Reinforcement Effects of Isolation Piles on the Adjacent Existing Tunnel in Building Construction

Abstract

Similar material model test and numerical simulation method were used to study the reinforcement effect of isolation piles on the existing shield tunnel structure in the adjacent building construction for analyzing foundation pit excavation and new building construction approaching existing shield tunnel engineering. The numerical simulation orthogonal experiment was used to optimize four isolation pile parameters. The conclusions were obtained as follows: (1) Isolation piles could share horizontal load of the soil at the rear side of the support structure and reduce horizontal displacement of the soil. As a result, maximum horizontal displacement of the tunnel structure and differences in horizontal displacement between the tunnel structure roof and the floor after foundation pit excavation and building loading were decreased. The horizontal displacement and torsional deformation of the tunnel structure toward the direction of the foundation pit were controlled, and the increase in internal forces of the transverse tunnel structure was also restrained. (2) At the elevation above the tunnel roof, the increase in burial depth of the isolation pile top slightly affected the reinforcement effect on the tunnel structure. The increase in burial depth of the isolation pile bottom could improve the reinforcement effect. Thus, burial depth of the isolation pile bottom should be properly increased in the engineering practice. The reduction in pile spacing could improve the reinforcement effect. Accordingly, pile spacing should be properly selected in the engineering practice. With the increase of diameter of the isolation pile, the reinforcement effect of isolation piles increased obviously. (3) Pile diameter had the greatest influence on the reinforcement effect of isolation piles, followed by burial depth of the pile bottom, pile spacing, and burial depth of the pile top. Orthogonal experiments indicated the following optimal parameter values: a pile diameter of 1.2 m, a burial depth of the pile bottom of 2H, a pile spacing of 1.6 m, and a burial depth of the pile top of 0.75Z.

Numerical Investigation on the Influence of Super-Large-Diameter Shield Tunneling on Nearby Existing Metro Tunnels and the Protection Scheme

“…According to the partitioning effect and economic considerations of these prevention and control measures, isolation piles are often selected for partitioning. During foundation pit excavation and shield construction, isolation piles are often used to protect the surface (Nie G et al [33], Wei G et al [34]), adjacent buildings (Yao A et al [35,36]) and pile foundations (Tang J et al [37]). In recent years, isolation piles have gradually been adopted in shield construction to protect existing subway lines (Lv J et al [38], Schroeder F.C et al [39]), but there are relatively few studies on this practice.…”

Study on the restraint control of an isolation pile on an existing high-speed railway during the close passing of a shield machine

“…The scale of the high-speed railway network will continue to expand, which will inevitably lead to tunnel crossing and passing. However, the construction of a shield tunnel laterally passing a high-speed railway with a pier pile foundation will disturb the stress state of the surrounding strata and soil and thus cause stress changes and deformation of the surrounding and upper soil layers, threatening the operational safety and driving comfort of existing high-speed railways (Yao et al, 2012;Liao and Sangrey, 2016;Yao et al, 2019;Jia et al, 2022). The lateral passing of shield structures past existing highspeed railway lines in a water-rich sand layer is characterized by a wide range of stratigraphic disturbances, high line deformation requirements, and difficult construction control.…”