Abstract
Three-dimensional model is established with finite difference method to simulate construction process based on design and construction plans of existing overpass pile foundation adjacent to certain large-section railway tunnel in Chengdu, China. Ground, isolation pile, main bridge pier and ramp pile near the tunnel are taken as research object, and surface settlement amount, displacement change law of each pile foundation and structural mechanics property are analyzed to further judge whether safety of adjacent overpass structure can be ensured during construction in accordance with used tunnel design and construction plans. Research result shows that the maximum value of surface settlement amount is 13 mm, and settlement range is within 8 m at two sides of tunnel axis; and the settlement amount of pile top of main bridge pier is greatest, referring to 47 mm. Axial force and bending moment borne by the main bridge pier are greatest, and horizontal displacement and bending moment distribution at different positions of the main bridge pier at two sides of the tunnel have the characteristics of right-and-left symmetry, and point of inflection is at the position being 1/3 of pile length away from the pile top, while point of inflection of isolation pile is at the position being 2/5 of pile length away from the pile top, and reinforcement of the pile body may be adjusted accordingly. The pile with minimum safety factor is the isolation pile which is closest to the tunnel, and the minimum safety factor is 3.5. As displacement value of each pile foundation is within allowed range, and safety factor meets standard requirement, so construction as per the design and construction plan may ensure safety of adjacent overpass structure.
Highlights
In recent years, the conditions of new tunnel adjacent to the construction pile foundation and the tunnel crossing the pile foundations with the intercity high-speed railway increasing
Analyze the bending moment distribution of the isolation pile, overpass main pile and ramp pile at both side of the tunnel after the tunnel excavation completed according to the calculation results, as shown in Fig. (8)
The minimum safety coefficient of each pile in turn: For isolation pile on the left, minimum safety coefficient is 4.2 at the part 16m from the pile top; For main pile on the left, minimum safety coefficient of pile body is 7.34; For ramp pile on the left, minimum safety coefficient of pile body is 43.58; For isolation pile on the right, minimum safety coefficient is 3.5 at the part 15m from the pile top
Summary
The conditions of new tunnel adjacent to the construction pile foundation and the tunnel crossing the pile foundations with the intercity high-speed railway increasing. Mair and others study on the influence of tunnel excavation on the ground settlement using analytical method based on Peck formula [11,12,13]. Based on the design and construction scheme of a new large section intercity railway tunnel crossing existing overpass pile foundation in Chengdu, using finite difference method, this paper constructed a three dimensional model to simulate the construction process, selected adjacent substances such as the ground, the isolation pile, the main pile. 428 The Open Civil Engineering Journal, 2014, Volume 8 and the ramp pile adjacent to the tunnel as research objects, analyzed ground settlement as well as displacement law and mechanical properties of existing overpass pile foundation in the process of new tunnel construction
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