologyBeijing 100124China

In order to investigate the influence of face instability for tunnels with different burial depths in sandy cobble strata on earth pressure and the instability region,geomechanical model tests and numerical simulations were performed.The continuous excavation method was adopted to reduce the pressure of the soil bin and restore the real engineering situation.Earth pressure in three directions of the obser-vation section in front of the tunnel face was monitored during the tunneling of the shield.Evolutions of the lateral stress ratios at dif-ferent stages were also investigated.The instability area of the shield tunnel face in sandy cobble strata with different burial depth ratios during the instability stage was obtained based on the change ratio of earth pressure and compared with existing researches.The earth pressure began to change when the excavation was one shield diameter away from the observation section,and when the excavation reached the observation section,the earth pressure decreased significantly.The burial depth of shield tunnel in the sandy cobble strata has a significant impact on the evolution of soil arch and the size of the failure area.The numerical simulation of the continuum medium cannot reflect the stress redistribution characteristics of the granular body like sandy cobble strata,and the failure area or stress distur-bance area obtained by the model test is larger than the numerical simulation result.Existing methods have deviations in analyzing the failure area of shield tunnel face in sandy cobble strata.It provides not only guidance for shield tunnel excavation engineering in sandy cobble strata,but also a reference for the theoretical research on failure areas.

关键词： Geomechanical model test Sandy cobble strata Face stability Arching effect Shield tunnel

Bearing capacity and failure behavior of disconnectable coupling joint with double row wedges(DCJD)used in the prestressed internal bracing

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Underground Space 2022年第4期7卷 498-513页

作者： mingju zhang Zhitian Xie Pengfei Li Key Laboratory of Urban Security and Disaster Engineering Ministry of EducationBeijing University of TechnologyBeijing 100124China

A disconnectable coupling joint with double row wedges(DCJD)is a crucial component of the prestressed internal bracing in subway foundation pits.However,only a few studies have been conducted on the bearing capacity of the joints;moreover,the yield load and compression stiffness of DCJDs are typically determined from experience.The aim of this study was to quantitatively determine the bearing capacity and propose accurate formulas for calculating the yield load and compression stiffness of DCJDs.Hence,a DCJD was selected from a foundation pit in Beijing,China,and loading experiments were conducted under axial force.Load–displacement and load–strain curves were obtained,and the failure modes of the joint were analyzed.The experimental results were verified through several finite element models.Subsequently,parametric analyses were performed to investigate the effects of the dimensions of the key position on the DCJD’s bearing capacities.Moreover,regression analysis was used to obtain the formulae for estimating the initial compression stiffness and yield load of the DCJD.Finally,the fitting formulae results were compared with the numerical and experimental results.The comparisons showed that the fitting formulae were highly accurate in estimating the bearing capacity of the DCJD.

关键词： Deep foundation pit Disconnectable coupling joints Loading experiments Parametric study Formulae fitting

Analytical solutions of ground settlement induced by yaw in a space curved shield tunnel

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Underground Space 2023年第6期13卷 86-103页

作者： Jiannan Xie Pengfei Li mingju zhang Fei Jia Shaohua Li Key Laboratory of Urban Security and Disaster Engineering Ministry of EducationBeijing University of TechnologyBeijing 100124China China Railway No.3 Engineering Group No.4 Engineering Co. Ltd.Beijing 102300China China Railway 15th Bureau Group Co. Ltd.Shanghai 200070China

This paper aims to provide the analytical solutions of the ground settlement for a space curved shield tunnel in the case of yaw construction.Settlement inducements include ground loss and construction loads,and two corresponding analytical models have been proposed in this study.Three-dimensional image theory has been adopted to calculate the ground settlement due to ground loss.Yawrelated parameters are introduced into the calculation model to deduce the relevant laws of the ground settlement.Based on modified Mindlin solutions,analytical models are established to calculate the ground settlement induced by construction loads,such as the frontal additional thrust,axial friction of shield shell,and the grouting pressure.The method of calculating the position of the shield machine in the ground is refined,and the influence area of construction loads from the shield machine is optimized.Subsequently,the obtained solutions are validated by a numerical model and field data.Besides,a comparison reveals that the proposed model is the composition of three classical analytical models,thus it excels them in solving the problem mentioned.Finally,parametric analyses of yaw are conducted to examine yaw angle and pitch angle on ground settlement.The proposed model can effectively predict ground settlement caused by the spatial linear shield tunneling process.

关键词： Shield tunnel Space line Yaw excavation Ground loss Construction load Ground settlement

Analytical algorithms of compressive bending capacity of bolted circumferential joint in metro shield tunnels

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结构与土木工程前沿:英文版 2023年第6期17卷 901-914页

作者： Xiaojing GAO Pengfei LI mingju zhang Haifeng WANG Zenghui LIU Ziqi JIA Key Laboratory of Urban Security and Disaster Engineering Ministry of EducationBeijing University of TechnologyBeijing100124China Nantong Railway Construction Component Co. Ltd.Nantong226000China

The integrity and bearing capacity of segment joints in shield tunnels are associated closely with the mechanical properties of the joints.This study focuses on the mechanical characteristics and mechanism of a bolted circumferential joint during the entire bearing process.Simplified analytical algorithms for four stress stages are established to describe the bearing behaviors of the joint under a compressive bending load.A height adjustment coefficient,α,for the outer concrete compression zone is introduced into a simplified analytical model.Factors affectingαare determined,and the degree of influence of these factors is investigated via orthogonal numerical simulations.The numerical results show thatαcan be specified as approximately 0.2 for most metro shield tunnels in China.Subsequently,a case study is performed to verify the rationality of the simplified theoretical analysis for the segment joint via numerical simulations and experiments.Using the proposed simplified analytical algorithms,a parametric investigation is conducted to discuss the factors affecting the ultimate compressive bending capacity of the joint.The method for optimizing the joint flexural stiffness is clarified.The results of this study can provide a theoretical basis for optimizing the design and prediciting the damage of bolted segment joints in shield tunnels.

关键词： shield tunnel segment joint joint structural model failure mechanism

Bending failure performance of a shield tunnel segment based on full-scale test and numerical analysis

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Frontiers of Structural and Civil Engineering 2023年第7期17卷 1033-1046页

作者： Pengfei LI Ziqi JIA mingju zhang Xiaojing GAO Haifeng WANG Wu FENG Key Laboratory of Urban Security and Disaster Engineering of Ministry of Education Beijing University of TechnologyBeijing 100124China Nantong Railway Construction Component Co. Ltd.Nantong 226000China

This study focuses on the bending failure performance of a shield tunnel segment.A full-scale test was conducted to investigate deformation and failure characteristics.During the loading,the bending failure process can be divided into four stages:the elastic stage,working stage with cracks,failure stage,and ultimate stage.The characteristic loads between contiguous stages are the cracking,failure,and ultimate loads.A numerical model corresponding to the test was established using the elastoplastic damage constitutive model of concrete.After a comparative analysis of the simulation and test results,parametric studies were performed to discuss the influence of the reinforcement ratio and proportion of tensile longitudinal reinforcement on the bearing capacity.The results indicated that the change in the reinforcement ratio and the proportion of tensile longitudinal reinforcement had little effect on the cracking load but significantly influenced the failure and ultimate loads of the segment.It is suggested that in the reinforcement design of the subway segment,the reinforcement ratio and the proportion of tensile longitudinal reinforcement can be chosen in the range of 0.7%–1.2%and 49%–55%,respectively,allowing the segment to effectively use the reinforcement and exert the design strength,thereby improving the bearing capacity of the segment.

关键词： shield tunnel bearing capacity failure mechanism segment reinforcement

Three-dimensional theoretical analysis of seepage field in front of shield tunnel face

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Underground Space 2022年第4期7卷 528-542页

作者： Qiguang Di Pengfei Li mingju zhang Caixia Guo Fan Wang Jie Wu Key Laboratory of Urban Security and Disaster Engineering Ministry of EducationBeijing University of TechnologyBeijing 100124China

To evaluate hydraulic head distribution in front of a shield tunnel in a saturated soil layer,theoretical analysis and numerical simulations are carried out in this study.Based on the partial differential equilibrium equation of seepage flow,a three-dimensional(3D)theoretical analytical model of the shield tunnel face and the seepage field in front of it is established using the eigenfunction and the Fourier series expansion methods,and the hydraulic head calculation formula is derived.Combined with engineering cases,the theoretical analysis results and the 3D numerical simulation results are compared and analyzed.The effect of the water pressure of the tunnel face on the hydraulic head distribution is also analyzed.The results of the proposed analytical solution are in agreement with those of the numerical simulation solutions;moreover,the proposed analytical solution requires less time to calculate the seepage hydraulic head than the numerical simulation.The ratio of the initial water table to the diameter(D)of tunnel face has a more significant impact on the hydraulic head distribution at a position 0.5D above the tunnel vault.When the water pressure on the tunnel face is not considered,the values of the hydraulic head are significantly underestimated.

关键词： Seepage flow Hydraulic head distribution Shield tunnel Numerical simulation Water pressure

信贷资产证券化能提升城商行盈利能力吗:基于10家城商行面板数据的实证研究

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中国软科学 2024年第1期 164-174页

作者：朱军唐凯张鸣菊蒋先进泰州学院经济与管理学院江苏泰州225300 南京大学工程管理学院江苏南京210012 中国人民银行泰州市中心支行江苏泰州225300

城商行创新发展的质量关系着地方经济社会的高质量发展。普遍观点认为,相较于全国性大银行,城商行自有资本金不充足、运营区域受限,导致盈利能力有限,探索信贷资产证券化创新,可以提升自身盈利能力。本文选取信贷资产证券化发行规模排... 详细信息

城商行创新发展的质量关系着地方经济社会的高质量发展。普遍观点认为,相较于全国性大银行,城商行自有资本金不充足、运营区域受限,导致盈利能力有限,探索信贷资产证券化创新,可以提升自身盈利能力。本文选取信贷资产证券化发行规模排名靠前的10家城商行面板数据进行了实证研究。实证结果表明,信贷资产证券化业务并未显著提升城商行单位资产经营获利能力,与普遍观点不一致。究其原因,通过城商行信贷资产证券化案例梳理分析,发现城商行推动信贷资产证券化业务的最大动机并非是增加盈利,而是基于可持续运营、维护品牌声誉的考虑。

关键词：信贷资产证券化城市商业银行盈利能力

盾构隧道缓和曲线段管片组合轴线拟合计算方法

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铁道标准设计 2024年第2期68卷 150-157页

作者：张明聚谢剑楠李鹏飞王晓北京工业大学城市与工程安全减灾教育部重点实验室北京100124 中交四航局第六工程有限公司广东珠海519000

盾构隧道在缓和曲线部分存在管片拼装问题,因缓和曲线线型复杂,管片拼装点位多变,一直是施工过程中的一个难题。基于错缝拼装要求与楔形管片特点,提出一种在平面范围内,利用循环计算与误差控制的条件判定,综合比选标准环与楔形环组合,... 详细信息

盾构隧道在缓和曲线部分存在管片拼装问题,因缓和曲线线型复杂,管片拼装点位多变,一直是施工过程中的一个难题。基于错缝拼装要求与楔形管片特点,提出一种在平面范围内,利用循环计算与误差控制的条件判定,综合比选标准环与楔形环组合,完成每环管片拼装施工,最终拟合出既满足规范与控制指标,又可保证线型较为均匀的管片拼装轴线的管片施工设计方法与验证方法。并根据实际工程需要,提出最大允许偏差控制方法和缓圆点附近的管片拼装优化措施,结合珠海市珠机线湾仔北站—湾仔站区间盾构隧道实例,证明了此方法的准确性与适用性,为缓和曲线上控制管片拼装质量提供理论依据。

关键词：盾构隧道缓和曲线轴线拟合方法管片拼装效果评价

反拉式顶管法施工联络通道对地铁盾构隧道力学性能影响

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隧道建设（中英文） 2024年第6期44卷 1165-1173页

作者：张明聚康博李鹏飞庞跃魁王锡军吴昊北京工业大学城市与工程安全减灾省部共建教育部重点实验室北京100124 北京建工土木工程有限公司北京100015

为探究采用反拉式顶管法施工盾构隧道联络通道过程中主隧道的力学响应机制,依托北京地铁某盾构区间,建立模拟联络通道施工过程的有限元模型,通过与现场监测数据对比验证模型的准确性。继而研究联络通道施工对主隧道管片间错台位移、特... 详细信息

为探究采用反拉式顶管法施工盾构隧道联络通道过程中主隧道的力学响应机制,依托北京地铁某盾构区间,建立模拟联络通道施工过程的有限元模型,通过与现场监测数据对比验证模型的准确性。继而研究联络通道施工对主隧道管片间错台位移、特殊管片应力及变形、螺栓受力的影响,并分析反力模式对主隧道管片力学特性的影响。结果表明:1)始发管片破除对主隧道力学性能影响较大,随着联络通道进一步开挖,主隧道受力和变形缓慢增大。2)管片间最大错台位移为1.17 mm,发生在特殊管片与普通管片接缝底部。特殊管片最大拉应力为18.6 MPa,出现在开口的顶、底部;最大压应力为27.0 MPa,出现在开口的腰部;最大横向扩张位移和竖向收敛位移分别为2.13 mm和4.56 mm。主隧道管片环间螺栓最大拉应力为213 MPa。3)背推式反力模式更利于控制开口处的横、竖向位移,反拉式反力模式更利于控制开口对面管片应力变形及其接缝处错动位移。

关键词：地铁盾构隧道联络通道反拉式顶管法机械法力学性能