Analysis and Practice on the Influence of Large-Scale MJS Construction on Adjacent Existing High-Speed Railway Bridges

To explore the impact of large-scale reinforcement construction using Metro Jet System （MJS） piles on existing high-speed railway bridges in coastal soft-soil areas and to optimize the construction scheme， this study is based on a large-scale soft-soil foundation reinforcement project along a railway in the Binhai area of Fuzhou. A three-dimensional mechanical model was developed to analyze the influence of both test-pile construction and large-scale reinforcement construction on adjacent existing high-speed railway bridges， and the optimized scheme was subsequently verified through field tests. The results indicated that the MJS test-pile construction induced deformation in the pier platform and pile foundation on the side adjacent to the reinforcement area. Specifically， the settlement of the pier platform was 0.16 mm， the horizontal displacement of the pier platform ranged from 0.45 mm to 0.72 mm， and the deformation of the pier-platform pile foundation varied between 0.27 mm and 0.42 mm. The deformed section of the pile foundation was primarily distributed in the middle and lower parts of the reinforced zone， with displacement increasing gradually from bottom to top with depth. All deformation values remained far below the control limits. For the large-scale MJS reinforcement construction， the differential settlement generated by the vertical construction sequence was 5.1% greater than that of the horizontal sequence and 10.75% greater than that of the outside-in sequence. In other words， the outside-in construction scheme proved to be the most effective， owing to the shielding and isolation effects provided by the piles that had hardened first. The group-pile disturbance effect induced by large-scale MJS pile construction on the high-speed railway bridge cannot be ignored. These findings offer practical guidance for the optimization of on-site construction schemes.