Abstract
The rigid long-short-pile composite foundation has been increasingly used as an effective and low-cost reinforcement method. The pile-soil interaction in this foundation type is more complicated than that in the equal-length pile composite foundation. In this study, several physical model tests were conducted to investigate the pile-soil synergistic mechanism of the rigid long-short-pile composite foundation. A comparative analysis was conducted of the static load test data of single-pile and long-short pile composite foundations to assess the load-bearing characteristics and stiffness evolution of the composite foundation and pile-soil unit. The result indicated a positive correlation between the pile length and the overall bearing capacity of the single-pile composite foundation. The overall stiffness of the four-pile composite foundation was lower than that of the single-pile composite foundation due to an increase in the areas of the soil stress and the pull-down effect caused by multiple piles. The long pile exerted a greater influence on the overall settlement than the short pile. In addition, the correction coefficients were obtained to determine the pile-soil stiffness of the four-pile composite foundation based on that of the single-pile composite foundation, providing a theoretical reference for the optimal design of composite foundations.
Highlights
A long-short-pile composite foundation bears the load jointly by piles of different lengths and the soil between the piles. e pile tips of the long and short piles are located in bearing layers of different depths, improving the bearing capacity of the composite foundation and reducing foundation settlement.is foundation type solves several engineering problems, is economical, and has been widely used in practical engineering [1, 2]
The action mechanism of different pile types and soils is comprehensively described by the bearing capacity coefficient obtained from experiments. e working mechanism of the pile-soil interaction is challenging to determine, because the efficiency factors are independent of the components [5]. e bearing capacity of the rigid long-short pile composite foundation is generally determined by conducting static load tests on long-pile and short-pile composite foundations, respectively
The bearing capacity can be determined by using the weighted average of the long-pile and short-pile areas as the bearing capacity characteristic value of rigid long-short pile composite foundations. is method reduces the load requirements in the field load test
Summary
A long-short-pile composite foundation bears the load jointly by piles of different lengths and the soil between the piles. e pile tips of the long and short piles are located in bearing layers of different depths, improving the bearing capacity of the composite foundation and reducing foundation settlement. Previous studies used the finite element method to verify the reliability of a discrete element simulation of sand media and investigated the stress state and load transfer of the long-short pile composite foundation by changing the parameters, such as the pile length and cushion modulus [10,11,12]. Current research on rigid long-short-pile composite foundations is mostly limited to the analysis of the bearing capacity and the mechanical characteristics of long piles, short piles, and the soil [29, 30], and studies on the stiffness changes of longshort-pile composite foundations are lacking. A series of static load tests of composite foundations are conducted to analyze the basic force state of a rigid long-short pile composite foundation under a vertical load. A series of static load tests of composite foundations are conducted to analyze the basic force state of a rigid long-short pile composite foundation under a vertical load. e slope of the secant line between the stress and the settlement on the top of the pile-soil element is regarded as the stiffness of the pile-soil element. e change in the overall stiffness and pile element stiffness is crucial. e load sharing of the composite foundation and the pile-soil unit is analyzed under the same foundation stress and settlement to describe the load distribution and the change in stiffness. e stiffness correction coefficients of the long pile, the short pile, and the soil are obtained after calculating the stiffness of the four-pile composite foundation based on that of the single-pile composite foundation
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