Instrumented Static Load Testing of Bored Piles for the Mega Transportation Hub of Beijing Sub-Central Station

ABSTRACT Predesign static load testing of tentative piles is an important means to provide the basis for the pile foundation design before construction. This paper focuses on the tests performed on 12 instrumented superlong piles with a large diameter and high loading, intended for use in the comprehensive transportation hub project at Beijing urban sub-central station. The influences of pile construction techniques, such as base expansion and pile shaft and base grouting, on the bearing characteristics are discussed. Strains imparted in the reinforcement are measured by the vibrating wire gage installed along with the longitudinal reinforcement in these piles. Furthermore, the axial force against the depth of each test section is derived and the shaft friction resistance at the pile−soil interface is calculated. The results obtained for each pile indicate that the axial force at each test section increases as the load increases, but its magnitude gradually decreases from top to bottom under the same level of the load. In addition, the shaft friction resistance increases with the increase of the load, and the pile bearing capacity is significantly improved by applying relevant techniques such as base expansion and shaft grouting.