【作者】 石钰锋；

【导师】 阳军生；

【作者基本信息】 中南大学 ， 土木工程， 2014， 博士

【摘要】 摘要：浅覆软弱围岩隧道施工过程中,需采取有效的超前预支护才能保证围岩稳定、满足围岩和地表的变形控制要求。在软弱围岩变形特征及控制技术总结基础上,依托多个浅覆软弱围岩隧道工程,采用现场测试、数值计算、解析求解等手段,重点对长管棚、水平旋喷预支护作用机理进行探讨。论文主要研究内容及成果如下：(1)将隧道围岩变形从空间上分为超前沉降、掌子面挤出变形及掌子面后方变形,总结出浅覆软弱围岩隧道变形存在超前沉降范围大、在总沉降量中所占比例大、掌子面挤出变形大的特征,提出浅覆软弱隧道围岩预支护(加固)方法的选择规律及范围的确定方法。(2)依托石头岗浅覆软弱围岩隧道,在长管棚现场测试分析基础上,建立精细化的数值模型对长管棚作用机理进行研究,提出管棚预支护结构受力的纵向分区,按其与掌子面相对位置分为前方受拉区、后方受压区及靠近洞口受拉区。总结各区应力及范围分布随掌子面掘进的变化规律表明,各区应力随隧道掘进而增长,且表现为先快后慢趋势,各区长度除掌子面前方受拉区基本稳定外,其余两区长度随掌子面掘进而增长,可供预支护设计参考(3)针对既有弹性地基梁的不足,提出考虑初支综合延滞效应、掌子面前方岩土体变基床系数、围岩应力释放时空效应等因素的改进模型,根据有限差分原理,以石头岗隧道为例对改进的Winkler弹性地基梁模型进行求解,现场测试结果验证了该方法的有效性。(4)依托富水软弱地层隧道工程,在对围岩加固前后现场取样,进行物理力学参数实验基础上,建立考虑流固祸合的三维数值模型,对水平旋喷预支护作用机理及效果进行研究提出,水平旋喷桩在纵向上起支护梁作用,横向上为受压拱效应,可有效改善围岩条件及隧道受力。(5)受材料特性、工艺所限,水平旋喷预支护存在抗拉(剪)强度低、完整性较差等缺陷,为此提出水平旋喷与管棚组合的预支护方式,并用数值手段论证,该方式可减小桩体的塑性区范围、拉应力,改善旋喷桩的受力,形成能充分发挥各自力学优点的组合结构,并成功应用于江门隧道下穿泄洪道工程。(6)掌子面加固可提高掌子面稳定性的同时,改善水平旋喷的受力,是水平旋喷桩缺陷克服的另一有效措施,对水平旋喷预支护及掌子面加固进行参数研究表明,水平旋喷预支护桩径、刚度及掌子面加固的面积比超过一定值后,加固效果增长有限,应根据具体工程选择最佳值。(7)对管棚与水平旋喷的设计与施工进行了探讨,设计中需根据具体工程条件及控制要求,本着安全、经济、高效的原则,选择预支护(加固)手段及参数,特殊工程需考虑局部加强或多手段结合,针对管棚、水平旋喷的施工问题应加强参数控制与施工管理。本文有图96幅,表36个,参考文献160篇。更多还原

【Abstract】 Abstract:Tunneling with lower overburden in weak stratum, Effective advanced support is essential to ensure stability of surrounding rock and meet the control standards of ground deformation. Based on the summary of deformation mechanism and controlling techniques for weak rock tunnel, and taking several real projects as examples, the reinforcement mechanism of pipe-roof and sub-horizontal jet-grouting were discussed by means of the analytical solution, field test, numerical analyses and so on. The main contents of this thesis are:(1) The deformation of tunnel surrounding rock can be divided into pre-convergence、face extrusion and convergence. Tunneling in weak ground usually results in wider pre-convergence range which takes a greater percentage of the total deformation. A large tunnel face extrusion is accompanied with in soft and weak ground than normal ground. Suggestions on the selection of pre-reinforcement method for tunneling in weak ground with low overburden were proposed.(2) A specific numerical model was established to study the mechanism of long pipe roof based on field test carried out at Shitougang Tunnel. The pipe roof turns out three stress region with respect to the position tunnel face:tension area in front of excavating face, compression area behind the excavation face, and tension area at the tunnel entrance. The length of the tension area in front of tunnel face is constant while the other two tension areas increase with the advance of the tunnel face, and they fall into a regular "slow after the first fast" pattern.(3) In order to overcome the deficiencies of the original elastic foundation beam, Improved elastic foundation beam model has been proposed. The new model considers comprehensive carryover effect of initial support、variable bedding value of surrounding rock in front of the tunnel face and time-space effect of rock or soil stress release. Numerical analysis based on Shitougang tunnel shows that, The modified Winkler elastic foundation beam model can results a good agreement with field testing. The effectiveness of the modified Winkler elastic foundation beam model has been highlighted.(4) Soil samples was taken from the spillway section of Jiangmen Tunnel which is pre-reinforced by sub-horizontal jet-grouting. Physical and mechanical parameters of the soil before and after reinforcement was obtained by lab test. The specific numerical model which consider the fluid-structure interaction is established to study the mechanism of sub-horizontal jet-grouting. Results show that sub-horizontal jet-grouting can play good "arch effect" in transverse direction and significant "beam effect" in the longitudinal direction. As a result, the stability of surrounding rock and the effects of reinforcement has been increased.(5) Sub-horizontal jet-grouting have some unconquerable defects because of limitation on the material properties and construction techniques, such as the tensile and shear strength is very low. The measure of combining with pipe roof has been proposed to add pipe roof under sub-horizontal jet-grouting pile. Numerical simulation shows this method can reduce plastic zone and tensile stress of the pipe, and improve force of columns. The composite structure brings their respective mechanical advantage into full play. It has been applied successfully in the spillway section of Jiangmen Tunnel.(6) Tunnel face reinforcement not only can reduce the face extrusion deformation increasing the stability of working face, but also change the stress pattern of sub-horizontal jet grouting columns. This is another method to overcome the defects of sub-horizontal jet-grouting. The study on reinforcement parameter for sub-horizontal jet-grouting and face shows that the effect on controlling the surface settlement is very limited after the diameter and stiffness of sub-horizontal jet-grouting columns and the ratio of reinforcement area to tunnel face reaching to a certain amount. These values should be chose according to the circumstance.(7) Based on the existing design theory and construction technology of pipe-roof and sub-horizontal jet-grouting, the design parameters of pre-support (reinforcement) should follow the principles of safe, economical and efficient according to engineering ground conditions and control requirements. In special circumstances, comprehensive measures are necessary, and the parameters for control and management should be strengthened. There are95figures,36tables and160references.更多还原