Abstract: Based on the summarized characteristics of vein rockburst in the Uzbekistan Kamchik tunnel, the paper analyzed the formation mechanism of vein rockburst, established the mechanical model of the most dangerous vein rockburst in side wall of Kamchik tunnel and proposed corresponding controlling technology for rockburst. The research shows that the characteristics and hazards of vein rockburst are closely related to the location and thickness of the vein. The formation mechanism of this rockburst type is inconsistent with rockburst under single lithology. Vein rockburst occurred in vault of Kamchik tunnel results from the maximum tangential stress on vault after tunnel excavation. Exposed vein rockburst of side wall is caused by excavation unloading and vertical stress concentration in side wall, and the mechanical model can be simplified as the crushing instability when the thin vein plate is cut by unloading crack after the vertical stress concentration. Hidden vein rockburst behind side wall is mainly due to the horizontal extrusion of the vein behind granite and the vertical stress concentration of side wall after tunnel excavation. The mechanical model can be simplified as the bending and breaking of the free rock plate (pillar) of the side wall under the combined action of vertical stress and horizontal compression of the vein. The horizontal extrusion of vein towards granite rock plate (pillar) of the side wall is a major contributor to hidden vein rockburst behind side wall. It mainly comes from the "Wedge extrusion" caused by intrusion of vein and the horizontal extrusion from the horizontal differential deformation between vein and granite that are suppressed by granite. Hence, timely application of anchors on the side wall is an efficient way to prevent vein rockburst of side wall.

Key words: tunnel, vein, rockburst, extrusion, mechanical mechanism, prevention