Experimental Study on Coefficient Value of Subgrade Reaction in Seismic Analysis of Underground Structures

In seismic analysis of underground structures, the precision of the coefficient of subgrade reaction directly determines the accuracy of response displacement method. Considering the deficiencies of relevant research on the coefficient of subgrade reaction, a quasi-static test method was proposed, a large quasi-static model box was developed, and two groups of tests with and without axial load in sandy soil were carried out. On this basis, a correction method for the coefficient of subgrade reaction along depth is proposed and verified by an example. Results indicate that the horizontal coefficient of subgrade reaction decreases with an increase in the pushover level and increases with the soil depth. Moreover, the additional stress has great influence on the coefficient value; using modified coefficient can significantly improve the accuracy of the response displacement method. Compared with the result adopting the coefficient in terms of static finite element method in the code, the maximum bending moment error of the underground structure can be reduced from 16.7% to 9.1%, and the relative displacement error between roof and floor can be reduced from 35.0% to 18.8%. Thus, the feasibility of the new coefficient measuring method and the rationality of the coefficient modified method are validated.