Numerical Analyses of Sequential Tunneling in Chicago Glacial Clays Abdolreza Osouli 1 , Siavash Zamiran 2 , Sree Kalyani Lakkaraju 3 1 PhD, P.E., Assistant Professor, Dept. of Civil Engineering, Southern Illinois University Edwardsville, Edwardsville, Illinois, USA, Email: aosouli@siue.edu, Phone: +1 (618) 650-2816 2 PhD Candidate, Instructor, Dept. of Civil Engineering, Southern Illinois University Carbondale, Carbondale, Illinois, USA, Email: zamiran@siu.edu, zamirans@gmail.com, Website: www.zamiran.net, Phone: +1 (618) 334-4572 3 Graduate Student, Southern Illinois University Edwardsville, Edwardsville, Illinois, USA 48 th US Rock Mechanics / Geomechanics Symposium held in Minneapolis, MN, USA, 1-4 June 2014 Postprint version Citation: Osouli, A., Zamiran, S., & Lakkaraju, S. K. (2014). Numerical Analyses of Sequential Tunneling in Chicago Glacial Clays. In 48th U.S. Rock Mechanics/Geomechanics Symposium. Minneapolis, Minnesota: American Rock Mechanics Association. 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. Keywords: One-pass and two-pass lining systems, Chicago Glacial Clays, Load Reduction Method, Modified Cam Clay material model 1. INTRODUCTION Tunnels are constructed with excavating soil or rock material and providing lining support. Tunnels are excavated in various projects such as highways and sanitary system construction, or subways. Tunneling in urban areas is challenging because in addition to presence of plenty of common uncertainties such as soft soil, sensitiveness of ground deformation, environmental difficulties, etc, the foundation of surrounding structures and effect of ground deformation on adjacent structures need to be considered.