Last data update: Sep 16, 2024. (Total: 47680 publications since 2009)
Records 1-2 (of 2 Records) |
Query Trace: Molinda G [original query] |
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In situ estimation of roof rock strength using sonic logging
Oyler DC , Mark C , Molinda GM . Int J Coal Geol 2010 83 (4) 484-490 Sonic travel time logging of exploration boreholes is routinely used in Australia to obtain estimates of coal mine roof rock strength. Because sonic velocity logs are relatively inexpensive and easy to obtain during exploration, the technique has provided Australian underground coal mines with an abundance of rock strength data for use in all aspects of ground control design. However, the technique depends upon reliable correlations between the uniaxial compressive strength (UCS) and the sonic velocity. This paper describes research recently conducted by NIOSH aimed at developing a correlation for use by the U.S. mining industry. From two coreholes in Illinois, two from Pennsylvania, and one each from Colorado, western Kentucky and southern West Virginia, sonic velocity logs were compared with UCS values derived from Point Load tests for a broad range of coal measure rock types. For the entire data set, the relationship between UCS and sonic travel time is expressed by an exponential equation relating the UCS in psi to the travel time of the P-wave in s/ft. The coefficient of determination or R-squared for this equation is 0.72, indicating that a relatively high reliability can be achieved with this technique. The strength estimates obtained from the correlation equation may be used to help design roof support systems. The paper also addresses the steps that are necessary to ensure that high-quality sonic logs are obtained for use in estimating UCS. 2010. |
Ground failures in coal mines with weak roof
Molinda G , Mark C . Electron J Geotech Eng 2010 15 1-42 Coal miners who work and travel under supported roof expect to be protected from rock falls. However, rock fall accidents and injuries continue to occur in coal mines that have been supported according to the roof control plan. Experience at coal mines with large numbers of falls indicates that many have weak roof. Control of this roof may require additional ground control measures. An understanding of the geologic and stress conditions which lead to roof falls is necessary to assess the risk of failure and to design roof reinforcement to improve stability. Six common roof fall types, with attached field examples, are described. Roof support practices for each fall type are also described. |
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