Improved equations of ground pressure for shallow large-diameter shield tunnel considering multiple impact factors

Abstract

Reasonable estimation of ground pressure is of vital importance for lining segments design in shield tunnelling. With the rapid development of the urban transportation, the diameter of the shield tunnel tends to become larger. The existing prediction of the ground pressure may overestimate the ground pressure of the shallow large-diameter shield tunnel and thus produce higher cost for the shield tunnel construction. To provide more reasonable solution for ground pressure surrounding the shallow large-diameter shield tunnel, a series of improved equations are proposed in this study. The two-stage method with non-uniform displacement pattern through numerical modelling is used to simulate the shield tunnelling at first. Secondly, the effect of multiple impact factors on horizontal and vertical ground pressure at tunnel vault, haunch and invert is analyzed and five key impact factors are determined. Thirdly, a series of improved equations are presented based on a large number of numerical modelling through nonlinear regression analysis. These improved equations can consider the effect of multiple impact factors and predict the ground pressure varying with position which is more realistic for the shallow large-diameter shield tunnel. Therefore, when compared with both the numerical modelling results and field measurements for 70 case histories, the improved equations show good performance. Also, the ground pressure of the above cases is calculated by traditional methods such as overburden pressure, Protodiaconov's formula and so on. By contrast to 7 traditional methods, the improved equations predict more reasonable result of ground pressure. At last, the influence of the tunnel axis depth, tunnel diameter, GAP parameter, ground classification and in-situ coefficient of lateral pressure at rest on the vertical ground pressure at tunnel vault is investigated through the improved equations. The results indicate that the tunnel size is of significant importance to the ground pressure as expected and thus special attention should be paid to shallow large-diameter shield tunnel. However, engineers may save the cost when tunnel diameter outweighs 15 m as ground pressure varies insignificantly. Furthermore, the initial stress as well as the GAP parameter which represents the shield tunnel construction details also play a vital role in ground pressure.