Study on the Bearing Capacity of Extra-Large-Diameter Piles in Complex and Thick Lacustrine Deposits

To reveal the influence mechanism of complex and thick lacustrine sedimentary strata on the bearing performance of large-diameter and ultra-long piles, experimental and numerical simulation studies were carried out in view of the special engineering properties of peat soil in the strata. Three test piles with a diameter of 1 m and lengths of 98 m, 93 m, and 92 m, respectively, were taken as the research objects. The bearing characteristic parameters were obtained through static load tests, and the influence laws of parameters such as the thickness of the weak layer, pile length and pile diameter in the peat soil layer were analyzed in combination with numerical simulation. The results show that in the geological conditions of thick lacustrine sedimentary strata, the Q-s curve of the ultra-long pile is steeply descending, and the ultimate bearing capacity is 28,800 kN, showing the characteristics of end-bearing friction piles. The side friction resistance of the pile shows a typical “triangle” distribution in the upper part and reaches the ultimate value in the middle and lower parts, presenting a multi-hump “R” shape distribution. When the thickness of the weak layer increases from 10 m to 30 m, the settlement increases sharply, and when it reaches 40 m, the settlement almost remains unchanged. The change of pile length has a relatively small impact on the bearing capacity and can be ignored in terms of settlement change. When the pile diameter increases from 0.5 m to 1.0 m, the settlement decreases sharply, and when the pile diameter exceeds 1.5 m, the settlement fluctuates very little. The research confirms that the change of pile diameter has the greatest impact on the ultra-long pile, followed by the thickness of the weak layer, and the pile length has the least impact. The research results can provide theoretical basis and technical support for the design and construction of large-diameter and ultra-long piles in similar complex lacustrine sedimentary strata.