Effect of Embedment on Soil Subgrade Reaction

Introduction

The static stiffness of a soil-foundation system tends to increase with the depth and the embedment of a foundation. Subsequently, the settlement of the ground is decreased. The equations that take into consideration the depth and embedment effect for a square shaped foundation (Figure 1) are tabulated in Table 1.

The static stiffness is derived using the stiffness of a surface foundation multiplied by two scaling factors, a & b, incorporated to take into account the depth and the embedment effect, respectively.

Table 1: Static stiffness of the soil-foundation system for a square shaped foundation on a homogeneous, isotropic elastic half-space considering the effect of depth and embedment.

Calculation Example

A rigid square shaft is founded at a depth equal to its width (D=2B). Using the equations presented in Table 1 (D/B= 2), the static stiffness of the embedded foundation, K, with respect to that of a surface foundation, K_sup, is obtained as:

The results indicate that the depth and embedment can have a significant effect on the static stiffness of a soil-foundation system.

References

Gazetas G. (1983). Analysis of machine foundation vibrations: State of the art. International Journal of Soil Dynamics and Earthquake Engineering, Volume 2, Issue 1, https://doi.org/10.1016/0261-7277(83)90025-6.