Relating volume loss and greenfield settlement

This paper develops a numerical procedure for investigating settlement induced by circular tunnels in soft soils. The numerical procedure aims to simulate the movement and relaxation of the soil around the shield and lining annulus that occurs due to the overcutting and grouting of the tunnel void by a tunnel boring machine. A stress relaxation technique that progressively reduces the tunnel support pressure from a specific amount until a point of failure is detected. For three separate stages before this point of failure, the surface settlement data is exported for analysis. Using a regression of the commonly used Gaussian equation on the settlement data, ix values can be determined for each case. This is done for a number of geometry and soil stiffness and strength ratios which will cover the most practical range for soft cohesive soils. The results of this study are quite positive, settlement results compare well with previous experimental and observational results. Design charts using dimensionless ratios have therefore been presented.