Estimation of mechanical properties of weak rocks by rod penetration test

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A knowledge of the mechanical properties of weak rocks such as shale, sandy shale and coal is essential for ground control in underground coal miningMost tests which are usually used to determine the strength of rock require the specimen to be in the precisely prescribed shape. However, with weak rocks it is often difficult, or practically impossible in some cases, to prepare the specimen as required by these tests.From this point of view rod penetration test has been carried out, because in this method an unprepared specimen can be used.The results of this study are summarized as follows:1. The size of specimen should be at least 10 times the rod diameter.2.It is necessary to avoid the size effect of rod on penetration strength Srp.3.Penetration modulus Erp is not dependent on the rod size.4.Uniaxial strength Sc and tangent young's modulus at 50% of compressive strength E_<50> can be estimated with penetration strength Srp and penetration modulus E_<50> as follows: Sc = 0.11 Srp, E_<50>= 2.3 Erp5.It is possible to estimate the strength reduction with water quantitatively by this test.