Experimental evaluation of negative skin friction on floating pile in gypseous soil

Gypseous soils are characterized by an open structure with developed porosity and high gypsum content, which determines their metastable state. When saturated with water, a decrease in volume occurs as a result of a decrease in matrix suction and degradation of cementation bonds, leading to rapid settlement. When a pile is installed in this type of soil, this can cause negative skin friction (NSF) along its surface, which increases the load pressure and reduces the safety factor. In this study, a laboratory model was used to evaluate NSF developed along the external surface of a steel pile embedded in gypseous soil. The effect of the degree of saturation, dry unit weight, length/diameter (L/D) ratio, and relative settlement between the soil and the pile on the magnitude of NSF, which can be described as a downward drag load along the pile shaft, has been studied. The results show that NSF increases with increasing L/D ratio by 66% at the maximum collapse potential and decreases with increasing dry unit weight and degree of saturation by 26−60% for L/D = 15 and by 78−137% for L/D = 10. The maximum drag load occurs with zero water content and L/D = 15.