collapsible loess;  Manually digging holes and expanding long piles;  Static load test;  vertical bearing characteristics;  Side resistance

The on-site static load test was carried out on the manually dug hole and bottom-expanding long piles placed in the loess layer and supported in the silty clay layer, and the pile top settlement S and pile bottom settlement Sb under each stage of load were measured, and the vertical bearing characteristics of the extended bottom long piles were analyzed. It is pointed out that the stress mechanism of the extended long pile is obviously different from the short pile with the bottom expansion, and the bearing characteristics of the extended long pile placed in the loess layer are basically the same, and its ultimate bearing capacity is mainly based on side resistance, which has the characteristics of significant end-bearing friction pile. In addition, the experimental data show that water immersion will have a great influence on the pile side friction resistance of collapsible loess.