What blasting should be used for rock burst tunnel excavation?

Smooth blasting or presplitting blasting technology should be adopted in rock burst tunnel excavation.

Brief introduction of smooth blasting;

Smooth blasting is a kind of controlled blasting technology, which keeps the new wall flat and has no obvious damage. It is characterized in that a row of smooth blasting holes with hole spacing matching the minimum resistance line are drilled on the designed excavation contour line, and uncoupled charging or other special charging structures are adopted.

After the main body of the excavation is blasted, the charge in the smooth blasting hole is detonated at the same time, thus forming a smooth and flat excavation surface that runs through the smooth blasting hole. Smooth blasting technology is not only used in open-pit excavation, but also has achieved good results in many underground projects in China.

Especially in the construction of some hydraulic tunnels, it can not only reduce the situation of over-excavation and under-explosion, but also reduce the hydraulic friction coefficient to the level of smooth surface achieved by special lining.

Brief introduction of presplitting blasting;

Pre-splitting blasting refers to blasting through cracks with a certain width on the design contour line before blasting in the main blasting area when excavating stone. In order to buffer and reflect the vibration wave of excavation blasting and control its destructive influence on the reserved rock mass, a relatively flat excavation contour line can be obtained.

Presplitting blasting is not only widely used in vertical and inclined excavation walls; Presplitting blasting is also used for regular surfaces, twisted surfaces and horizontal foundation surfaces. Presplitting blasting is suitable for weak rock strata with poor stability and need to control the excavation contour.

Matters needing attention in rock burst tunnel excavation:

1, rockburst position analysis:

If there is a parallel pilot tunnel, the horizontal pilot should push the main tunnel to a certain distance, so as to understand the geology, analyze the position where rock burst may occur, strengthen prevention and control when the main tunnel is constructed to the corresponding position, and take necessary measures.

2. Selection method:

When blasting, methods such as presplitting blasting, slit cutting and hole arrangement should be selected to release part of the energy in advance, so as to release part of the original stress of the rock stratum in advance, so as to reduce the occurrence of rockburst. The blasting dosage should be strictly controlled to minimize the impact of blasting on surrounding rock.

3. Consider shortening the lens:

According to the frequency and scale of rockburst, shortening the blasting cycle footage should be considered when necessary. The initial support and lining should follow the excavation face closely to minimize the exposure time of rock strata and prevent rockburst.