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Blasting Impacts Assessment for the Proposed GCC Rio Grande, Inc. Quarry in Pueblo County, Colorado <br />3.0 PHYSICAL CHARACTERISTICS OF BLAST EFFECTS <br />Before proceeding to analyze the Red Rock Plant and Mine blasting plant, the following pages and <br />subsections 3.1 through 3.5 set forth a review of the physical characteristics and forces involved in <br />the detonation of explosive charges used in mining applications. When explosive charges detonate <br />in rock, they are designed so that most of the energy is used in breaking and displacing the rock <br />mass. However, some of the energy can also be released in the form of transient stress waves, <br />which in turn cause temporary ground vibration. Detonating charges also create rock movement <br />and release of high - pressure gas, which in turn induce air - overpressure (noise), airborne dust and <br />audible blast noise. <br />In the very-near zone, crushing usually occurs in the rock around the charge. The extent of this <br />compressive and shear failure zone is usually limited to one or two charge radii. Beyond the <br />plastic crushing zone, the rock or ground is temporarily deformed by elastic strain waves. For <br />some distance, tangential strain intensity exceeds the rock's strength and new fractures are created. <br />The magnitude of dynamic strain and particle motion decreases as distance from the charge <br />increases. From the crushed zone out to about 26 charge radii, radial cracks are created as a result <br />of the strain that exceeds the rock's tensile strength. <br />3.1 Vibration Ground Waves <br />Within and beyond the cracking zone, stress waves spread through the rock mass and along the <br />ground surface. Some waves pass through the "body" of the rock mass. Primary compression <br />waves and shear waves are examples of body waves. Other surface vibration waves travel along <br />the ground surface similar to the way waves travel along the surface of water. In an ideal isotropic <br />and homogenous rock mass, wave energy would travel evenly in all directions. However, most <br />rock masses are far from ideal, so wave energy is reflected, refracted and attenuated by various <br />geological and topographical conditions. The elastic properties of rock greatly influence vibration <br />magnitude and attenuation rate. When seismic waves pass through the ground, ground particles <br />oscillate within three- dimensional space. Soon after blasting has stopped, vibration energy <br />dissipates and the ground particles become still. <br />REVEY Associates, Inc. Page 4 July 2002 <br />