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Study on Health Evaluation Method of Large-Span Highway Tunnel with Fractured Surrounding Rocks
(1 Tongji University, Shanghai 200092；2 Shanghai Engineering Research Center of Underground Infrastructure Detection and Maintenance Equipment, Shanghai 200092；3 Shenzhen Transportation Public Facilities Construction Center, Shenzhen 518000)
Abstract At present, there are few research on the mechanism of deformation and damage evolution of large-span tunnel structure under loose load, lacking health evaluation system and early warning standard of the tunnel structure in operation, which is not conducive to understand the safety state of tunnel structure. Aiming at these problems, this paper studies the mechanical and deformation characteristics of large-span tunnel structure under loose load in the surrounding rocks of grade Ⅳ and Ⅴ by establishing two-dimensional and three-dimensional numerical analysis models. A 5-grade evaluation system and 3-level early warning standard are established based on the characteristics of deformation and damage. It comes to the following conclusions: (1) the failure process of the large-span tunnel under loose load is divided into four stages, namely elastic stress stage under designed load, elastic stress stage under loose load, plastic working stage after structure cracking and accelerated deformation and failure stage;(2) under designed load, the tunnel deformation obtained by three-dimensional numerical simulation method is basically consistent with that by the calculation method of load code, which verifies the feasibility of numerical calcula? tion. By numerical calculation, it is found that in the surrounding rocks of grade Ⅳ, the ultimate bearing capacity is 734 kPa, the crown settlement is 6.75 cm, the convergence of sidewall is 1.56 cm; in the surrounding rocks of grade V, the ultimate bearing capacity is 812 kPa, the crown settlement is 10.47 cm, the convergence of side-wall is 4.06cm; (3) a health degree evaluation system and early warning standard of large-span tunnels in the surrounding rocks of grade IV and V are established by taking the vault cracking, local buckling, vault and haunch buckling, haunch buckling depth reaching 1/3 of lining thickness and rebar tensile rupture as the key nodes and structure stress,crown settlement and side-wall convergence as the evaluation indexes.
Abstract：
At present, there are few research on the mechanism of deformation and damage evolution of large-span tunnel structure under loose load, lacking health evaluation system and early warning standard of the tunnel structure in operation, which is not conducive to understand the safety state of tunnel structure. Aiming at these problems, this paper studies the mechanical and deformation characteristics of large-span tunnel structure under loose load in the surrounding rocks of grade Ⅳ and Ⅴ by establishing two-dimensional and three-dimensional numerical analysis models. A 5-grade evaluation system and 3-level early warning standard are established based on the characteristics of deformation and damage. It comes to the following conclusions: (1) the failure process of the large-span tunnel under loose load is divided into four stages, namely elastic stress stage under designed load, elastic stress stage under loose load, plastic working stage after structure cracking and accelerated deformation and failure stage;(2) under designed load, the tunnel deformation obtained by three-dimensional numerical simulation method is basically consistent with that by the calculation method of load code, which verifies the feasibility of numerical calcula? tion. By numerical calculation, it is found that in the surrounding rocks of grade Ⅳ, the ultimate bearing capacity is 734 kPa, the crown settlement is 6.75 cm, the convergence of sidewall is 1.56 cm; in the surrounding rocks of grade V, the ultimate bearing capacity is 812 kPa, the crown settlement is 10.47 cm, the convergence of side-wall is 4.06cm; (3) a health degree evaluation system and early warning standard of large-span tunnels in the surrounding rocks of grade IV and V are established by taking the vault cracking, local buckling, vault and haunch buckling, haunch buckling depth reaching 1/3 of lining thickness and rebar tensile rupture as the key nodes and structure stress,crown settlement and side-wall convergence as the evaluation indexes.
LIU Xuezeng1,
2 CAI Xin3 DING Maorui3 CHEN Fubin3 DENG Feng3
.Study on Health Evaluation Method of Large-Span Highway Tunnel with Fractured Surrounding Rocks[J] MODERN TUNNELLING TECHNOLOGY, 2020,V57(1): 26-35
2020, Vol. 57 