Experimental study on the strain rockburst of calcareous sandstone containing joint surface

Abstract

n order to study the failure law of rockburst phenomenon which happened frequently at rock mass with joints in deep fault zone of XinJiang water delivery tunnel. The field prediction and prevention of rockburst are guided, so that the construction process can be carried out safely and efficiently. The rockburst test of intact rock specimens and jointed rock samples was carried out by the modified true-triaxial apparatus (MTTA). Firstly, the high-speed photography and the acoustic emission (AE) system were applied to record the experimental process. The crack propagation and failure process were recorded and the acoustic emission signals of this process were analyzed. At the same time, the acoustic emission signals during crack propagation and failure are analyzed by wavelet analysis and fast Fourier transform (FFT). Then, the numerical simulation software named PFC was adopted to simulate the whole process of crack propagation in the rockburst of two kinds of specimens. And the simulation result is consistent with the experimental result. Some conclusions were drawn as follows: for calcareous sandstone with uniaxial compressive strength of 135.7 MPa, the rockburst of complete rock sample occurred at 129.6 MPa, and the joint rockburst occurred at 82.42 MPa. The more sudden time of joint rockburst was less than 0.1 s. During experiments, the main frequency band of complete sample is 62.5–250 MHz, while the main frequency band of jointed rockburst is lower and more concentrated at 62.5–125 MHz. The normalized energy proportion at the time of rockburst is focused at frequency part (62.5–250 MHz), and both types of rockburst energy exceed 80%, this signal can be used to judge the stage of stress adjustment in rocks. Therefore, it is considered that the existence of joint plane reduces the critical strength of rockburst and makes rockburst occur in a lower stress state. The distribution of the main frequency band can judge the extent of rock damage and help to predict rockburst disaster.