Prediction of tunnel lining loads using correction factors

A design method for the prediction of lining loads should include the decrease of lining loads due to the stress release before lining installation and the increase of lining loads due to development of ground yielding. Schwartz and Einstein included both factors in their original closed form solutions in the form of a support delay factor λd and a yield factor λy respectively. The validity of the design method is reviewed by comparing the loads calculated using the methods with the field measurements obtained from several tunnels. The possible causes of the load discrepancy between measurements and predictions are presented.Schwartz and Einstein's proposed method gives reasonable results for tunnels with short delay lengths. However, the method could not be used reliably for tunnels either with long delay lengths or with voids between the soil and TBM due to the difficulties finding the pre-support ground movements and therefore λd.