Inverse Analysis of Settlement and Convergence Data During Resalat Tunnel Construction (Technical Note)

A fairly complete monitoring of soil-structure interaction was performed during the construction stages of Resalat tunnel, a large span highway twin tunnel, and the instrumentation results were processed and analyzed. This project is one of the limited numbers of urban tunnels with a large span of 16 m and a low overburden (6 to 30 m) which are excavated through soft ground and passes underneath several deformation-sensitive urban areas. The proximity of two large span tunnels makes this project very special. Excavation of each 16 m span tunnel was designed to be done in five stages by a sequential excavation method and the number of stages sometimes was increased to 8 and more in order to restrict the ground deformation and surface settlements. Since measurement of some geotechnical parameters of course grained alluvial of Tehran is extremely difficult and sometimes impossible by conventional laboratory tests or even in-situ tests, the inverse analysis of instrumentation data can be used as an effective alternative for assessment of these parameters. These parameters mainly include the coefficient of cohesion due to soil cementation C, at rest coefficient of soil lateral pressure Ko, and to some extent the modulus of elasticity E. In this paper, the construction stages of Resalat twin tunnel are simulated by a finite element based numerical model and the possible sets of geotechnical parameters of the host ground are assessed.