Characteristics of Rock and Geology influence Surface, UG and Tunnel Rock Blasting Results

Characteristics of Rock and Geology influence Surface, UG and Tunnel Rock Blasting Results

1. GENERAL CHARACTERISTICS OF ROCK – The result of any blast is more dependent on the characteristics of the rock than on the explosives being used to break it. The more important characteristics of the rock influencing the blasting result include:

  • Tensile and compressive strength,
  • Density and
  • Seismic velocity (acoustic velocity).

a. Tensile and Compressive Strength – Most types of rock have a compressive strength which is 8 to 10 times greater than the tensile strength. These properties are important factors in rock blasting.

Type of rock Compressive strength (kg/cm2) Tensile strength (kg/cm2)
Granites 2000-3600 100- 300
Diabase 2900-4000 190- 300
Marble 1500-1900 150- 250
Limestone 1300-2000 170- 300
Shale 300-1300
Sandstone, hard 3000 300

b. Density – Rock of high density is normally harder to blast than rock of lower density. One reason for this is that high density rock is heavier to move during detonation.

c. Seismic Velocity – The seismic velocity (acoustic velocity) of the various types of rock varies from 1500-6000 m/s. Hard rock of high seismic velocity will shoot more easily, spe­cially when explosives with high velocity of detonation are being used.

Type of rock Density (kg/dm3) Seismic velocity (m/s)
Granite 2,7-2,8 4500-6000
Gneiss 2,5-2,6 4000-6000
Limestone 2,4-2,7 3000-4500
Dolomite 2,5-2,6 4500-5000
Sandstone 1,8-2,0 1500-2000
Clay mudstone 2,5-2,7 4000-5000
Marble 2,8-3,0 6000-7000
Diabase 2,8-3,1 4000-5000

2. ROCK STRUCTURE – The planning process should include a survey of the rock structure and other rock characteristics so that the drilling and loading pattern and direction of advance can be optimized as far as possible.

The rock structure included cracks and fissures and other zones of weakness.

Two expressions commonly used to describe the rock structure are ‘strike’ and ‘dip’. Strike is the horizontal direction of the structure on the rock surface. Dip is the angle of the structure relative to the horizontal rock surface.

 

For further reading refer following paper:

https://miningandblasting.wordpress.com/2010/12/21/modification-of-blasting-techniques-as-per-geological-conditions-of-strata/

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