Laserfiche WebLink
Janice Lynn Bennett - 81422.PDF Page 8 <br />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 <br />and subsections 3.1 through 3.5 set forth a review of the physical characteristics and forces <br />involved in the detonation of explosive charges used in mining applications. When explosive <br />charges detonate in rock, they are designed so that most of the energy is used in breaking and <br />displacing the rock mass. However, some of the energy iscan also be released in the form of <br />transient stress waves, which in turn cause temporary ground vibration. Detonating charges also <br />create rock movement and release of high - pressure gas, which in turn induce air - overpressure <br />(noise), airborne dust and 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 <br />created. The magnitude of dynamic strain and particle motion decreases as distance from the <br />charge increases. From the crushed zone out to about 26 charge radii, radial cracks are created as a <br />result 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 waves, like Rayleigh waves [PLEASE <br />DEFINE TERM], travel along the ground surface. In an ideal isotropic and homogenous rock <br />mass, wave energy would travel evenly in all directions. However, most rock masses are far from <br />ideal, so wave energy is reflected, refracted and attenuated by various geological and <br />topographical conditions. The elastic properties of rock greatly influence vibration magnitude and <br />attenuation rate. When seismic waves pass through the ground, ground particles oscillate within <br />three - dimensional space. Soon after blasting has stopped, vibration energy dissipates and the <br />ground particles become still. <br />1 REVEY Associates, Inc <br />Page 5 July 2002 <br />