Side Friction of Rock‐Socketed Piles Involving Thick Sediment

Abstract

This paper investigates the skin friction transfer characteristics of the rock-socketed section of a rock-socketed pile resting on thick sediment by conducting in situ core-drilling tests and static loading tests. Test results show that when using the impact hole-forming method in weakly cemented soil, a layer of sediment is deposited at the pile bottom. Due to the existence of sediment, when the load reaches a certain value, sudden and large subsidence is observed. This indicates that the end resistance does not contribute to the bearing capacity. Thus, it is not appropriate to consider both end resistance and side resistance in the existing design method of a rock-socketed pile. The bearing capacity of a single rock-socketed pile should be determined according to the side resistance of the soil layer and rock-socketed section only. Numerical analysis is performed to determine the deformation and load-carrying capacity of the pile and the distribution of friction on the sides of the rock-socketed segment. Under a given applied load, small settlement is observed when socketed thickness and rock strength are relatively large. The distribution of side friction of the socketed segment along the vertical direction shows a double-peak saddle shape. When the socketed thickness and rock strength are relatively smaller, the lower peak is higher than the upper peak, and conversely, when the socketed thickness and rock strength are relatively larger, the lower peak is smaller than the upper peak. For a given applied load on the pile top, smaller socketed thickness results in larger settlement and side friction. Due to the thick layer of sediment, the axial force of the rock-socketed segment of the pile gradually decreases along the vertical direction from the applied load on the pile top to zero at the bottom. According to the mechanical properties at different shear stages, a function is derived for the complete constitutive model for a pile-rock interface. Analytical solutions for the friction of a single pile are obtained under the conditions of failure and elasticity deformation of the surrounding rock. Its load transfer equation is derived as well. Accordingly, an equation is proposed for calculating the bearing capacity of rock-socketed piles resting on sediment at the bottom.

Calculation Model of Vertical Bearing Capacity of Rock-Embedded Piles Based on the Softening of Pile Side Friction Resistance

“…Wang et al carried out the study of the friction resistance transfer characteristics of rock-socketed piles on thick sediment, and derived the complete constitutive model function of the pile-rock interface. They concluded that the smaller the rock-socketed thickness, the greater the settlement and lateral friction resistance, the relatively small rock-socketed thickness and rock strength, with the lower peak was higher than the upper peak [25]. Liu et al carried out a study on the lateral response of vertical loads to piles, and conducted a comparative analysis of the lateral response of vertical loads to rock-socketed piles in normal consolidated clay and over-consolidated clay, concluding that, with the application of vertical load, the initial lateral stiffness and ultimate bearing capacity of the normal consolidated clay increased by 10.0% and 49.4%, respectively.…”