Performance of an asymmetric pit-in-pit excavation supported by diaphragm wall and multi uplift piles system in coastal areas

The performance of asymmetric pit-in-pit excavation supported by diaphragm wall and multi uplift piles in coastal areas has been rarely reported. In this work, a case study is conducted to investigate the mechanical characteristics of such excavation. A numerical model is established using the ABAQUS finite element platform, and its effectiveness is evaluated by comparing with the field monitoring data. After evaluation, the effects of uplift piles on excavation-induced deformations are investigated. The results show that the maximum wall deflections ( δ hm ) are 0.02%–0.22% of the excavation depth ( H e ), with the ground surface settlements of less than 0.6%· H e and the settlement influence zone extending beyond 4 H e . As the soil is excavated, the top wall shows outward deformations to the active zone, and the transverse support is under tension. The use of combined diaphragm wall and multi uplift piles reduces the embedment ratio of diaphragm wall to a minimum value of 0.14 and decreases the δ hm and rebound of base soil ( δ vrm ) by 42% and 63%, respectively. A design suggestion is proposed for pile diameter ( D), pile length ( L), and pile spacing ( S) to fall within the range of 0.4–0.8 m, 10–20 m and 6–8 D, respectively.