Research conclusions: The maximum treatment depth of piles thrusted － expanded in column － hammer is 20 － 30 m． The result show that，dealed with 22 m piles thrusted － expanded in column － hammer，the roadbed rarely occures settment and the collapsibility of reinforced layer also eliminates． The roadbed don' t need to preload． Thus，piles thrusted － expanded in column － hammer can obtain the expected results in settlement controlling in large thickness collapsible loess site．