地下水位变幅较大区域柱锤冲扩碎石桩复合地基处理工程实录

Case history of composite foundation treatment with column hammer expanding gravel pile in area with large variation of groundwater level

北京市丰台区某杂填土地层碎石桩复合地基处理工程受南水北调影响,场区内地下水位多次出现快速升降,施工图设计阶段与地基处理施工阶段水文地质及工程地质条件不完全一致,试验性施工阶段出现复合地基承载力不足的问题。该工程出现复合地基承载力不足的原因除设计条件变化外,还有施工质量控制不到位及设计基本参数取值偏大等。采取换填与挤密桩结合的补强措施。实践结果表明,设计条件发生变化时,需要对方案作出相应调整;存在地基被浸泡的可能时,应提前评估柱锤冲扩碎石桩的适用性;雨季施工要严防雨水浸泡,预留足够厚度的施工保护层;应根据杂填土的成分、厚度及压缩性等分区进行评价,调整相应的设计参数及处理措施。

Affected by the South-to-North Water Diversion Project,the ground water level of a gravel pile composite foundation treatment project in Fengtai District of Beijing has experienced rapid rise and fall for many times,The hydrogeological and engi-neering geological conditions in the design stage and the construction stage are not completely the same,and the composite foun-dation bearing capacity is insufficient in the experimental construction stage.Based on the case of this project,The reasons for in-sufficient bearing capacity of composite foundation are analyzed,including changes in design conditions,inadequate construction quality control,and excessive values of basic design parameters.Introduced the reinforcement measures of combining replace-ment and compaction piles.The practice results show that when the design conditions change,the scheme should be adjusted ac-cordingly;When the foundation is likely to be soaked,the applicability of the column hammer expanded gravel pile shall be evalu-ated in advance;During construction in rainy season,the foundation shall be strictly prevented from being soaked by rain;The evaluation shall be carried out according to the composition,thickness and compressibility of the fill,and corresponding design parameters and treatment measures should be adjusted.