A method for calculating subgrade reaction coefficient and its application in reaction displacement method

The value of the traditional subgrade reaction coefficient adopted in the seismic analysis of underground structures is always limited by the empirical one. The empirical value cannot reflect the adverse deformations of soil deposits and the effects of buried depth, thus a certain calculation error will be generated. The evolution rules of shear stress-displacement of sandy soil are analyzed on the basis of shaking table tests on an unsaturated sandy site and the one-dimensional shear beam model for soil layers, and then a model is proposed to calculate the subgrade reaction coefficient considering the seismic responses of the soil layers and buried depth. The reasonableness and applicability of the proposed method are verified through an example of seismic analysis of an underground structure. The test results indicate that the hysteretic characteristics of the shear stress-displacement of soil deposits are affected by the features of seismic spectrum and peak ground acceleration (PGA). The equivalent subgrade reaction coefficient increases with the increase of the buried depth. The proposed method can be used to modify the response displacement method for simulating the restraint effects of soil on underground structures. Based on the dynamic time-history analysis, the accuracies of bending moments of side wall, central column and story drifts obtained by the modified response displacement method are improved as compared to those of the traditional response displacement method, (with the calculation errors of 2.11%, 10.69%, and 0.07%, respectively).