Abstract

Prebored precast pile with an enlarged base (PPEB pile) is a new type of green and environmental protection pile foundation developed in China in recent years, which has complex bearing characteristics and many influencing factors. Based on the static load tests and key parameters’ tests in deep soft soil in Shanghai, a three-dimensional numerical analysis model was established using ABAQUS finite element software. The transfer law of load among the precast pile, cement soil, and soil around the pile and the action mechanism of the enlarged base were analyzed emphatically, and a sensitivity analysis of the main factors affecting the bearing performance was carried out. The calculation results show that the existence of the enlarged base can greatly improve the compressive bearing capacity, increasing the diameter and height of the enlarged base is beneficial to the bearing capacity, and the influence of the diameter expansion ratio is more effective. With the increase of the proportion of nodular piles, the ultimate bearing capacity increases slightly, but the deformation increases obviously. Under the condition of cement soil of the test piles, the spacing of the neighboring nodules of nodular piles has no obvious effect on the bearing capacity, and the 1 m spacing commonly used in engineering applications can be optimized. The increase of cement soil thickness is beneficial to the improvement of pile bearing capacity, but the efficiency is low. Finally, some improvement measures for the construction technology of the PPEB pile were put forward.

Highlights

  • The premade base-forming cement grout with a water/cement (w/c) ratio of 0.6 is injected into the enlarged base, and side-forming cement grout with a w/c ratio of 1.0 is injected into the borehole. erefore, the pile body will be in the form of cement soil with low strength around the precast pile and cement soil with high strength at the enlarged base. e inner concrete precast piles can be made up of prestressed high-strength concrete (PHC) piles, PHC nodular piles, prestressed reinforced high-strength concrete (PRHC) piles, and so on

  • For the nonenlarged base part, the stiffness of the cement soil around the pile was lower, so the axial force of the PPEB pile was mainly controlled by the precast pile

  • Based on the static load test and key parameters test in deep soft soil in Shanghai, a three-dimensional finite element analysis (FEA) model was established using ABAQUS. en, the bearing characteristics of the PPEB pile were analyzed. e main conclusions are as follows: (1) e Mohr–Coulomb elastic-plastic model was adopted for the cement soil around the pile shaft and at the enlarged base, and the elastic modulus was 150 MPa and 1500 MPa, respectively. e friction coefficients of precast pile-cement soil interface and cement soil-soil interface were 0.80 and 0.53, respectively. e numerical results well simulated the bearing and deformation behavior of the field test pile

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Summary

Introduction

Rough numerical analysis, Ye et al [7,8,9] discussed load transfer law and the effect of reinforced core on the performance and failure behavior of stiffened deep cement mixing piles. Based on the engineering application of PPEB pile technology in Zhejiang Province, China, Yang et al [10], Zhou et al [11], and Xie et al [12] used the numerical simulation method to analyze the influence of structure size of precast pile, soil properties, cement soil characteristics, and other factors on bearing capacity, which enriched the understanding of the characteristics of PPEB piles. In this paper, based on the above static load tests and key parameter tests, the load transfer law between precast pile, cement soil, and soil around pile and the action mechanism of enlarged base were further analyzed by numerical simulation. Detailed test results were described in a previous paper [2]

Finite Element Numerical Simulation
Compressive Bearing Characteristics of the PPEB Pile
Parameter Analysis
Findings
Conclusions
Full Text
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