Influence of group pile effect on hammering resistance of multi-well risers

The group pile effect increases the hammering resistance of multiple well risers, leading to complex issues like repelling hammering, which severely affects the efficiency of installing the risers. To address the impact of the group pile effect on the hammering resistance of multiple well risers, a simulation experiment was conducted using a single well riser to explore its influence on the surrounding soil. In addition, a simulation experiment involving multiple well risers was performed to study the influence of the group pile effect on the hammering resistance of multiple well risers. The results show that with increasing hammering depth of single well riser, the radial stress around the riser initially increases and then decreases. After the hammering is completed, the radial stress continues to rise with the increase of the standing time, and the radial stress gradually stabilizes after standing for 24 h. In the silt layer, with the increase of the horizontal distance of the multi-well risers, the radial stress increment shows a decreasing trend. When the horizontal distance is less than 3.0 meters (4.9 times the pile diameter), there is a significant increase in the radial stress increment due to a prominent group pile effect. However, when the horizontal distance exceeds 3.0 meters, the increment of radial stress is relatively small, and the impact of the group pile effect on the hammering resistance can be ignored. Comparing the number of hammer strikes at different positions, it was found that the hammering resistance of the center pile is 2.47 times that of a single pile. The number of blows for edge piles and corner piles is 1.66 and 1.69 times that of a single pile, respectively. When designing the hammering sequence of multi well waterproof conduits, the waterproof conduits at the center pile position should be hammered first to avoid situations such as refusal of hammering caused by excessive hammering resistance of the center pile under the influence of pile group effect.