穿越巨厚卵石层超长嵌岩桩施工技术与成桩质量分析

CONSTRUCTION TECHNOLOGY AND PILE QUALITY ANALYSIS OF SUPER-LONG ROCK-SOCKETED PILE CROSSING A HUGE-THICK GRAVEL LAYER

介绍温州高350m的超高层建筑超长嵌岩桩穿越地层中夹有约40m巨厚卵石层的施工实例。从钻机选择、不同地层中的钻进方法、穿越巨厚卵石层的施工措施、泥浆配制、清孔方式等方面,详细阐述桩长超过100m的超长嵌岩桩施工技术,并结合成孔时孔径检测和成桩后超声波检测结果,分析试桩成孔质量和桩身混凝土质量,同时利用大吨位静载试验分析超长试桩的受力特性。实践表明:超长桩成孔时,应根据不同地层变工艺钻进并采用优质泥浆护壁。钻进到巨厚卵石层时可通过调节泥浆性能解决漏浆和卵石层塌孔的问题,并通过变径钻头和泵式反循环钻进工艺提高钻进效率。静载试验结果显示,在设计使用荷载下,超长桩桩顶沉降的90%以上来自桩身压缩。同时,桩底沉渣清除的干净与否,直接影响超长桩的沉降性状。

An engineering project of the super-long rock-socketed bored piles crossing a huge thick gravel layer with about 40 m depth was conducted at a 350 m high-rise building in Wenzhou area. The selection of drilling machine,the drilling method in different soil layers,the construction technology in crossing a huge thick gravel layer,the preparation of mud and the bore hole cleaning technology were presented to discuss details of the construction technology of the over 100-meter super-long bored piles. Moreover,the pile diameter and the ultrasound test were used to analyze the quality of drilled hole and pile shaft,respectively. In addition,a large tonnage static load test was conducted to capture the bearing capacity and the settlement of test pile. Some key findings indicate that the varying drilling processes,the high quality mud and the variable drilling methods can be adopted in different soil layers during the construction of the super-long bored piles. During a super-long pile construction in a gravel layer,the mud leakage and the borehole collapse can be solved by adjusting the property of mud,whereas the bits with variable diameter and the pump suction reverse circulation drilling can be adopted to improve the drilling efficiency. The static load test shows that the percentage of the super-long pile settlement at the pile head caused by the pile compression is over 90% within the working load. It can also be concluded that the thickness of the sediments at the pile end has an influence on the settlement of the super-long pile.