Model Testing and Numerical Simulation on the Bearing Mechanism of Bag-Sealed Piles in Karst Regions

Abstract

To tackle the problem of poor construction quality of pile foundations in karst areas for transportation projects, a specialshaped bored pile known as the bag-sealed pile was examined in this paper. Featuring its unique branched structures for cavity filling, the pile was designed to improve the reliability of pile foundation quality. Two sets of indoor static load tests were designed to verify the superiority of the bag-sealed pile in bearing capacity, and eight sets of numerical simulations were conducted to investigate the bearing mechanism of the bag-sealed pile. The test and numerical simulation results were demonstrated to show that: (1) The load-settlement relationship of the bag-sealed pile is presented as a gradual pattern without an obvious sharp drop point, and its ultimate bearing capacity is determined based on the maximum allowable settlement at the pile top; (2) The essence of the enhanced bearing capacity of the bag-sealed pile in karst areas is found to lie in the expansion of the pile shaft cross-section, by which the surrounding rock mass is mobilized to participate in load bearing; (3) The bearing capacity of bag-sealed piles can be enhanced with the increase in their length, yet there is a threshold for such enhancement. The results of the tests and numerical simulations in this study can provide ideas and a basis for the application of bag-sealed piles in karst areas.