抄録
The aim of this study is to clarify the fracturing process of granodiorite, known for its unstable behavior in-situ, under various conditions. A stiff, closed-loop servo-controlled testing machine developed recently was used to control the unstable brittle failure and to observe the time dependent fracture under uniaxial compression precisely. The tests of the constant deformation rate, the creep, the relaxation and the cyclic loading were conducted along with the A. E. measurements.
The results obtained are summarized as follows: (1) The granodiorite is not stable even in the region below the load vs. axial deformation curve. (2) From the results of the A. E. measurements, the microfracturing is mainly of a tensile crack type which occurs along the axis of the applied load. (3) The pattern of the microfracture accumulation characterizes the inelastic behavior of the rock specimen and the main failure. (4) The dilatancy hysteresis due to the radial strain hysteresis and the absence of A. E. in the unloading cycle seem to show that only the tensile microfacturing contributes to the dilatancy hysteresis.
The main feature of these observations is supported by a lack of the shear-related microfracturing except those which might occur just under the platen. From this point of view, to obtain the complete load vs. axial deformation curve, the radial deformation instead of the axial deformation should be selected for the feedback signal of the servo-control system. The complete load vs. axial deformation curve was obtained in this way, and this curve seemed to give the criterion of the failure of granodiorite. It is also concluded that the granodiorite used in these experiments can be classified as the“class-II”type rock defined by Wawersik and Fairhurst.
