Smooth Blasting Technology for Tunnel Inverted Arch and its Engineering Application

The dislocation and overbreak of tunnel inverted arch are serious when traditional blasting excavation technology is used. This is because traditional blasting technology does not adopt the smooth blasting method, and the angle of the perimeter holes is too large when drilled by manual rock drilling rigs. By therefore analyzing the traditional blasting excavation technique of invert, the cause of serious studiedthe smooth blasting technology for inverted arch is proposed based on the smooth blasting theory and a large quantity of engineering practice. Water decking charge structure is adopted in the perimeter holes, which can be adjusted according to the inverted arch shape. The spacing between the perimeter holes is 30~50 cm, and the thickness of the smooth blasting layer is greater than the perimeter hole spacing by 10~30 cm. Additionally, a drilling counterforce support is used to reduce the angle of the perimeter holes which can ensure each blast hole to be drilled to the design depth. After comparing the blasting effects of the proposed smooth blasting technology and traditional blasting technology for the inverted arch by field tests, the contour overbreak by the smooth blasting technology is far less than that of traditional blasting technology, and the cost of every 12 m tunnel excavation is reduced by 35.14%.