【作者】 王海涛；

【导师】 贾金青；

【作者基本信息】 大连理工大学 ， 结构工程， 2009， 博士

【摘要】 在软弱破碎地层中修建山岭隧道,或采用浅埋暗挖法修筑城市地铁隧道时,为了防止隧道发生塌方、有效控制地表沉降,并全面保证围岩处于稳定状态,常采用一些辅助措施对围岩进行预支护。管棚预支护是其中广泛使用的一种隧道顶部预支护措施。该技术是在拟开挖的隧道外周边钻设水平孔,然后安装钢管,再进行灌浆固结,使拱顶形成加固的伞形保护环,在该保护环的支撑下,进行循环掘进和支护施工。该技术能同时提高隧道周边围岩的强度及抗渗性能,从而保证隧道的安全施工。本文以隧道施工过程中管棚的力学机理及管棚预支护条件下隧道开挖面的稳定性为研究对象,利用理论分析、数值模拟、现场试验等多种研究手段,得到一些直接应用于工程实践或供理论参考的研究成果。主要研究内容如下:(1)借鉴隧道围岩压力确定方法的合理观点,综合考虑了隧道埋深、围岩条件、开挖条件以及管棚作为临时支护结构的特点等因素,分别推导了深、浅埋隧道管棚受力荷载的计算公式,并基于Pasternak弹性地基梁理论建立了管棚的力学分析模型。以二郎山隧道为工程实例,分别采用Winkler模型和Pasternak模型对隧道施工过程中管棚的力学行为进行计算,并将理论计算结果与现场测试结果进行比较。对比分析表明:在开挖面附近,Pasternak模型较Winkler模型的计算结果与现场测试结果吻合更好,但随着距开挖面距离越来越远,理论计算曲线较现场测试曲线衰减的更快。管棚的设计参数分析表明:管棚长度及钢管直径均存在最佳值。(2)采用三维弹塑性有限元分析软件对乔庄隧道入口管棚预支护段的施工过程进行数值模拟,并在隧道施工过程中,进行了现场量测试验。通过数值模拟,重点分析了隧道开挖过程中管棚、隧道围岩及支护结构的受力与变形特征,并对管棚预支护条件下隧道开挖面的稳定性进行了评价。通过现场量测试验,得到了钢支撑、喷射混凝土和二次衬砌等支护构件的受力和地表沉降及围岩位移收敛状况。有限元计算结果与现场实测结果吻合较好,说明采用现场动态监控量测与有限元仿真模拟相结合的方法,可为管棚预支护条件下隧道的设计和施工提供科学依据和技术指导。(3)将塑性极限分析上限定理与强度折减技术相结合,建立了隧道开挖面三维稳定性分析模型,经算例分析验证了其合理性;在此基础上,改进力学模型应用于管棚预支护条件下隧道开挖面稳定性分析及考虑渗流力的管棚预支护条件下隧道开挖面稳定性分析,由此确定开挖面稳定系数及其相应的潜在破坏模式,对隧道开挖面的稳定性进行定量的描述。分析渗流力及管棚预支护对开挖面稳定性的影响,并对隧道埋深、地下水位、隧道洞径及围岩条件等影响开挖面稳定的因素进行讨论。研究表明:渗流力严重影响开挖面的稳定性,采用管棚预支护技术可以有效地减小隧道开挖面渗流力,但不考虑渗流力时,管棚预支护技术对提高开挖面稳定性的效果并不明显。(4)基于三维弹塑性有限元方法对隧道开挖面正面预支护及管棚预支护进行了参数分析。研究了有无管棚预支护条件下不同核心土长度、不同台阶长度、不同开挖步距、不同管棚布置方式以及在有无地下水情况下,不同管棚预支护长度、不同地下水位时,隧道开挖对管棚力学行为、地层沉降及开挖面稳定性的影响。总结一些规律性的认识,为复杂地质条件下隧道施工及管棚预支护设计提供一定参考。(5)采用三维弹塑性有限元数值模拟方法,研究管棚预支护条件下隧道开挖面极限支护力;以不同工况下地层参数及其极限支护压力比作为样本,待BP神经网络训练完毕后,即可预测大量给定地层参数工况下的开挖面极限支护压力比,对其进行统计,得到概率分布特征;在理论分析的基础上,结合工程实际,建立了管棚预支护条件下隧道开挖面稳定的极限状态方程,运用粒子群优化算法,对其进行可靠度分析。本文除能科学合理的评价管棚预支护条件下开挖面的稳定程度外,对软弱围岩条件下,隧道开挖面正面预支护措施的合理设计与选择也具有一定的参考作用。更多还原

【Abstract】 In order to prevent tunnel collapse, restrain ground movement and control ground surface settlement when tunnels would be constructed in soft or weak geology stratum, several pre-reinforcement methods of heading have been developed. One of such methods is the pipe roof reinforcement method. This method consists on installing, prior to the excavation of a length of tunnel, a series of pipes, either parallel to the tunnel axis or at a certain angle with it. By injecting grout through the pipes, the ground in between the pipes is stiffened and the pipes are connected, creating a kind of ’umbrella’ above the area to be excavated. This technique combines the advantages of the modern fore poling system with the grouting injection method. In other words, the improvement of the mechanical characteristics and the impermeability of the ground around the tunnel can be achieved simultaneously. Taking the mechanism of pipe roof reinforcement and the tunnel face stability as the objects to be investigated, using theoretical analysis, numerical simulation, field tests and other research tools, a series of results were obtained.(1) Based on the predecessors surrounding rock pressure calculating method, the equations for pipe roof reinforcement loading were proposed according to Terzaghi theory. Compared with the traditional theory, it can more reasonably describe the effects of the tunnel cover depth, the geological conditions and manners of excavation on the surrounding rock pressure.Considering the delay effect of initial lining, an analytical approach based on Pasternak elastic foundation beam theory for pipe roof reinforcement was put forward. With the example of Erlangshan tunnel excavation, the comparison of the values of longitudinal strain of reinforcing pipe between field monitoring and analytical approach was made. The results indicate that although Pasternak model gives more accurate calculation and agree better with the result of field monitoring at tuunel face than Winkler model, the general trend of decreasing longitudinal strain with increasing distance from the tunnel face for analytical approach and field monitoring are different. A systematic parameter study was conducted to study the effects of important design parameters such as the pipe diameter, pipe length, and overlap length on the mechanical behavior of pipe roof reinforcement. The findings illustrate that there exists a critical value of each reinforcement parameter, with these critical values, the maximum reinforcing effect can be achieved. (2) A three-dimensional elasto-plastic finite element code was employed to simulate the interaction between tunnel excavation and pipe roof in entrance of Qiaozhuang Tunnel. And the convergence deformations of surrounding rocks, the stresses of I-steel supporting, shotcrete and secondary lining were obtained by field test. The mechanical behaviours and deformation characteristics of pipe roof reinforcement, surrounding rock and tunnel lining were individually analyzed in tunnel excavation, and the effect of pipe roof reinforcement on tunnel face stability was also evaluated. The simulated results were compared with field test results, it is verified that not only the field test but also the finite element method be important for successful construction of the tunnel with pipe roof reinforcement.(3) Based on the kinematic method of limit analysis and the shear strength reduction technique, a three-dimensional model for expressing the tunnel face stability was established and was employed to define the safety factor and its corresponding critical failure mechanism for a given tunnel. For a typical example, the solutions computed by the proposed approach are compared with the results given by wedge model, trapezoid wedge model and centrifugal-model test to verify the reasonability of the method. Furthermore, by modifying the mechanics model, the complicated conditions such as tunnel with pipe roof reinforcement and underwater tunnel with pipe roof reinforcement were respectively considered. And the effects of pipe roof reinforcement and seepage force on tunnel face stability were individually examined. The proposed approach was also employed to study how cover depth of tunnel, groundwater level, tunnel diameter and soil parameters affect the tunnel face stability. The studies revealed that the existence of groundwater may seriously affect the tunnel face stability, and there was a relatively large reduction in the seepage pressure by adopting the pipe roof reinforcement technique, but in dry condition, the effect of pipe roof reinforcement on tunnel face stability is not significant.(4) Based on three-dimensional elasto-plastic finite element method, the design parameters of pipe roof reinforcement were analyzed. The effect of the length of bench and core soil, excavation length, length of steel pipe, underwater level and arrangement of pipe roof reinforcement on the squeezing of tunnel working face, the displacement ahead of the face and mechanical behaviours of pipe roof reinforcement are analyzed. Some valuable conclusions for the construction of tunnel with pre-reinforcement were proposed.(5) The limit support pressure at tunnel face was studied by elasto-plastic finite element method. First, BP neural net work was trained with parameters of surrounding rock and ratio of limit support pressure of tunnel face as training samples. After training, the net work can predict ratio of limit support pressure when lots of parameters were imported. The statistics character of ratio of limit support pressure was gained. Limit state function of face stability of tunnel with pipe roof reinforcement was established, and reliability was solved with the particle swarm optimization. Using this method, not only stability of tunnel face can be appraised rationally, but also it was reference to select pre-reinforcement technique rightly.更多还原