Abstract: 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.

Key words: collapsible loess, ground treatment, compaction pile, immersion test