Time-dependent dilatancy for brittle rocks

This paper presents a theoretical study on time-dependent dilatancy behaviors for brittle rocks. The theory employs a well-accepted postulation that macroscopically observed dilatancy originates from the expansion of microcracks. The mechanism and dynamic process that microcracks initiate from local stress concentration and grow due to localized tensile stress are analyzed. Then, by generalizing the results from the analysis of single cracks, a parameter and associated equations for its evolution are developed to describe the behaviors of the microcracks. In this circumstance, the relationship between microcracking and dilatancy can be established, and the theoretical equations for characterizing the process of rock dilatancy behaviors are derived. Triaxial compression and creep tests are conducted to validate the developed theory. With properly chosen model parameters, the theory yields a satisfactory accuracy in comparison with the experimental results.

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 I1 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.