PERFORMANCE ASSESSMENT OF TUNNELS IN COHESIONLESS SOILS

The ground behavior near circular tunnels in cohensionless soils, including the initial elastic response, the intermediate yielding, and the ultimate collapse, is explored in detail. Different modes of tunnel behavior are identified and the conditions for their occurrence are estimated using analytical solutions. The results compare well with those from finite-element analyses, model tests, and field measurements. The ground convergence curve concept is applied as an analytical tool to interpret the response of the ground to tunneling. It is demonstrated that this method quantitatively relates the development of pressure on the lining to the tunnel wall displacement for the entire spectrum of the ground behavior, and thus provides an optimum design tool for lining pressure or ground-displacement control. The validity and limitations of currently available lining design models are also addressed.