A new Kumazawa-type rock deformation apparatus for improved stress measurements at confining pressures up to 2 GPa

Solid-medium deformation apparatuses of the Griggs type have been widely used for experimental studies of rock and mineral rheology at high pressure and temperature, but precise determination of differential stress has long been limited by friction within solid confining media. In the 1960s, Kumazawa independently developed a double piston-cylinder type deformation apparatus, which enables independent and simultaneous measurements of axial and confining forces using two pairs of load cells. However, the potential of this design for accurate stress measurements has not been fully explored. Here, we present a newly developed Kumazawa-type deformation apparatus designed for high-pressure (up to 2 GPa confining pressure) and high-temperature experiments. The apparatus allows simultaneous, real-time monitoring of axial stress and confining pressure, making it possible to quantitatively evaluate frictional stresses acting within solid sample assemblies. We review the design principles of the original Kumazawa apparatus, describe the methodology for stress measurement and correction, and report results from preparatory calibration tests and deformation experiments at room temperature using a newly developed system. The results demonstrate that frictional stress variations during pressurization, heating, and axial deformation can be resolved in real time, providing a basis for improving the reliability of differential stress measurements in solid-medium deformation experiments.