AN INVESTIGATION INTO THE EFFECT OF SAMPLE SHAPE ON ELASTIC DYNAMIC AND ELASTIC STATIC PROPERTIES OF LIMESTONE

Dynamic methods are, nowadays, fast and inexpensive ways of estimating elastic constants in rock engineering. Therefore, In order to get reliable outputs all effective factors of such methods are to be assessed. One of fundamental factor affecting the test results is the shape or height/diameter (L/D) ratio of the tested specimen. The existing standards, namely ASTM and ISRM standards imply that, in spite of the great role of the (L/D) ratio on the static test results, this ratio does not play an important role on dynamic test results. With aim of determining the exact role of (L/D) ratio on static and dynamic properties of rocks, 3 dynamic and 5 static tests were conducted on Neka Limestone samples with 6 various (L/D) ratios of 0.5, 1, 1.5, 2, 2.5 and 3 (48 sets of tests in all).The data produced through these tests showed that varying (L/D) ratio from 0.5 to 3 results in ample variation of mechanical parameters in both types of tests. The laboratory produced data indicated that static tests are affected more by (L/D) ratio than dynamic ones. It was also concluded that when the value of (L/D) gets close to 3, elastic dynamic parameters reach more or less constant values whereas static parameters are still in change. These finding show that the effect of sample shape on dynamic properties of rock has not been counted for properly. This importance of this factor has to be recognized. Also, when static tests are concerned, the previously recommended ratio of (L/D) has to be further assessed.