节理岩体各向异性特性和隧道支护计算方法研究

Rock masses through which tunnels are excavated often exhibit anisotropy, induced by the existence of discontinuities such as joints, faults, and bedding planes. As a consequence, the fracture behaviors of a jointed rock mass around a tunnel may be different from those of an isotropic rock mass. The existence of discontinuities alters the stress distribution pattern around underground openings compared with conditions in anisotropic rock mass. The effects of the discontinuities may include changes in the magnitude and orientation of the peripheral stress around a tunnel. This may result in different modes of rock mass failure around the opening compared with the modes observed in isotropic rock masses. Although many attempts have been made in the past to describe the anisotropy of jointed rock mass, no general methodology has emerged yet..Numerical modeling of the mechanical behavior of jointed rock masses is a difficult task as the discontinuities not only require special modeling consideration, but also require different treatments depending upon the scale of problem involved. A two-scale modeling concept will be proposed within the framework of the numerical manifold method. The joints among rock mass are denoted as the primary discontinuity set and the secondary discontinuity set. The primary discontinuity set be modeled explicitly, whereas the secondary set be modeled through an equivalent elasto-plastic continuum. .The present study includes the investigation of rock mass and joint behaviors around a tunnel in a jointed rock mass through experimental and numerical analyses. Among the many parameters of joint configuration, the dip angle and smooth of surface as well as space of joints are variables in this study. Therefore the main purpose of this study is to investigate rock fracture and joint sliding behaviors around a tunnel in a rock mass having a single joint or one and two sets of joints. The excavation process of a tunnel was simulated and the effects of various joint dip angles and spacings on the tunnel construction are investigated. From the numerical and experimental analyses, a joint geometry dependent failure process can be observed and empirical equations will be proposed to calculate the support pressure and coefficient of rock resistance. The proposed approach can serve as a useful framework for applications from estimating jointed rock mass properties to tunnel engineering analysis and support design.

岩体中众多节理、断层等结构面的存在导致的节理岩体各向异性给隧道支护设计和稳定分析造成了极大困难，如何确定围岩压力以及围岩的抗力系数等成为此类隧道支护设计的关键。本项目针对节理岩体各向异性特性以及隧道支护计算方法，以优势节理岩体模型为基础对数值流形法进行改进，将优势节理作为不连续面，含有密集分布节理、裂隙的岩体等效为符合H-B准则的弹塑性连续介质，建立可模拟隧道施工过程的节理岩体弹塑性数值流形方法。通过物理模拟和数值模拟，分析层状结构岩体和块状结构岩体以及随机分布节理岩体在不同尺度条件下的基本变形规律和破坏机理，揭示不同地应力条件下节理岩体各向异性对隧道变形和稳定性的影响规律，得出围岩松动压力和围岩抗力系数与节理分布参数之间的统计关系及其预测方法。通过优化分析提出隧道的合理支护参数，指导此类隧道的设计。

节理、裂隙、断层等各类结构面的存在破坏了岩体的连续性，是导致岩体各向异性的主要原因，基于均质、连续、各向同性假设的传统计算方法已经难以满足复杂地质条件下的隧道支护设计和稳定分析，开展节理岩体各向异性特性研究对于提高隧道与地下工程支护设计水平具有重要理论意义和应用前景。. 本项目采用理论分析、基于数值流形方法和离散元法的数值模拟以及现场监测相结合的研究方法，重点研究了层状节理岩体和含有两组斜交节理岩体的各向异性特征及强度预测方法、围岩抗力系数分布特征和影响因素、浅埋大跨隧洞松动破坏机制和松动区分布特征及松动压力计算方法等，取得的主要成果包括：1）层状结构岩体强度随节理倾角的变化曲线呈勺子型，节理附近应力集中和节理的剪切滑动破坏是导致岩体强度各向异性的主因；2）含有两组节理岩体的强度也具有显著的各向异性特征，两组节理之间的相互作用控制着岩体的破坏模式与强度；3）建立了根据节理间距、倾角、节理和岩石强度以及围压预测层状岩体三轴抗压强度的计算公式，该公式简单、实用、预测精度高，所有参数均有明确物理含义，且可通过常规室内试验获取；4）含有两组斜交节理岩体的围岩抗力系数分布曲线呈卵形，节理的倾角对隧道各个方向围岩抗力系数值影响明显，平行于节理方向的抗力系数明显大于其他方向。节理法向刚度、岩石的弹性模量、节理间距、两组节理间的夹角是影响抗力系数的主要因素；5）提出的围岩抗力系数预测公式可根据岩石的弹性模量、节理法向刚度、节理间距、节理间夹角计算隧洞各个方向上的围岩抗力系数值，合理反映节理分布状态对抗力系数的影响；6）基于节理岩体中地下洞室围岩松动区分布特征，以应力传递原理和极限分析上限法为基础，分别推导出节理岩体中浅埋地下洞室围岩松动压力计算的应力传递法计算公式和极限分析上限法理论计算公式，除了可考虑洞室尺寸、埋深以及岩体性质的影响外，还能考虑岩体中各类结构面产状、岩体完整程度以及上部软弱地层厚度等的影响，研究成果已用于大连地铁车站隧道的支护设计，取得了显著的经济和社会效益。