Numerical Ultimate Load Analysis Based Study on Safety Monitoring Reference Value for Tunnels in Weak Rock

Abstract

It is usually hard to ensure overall stability and construction safety when tunneling in weak rock. Therefore, it is of practical engineering significance to conduct safety monitoring reference value study based on numerical ultimate load analysis by building an equivalent rock model. In this paper we investigate ultimate strains of equivalent rock masses of different classes based on numerical ultimate load analysis by building an equivalent surrounding rock model; examined the deformation reduction factor changes for different classes of surrounding rock by building a plane model for calculation and analysis; established tunnel stability assessment criteria through observation of ultimate shear strain diagrams under different reduction factors; and determined appropriate management measures according to warning levels. Our analyses show (1) under different loads the higher the rock mass classification the smaller its vertical displacement and hence its ultimate strain; (2) the higher the rock mass classification the more susceptible it is to strength, creep and instabilities; (3) Assessment criteria are established by comparing displacement U measured during tunneling with the ultimate displacement U0, i.e. the tunnel is stable if U < U0 and unstable if U > U0.