Analysis of Bearing-settlement Characteristics of Extra-long Bored Piles in URT Deep Soft Stratum Underground Station

Abstract

Objective To effectively control the deformation of station structure during the excavation and usage of deep foundation pit in soft soil stratum, and to increase the bearing capacity of foundation pit bottom, it is necessary to conduct an in-depth study of the bearing-settlement characteristics of extra-long bored piles (hereinafter as EBP) with void in the upper part. Method Using an urban rail transit double-line L-shaped cross transfer station as example, the influencing factors of the bearing-settlement characteristics of EBP are analyzed through static load tests by self-balanced method and numerical modeling. The relationship between the bearing characteristics of EBP and the pile length, pile stiffness, and pile diameter is explored. Result & Conclusion The static load test results indicate that, during the incremental loading in load box of EBP with void in upper part, both the pile top displacement and the displacement growth rate gradually increase, with pile top exhibiting displacement rebound phenomenon during unloading. Numerical simulation analysis shows that the axial force of EBP shaft decreases gradually from pile top to pile end. When the pile top is under ultimate load, the axial force at pile shaft upper part is significantly greater than at pile end. Changes in pile shaft length and stiffness affect the bearing-settlement characteristics of extra-long piles with void in upper part, while changes in pile shaft stiffness have little impact.

Keywords

• urban rail transit (urt)
• underground station
• extra-long bored pile
• bearing-settlement characteristics
• deep soft soil stratum