Study on the proportional coefficient m of horizontal subgrade reaction for Shanghai clayey soils and engineering verification

The proportional coefficient of horizontal subgrade reaction m is a key parameter to calculate the deformation of retaining wall in excavations using beam on vertical elastic subgrade method. However, the range of m value recommended in design code is quite large and does not yet consider the effects of soil property and excavation dimension. In this study, the differences and deficiencies of the m value in different engineering codes are firstly discussed, pointing out that actually m is a simplified parameter for deformation calculation in the engineering. For excavation, m should be related to soil properties, excavation width and depth. By numerical analyses with hardening soil model with small strain and appropriate soil parameters, lots of excavation deformation data are obtained by changing excavation dimensions and void ratio of soils. Then inversion calculation was performed to determine the m value based on the deformation data and an empirical formula for determining m is proposed. With this method, the m values of the soils in 25 excavation projects in Shanghai are determined and the associated deformations are calculated using beam on elastic subgrade method. The results show that the calculated maximum horizontal displacements of retaining wall are close to the measured ones, with an average error of 2.6%. This proposed method provides an accurate and efficient approach to determine the m value for Shanghai clayey soils as well as an important reference for determining the m value of soils in other regions.