Experimental Study on Negative Skin Friction on Piles in Collapsible Soils due to Inundation

Collapsible soil is a special type of soil, classified as problematic soil. It possesses a high strength in the unsaturated phase and loses its strength and exhibits substantial settlement when inundated. Many foundation failures occur around the world, many of which involve loss of lives, caused by problems associated with collapsible soils. One of the most commonly used type of foundation in collapsible soils is end-bearing piles resting on firm soil strata. However, these piles will be subjected to negative skin friction during wetting of the collapsible soil, inducing additional loads. Various case studies have reported foundation failures and excessive settlements upon the wetting of collapsible soil. Researchers are facing serious challenges in dealing with piles in collapsible soils due to the complexity of the problem and the difficulties associated with modeling this behaviour numerically and experimentally. Relatively few investigations pertinent to pile foundations in collapsible soils subjected to inundation are available in the literature. An experimental investigation was carried out to simulate the complex interaction between collapsible soil and a single end-bearing pile under various wetting and loading conditions. The experimental prototype setup was developed and calibrated in the laboratory in order to measure the drag load and accordingly the negative skin friction acting on the pile’s shaft for given soil/wetting/loading conditions. Collapsible soils with different collapse potential values were created in the laboratory by mixing kaolin clay with fine sand at predetermined ratios. A two-dimensional axi-symmetrical numerical model was generated in order to conduct a parametric study by extending the data for a wider range. The numerical model was validated by experimental results obtained from this study. Based on the results obtained from the experimental and numerical models, a design theory capable of taking into account the effect of soil collapse under different wetting schemed was developed and recommended for use in practice