Abstract
Necking in different positions of a pile body has a significant influence on the bearing performance of a single pile. The transparent soil model experiment was adopted to investigate the impacts of necking positions on the vertical bearing capacity of a single pile and the soil deformation around the pile, and subsequently, the causes of the variation of bearing capacity were analyzed. The results show that the existence of necking does not change the bearing behavior of single pile as pile friction resistance. The bearing capacity of piles decreased by 8.21% and increased by 7.30% when the necking is located in the shallow and middle pile body, respectively, while it did not change significantly when the defects were in the deep part of the pile. The necking position has a significant effect on the deformation and deformation range of soil. The soils at the top, side, and near the end of a pile were mainly influenced by shallow necking, middle necking, and deep necking, respectively. The soils at the location of necking had apparent settlement phenomenon as the piles subsided. The soils at shallow necking’s locations were relatively loose, which reduced the side friction force of piles and finally resulted in a reduction of bearing capacity of a single pile. With the increase of the load, the soil around piles gradually developed penetration phenomenon (large deformation), while the soil at the end of pile moved up against pile settlement, which made the necking soil in the middle denser. The loss of side friction resistance was less than the resistance from the necking, which gave birth to an increase in the bearing capacity of a single pile. It was finally found that the side friction resistance and the resistance caused by necking were the main factors governing the bearing capacity of necking single piles.
Highlights
As an important form of deep foundation, pile foundation has the advantages of high bearing capacity and low settlement rate and is widely used in high-rise buildings, bridges, and ports
Due to the influences of construction technology and other factors, cavity, crack, diameter reduction, and other defects may develop in pile bodies. Such defects were proved to be in presence by integrity inspection of foundation piles [1, 2]. e existence of these defects will affect the bearing capacity of foundation piles and lead to engineering safety hazards [3,4,5]
Load-settlement curves were obtained for the four groups of tests to analyze the influence of necking position on the vertical bearing capacity of single piles. e displacement vector diagram and contour map of four groups of soil around pile corresponding to different loads were calculated by using MatPIV software. e deformation characteristics of soil around piles were studied and the causes for the change of bearing capacity were obtained
Summary
Received 11 November 2021; Revised 14 December 2021; Accepted 3 January 2022; Published 7 February 2022. E bearing capacity of piles decreased by 8.21% and increased by 7.30% when the necking is located in the shallow and middle pile body, respectively, while it did not change significantly when the defects were in the deep part of the pile. E soils at the top, side, and near the end of a pile were mainly influenced by shallow necking, middle necking, and deep necking, respectively. E soils at shallow necking’s locations were relatively loose, which reduced the side friction force of piles and resulted in a reduction of bearing capacity of a single pile. With the increase of the load, the soil around piles gradually developed penetration phenomenon (large deformation), while the soil at the end of pile moved up against pile settlement, which made the necking soil in the middle denser. It was found that the side friction resistance and the resistance caused by necking were the main factors governing the bearing capacity of necking single piles
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