The excessive cracking of concrete lining in a highway tunnel is discussed, where two longitudinal cracks were spotted in the arch areas. The crack-mouth-opening displacement (CMOD) of the inner crack had reached a maximum width of 7 mm. Field investigations found that a narrow fault ran through the tunnel cross section from the upper right to the lower left. A loosening zone with a depth of more than 3 m was found along the fault. In order to carry out remedial works on the tunnel, the earth pressure exerted on the concrete lining by the loosening zone needs to be determined.
Two modeling methods are employed to solve this problem: a nonlinear FE model for the concrete lining with spring supports and a pseudoshell model that includes an imaginary shell which is rigidly connected to the lining. The spring support and the pseudoshell represent two different approaches to the earth-tunnel interaction. To obtain the pressure loads crack analysis is carried out. While the approach using spring supports calculates the earth pressure directly, the obtained pressure loads at the designated CMOD may subject to change depending on the spring coefficients. On the other hand, the pseudoshell model takes two steps to evaluate the pressure loads. It obtains the cross-sectional deformation of the tunnel at the given CMOD first, and then calculates the earth pressure through iterative computations of a quasi loosening zone model. This two-step computational approach ensures the earth pressure to be uniquely determined.