A Study on the Load-Bearing Characteristics and Load Transfer Mechanism of Bag Grouting Pile in Soft Soil Areas

In soft soil areas, to compare the load-bearing characteristics of bag grouting piles and cement mixing piles and study the load-bearing mechanism of bag grouting piles, field tests are conducted in this study, including the comparative compressive test of bag grouting piles and cement mixing piles, and the analysis of pile axial force, pile side friction resistance, and pile end resistance. Moreover, a numerical simulation is developed using ABAQUS 2020 (finite element analysis software) for three-dimensional modeling. The numerical simulation results are compared with the field test results to verify the reliability of the numerical simulation. Furthermore, the influences of five factors are studied; namely, pile length, pile diameter, pile spacing, the thickness of the bedding layer, and grouting pressure are studied for their effects on the compressive bearing characteristics of the bag grouting pile. The results show the following: (1) For composite foundations, bag grouting piles are more effective than cement mixing piles in soft soil areas, and the former provide an 8.8% increase in the bearing characteristics. (2) With an increase in the load, the bag grouting pile experiences greater compression in the middle of the pile body, and the pile side friction resistance is increased; therefore, the pile side friction resistance can be fully developed, and the bag grouting piles have the ability to transfer the load from the top of the pile to the soil at the bottom of the pile. (3) When the external load is maximized, the sharing ratio of pile side friction resistance reaches 96.3%, which shows the excellent frictional performance of bag grouting piles. (4) Among the five factors mentioned above, the most important one is the pile diameter, followed by the pile length and pile spacing, the thickness of the bedding layer, and finally the grouting pressure. The optimal combination in this paper is a pile length of 18 m, pile diameter of 0.4 m, pile spacing of 1.0 m, bedding thickness of 0.3 m, and grouting pressure of 0.6 MPa. Therefore, changing the pile diameter can be given priority during the construction design. The findings in this paper can provide valuable insights and practical experience for the design of similar engineering projects.