Boundary Element Analysis of a Lined Tunnel Problem

The boundary element technique is a practical problem-solving tool and useful in comparison to other currently popular alternatives. In this paper, a circular tunnel of a diameter 3.4 m is to be excavated through a clayey soil and surrounded by concrete lining of a thickness 0.2 m, so the clear internal diameter is 3.0 m. A plane strain analysis is adopted for such problem and the soil is assumed to be homogeneous, isotropic and linearly elastic medium. The program MRBEM (multi-region BEM) is adopted to analyze a 2D circular lined tunnel in a soil medium of an infinite extent.  The existence of a lined tunnel, as in the case of any structure, through the soil medium is affected by and affects the surrounding soil. This may be understood throughout the study of many parameters that influence the tunnel's behavior. The parametric study for the lined tunnel covers the influence of the following factors: Depth of the tunnel Undrained shear strength of soil.            It was found that Ground surface settlement, due to the effect of surcharge load, shows its maximum value at both sides of the lined tunnel and not above the center of the tunnel. The maximum positive stresses at the lining interface occur at the crown and invert regions. These stresses tend to decrease gradually until they reach their minimum negative values at the springline region.