8What is secondary breakage? Secondary breakage is when the impact hammer reduces the size of existing blocks of:concrete orrockinto smaller pieces, such as joint blocks of rock as illustrated in the next slide.
11Rock Properties Control! What rock properties control the breakage of rock by impact hammer?Primary breakage depends on the rock intact propertiesSecondary breakage depends on the rock mass properties
12Rock PropertiesWhat are rock …Intact andMassproperties?
13Engineering Properties of Rock Rock Intact & Mass Properties
14Rock Intact Properties Rock intact properties are determined by testing of intact samples in terms of:Unconfined compressive strengthTensile strengthTotal HardnessSonic VelocityEtc
15Rock Mass Properties Rock discontinuities and their properties: SpacingNatureOrientationSeismic velocity (similar to use in Caterpillar Ripping Chart)RQD (Rock Quality Designation)
16Using RQD (relative to depth) Minimum, Average, and Maximum b
17Using RQD (top of rock to 15 ft) Impact Hammer ExcavationGreens - efficientGrays - difficult/slowReds - tedious