Study on the kaiser effect of rock-like materials under triaxial compression

本计画的目的是比较岩石类材料三轴压缩与单轴压缩之凯塞效应。对荻野凝灰岩进行了恒应变比三轴压缩试验，并测量了声发射活动。两个声发射传感器分别放置在上下加载板的内侧。主要包括以下三个系列的实验：（1）静水压作用下岩石声发射活动的观测。(2)三轴压缩下的凯塞效应。(3)通过在三轴压缩下预加载的大尺寸试样（PHI 100 mmX 200 mm）制成的小尺寸试样（PHI 30 X60 mm），使用单轴压缩试验来估计先前应力。实验结果和结论如下：（1）在静水压力（25、50 kgf/cm ^2）下，在不同的应力水平下观察到Kaiser效应。(2)用三轴压缩预压法估算三轴应力值的精度优于单轴预压法。特别是在最大剪应力方向钻孔的小试样，其Kaiser效应仍不令人满意。(3)由上述结果（2）可知，若主应力轴之一与试样轴重合，则用Kaiser效应估算单轴压缩试验的前期应力的精度在一定程度上是令人满意的。

The aim of this project is to compare the Kaiser effect of rock-like materials using triaxial compression test wit husing uniaxial compression test for the specimens pre-loaded under triaxial compression. Triaxial compression tests of Ogino Tuff were carried out under constant strain ratio and the AE activities were measured. Two AE sensors were put the inside of the upper and lower loading plates respectively. Three series of the experiments is as follows ; (1) Observation of the AE activities of rocks under Hydrostatic pressure. (2) The Kaiser effect under triaxial compression. (3) Estimation of the previous stress using uniaxial compression test by the small size specimens(PHI30X60mm) which were made of a large size specimen(PHI100mmX200mm) per-loaded under triaxial compression. These small size specimens were drilled to the three directions, that is, parallel, direct and 45 degree to the axis of the large size specimen.The experimental results and concluding remarks are as follows : (1) The Kaiser effects under hydrostatic pressure(25,50 kgf/cm^2) were observed at each stress level. (2) The accuracy of the estimated previous triaxial stress value using triaxial compressive pre-loading is better than the uniaxial one. Especially, the Kaiser effect of small specimen drilled to the direction of the maximum shear stress is not still satisfactory. (3) From the above results (2), if one the principal stress axis coincides with the speciemn axis, the accuracy of the estimated previous stress using the Kaiser effect on uniaxial compression test is satisfactory to a certain degree.