Abstract
Understanding the effect of water saturation on dynamic failure of rocks is of great importance to tunnel excavation at water‐rich coal mines and prevention of rock bursts by water injection. Dynamic Brazilian disc tests are performed to study mechanical behaviour of sandstones in this paper. The results indicate that water saturation significantly weakens the dynamic tensile strength of sandstones and increases the specimen strain at which the specimen fails. The damage degree of sandstones reduces gradually with increasing water contents. Failure of the sandstone specimen includes the crack initiation at the center of the specimen, macroscopic crack propagation, and stretch of the macroscopic crack through the specimen. In addition, parallel macroscopic crack propagation is found in the specimen with a low water content. From the observation of fracture sections, microstructures are compact in the specimen with high water contents. This is due to the swell of the kaolinite in the specimen after water saturation. The failure mechanism of microstructures is typical brittle failure in the specimen with a high water content, whereas ductile fracture is found in the specimen with a low water content. Different failure processes of microstructures lead to the differences between mechanical properties and macroscopic failure characteristics of the specimens with various water contents.
Highlights
Mechanical properties of coal and rock masses in underground coal mining are affected by many factors, such as water
For the four strain rates considered in this study (ε_ 53.04 s− 1, 73.16 s− 1, 89.04 s− 1, and 104.87 s− 1), the tensile strength decreases from 5.75 MPa, 8.32 MPa, 10.41 MPa, and 12.73 MPa to 4.44 MPa, 6.51 MPa, 7.06 MPa, and 9.50 MPa, respectively, if the water content increases from 0.31% to 1.09%. e water in the specimen leads to the swelling and weakening of kaolinite composition. is reduces the frictional force between particles and weakens the deformability of the specimen
Dynamic Brazilian disc tests are performed on sandstone specimens with different water contents in the split Hopkinson pressure bar system in this paper. e failure processes and microstructure failure in the sandstone specimens with different water contents are observed by using a highspeed camera and the scanning electron microscope system, respectively. e results of dynamic Brazilian disc tests show that, under a given strain rate, both the specimen strain at which the compaction stage ends and the specimen strain at which the specimen fails increase with a higher water content, whereas the tensile strength reduces in a linear tendency as the water content increases
Summary
Mechanical properties of coal and rock masses in underground coal mining are affected by many factors, such as water. Mechanical and physical properties of coal and rocks change remarkably in states of high water contents due to the existence of hydrophilic substances in these materials. E coal and rock masses under this condition exhibit totally different mechanical behaviour from that under dynamic loading. Zhou et al [29] carried out Brazilian disc tests on saturated sandstones with the SHPB system and concluded that tensile strength of the sandstone specimen decreases with a higher water content. More efforts are still needed to disclose how water saturation influences tensile properties of rocks under dynamic loading conditions. Brazilian disc tests on sandstone specimens with different water contents are performed in the SHPB system with the purpose of understanding the effects of water saturation on dynamic tensile failure of the sandstone specimens. E failure mechanism of sandstone specimens under dynamic tensile loading is studied
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