Rockburst control method for advanced blasting pressure relief of tunnel face under asymmetric high stress

A rockburst control method for advanced blasting pressure relief of a tunnel face under asymmetric high stress, comprising the following steps:

• Step 1:
• based on a tunnel engineering geological survey report, determining stress concentration zones of the tunnel face according to initial in-situ stress of virgin tunnel rocks, distribution of an excavation-induced stress field, and geometrical characteristics of tunnel cross-sections;
• Step 1.1:
• based on the tunnel engineering geological survey report, inverting the initial in-situ stress of the virgin tunnel rocks and the distribution of the excavation-induced stress field by a numerical simulation method, so as to determine stress distribution situations of the tunnel face in tunnel excavation engineering;
• and
• Step 1.2:
• obtaining the stress concentration zones of the tunnel face according to a spatial relationship between the stress distribution situations of the tunnel face and a geometrical shape of the tunnel face:
• Step 2:
• based on the tunnel engineering geological survey report, predicting a grade of rockburst of surrounding rocks by using a rockburst intensity assessment method;
• Step 2.1:
• based on the tunnel engineering geological survey report, obtaining actual conditions of the surrounding rocks comprising a buried depth of the surrounding rocks of the tunnel face, formation lithology, the initial in-situ stress, uniaxial compressive strength of rocks, classification of the surrounding rocks, and hydrogeological conditions;
• and
• Step 2.2:
• according to the actual conditions of the surrounding rocks, compiling a comprehensive tunnel rockburst intensity assessment table, and comprehensively analyzing and predicting the grade of the rockburst of the surrounding rocks, wherein the grade of the rockburst of the surrounding rocks comprises:
• no rockburst, mild rockburst, moderate rockburst, and intense rockburst:
• Step 3:
• based on the stress concentration zones of the tunnel face and the grade of the rockburst of the surrounding rocks, determining a rockburst control scheme for blasting pressure relief of tunnels;
• Step 3.1:
• determining arrangement positions of advanced blasting stress pressure relief holes according to the stress concentration zones of the tunnel face;
• and
• Step 3.2:
• matching different rockburst control schemes for advanced blasting pressure relief of the tunnel faces according to the grade of the rockburst of the surrounding rocks, so as to determine the rockburst control scheme;
• wherein the rockburst control scheme for advanced blasting pressure relief of the tunnel faces comprises:
• (1) for tunnel faces with the grades of no rockburst and mild rockburst, a blasting stress relief method is not used;
• (2) for tunnel faces with the grade of moderate rockburst, 9-14 shallow extended-driven blast holes are arranged within the stress concentration zones for advanced blasting pressure relief;
• and
• (3) for tunnel faces with the grade of intense rockburst, 3-5 deep holes are arranged within the stress concentration zones for advanced blasting pressure relief, if an intensity of the grade of the rockburst increases, the 3-5 deep holes are arranged for use in combination with 9-14 shallow extended-driven blast holes for advanced blasting pressure relief, in which the shallow holes are arranged in peripheral zones of the stress concentration zones;
• wherein a construction basis for the rockburst control scheme for advanced blasting pressure relief of the tunnel face comprises a construction cross-section drawing, a pressure relief hole arrangement drawing, and a blasting parameter table;
• and
• Step 4:
• effect inspection:
• after each blast, inspecting a blasting effect;
• wherein the inspecting the blasting effect comprises:
• (1) inspecting whether a misfire detonation phenomenon occurs, if the misfire detonation phenomenon occurs, treating the misfire detonation phenomenon according to misfire treatment procedures specified in Safety Regulations for Blasting;
• and
• (2) if no misfire detonation phenomenon occurs, observing a blasting crushing zone and a blasting fracture zone;
• according to observations from a borehole, the blasting crushing zone is defined in a manner that a central line of an original borehole is used as an axis, and a diameter thereof is in a range of 50-70 mm;
• within a range of the diameter being 100-160 mm, an increase in fractures is observed and determined to be caused by blasting, rock masses within the range exhibit significant loosening, and according to a rock mass damage condition within the range, the zone is determined as the blasting fracture zone;
• and confining pressure loosening is observed in the blasting fracture zone and a blasting vibration zone, and high in-situ stress in the blasting fracture zone and high in-situ stress in the blasting vibration zone are both released.