挤密桩处理湿陷性黄土地基的现场试验研究

湿陷性黄土地区的多层建筑大多数都会遇到地基处理的问题，用素土桩、灰土桩、碎石桩等各种桩处理地基的湿陷性是常用的方法。为检验挤密桩处理湿陷性黄土地基的效果，设计了现场试验，试验方案中考虑了桩心距、处理深度、处理范围及桩孔填料等不同影响因素，设置了8个试验点。各点处理后测得了两桩间和3桩间等距离的5个点上的土体密度变化数值。之后对各点加载200 kPa，做小面积（小坑）浸水测试和大面积（整个场地，28 m×16 m）浸水测试，测量两种浸水条件下各试验点的湿陷量。由此总结了该种工程方法处理地基湿陷性的效果和规律性。结果表明：桩心距应控制在2.5倍桩径以内，可保证消除挤密桩间所有面积的湿陷性，超出挤密桩长以下地层的湿陷性仍然存在；小面积浸水发生的湿陷为外荷湿陷，大面积浸水才能释放试验场地地基的全部湿陷量，而与处理深度无关；灰土填料显然优于素土填料，在地基主要持力层内须用灰土填料，但对于其下地层或自重湿陷不严重的部位强调使用灰土填料是不必要的。

A field experimental study of compaction piles in collapsible loess foundation

Most of multistorey buildings on loess areas encounter the ground treatment problems.It is common treatment methods to deal with the collapsibility of foundation with a variety of piles(pure-soil pile,lime-soil pile,crushed-stone pile,etc.).In order to test the effect of the compaction pile in collapsible loess foundation,a field test was conducted.To consider the different factors(distance of two piles center,processing depth,processing area,pile hole filling),eight pilot sites were set up in the experimental field.First of all,the change of soil density at the five points equidistant between two piles and three piles were tested after pilot sites were set up;then,after the loading(200 kPa) on the every pilot site,the small area(small pit) immersion and the large area(the entire location,28 m×16 m) immersion were conducted;the every site’s collapse volume was measured respectively.From above experiment the effect and regularity of the treatment methods were obtained.The results show that: to ensure eliminating the collapsibility of all inter-area of compaction pile,the distance of two piles center must be controlled within 2.5 times of the pile diameter.The collapsibility still exists under layer exceeding compaction pile’s length.The settlement after small area immersion is loading collapse,exclusively the large area immersion the whole collapse is eliminated,and it is no matter with the processing depth.The lime-soil filling obviously surpasses the pure-soil filling.Within main bearing stratum the filling must be lime-soil.But it is unnecessary to use lime-soil filling under main bearing stratum and some light collapsibility location.