Deformation Analyses And Optimization Designs Of Braceless Excavation

Braceless excavations have great advantages,which have been widely applied in practical engineering.Multi-bench retaining structures and inclined pile retaining structures can efficiently limit the deformation of retaining structures,save the cost and reduce the duration of the construction.However,there are few researches on the theories and technologies about these two retaining structures.In this study,finit element method is conducted to evaluate the influence of geometric parameters on the displacement of multi-bench retaining structures and inclined pile retaining structures.The main contents are proposed as follows:(1)This paper first presents a case history in Tianjin,China.A numerical model incorporating the hardening soil small strain(HSS)model is used to evaluate the influences of the geometric parameters on the retaining structures response.Significant pile lengths and bench width values are required for ensuring the performance of excavations.An optimal second excavation depth equals to 0.5 excavation depth.(2)Followed by a validation of a case of inclined pile retained excavation in Tianjin,a series of inclined pile retained excavation models simulated by FEM software Plaxis3 D using the HSS model are presented to estimate the characteristics of pile deflection and ground settlement of several different inclined pile retained excavations.For outward-inward inclined pile retained excavation,inward inclined pile can better reduce the displacement of the retaining structure.Increasing the inward and outward inclined pile lengths provides more horizontal forces to the retaining structure.With an increase in inward and outward inclined pile angles,the displacement of the pile tip decreases.(3)Based on the parametric studies of both retaining structures,sensitivity analysis is performed,and the optimal layout of a multi-bench retaining structures and inclined pile retaining structures are estimated through a multivariate adaptive regression splines(MARS)procedure.For the multi-bench retained excavation,a large bench width greatly reduces the maximum displacement of retaining piles.Long pile lengths are required for ensuring the performance of excavations when the bench width is small.In addition,increases in the first row of the retaining piles have a more apparent effect than increasing the second row of the retaining piles.For inclined pile retained excavation,a large inward inclined pile angle greatly reduces the displacement.Increasing the inward inclined pile length have a better effect than increasing the outward inclined pile length.When the outward inclined pile angle is large,an increase in the outward inclined pile can effectively limits the deformation.