ASSESSMENT ON SAFETY OF LATTICE GIRDER REINFORCED SHOTCRETE SUPPORT FOR TUNNELS
LI Hongquan1，YANG Chengyong1，XU Mingxin1，LU Jinghui2
(1. Research Center of Tunnel and Underground Engineering，Beijing Jiaotong University，Beijing 100044，China； 2. Beijing Gas and Heating Engineering Design Institute Co.，Ltd.，Beijing 100032，China)
Abstract：Based on the previous research，lattice girder reinforced shotcrete support is dealt with，and a method is set up to evaluate the safety of this kind of support for a tunnel in construction. Firstly，performance functions to a cross-section of the support are put forward according to the correlative formulae from Chinese codes. Then，parabola is employed to interpolate the central axis of an arch-like support segment，and the formulas to calculate internal forces of the support are derived through measured displacements under assumptions of linearly elastic material，small deformation，and plane cross-section etc.. After that，the uncertainty of the basic random variables，such as mechanical properties of rebars(compressive strength，tensile strength and modulus of elasticity)，the sectional area of rebars and thickness of shotcrete cover，is discussed. At last，case studies are conducted in two tunnels，Wushaoling Tunnel at the second line of Lanzhou—Xinjiang Railway and Huangzhuang Station at Line 4 in Beijing subway. Case studies show that the obtained results are consistent with in-situ situations and calculated reliability indices fall into the interval required by national codes. This work improves the so-called displacement- based method and addresses the very real need of assessing the safety of lattice girder shotcrete support during tunnel construction. This study is of both theoretical and practical significances.
