The Mechanism of Depth Effect on Point Resistance of Pile in Sand

Model tests of displaced pile in laboratory, performed in uniform grain and evenly filled Pin-Tan standard sand are used to study the mechanism of depth effect on point resistance. Pile models penetrated into different density fill with different penetrated depth were tested. The displacement field indicated by marks around the pile shaft were observed with a measuring microscope. The distribution of additional stress around the pile tips was measured with pressure cells.In the process of testing, below the critical depth, for various cases, "quasi-stable" point resistance was observed. After the occurrence of "quasi-stable" phenomenon, soil displacement field and incremental displacement field had tendency to become stable.Analyzed the actual chracteristics of the ahear and compression mechanism and their difference and transition of model pile, during the pile penetration into sand some depth and consequent penetration to a certain depth, the mechanism of depth effect was further explained. From the analysis, it would become the basis for the proposal of a new method of calculation for pile point resistance with consideration of the depth effect.