Rock Uniaxial Compressive And Tensile Properties Directly Under Cyclic Loading Conditions

It is well known that rocks bear compressive stress rather than tensile stress in most cases. As a consequence, the deformation parameters and the constitutive models of rocks deduct from only compressive tests in the practical rock engineering. However, some researches have shown that Young's modulus in direct tension, ET, is much smaller than the modulus in compression, EC, for some rocks. For such rocks, large error may be produced if their constitutive models and the deformation parameters such as Young's modulus and Poisson's ratio are obtained from only compressive tests, and the larger difference between EC and ET, the greater error would be produced.Up to now, a lot of researchers have done investigations on the compressive and splitting test. But, the researches about deformation behavior under compressive and tension are too little.The understanding about importance of deformation characteristics of compressive and tension is not enough. The constitutive models of rocks and failure criterion are very incomplete under tension and compression. More researches are then needed to investigate the deformation behavior of rocks under both tension and compression.In the research works involved in this paper, the compression-tension cyclic loading tests with different loading routes and stress levels were porformed with four rock types. It was developed by Kunming University of Science and Technology that the testing apparatus can conduct both compression and direct tension tests with the same rock sample.Following conclusions are obtained:(1) For two types of tested sandstone, Young's modulus in compression,ECA, are much larger than the modulus in direct tension, ET. ECA/ETA of the amaranthine sandstone is6.09, ECA/ETA of the khaki sandstone is2.14. For the Dahongshan copper mine marble, Young's modulus in tension is nearly equal to the modulus in compression. ECA/ETA is2.14.(2)In splitting test, for two types of tested sandstone, Young's modulus in compression, ECA, are much larger than the modulus in tension, ETA.ECA/ETA of the amaranthine sandstone is2.07, ECA/ETA of the khaki sandstone is2.18.(3)In tension and compression cyclic loading tests, the values of Young's modulus and the Poisson's ratio in compression continously increase as stress is applied, while the values decrease in tension. (4)If the compress stree is smaller in compression and tension cyclic loading tests, the Young's modulus of tension is larger. If the compress stree is larger, the Young's modulus of tension is smaller.(5)Both compression and tension, the modulus of unloading is higher than the modulus of loading.(6)In compression and tension cyclic loading tests, both compression and tension are prominent plastic. The plastic is much more significant in tension than compression.