collapse section, broken soil and rock pile section, shallow buried and large bias pressure, and the support for the excavation of tunnel entrance and exit sections are also mostly used in the excavation of underground projects such as subway crossing urban areas. It can be used as an auxiliary method for building tunnels under existing buildings, highways,dth button bits, railways and underground structures;The pipe diameter of the small pipe shed is generally within the range of φ32 ~ 50mm,overburden drilling systems, and the steel pipe with the pipe diameter of φ42mm is mostly used. The pipe length is preferably 3.5-5m, the circumferential spacing is generally 0.3-0.4m, and the horizontal overlapping length is 1-1.5m. The pipe diameter of the middle pipe shed is generally in the range of φ50-φ89mm, the pipe length is generally not more than 20m, the circumferential spacing is generally 0.3-0.4m, and the horizontal overlapping length is 1-2m. φ89-φ159 mm steel pipe can be used for large pipe shed. The common pipe diameter is φ108 mm, and the pipe length should not exceed 40 m. the treatment range of the advanced small conduit is generally about 6 meters. The small conduit is a steel pipe with a wall thickness of 5 mm and a diameter of 42 mm. It is a method to consolidate the relatively broken surrounding rock in front of the tunnel face by small pipe grouting, so that the surrounding rock can form a whole before the next step. The pipe shed is used when the geological conditions at the entrance of the tunnel are very poor (such as sandy soil, seriously broken rocks, loess, etc.). Generally, the length is about 20-30 meters. The pipe shed is a steel pipe with a wall thickness of 3.5mm and a diameter of 108mm. Of course,dth rock bit, the pipe shed can also be used when the geological conditions in the tunnel are very poor (for example, the length along the axis of the tunnel caused by roof fall in the tunnel is large, and the volume is large). Return to Sohu to see more Responsible Editor:. wt-dthtools.com