Experimental research on composite foundation of borehole tamping rammed piles in collapsed loess

Borehole tamping rammed pile is usually adopted to treat with thick significant collapsible loess subsoil in LanZhou area. The characteristics, similar static test curves and same failure mode which damage gradually, are indicated by static test results conducted on individual pile rammed with different tamping (plain soil and 2:8 lime soil), soil between piles and composite foundation. The bearing capacity and pile-soil stress ratio are obviously affected by different filling material. For lime soil pile, the characteristic value of bearing capacity of a single pile is 1500 kPa and bearing capacity of composite foundation is 450 kPa and pile-soil stress ratio is 3.8; for plain soil pile, the characteristic value of bearing capacity of a single pile is 650 kPa and bearing capacity of composite foundation is 350 kPa and pile-soil stress ratio is 2.5. But, the compaction effective on soil between piles responds weakly to different pile tamping materials.