Analyses on deformation characteristics of coastal deep excavation considering the effect of engineering piles

To investigate the effect of engineering piles (uplift piles and upright post piles) at the excavation bottom, the deformation characteristics of a deep excavation in Zhuhai were analyzed based on field measurements. The impact mechanism of the pile diameter, pile length, and longitudinal pile spacing on excavation deformations and the internal force of the diaphragm wall was analyzed via three-dimensional finite element simulations. The results show that: (1) The deformations of this excavation were greater than typical excavations in Shanghai, Suzhou, and Taiwan due to the effect of coastal deep soft silt strata, the deformation still has a large growth after the excavation base was sealed, and the maximum increments of the lateral displacement of the diaphragm wall and the ground surface settlement reached 30%~40%. (2) The engineering piles can effectively suppress the deformations of excavation, compared with the no-pile case, the engineering pile with 0.4 m diameters can reduce the maximum horizontal displacement of the underground diaphragm wall by 18% and the uplift of the pit bottom by 20%. (3) There is an obvious marginal effect of the influence of the length of engineering piles on the excavation deformation. When the pile length exceeded 1.4He (He is the excavation depth), the suppression effect of increasing pile length on the lateral displacement of the diaphragm wall is no longer obvious, and when the pile length exceeds 2.0 He, increasing the pile length cannot effectively reduce the deformation of the excavation bottom. (4) The suppressing effect of longitudinal pile spacing on the excavation deformations has an effective domain, which is about 10D~6D (D is pile diameter); especially when the pile spacing is reduced from 7 D ~6 D. (5) Similar to the impact on deformations, the engineering pile can reduce the bending moment of the diaphragm wall; the maximum bending moment decreases continuously with increasing pile diameter, there is a marginal effect of pile length on bending moment, and the suppressing effect of longitudinal pile spacing showed an effective domain as well. The research results can provide reference and guidance for the rational design of engineering piles at the excavation bottom. © 2023, Central South University Press. All rights reserved.