Improvement of shaft capacity in steel displacement piles in clay

Abstract

In this study, clay specimens were consolidated with 100 kPa pressure and split samples consisting of mild steel at the bottom half and clayey soil at the top half were prepared to test the interface shear strength parameters with direct shear tests. In order to enhance the interface shear strength between steel and clay, hydrated lime was placed in the carved inclusions on the steel surface. The effects of including lime on the clay-steel interface, and the behavior of lime treated clay-steel interface under the action of shearing forces are then investigated and evaluated. Clay samples with two activities (0.32 and 1.15) are prepared with overconsolidation ratios of 1, 1.5, and 2.5. Two different treatment area ratios are used (3.8% and 8.8%) and the split samples were cured for 7, 15, and 28 days for the diffusion of lime to take place. Including lime in the clay-on-steel interface increased interface adhesion and interface shear resistance angle. An increase in the shear strength parameters in the interface of clay and steel was seen with increasing curing time and increasing lime amount placed at the interface. Clay samples which had montmorillionite in had lower shear strength parameters than that of kaolinite samples but for the samples with montmorillionite enhancement of shear strength parameters were more pronounced with lime treatment. For the overconsolidated clays the shear strength parameters did not change as significantly as the normally consolidated clays. The interface efficiency of the samples decreased with increasing applied normal stress. It was experimentally shown that the interface efficiency of the samples could be increased more than two folds. For a 10 m long pile with a diameter of 400 mm, there is a skin friction increase of 15% when the proposed method is utilized.