Development of in situ rock property measurement technique using a borehole penetrometer

Coal mine roof fall and pillar failure problems may be reduced if it is possible to determine the best anchorage horizons for roof bolts and to design a reliable supporting pillar based on rock or coal strength. The conventional practice of laboratory strength testing of rock or coal specimens is both expensive and time consuming. A fundamental problem for conventional testing is the inability to determine the weakest strata, since part of the core is often disintegrated during pre-testing drilling and sample preparation.;An in-situ testing technique, based on the resistance of the rock or coal to penetration of an indenter on the surface of a borehole in the mine roof or coal pillar, has been developed to determine in-place geotechnical properties. The main objective of this research has been achieved by measuring the pressure and displacement for samples of different rocks in the laboratory and in the field using the penetrometer. Laboratory experiments were conducted to investigate failure pressure and displacement on several types of rocks, and field tests were performed in both a hardrock mine and several coal mines. The results obtained from penetrometer tests can be utilized in the design of strata control measures such as roof bolting, hydraulic power support selection for longwall mining, and other geotechnical engineering applications.;A finite element model has been developed to identify stress distribution and concentration around the test borehole, which are caused by the load under the penetrometer indenter. The influence of the confined pressure on penetrometer testing can also be explained by finite element modeling.;This dissertation quantifies the relationship between penetrometer failure load pressure and uniaxial compressive strength. It also illustrates that penetrometer testing is an efficient and economical method for in-situ rock strength determination.