Plate Load Tests on Cemented Soil Layers Overlaying Weaker Soil

This paper addresses the interpretation of plate load tests bearing on double-layered systems formed by an artificially cemented compacted top soil layer (three different top layers have been studied) overlaying a compressible residual soil stratum. Applied pressure-settlement behavior is observed for tests carried out using circular steel plates ranging from 0.30 to 0.60 m diameter on top of 0.15 to 0.60-m-thick artificially cemented layers. The paper also stresses the need to express test results in terms of normalized pressure and settlement—i.e., as pressure normalized by pressure at 3% settlement $\left(p/p_{3\%}\right)$ versus settlement-to-diameter $\left(\delta /D\right)$ ratio. In the range of $H/D$ (where $H=$ thickness of the treated layer and $D=$ diameter of the foundation) studied, up to 2.0, the final failure modes observed in the field tests always involved punching through the top layer. In addition, the progressive failure processes in the compacted top layer always initiated by tensile fissures in the bottom of the layer. However, depending on the $H/D$ ratio, the tensile cracking started in different positions. The footing bearing capacity analytical solution for layered cohesive-frictional soils appears to be quite adequate up to a $H/D$ value of about 1.0. Finally, for a given project, combining Vésic’s solution with results from one plate-loading test, it is possible (knowing of the demonstrated normalization of $p/p_{3\%}\text{-}\delta /D$ , where the pressure-relative settlement curves for different $H/D$ ratios produce a single curve for all values of $H/D$ ) to estimate the pressure-settlement curves for footings of different sizes on different thicknesses of a cemented upper layer.