层状岩体中大跨度地下洞室拱肩开裂机理分析

Analysis of cracking mechanism at the spandrel of large underground opening in laminar rock strata

针对金沙江鲁地拉水电站地下厂房洞群开挖过程中三大洞室下游拱肩出现裂缝的问题,结合地质资料、地应力、监测资料、数值模拟等分析,认为洞室拱肩开裂的主要原因是层状岩体各向异性及地应力偏压导致下游拱肩应力集中,顺洞向反倾裂隙构成的薄层岩体在侧向卸荷下发生了压弯挠曲变形。在深入分析洞室拱肩变形影响因素的基础上,提出了薄层岩体压弯溃曲指数的概念,据此量化了拱肩开裂的范围、深度,明确了洞室拱肩开裂属于围岩局部浅表层变形稳定问题。分析成果为最终的工程处理提供了科学依据。

The underground cavern group of the Ludila hydropower station is one of the largest underground projects on Jinsha River.When its excavation was completed,a number of splits appeared at its downstream spandrel,a similar phenomena that has been found in other underground powerhouses.This work took the Ludila underground powerhouse as a case study to find the causes for such phenomenon that is vital to stability of large caverns,and to explore reasonable reinforcement measures,through analyzing the geological features,initial stress,monitored displacements and numerical simulations.The results indicate that stress concentration was induced by tilt geo-stress and anisotropy of the rock mass and rock deflection at the downstream spandrel under excavation unloading.A concept of deflection index is put forth for evaluation of the depths and range of the splits.