深厚强风化岩层冲孔灌注桩质量问题原因分析  

Analysis on the quality defect of bored pile in deep and thick highly decomposed rock

作　　者：林志强[1,2] Lin Zhiqiang(Fujian Academy of Building Research,Fuzhou 350025,China;Fujian Key Laboratory of Green Building Technology,Fuzhou 350025,China)

机构地区：[1]福建省建筑科学研究院 [2]福建省绿色建筑技术重点实验室

出　　处：《工程勘察》2019年第11期23-28,34,共6页Geotechnical Investigation & Surveying

基　　金：福建省科技计划项目(2014Y0016);福建省建设科技研究开发项目(2012K15)

摘　　要：本文依托某冲孔灌注桩工程质量事故实例,开展现场调查、资料分析及试验研究。综合地质条件、设计、施工、现场试验及相关规范等多方面资料,利用端承摩擦桩竖向抗压承载力荷载传递机理,分析工程质量事故的主要原因并提出建议。分析结果表明:对于端承摩擦冲孔灌注桩,桩周围全风化粉砂岩、砂土状强风化粉砂岩层遇水极易软化,层厚达40m以上,桩侧岩土层受到振动、挤压、卸压回弹、浸水、崩解、软化等作用,结构强度基本丧失、土体强度显著下降,形成桩侧软化土层厚约20~30mm;又处在地下水位以下,工后软化土层仍保持湿润,土体强度提升幅度较小,桩的极限侧阻力值远低于现行桩基规范提供的经验值,是本工程质量事故的主要原因。建议对现行桩基规范提供的经验值进行适当折减,并在备注做出对应条件说明,减少类似工程质量事故发生。研究成果可为类似桩基工程特别是穿越深厚全风化、砂土状强风化岩层摩擦型冲孔灌注桩的设计、施工及相关理论研究提供借鉴。The field investigation,data analysis and experiment study was carried out in a bored pile quality defect case.The cause of bored pile quality defect was analyzed and the remedial measures were proposed based on the load-transfer mechanism of friction pile under vertical compression load considering the geological condition,design,construction and in-situ test.The main reasons are that the main strata along pile shaft are more than 40 m completely to highly decomposed sandstone which is soften in water;a weaken lining would formed along pile shaft due to the soil structure and strength deteriorate for vibration,squeezing,unloading,soaking,slacking etc.;the soil strength recovery is limited;the ultimate friction is lower than recommendation value in the pile code.The empirical value suggested by the current Technical code for building pile foundation should be reduced and the application condition should be listed in order to prevent the similar quality accident happens again.The study results could be referred by the similar pile design,construction and research of the friction pile through completely to highly decomposed sandstone.

关 键 词：冲孔灌注桩 工程质量事故 原因分析 荷载传递机理 端承摩擦桩 

分 类 号：TU473[建筑科学—结构工程]