Stability Analysis of Hole Wall for Bored Piles

Abstract

Based on the theory of small hole expansion and elastic-plastic theory, this paper studied the instability mechanism of the hole wall of bored pile, gave the stress expansion solution of the soil layer after the excavation of pile holes in the semi-infinite elastic soil layer, and established its mechanical model. Then, the stability of hole wall of bored pile in cohesive soil layer and sandy soil layer was analyzed, and the calculation formula of pile hole wall stability was obtained. Finally the stability of hole wall of bored pile under the action of mud slurry was calculated, and the stress on the pile hole wall was analyzed when local instability and overall instability occur, respectively. The results show that in sandy soil layer, the safety factor of hole wall of bored pile when it is stable has no connection with the depth of pile hole, but is related to the density of mud slurry in the pile hole. For the region of third stage expansion project of Lanzhou Zhongchuan International Airport, the critical safety stability factor for the instability of hole wall of bored pile is 0.47. When the safety stability factor is less than 0.47, the soil layer of the hole wall of bored pile would be unstable, and the hole wall will collapse. In the unstable soil layers, the pile hole wall was prone to instability, and the stability of hole wall could be improved by appropriately increasing the gravity of mud slurry. With the increase of pile diameter, the lateral displacement and deformation of hole wall increase, and the displacement of soil layer increases when the hole wall is unstable, resulting in increasing the possibility of forming variable cross-section piles correspondingly.