岩体中地铁大跨隧道松弛压力和围岩抗力系数确定方法及统计特征研究

Along with the increasingly development of urban rail transit system in china, how to correctly assess the statistical randomness of the relaxation pressures of the surrounding rock and the rock types that relative to the resisting force of the supporting structures, has become an important research topic which have a great influence on problems such as the reliability analysis problems, the construction costs problems, and the construction safety problems of the large-span metro tunnels in rock strata. As a basic research on the statistical characteristics of two basic random variables which involved in the tunnel load-structure model, the poor integrity rock of Ⅳ and Ⅴ levels will be taken as research projects, and the influence of the weathered overburden is also considered in the present research. In accordance with large-span metro tunnels in upper-soft lower-hard rock strata, the deformation and failure mechanism, the failure mode, the loose zone area of the surrounding rock, the relaxation pressures calculation methods, the statistical characteristics of the typical geometric quantities of the loose zone, the statistical characteristics of the rock resistant coefficient and its calculation method are analyzed thoroughly by collecting the statistical data of the collapse height of tunnels, conducting test research including the model indoor tests, the numerical simulations, the site test method. Through theoretical analysis, suitable calculation methods of the relaxation pressures and the rock resistant coefficient of large-span metro tunnels in rock strata will be proposed. The statistical characteristic of quantities including the range of the geometrical parameters of the loose zone, the relaxation pressures, and the rock resistant coefficient are obtained. The above results would provide essential research data to the reliability design of the large-span metro tunnels in rock strata, and promote the development of the metro tunnel design method. The results also have some reference value for the similar underground engineering.

随着我国城市轨道交通的发展，如何正确评价支护结构上的围岩松弛压力和围岩对支护结构抗力的随机性，成为影响岩质地层中地铁大跨隧道可靠性、建设成本以及施工安全的重要课题之一。本项目作为隧道结构-荷载模型涉及的两个基本随机变量统计特征的基础性研究，拟以完整性较差的Ⅳ、Ⅴ级围岩为对象，并考虑上部风化层的影响，通过隧道塌方统计、物理模型试验、数值模拟、现场实测以及理论分析等，对上软下硬岩质地层条件下，大跨地铁隧道的变形破坏机制、塌方模式、围岩中松弛区和松弛压力的计算方法与松弛区几何参数的统计特征、围岩抗力系数的计算方法与统计特征开展系统地理论与试验研究，提出适合岩质地层地铁大跨隧道特点的围岩松弛压力和抗力系数的计算方法，得出松弛范围几何参数、松弛压力以及围岩抗力系数的统计特征，为岩质地层地铁大跨隧道的可靠度设计提供基础资料，以促进地铁隧道结构设计方法的发展。研究成果对类似地下工程也有一定参考价值。

随着我国城市轨道交通的快速发展，岩质地层中浅埋大跨地铁隧道的数量日渐增多，如何正确评价支护结构上的松弛压力和围岩对支护结构抗力的随机性，已成为此类隧道结构设计中面临的关键问题。作为隧道结构—荷载模型涉及的两个基本随机变量统计特征的基础性研究，针对岩质地层中地铁大跨隧道的特点，采用隧道塌方统计、数值模拟、理论分析以及现场实测相结合的研究方法，对上软下硬岩质地层大跨地铁隧道的变形破坏机制、塌方模式、松弛压力的计算方法与松弛区几何参数的统计特征、围岩抗力系数的计算方法与统计特征开展了系统研究，取得以下主要创新性成果。. （1）统计得出了隧道塌方规律和塌方高度的统计特征以及主要影响因素，建立了可同时考虑隧道埋深和高跨比的隧道塌方高度和松弛压力的计算公式。. （2）揭示了上软下硬岩质地层中浅埋大跨隧道围岩松弛、破坏机制，推导出松弛区几何参数计算公式和以应力传递原理为基础的浅埋大跨隧道松弛压力计算公式。该公式不仅可以考虑隧道结构尺寸、埋深以及地层物理力学参数等的影响，还能考虑岩体中各类结构面产状、岩体完整程度以及上部风化层厚度等的影响，有效解决了上软下硬岩质地层中浅埋大跨地铁隧道松弛压力计算的难题。. （3）研究发现：无论是浅埋隧道，还是深埋隧道，无论考虑几个随机变量，当岩体重度、结构面粘聚力和摩擦角以及结构面倾角均服从正态分布，结构面间距服从负指数分布时，隧道松弛压力均呈正态分布规律，随机变量数量对松弛压力统计参量有一定影响，为隧道结构可靠度计算提供了科学依据。. （4）分别建立了适用于均质岩体、层状岩体、共轭节理岩体以及裂隙岩体中隧道围岩抗力系数的计算模型与计算方法，揭示了围岩抗力系数的统计特征。提出的计算方法充分考虑了各种岩体结构类型的特点，真实反映节理产状和节理密度对围岩抗力系数的影响以及抗力系数的各向异性特征，解决了传统方法存在的明显问题，有效解决了隧道支护设计时抗力系数的取值难题。