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该工程位于福州市闽江下游北岸 ,地层岩性为第四系海陆交互相沉积形成的砂和淤泥组成的软弱土。由于种种原因 ,活套坑施工时 ,车间主厂房结构及地基碎石桩加固已施工完毕 ,而且活套坑距离柱基台仅 3 0m。经综合分析与论证 ,选择了用钢板桩围堰、大口径钻孔泵吸反循环工艺成井、水下砼灌注封底 ,再进行井壁钢筋砼及井底板钢筋砼二次封底的施工方案。在施工中碰到的问题及时治理 ,如 :土坍方、桩倾斜时用回灌闭坑或调整施工方案 ;接桩断焊跑桩而呈天窗时 ,用钢板焊接加固 ;对标高 - 4 6m以下的钢板桩缺陷 (大扣、接头焊缝等 )漏水处采取坑外注浆堵漏。对于类似的基坑工程 ,在不能使用沉井时 ,可以借鉴该施工方案
The project is located on the north bank of the lower reaches of the Minjiang River in Fuzhou. The lithology of the formation is a soft soil composed of sand and silt formed by the interaction of the Quaternary marine-continental facies. Due to various reasons, during the construction of looper pits, the main workshop structure and foundation gravel pile reinforcement have been completed, and the looper pit is only 30m away from the pillar abutment. After comprehensive analysis and demonstration, the construction plan of using steel sheet pile cofferdams, large borehole borehole pumping reverse circulation technology into wells, and submerged concrete boring and backfilling was selected, followed by borehole reinforced concrete and bottom plate reinforced concrete retanning. The problems encountered during construction are promptly managed, such as: backfilling the pit or adjusting the construction plan when the earthwork is piled or tilted; when the piles are broken and run, and the skylights are used, the steel plate is used for welding reinforcement; the elevation is -4 6m or less The steel sheet pile defects (big buckles, joint welds, etc.) leaks are taken out of the pit to prevent leakage. For a similar foundation pit project, when the caisson cannot be used, the construction plan can be used for reference.