Abstract: In order to effectively reduce the construction cost and the overbreak amount by drilling and blasting method, and improve the drilling and blasting construction technology, the operation mode of the rockdrilling jumbo is studied, and it is concluded that when the rockdrilling jumbo is used for tunnel drilling and blasting excavation, the external angle when drilling the peripheral blasting holes is difficult to be controlled, and the tunnel overbreak amount is always large due to the influence of the boom structure of jumbo, unclear field sight and relatively long visual distance. Furthermore, comparison and contrast is made on the overbreak amounts induced by matching construction of long and short blasting holes under different construction conditions, such as primary support closely following tunnel face and that not following tunnel face. It is concluded that under the premise of ensuring construction safety, the method that retaining a certain length of tunnel without construction drilling for primary support and using matching drilling and blasting technology of long and short blasting holes can effectively control the amount of tunnel overbreak during drilling and blasting by using rockdrilling jumbo. The results show that the maximum overbreak amounts of Grade Ⅱ and Ⅲ, Grade Ⅳ and Grade Ⅴ surrounding rocks when using long and short blasting holes are 12 cm, 19.5 cm and 21.5 cm less than that when using long blasting hole, respectively.

Key words: tunnel, long and short blasting holes, overbreak, rockdrilling jumbo, external angle, control standards, smooth blasting