In light of the properties of incompact sand and silt,the paper introduced the scheme of thin wall caisson used in drilled pile foundation The posibitility of subsidence is predicted and the measures helping sinking are proposed in the sinking process The paper also analyzed the control of deviation rectification and correction of deflection during caisson sinkin

By the engineering examples, the authors indroduced in the paper the methods and orperation essentials dealed with the droped iron pieces in the pile hole by using a submersible eletromagnetic fisher, which has practical value.

The method of 85 meters deep pouring piles can make pour fast,reduce the cost of project,guarantee project quality and construction safety,never happen quality defect or quality accident and the economic benefits are prominent,so,it can offer some reference for other construction departments.