Failure Mode Of Loose Surrounding Rock Of Shallow Buried Tunnel And Its Engineering Application

The landslides of shallow-buried tunnel engineering are increasing more and more in loose surrounding rock along with the highway construction. There are some disadvantages in the calculation of surrounding rock pressure and the design of supporting in conventional finite element method(Not considering the role of loose rock mass structural plane and the fall ) and the structural load method. Based on the theory of Peck formula and finite element method , the calculation model of describing the failure surface features of loose shallow-buried tunnel is proposed, and compared to verify its rationality. By using numerical method, the sensitivity of influence factors are analyzed..In this paper, a calculated method of surrounding rock pressure considering supporting opportunity is proposed. Based on the calculation model, a modified ground arch simulation discretization finite element method (GDFEM) is suggested, and its applicability and engineering practice are carried out by the numerical analysis.Through this study, the main conclusions can be drawn as follows:1. After the research of tunnel’s landslides , most of the damage model of surrounding rock is different from the method of specification and the traditional method in failure mode containing the location of damage and rupture angle In view of this, based on peck curve,a calculated model and the method are presented to determine the critical slip surface, and are contrasted with the model experiment and numerical experiment with the references and engineering examples to verify.2. Based on the calculated model of the fracture surface, the analysis of sensitivity of factors is made including the rupture Angle β, the surface rupture point i0 and tunnel span ratio w, elastic modulus E and poisson’s ratio μ, internal friction Angle φ, cohesive c and the class of surrounding rock (Ⅳ,Ⅴ,Ⅵ).3. According to the failure mode of the tunnel , the calculated method considering support opportunity of rock pressure is putted forward, and the influence of supporting opportunity are analyzed on surrounding rock pressure, and is compared with classical rock pressure calculated method, is revealed that the method of specification exist problems in the surrounding rock pressure and the design of supporting structure.4. Based on the fracture surface model, the improved GDFEM is putted forward, the influence of the deformation of surrounding rock and supporting force are analyzed about the supporting time, the critical slip surface location, structure, surface spacing, the intensity of structural plane, the Angle of the structural plane and rock parameters , and the applicability of this method is verified by engineering examples.