Influence of shrinkage and creep of lattice girder reinforced shotcrete on the safety of the primary support of tunnels

In the displacement-based method for reliability assessment of tunnel structures,the measured deformation of the primary support is not only related to loads,but also to the shrinkage and creep of the material of the support.In the study,GL2000 model is modified and used to calculate the shrinkage and creep of the support.The formulas to calculate the axial deformation and curvature change of the support are derived out,and the formulas to compute the internal forces of the support with shrinkage and creep considered are given.Case studies are done at two tunnels: Wushaoling Tunnel at Lanzhou-to-Xinjiang Railway Line and Huangzhuang Station at Line 4 in Beijing subway,through which the influence of shrinkage and creep of lattice-girder-reinforced shotcrete on the safety of the tunnels is addressed.Results show:(1) shrinkage has little influence on reliability index and could be neglected in the future;(2) creep makes an obvious increase in the index and should be considered in engineering practice.