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.
Highlights
Urban rail transit construction drives economic development along metro lines while relieving ground traffic jams
Because the model box stood still for 24 hours to simulate the intermittent time before building loading, the displacement of soil and tunnel continued to increase during the intermittent time. erefore, the horizontal displacement of the tunnel structure continued to increase after the foundation pit excavation was completed
Numerical simulation and similar material model test methods were used in this study to investigate building construction adjacent to the existing subway tunnel under the condition with isolation pile reinforcement. e reinforcement effects of isolation piles under the influence of different factors were obtained. e main conclusions were obtained as follows: (1) In the process of foundation pit excavation and building loading, deformation laws of the tunnel structure with isolation pile reinforcement were similar to those under the condition without isolation pile reinforcement. e tunnel structure first experienced displacement toward the foundation pit, and this displacement slightly recovered in the building loading phase; torsional deformation of the tunnel structure toward the
Summary
Urban rail transit construction drives economic development along metro lines while relieving ground traffic jams. Existing studies have investigated deformation laws of the adjacent tunnel structure due to foundation pit excavation and control measures Few of these works have paid attention to the reinforcement mechanism of isolation piles for the existing tunnel structure under unloading-loading effects of the building construction. E isolation pile reinforcement method has been applied to actual engineering to reduce horizontal displacement deformation of the soil at the rear side of the supporting structure in foundation pit excavation. In this process, the soil at the rear side of isolation piles extrudes pile bodies. E reinforcement effect of isolation piles is influenced by various factors, such as pile length, pile rigidity, and pile spacing. erefore, linearly arranged single-row isolation piles were used in this study to analyze the influences of burial depth of the isolation pile bottom, pile spacing, burial depth of the pile top, and pile diameter on the reinforcement effect on the existing tunnel structure
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