Development and application research of a compression shear fracture test device for multi-size rock

It is necessary to test the mechanical properties of crack initiation, crack propagation and slip process of fracture surface for multi-size rock under compression shear composite stress. A multi-dimensional rock compression shear fracture test device has been developed, which can apply compression load and shear load synchronously or successively on biaxial. In comparison, some deficiencies exist in existing related equipment, such as the sample size that can be tested is small and single specification, the maximum test force is not high, etc. The developed device is mainly composed of frame, loading and force measuring mechanism, sample box, sample positioning mechanism, electro-hydraulic servo control system, operation software, etc. Cube sample, cuboid sample with the same width or equal ratio can be tested in the size range of 50–300 mm. The maximum normal load is 1 500 kN and the maximum tangential load is 3 000 kN. The stiffness of the test loading system composed of frame and loading mechanism was analyzed. The transition condition from the load control before rock fracture to the displacement control during the slip process of the fracture surface was discussed. The load accuracy calibration of the test device has been carried out. The results show that the indication accuracy reaches 0.5% in the load test range of 2%–100%. A preliminary experimental study on the multi-size cuboid granites, with an aspect ratio of 2∶1, have been carried out. The results are as follows: Firstly, the minimum and large normal load were applied separately to granite samples. Test accuracy and stable loading have been showed by obtained relationship curves of shear load with time or displacement. Then, the test values of two tangential load cell, located at the loading end and support end of the sample box, were obtained. During the initiation and propagation of rock cracks, it is found that the measured values were not synchronized through comparative study. Then, the peak shear load increased with the increase of normal load when different normal loads were applied to the same size samples. Finally, when the normal stress of 10 MPa and 20 MPa was applied to three continuous size samples respectively, the peak shear stress was a nonlinear relationship with the increase of samples size. © 2022 Academia Sinica. All rights reserved.