高地应力陡倾互层千枚岩地层隧道大变形研究

Large deformation of tunnels in steep dip strata of interbedding phyllite under high geostresses

在高地应力陡倾软岩地层中开挖隧道,易引发围岩发生大变形。为了明确大变形的诱发因素,分析围岩的破坏机制、变形特征及支护结构的受力规律,提出合理的控制技术,依托杨家坪隧道进行相关研究。通过岩石试验,分析绿泥石千枚岩显著的各向异性力学特性,明确岩块的破坏形式与荷载角度的关系。通过现场观测和数值计算可知,围岩变形表现为整体内挤,水平收敛大于拱顶沉降,边墙围岩以水平向的弯折破坏和层面分离为主,其最大主应力呈"<",">"形分布,拱部和仰拱围岩以剪切滑移破坏为主,其最大主应力沿隧道切向。综合分析该隧道大变形的主要诱因是:高构造应力、不利岩层产状和低岩体强度。通过现场测试,总结了各支护结构的受力分布及发展规律。现场试验成果表明:与岩层大角度相交的长短组合锚杆配合注浆可有效加固围岩,改善围岩压力;减少开挖分部,使初支尽快成环,可充分发挥初支承载力;优化断面轮廓,可改善结构受力。

The large deformation of surrounding rocks is easily induced in the tunnel excavation in steep dip and soft rock strata under high geostress conditions. Yangjiaping Tunnel was investigated to identify the factors causing the large deformation,to analyze the failure mechanism and deformation characteristics of surrounding rocks and the internal forces in the supporting structure and to propose a rational method of control. The in-situ sampling was carried out to analyze the significant anisotropic characteristics of chlorite phyllite and to determine the relationships between the load direction and failure mode of rock. The in-situ observations and numerical simulation results showed that the deformation of surrounding rock converged as a whole and the horizontal displacement of convergence was larger than the vault settlement. The bending damage in horizontal direction and the separation of bedding planes were found mainly in the side walls of tunnel. The maximum principal stress in the side walls is distributed like＂＂and＂＂. The main failure mode of tunnel vault and invert is shear slip failure and the maximum principal stress is along the tangential direction of the tunnel. The factors inducing the large deformation are high tectonic stress,adverse stratigraphic occurrence and low rock strength. The results of in-situ experiments show that combinations of long and short bolts intersected with rock strata with large angles together with grouting can strengthen the surrounding rock effectively and adjust the surrounding rock pressure. Reducing the excavation steps led to the initial support be closed sooner and the bearing capacity of primary lining was thus fully utilized. Optimizing the cross section profiles can improve the loading on the support structures.