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The sonic log provides a measure of the time of travel of the compressional wave over a <br />certain interval of the formation immediately adjacent to the borehole. From the travel <br />time, the velocity of propagation of compressional waves in the formation can be <br />calculated and correlated with strength properties. <br />Time Domain Reflectometry (TDR) cables were installed in the three geotechnical <br />boreholes for monitoring changes in strata deformation resulting from mining directly <br />above the mains. By comparing the results from TC -03 -02 and TC -03 -03 over the mains <br />with TC -03 -01 north of the corridor, any mining - related deformation could be identified. <br />TDR measurements are useful for identifying the location of bed separation and shearing <br />along the entire overburden. For this monitoring, coaxial cables were cemented in the <br />boreholes from surface to below mining horizon. If beds separate and shear during <br />mining, the coaxial cable is faulted. By using geophysical techniques to measure the <br />distance to cable faults, the location of bed separation can be identified. <br />0 <br />• <br />Maleki Technologies, Inc. Page 8 <br />