A Method To Assess The Safety Of The Primary Lining Of Tunnels Under Construction With Consideration Of Shrinkage And Creep Of Shotcrete

To a tunnel under construction, a prompt assessment to the safety of the lining 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 previously proposed to evaluate the safety of tunnel support structures, the influence of shrinkage and creep of shotcrete on the stability of tunnels is approached in this paper. The properties of shotcrete on shrinkage and creep are discussed, and the formulas to calculate the internal forces of the shotcrete lining with shrinkage and creep considered are derived out. Then a performance function for the failure of a cross section is given. At last, three case studies are done.The results show that the method gives larger reliability index when shrinkage and creep of the shotcrete are taken into account. That is to say, the reliability index was underestimated in the past. In comparison with creep, shrinkage doesn't have much contribution to the increase of the reliability index, which means that shrinkage could be neglected in the analysis. The influence of creep depends on the dimension of the internal forces of the lining. When the forces are small, the influence of creep could be ignored. However, when the forces are big, the influence of creep should be taken into consideration.This work improves the accuracy of the displacement-based method.