Experimental investigation on the deformation characteristics of PC piles retaining structure based on the 3D printing technology

PC pile is an innovative pile consisted of steel pipe pile and steel sheet pile，and each individual pile are connected with each other via locking joints. PC pile has advantage of lower environmental impact，quick construction efficiency and recycle utilization，which was frequently applied as retaining structure in deep excavations. However，systematic studies of the deformation mechanism of the PC piles retaining structure in deep excavation are rarely reported and not well understood. In this study，a cantilevered excavation model test was designed and carried out according to the similarity principal. The whole excavation process from initial state to retaining structure failure was simulated in this experimental test. The strain of pile shaft，lateral displacement at the pile top，ground surface settlements，lateral earth pressure of pile shaft，the bending moment of the pile，displacement field behind PC pile were continuously measured during the whole process of excavation，respectively. The pipe pile models and sheet pile models were manufacture by using 3D printing technology. The excavation model test was conducted in dry sand. The experimental results show that，PC pipe model piles manufactured by the 3D printing have a good precision. During the whole process of excavation，a triangular settlement shape was observed at the ground surface. As excavation went deeper，an apparent slide failure plane appeared behind the PC piles，which is about 59 degrees to horizontal plane. When excavation depth increases，PC piles change from independent supporting state of each single pile gradually to an entire enclosure structure. A “S”shaped distribution of the bending moment was observed along the sheet piles and pipe piles shaft and the deflection of both piles were quite similar to cantilever beam subjected to distributed loads. The ratio of the bending moment between pipe pile and sheet pile is approximately equal to the ratio of the bending stiffness of two piles. In cantilevered excavation，the safe installation ratio of PC piles is suggested from 2 to 2.5. The sectional shape of the PC piles affects the distribution of the earth pressure against the wall. At supported side，the earth pressure on the protruding side of the PC piles retaining structure was larger than that on the denting side when the deformation of PC pile was small. The earth pressure at the protruding side was generally smaller than that on the denting side，when a large deflection occurs in PC piles. © 2023 Academia Sinica. All rights reserved.