مقايسه تاثير نسبت ابعاد نمونه و فشار جانبي بر مقاومت فشاري تك محوره و سه محوره سنگ

Comparison of the Effect of Shape and Confining Pressure on the Uni-Axial and Tri-Axial Compressive Strength of Rocks

In civil and mining, the design of some structures, such as pillars in mines and bridges, requires the knowledge of the effect of the relative size of dimensions (shape effect) on the strength of the structure. Therefore, to assess the effect of shape on the uni-axial strength of rocks, laboratory tests were conducted on samples of 3 different types of rocks (namely; Isfahan dolomite, Bookan limestone and Gadouk sandstone) with various sample relative dimensions. Analyzing the data of these tests resulted in an overall relationship as Sigma c=K Sigma radical D/L where D, L and Sigma c1 are the diameter, length and the uni-axial compressive strength of a sample with D/L=1 and K was obtained to be 1.14, 1.21 and 0.96 for the 3 rock types relatively. Also, as D/L and confining pressure affect uni-axial compressive strength and tri-axial compressive strength similarly, 3 axial tests, in various confining pressures, were conducted on the samples of the same rocks with D/L=0.5.Graphs of Sigma 1- Sigma3 and Sigma c - D/L were compared. After omitting the term Sigma c from these formulas the overall relationship of Sigma3= A(D/L) -B was obtained. Finally, for the 3 type of rocks, a single formula as Sigma3 =8.7515 D/L - 6.3789 with coefficient of determination of 0.9534 was introduced. By applying the simulation proposed in this study, within the limit of the results, the costly time consuming tri-axial tests can be replaced with uni-axial ones.