基桩最小中心距研究

摘要

以浙江省沿海某高速公路大直径钻孔灌注桩施工中混凝土拌合物串孔为对象,研究了混凝土拌合物串孔的原因,研究结果显示:大直径钻孔灌注桩孔壁面积大,在施工中孔壁周围土层受到扰动引起力学性能降低导致串孔.以上述研究结果为基础,提出了预防混凝土拌合物串孔的措施:场地中没有饱和黏性土,把钻孔灌注桩当作非挤土桩,以基桩中心距3.0d(d为直径)安排施工顺序;场地中有饱和黏性土,把钻孔灌注桩作为挤土桩,以基桩中心距4.5d安排施工顺序;《建筑桩基技术规范JGJ 94—2008》中基桩最小中心距改为5d是预防饱和黏性土中混凝土拌合物串孔最有效的措施.%Based on the concrete mix string hole of large-diameter bored pile in a coastal expressway of Zhejiang province,the reasons of concrete mix string hole are researched.Results show that because of the big hole wall area for large-diameter bored pile,the clay around the hole wall disturbing leads to perforation of the mechanical properties degradation.Measures of preventing string hole are put forward.If there is no saturated clay in the site,in order to prevent concrete mix from string hole in no saturated clay,the bored pile is regarded as non-squeezing pile and 3 times pile diameter is chosen to arrange the construction sequence of piles.If there is saturated clay in the site,the bored pile is regarded as squeezing pile and 4.5 times pile diameter is chosen to arrange construction sequence of piles. Modifying minimum center distance between two piles of Technical Code for Building Pile Foundations(JGJ 94—2008) into 5 times pile diameter is the most effective measure to prevent the concrete mix from string hole in saturated clay.