Abstract: The impregnated diamond bit is a micro-cutting edge formed by exposing diamond in the matrix, and realizes the drilling of broken rock by crushing and grinding the rocks under the action of drilling pressure and torque. It can be widely used in hard formation and complex formation drilling. However, conventional diamond drill bits have problems such as low drilling speed, slow footage and high costs in hard formations. Firstly, rock samples, which were sampled in different depths form holes adjacent to the borehole S2Z-45 in GanQing  tunnel, were taken for testing and analysis of their hardness, mineral composition, and drillability. It was determined that most of rock layers were mainly diorite, and the rock’s drillability level was eight. Then, according to the geological characteristics of Ganqing tunnel, the matrix hardness and bottom lip shape of impregnated diamond were optimized. The influencing factors of the performance of impregnated diamond bit was analyzed by field tests. The experimental results showed that the impregnated diamond bit had the best performance when its matrix hardness was HRC 15-20, a diamond particle size was 40-50 mesh, the volume fraction of diamond was 20%, and a bottom lip with a ring groove sharp tooth shape. It has a lifespan of 321 m and a drilling speed of approximately 1.17 m/h. Under the same diamond parameters, the hob type impregnated diamond bit with a matrix hardness of HRC 10-15 had advantages in drilling speed, which the drilling speed of the drill bit could reach 1.44 m/h. The sharp tooth bottom lip surface of the ring groove and high matrix hardness helped to improve the life of the drill bit, while the rolling tooth bottom lip surface and low matrix hardness were beneficial for improving drilling efficiency, but the life of the drill bit was relatively low.

Key words: GanQing , tunnel, impregnated diamond drill bit, ring groove sharp tooth type, hobbing type, drill bit matrix