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DRAFT <br />Table 7. Formulae for Predicting Fracture Zone Height <br />(modified from Peng, 1992 referencing Liu, 1981) <br />Rock Type SI System Enali~sh System <br />Hard and strong rock ht = x.200 2.o meters hf = o.sss~2.o feet <br />(Good water conductivity) <br />6 = ±8.9 meters 6 = 29.2 feet <br />Medium hard rock hf = x.600 s.s meters hf = o.ass°~s.sfeet <br />(Worse water conductivity) <br />6 = ±5.6 meters 6 = ±18.4 feet <br />Soft and weak rock hf = 3.00 s.o meters h f = o.9as0,ns.o feet <br />(Bad water conductivity) <br />6 = ±4.0 meters 6 = ±13.1 feet <br />Weathered soft and weak rock ht = s.om+ms.o meters ht = ~.52a0~s.ofeet <br />(Bad water conductivity) <br />6 = ±3.0 meters ~ _ ±9.8 feet <br />1. hf =fractured zone height, m =mining height, 6 =standard deviation. All units in meters (SI System) <br />or feet (English System). <br />2. Rock t pe is classified based on the uniaxial com ressive strength c)): hard and stron rock c > <br />5888 psi (39.23 MPa); medium hard rock c = 2644 p5888 psi 19.62 -9.23 MPa); soft and weak rock <br />c = 1200 - 2844 psi (8.28 - 19.62 Mpa). (Original in Peng, 199, p7) <br />Page 27 of 57 <br />