Assessment On The Safety Of Section-Steel-Girder-Reinforced Shotcrete Support Of Tunnels

To a tunnel under construction, a prompt assessment to the safety of support through in-situ measured data is of practical importance both for the dynamic design and to guarantee the stability of the tunnel. Among all the parameters measured during tunnel construction, displacement is widely used and thus accepted as a very essential quantity, due to its advantages in convenience, low cost and high credibility.In terms of the displacement-based method proposed to evaluate the safety of tunnel support structures, the influence of creep of shotcrete on the stability of tunnels is approached in this paper. The performance functions for components subjected to a large eccentric compression, as well as a small eccentric compression, are given. More data for random variables like thickness of shotcrete are collected. The properties of shotcrete on creep are discussed. The influencing factors on concrete creep are described. Both theoretical and experiential methods are used to study the influence of loading age on the properties of early-age shotcrete creep. The formulas to calculate the deformation and internal forces of the shotcrete support with creep considered are derived out. The effect of section steel on deformation, the protective layer and curing condition, etc. are taken into account. Monte Carlo method are employed to calculate the failure probability Pf and reliability index P of the function. Finally two case studies are done.The results show that it proves that the displacement-based method is reasonable and correct that the results matches the cases well whether creep is taken into account. If the level of stress is too high, creep which is harmful to the support should be considered.This work improves the accuracy of the displacement-based method.