Mechanical analysis of support structure based on over-under-excavated tunnels

LI Shuchen; ZHU Lin; SUN Aihua; ZHANG Luchen; XIE Can; YAN Qin

doi:10.13225/j.cnki.jccs.2017.0638

Abstract：Conventionally,the traditional design of shotcrete support structure has assumed that support structure is a prismatic layer with uniform thickness.Due to the influence of blasting,the surrounding rock surface of the tunnel with drilling and blasting method has different degrees of over-under-excavation,which results in the uneven thickness of the initial support structure layer.In the consideration of the possibility of rock surface irregularities caused by overunder-excavation,this paper,according to the shotcrete thickness,divides the irregular surface of the tunnel after supporting into three categories:not fully filled,partially filled,and fully filled.With utilizing the thick-wall cylinder theory of elastic mechanics,the theoretical formula of the parameters,such as equivalent support stiffness and maximum support pressure,are established under the support of shotcrete or shotcrete +steel grid.Based on the research findings mentioned above,this work analyzes the stability of a tunnel excavation project with the aid of the convergence-confinement method and calculates the safety factor of the support structure.The results show that the proposed method has a preferable applicability to the stability study of over-under-excavated tunnel,and the availability is verified preliminarily.