Investigating ground movements caused by the construction of multiple tunnels in soft ground using laboratory model tests

Abstract

The prediction of the ground movements above single tunnels in soft ground is well established and can be estimated using semi-empirical methods based on the Gaussian curve. However, the prediction of ground movements associated with closely spaced multiple tunnels, in particular side-by-side (sbs) tunnels, is not as well understood, and therefore simple predictive methods for this application are currently quite limited in terms of their accuracy. This paper describes results from a series of small-scale (1/50) laboratory model tests (conducted at 1g) carried out in Speswhite kaolin clay. These tests have been conducted to gain a greater understanding of the short-term ground movements associated with closely spaced multiple (sbs) tunnels. The observed ground movement results from these tests have shown many of the characteristics observed at full-scale in the published case studies. These results are compared to the commonly used Gaussian curve prediction method and demonstrate the potential inaccuracy in this approach for predicting ground movements associated with closely spaced multiple tunnels. A method that modifies the Gaussian curve approach is also applied to the laboratory data and shows improved predictions.Key words: tunnelling, ground movements, multiple side-by-side tunnels, physical modelling, settlement prediction.