Experimental and analytical study of shield tunnel face in dense sand strata considering different longitudinal inclination

摘要

Predicting the face support pressure and understanding the failure mode for shield tunnel with different longitudinal inclination, delta, in dense sand strata are crucial. Six laboratory model tests are conducted to explore the failure mechanism of tunnel face with delta = 15 degrees, 0 degrees, and -15 degrees. It shows that the face support pressure declines sharply to the elastic limit value, and further decrease slowly to the minimum value for all delta conditions. When delta = 15 degrees or 0 degrees, the face support pressure rebounds slightly to a residual value. However, rebound is not prominent for delta = -15 degrees. The influence of "soil arch" strength reduces when delta varies from -15 degrees, 0 degrees, to 15 degrees. The final shape of the failure zone shows a "chimney" pattern, in which the area of the failure zone increases with delta. Similar failure patterns are obtained from the numerical simulations. Based on the measured contours of failure zones, novel theoretical models are proposed to calculate the limit face support pressure for three inclination conditions. The face support pressure, p(u), is predicted to be the highest for delta 0 degrees, following by the cases of delta = 0 degrees and delta 0 degrees, and the change in p(u) is higher between delta 0 degrees and delta = 0 degrees.