Investigation of mechanical properties of fractured marbles by uniaxial compression tests

Uniaxial compression tests(UCTs)on 34 naturally fractured marble samples taken from the transportation tunnels of Jinping II hydropower station were carried out using the MTS815 Flex test GT rock testing system.Rockburst proneness index WET is determined for the marble samples with the UCTs.According to the number,size and spatial structure characteristics of the internal natural fractures of the marble samples,fractures are basically divided into 4 types,namely,single fracture,parallel fracture,intersectant fracture and mixed fracture.The mechanical properties of naturally fractured rocks(4 types)are analyzed and compared with those of intact rock samples(without natural fractures).Experimental results indicate that failure characteristics of fractured rocks are appreciably controlled by fracture distribution or fracture patterns.In comparison with intact rocks,the failure of fractured marbles is a locally progressive failure process and finally rocks fail abruptly.Statistically,the uniaxial compressive strengths(UCSs)of rocks with single,parallel,intersectant and mixed fractures are 0.72,0.69,0.59 and 0.46 times those of the intact rocks,respectively.However,the elastic modulus of the fractured Yantang marbles is generally not different from that of intact rocks.But the elastic moduli of Baishan marble with single,intersectant and mixed fractures are 0.61,0.62 and 0.45 times those of intact rocks,respectively.Experimental results also indicate that WET of fractured marbles is generally smaller than that of intact marbles,which implies that rockburst intensity of fractured marble in field may be controlled to some extent.In addition,the bearing capacity of surrounding rocks is also reduced,thus the surrounding rocks should be supported or reinforced timely according to practical conditions.