Estimation of tunneling induced ground settlement using pressure relaxation method

Abstract

The prediction of ground settlement caused by tunnelling is frequently estimated using a specified tunnel volume loss, and by applying a semi-empirical method involving the Gaussian equation, and relying on engineer's experiences. One of the key parameters in the semi-empirical method, K, is generally estimated using basic soil classifications, which has the potential to lead to inaccurate judgement from engineers. Better estimation of this constant K has had limited attention by other studies. This research uses a force relaxation technique and the finite difference program, FLAC, to estimate the transverse settlement profile for a range of different scenarios. A number of particular cases are numerically simulated with variation in the factors that influence the tunnel transverse settlement including tunnel depth to diameter ratios (C/D), clay strength ratios (γD/Su), Young's Modulus (E), and volume loss (% of tunnel). Using these settlement profiles, a K parameter can be accurately fitted for each case. Results from this study compare favourably with previous empirical and analytical studies. A range of K values is proposed for any combination of soil strength, Young's Modulus, tunnel geometry, and volume loss.