破碎围岩浅埋偏压隧道衬砌荷载的计算方法

隧道洞口大都会面临围岩破碎、浅埋和偏压等不良地质地形情况，现行规范只给出了偏压隧道衬砌荷载的计算方法。对于破碎围岩浅埋偏压隧道，根据现场情况及实测的衬砌受力和变形特征表明其与规范假定不同，不宜直接利用规范方法。通过工程实例分析及隧道三维数值分析结果提出了浅埋偏压隧道破碎围岩的破坏模式，即隧道开挖后深埋侧岩体滑塌下落挤压支护结构使其向外侧变形，从而外侧支护受到被动土压力。根据提出的破坏模式，将隧道开挖后围岩主要分为滑塌区和被动区，在此基础上利用极限平衡法推导出了衬砌荷载的计算公式。将计算得到的结果与现场实测值对比发现，对于围岩极其破碎且存在较严重偏压的浅埋隧道工程，提出的计算方法比采用规范方法更接近实际情况。

Load Calculation Method of Shallow Tunnel under Unsymmetrical Loadings in Broken Surrounding Rock

Tunnel portal section mostly faces unfavorable geologic and topographical conditions, such as broken surrounding rock, shallow and unsymmetrical loadings. The current Chinese code for design of road tunnel provides the load calculation method of tunnel under unsymmetrical. However, according to the mechanic and deformation characteristics of the tunnel lining on site, the assumption is not suitable for the shallow tunnel under unsymmetrical loadings in broken surrounding rock. Therefore, through engineering case analysis and results of three-dimensional numerical analysis, the failure mechanism of shallow tunnel under unsymmetrical loadings in broken surrounding rock is presented firstly, that is, deep buried side broken surrounding rocks slump down after excavation and squeeze the lining, which makes the lining deform outward and bear passive earth pressure. Through the failure mechanism, the surrounding rock mainly includes slumping area and passive area. Then the corresponding formulas are deduced based on limit equilibrium theory. Finally, a case study is adopted to verify the feasibility of the new method. It is show that the new method is more reasonable than the method of current code.