We present a newly developed monitoring system to directly visually observe the shear behavior of Shirahama sandstones under triaxial compression testing. The proposed visual monitoring system contains a commercially available webcam and a pressure-resistant steel housing device. The webcam records the video clip of the rock specimen surface during the triaxial compression test. The recorded video frames and their associated digital image correlation (DIC) results allow a better understanding of the evolution of the strain fields and fracture development. The implementation of the proposed monitoring system is simple, safe, and inexpensive, but allow new data to be measure and provides new insights into the progressive shear behavior under triaxial compression loads.
Triaxial compression testing of rock samples provides fundamental information for understanding the deformation and fracture behavior of rock mass, which is related to underground engineering applications such as tunneling, nuclear waste disposal, and carbon dioxide sequestration. Triaxial compression tests have been widely conducted and are widely accepted as a reliable test method and measurement system because of their simplicity, robustness, and repeatability (ISRM 1983; Paterson and Wong 2005). However, in general, triaxial compression test of rock samples are performed in the steel pressure vessel, and it is difficult to visually capture and observe the behavior of rocks, as in uniaxial compression tests.
We recently developed a new measurement system to directly visually observe the behavior of rock specimens from the inside of the pressure vessel of the triaxial test apparatus. This newly developed measurement system exhibited three primary advantages compared to the other conventional measurement system: (i) the measurement system allows direct observation of the mechanical behavior of the rock specimen from inside the pressure vessel under confining pressure, (ii) the measurement system is inexpensive. It requires only a commercially available digital camera and the simple steel housing, and (iii) the measurement system is safe and can be installed without any modification of the existing triaxial apparatus.
