Based on a large amount of laboratory and field experiments

and the excavation modeling experiment

through the analysis of the genesis

texture and structure of drifted material formed in different period

the engineering geologic conditions of forming hole in deep drified material are studied; and the physico-mechanaical parameters are achieved precisely. A wide span hole in deep drifted material has been successfully excavated at Xilongchi Pumped Storage Power Station. And the experimental excavation

observation and analysis are done to know whether the hole can be formed in the drifted material formed in the first period; and a lot of experiments in lab. and infield also are done. Finally

the physico-mechanical parameters of drifted material are achieved precisely. Through careful design and careful construction

it is successfal to dig big span hole in the deep drifted material.