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Comparative Test and Analysis of the Deformation in Enclosure Structure of Internally-braced and Cantilevered Locked Steel-pipe Pile Foundation Pits
(1. School of Engineering (Wuhan), China University of Geosciences, Wuhan 430074; 2. School of Civil Engineering and Architecture,Guangxi University, Nanning 530004; 3. Shanghai Construction Group Co., Ltd., Shanghai 200080)
Abstract Locked steel pipe (LSP) piles can form a row-pile enclosure structure by interconnecting the lock joints, and have been widely used in foundation pit projects in soft soil areas. To investigate the stress and deformation characteristics and differences between cantilevered and internally-braced LSP pile enclosure structures, this paper carries out similar model tests of the pit excavations of both cantilevered and internally-braced LSP pile enclosures respectively, and uses 3D printing technology to produce the piles with locked joints for the model tests. During the test, real-time monitoring and analysis were conducted for pile-top horizontal displacement, pile strain and soil surface settlement. The test results show that: (1) The LSP pile model made through 3D printing has the advantages of high precision and fast speed, implying that it can greatly reflect the joint characteristics of LSP piles; and (2) For the cantilevered enclosure structure with LSP piles, from the excavation of the foundation pit to the failure of the enclosure structure, the soil settlement distribution gradually shifts from a notch-type distribution to a triangle distribution, with the reverse-bending point of the pile moment appearing near the excavation surface and drops with the increase of the excavation depth. The ratio of the extreme value of the surface settlement to the extreme value of the horizontal displacement of the piles (δvm/δhm) is approximately 1, but when the enclosure structure loses its effectiveness, the position of the reverse-bending point almost has no change, while the ratio of the maximum settlement of the ground surface to the maximum lateral displacement of the piles (δvm/δhm) gradually decreases between the range of 0.5 and 0.75. For the internally-braced enclosure structure with LSP piles, under the same excavation depth, the soil settlement distribution is in a groove-type distribution, with the reverse-bending point of the pile moment remaining on the excavation surface the whole time, and the ratio of the maximum surface settlement to the maximum lateral displacement of the piles (δvm/δhm) gradually increases from 0.5 to 1.
Abstract：
Locked steel pipe (LSP) piles can form a row-pile enclosure structure by interconnecting the lock joints, and have been widely used in foundation pit projects in soft soil areas. To investigate the stress and deformation characteristics and differences between cantilevered and internally-braced LSP pile enclosure structures, this paper carries out similar model tests of the pit excavations of both cantilevered and internally-braced LSP pile enclosures respectively, and uses 3D printing technology to produce the piles with locked joints for the model tests. During the test, real-time monitoring and analysis were conducted for pile-top horizontal displacement, pile strain and soil surface settlement. The test results show that: (1) The LSP pile model made through 3D printing has the advantages of high precision and fast speed, implying that it can greatly reflect the joint characteristics of LSP piles; and (2) For the cantilevered enclosure structure with LSP piles, from the excavation of the foundation pit to the failure of the enclosure structure, the soil settlement distribution gradually shifts from a notch-type distribution to a triangle distribution, with the reverse-bending point of the pile moment appearing near the excavation surface and drops with the increase of the excavation depth. The ratio of the extreme value of the surface settlement to the extreme value of the horizontal displacement of the piles (δvm/δhm) is approximately 1, but when the enclosure structure loses its effectiveness, the position of the reverse-bending point almost has no change, while the ratio of the maximum settlement of the ground surface to the maximum lateral displacement of the piles (δvm/δhm) gradually decreases between the range of 0.5 and 0.75. For the internally-braced enclosure structure with LSP piles, under the same excavation depth, the soil settlement distribution is in a groove-type distribution, with the reverse-bending point of the pile moment remaining on the excavation surface the whole time, and the ratio of the maximum surface settlement to the maximum lateral displacement of the piles (δvm/δhm) gradually increases from 0.5 to 1.
LIANG Rongzhu1,
2 WEI Shi1 WANG Xinxin3 SUN Lianwei3 WU Xiaojian3
.Comparative Test and Analysis of the Deformation in Enclosure Structure of Internally-braced and Cantilevered Locked Steel-pipe Pile Foundation Pits[J] MODERN TUNNELLING TECHNOLOGY, 2022,V59(3): 172-182
2022, Vol. 59 