泥岩地基打入式预制桩承载力时效性分析

Time-effect analysis of bearing capacity of driven-type precast piles in mudstone foundation

以风化泥岩作为桩端持力层的预制桩,沉桩结束一段时间后常出现单桩承载力不足的现象。针对以上问题,依托青岛某实际工程,在锤击沉桩结束后不同休止时间内,开展3根试桩和2根工程桩的单桩竖向抗压静载试验,分析单桩竖向承载力随时间的演化特征,探究泥岩地基中打入式预制桩单桩承载力与休止时间的关联性。研究结果表明:以强风化泥质粉砂岩为持力层的打入式预制桩,沉桩结束后单桩承载力随休止时间增长而降低,降低幅度为10%,且从沉桩结束到出现承载力降低存在一个滞后期,滞后期为15 d;桩端泥岩遇水发生软化是单桩承载力随成桩时间降低的主要原因,但也有互层等非均质因素的影响;泥岩的水文、力学性质与其矿物成分、胶结类型密切相关,降雨、地下水渗流对泥岩中的泥质胶结特性产生负面效应,弱化泥岩作为持力层的承载能力。

The weathered mudstone is used as the prefabricated pile at the end of the pile, and the bearing capacity of the single pile is often insufficient after a period of time when the pile is driven. In view of the above problems,relying on an actual project in Qingdao, 3 test piles and 2 engineering piles were carried out for vertical compressive static load tests of single piles at different rest times after the hammering of the piles. The evolution characteristics with time were used to explore the correlation between the bearing capacity of single piles and the rest time of driven precast piles in mudstone foundations. The results show that for the driven precast piles, when strongly weathered argillaceous siltstone is taken as the bearing layer, the bearing capacity of a single pile decreases with the increase of the resting time after the pile driving, and the reduction range is 10%. There is a lag period in the reduction of the force, which is 15 d. The softening of the mudstone at the pile end in contact with water is the main reason for the reduction of the bearing capacity of a single pile with the pile formation time, but the influence of heterogeneous factors such as interlayers cannot be excluded. The hydrological and mechanical properties of mudstone are closely related with its mineral composition and cementation type, and rainfall and groundwater seepage have negative effects on the argillaceous cementation characteristics in mudstone, weakening the bearing capacity of mudstone as a holding layer.