洞身长管棚施工工艺新技术 : A new technique for long pipe roofs applied in tunnel barrel instead of the oldstyled technology when it gets through shallowly buried , biased and weak formations was introduced , which means that the aperture and pipe roof will be formed and completed synchronously by using 50 m Φ121 steel tubes to keep in step closely with the drilling bit without cleaning out the hole and