Abstract

The key factor in successful construction of urban tunnel projects is selecting a suitable excavation procedure in soft ground. The choice of the excavation procedure strongly influences the cost and time for tunnel construction. The aim of this paper is to analyze delay in liner installation for tunnel construction using one- and two-pass lining system via three-dimensional finite element numerical modeling. The tunnel is assumed to have a circular cross section in Chicago glacial clays with a diameter of about 3.8 m and a centerline at a depth of 10.5 m below the ground surface. The soil profile consists of compressible clay deposits (i.e. Blodgett and Deerfield) and a relatively incompressible hard silty clay stratum (i.e. Park Ridge) and the tunnel alignment is assumed within Deerfield compressible clay layer. The thickness of the inner liner is assumed 12.7 cm. The constitutive model used to characterize the clays in the simulation is the Modified Cam Clay model. The soil stratigraphy was assumed to be uniform within each layer. The one and two-pass lining systems are modeled in ABAQUS using Model Change option and Load Reduction method, respectively. For load reduction method, the concentrated loads in equilibrium with the initial stress field are applied along the perimeter of the tunnel. These forces were sequentially reduced after initial liner placement to evaluate the creep effect. The results of 3D finite element analyses with emphasis on ground stability, axial and radial deformations of the tunnel, and stresses transferred to the liner are presented for both analyses.

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