Inversion study on initial in-situ stress field of tunnels in soft and hard alternating rock area

The lithology on both sides of the structural surfaces in soft and hard alternating rock areas changes dramatically, leading to complex distribution of in-situ stress.In order to ascertain the influence of rock mass structural surface in the soft and hard alternating rock area on the in-situ stress field, a 3D numerical computational model containing elevation information was established for the Manmo No.2 Tunnel in Yunnan Province.The initial in-situ stress field of the tunnel axis was obtained by inversion with multiple linear regression method, and the influencing factors of the horizontal principal stress anomaly at the interface of soft and hard rocks were analyzed.The results show that the anomaly of the horizontal principal stress was related to the differences of elasticity modulus of country rock on both sides of the interface, the burial depth and the dip angle of structural surface.The significance of each influencing factors was evaluated by orthogonal test.It was found that the elasticity modulus of country rock and the burial depth had a significant influence on the horizontal principal stress, which were key factors for the anomaly of the horizontal principal stress.The research results can provide basis for country rock stability monitoring and the design of support scheme during tunnel excavation.