Model test of effect of lining thinning on tunnel structure bearing capacity

In order to study the influence of the thickness decrease of lining on the characteristics of tunnel structure mechanics behavior, the under-construction Bijia Mountain Tunnel of the Chongqing Municipality was taken as an in-situ prototype. Structure deformations, diseases, bearing capacity and other features caused by thickness decrease of lining under the conditions of different grades of surrounding rock and reinforcing modes were investigated. Conclusions show as below: Under the conditions of different grades of surrounding rock, no matter whether the thickness of vault lining is decreased or not, the loads where diseases happen are basically the same, however, structure deformations, failure modes and precedence of diseases vary significantly with different degrees of thickness decrease; the poorer the surrounding rock conditions, the severer the diseases caused by decrease of lining thickness; loads corresponding to occurrence of structure diseases rise with heightening of surrounding rock grades; after the influence of cavity backfilling disappears, the magnitude of thickness decrease of vault lining becomes the direct reason of increase of structure bearing capacity; the thickness decrease of lining has small influence on the distribution law of structure stresses under conditions of different grades of surrounding rock; reinforcing the internal surface of lining should be the first alternative to reinforce lining with thickness decreasing. The research results provide guidance for maintaining and reinforcing of tunnels in operation.