## 3 The Performed Test Procedure and Apparatus
### The Various Steps of the Test  
To demonstrate the reliability of this method, the triaxial test and the uniaxial test were carried out with the same rock sample to facilitate a consistent comparison. This required a thoughtful test procedure. At first, an attempt was made to carry out triaxial test Type II at three loading steps, without reaching the point of failure (point C in Figure 2b). After these steps, the sample was tested without confinement until failure to obtain the UCS. It was found in this test that the sample was significantly disturbed after the three loading steps during the initial triaxial test. Indications of fractures were observed at the surface of the rock core. Due to this disturbance, it was no surprise that the result of the consecutive UCS test was quite low--reaching only about 60% of the expected UCS (taken from NTNU/SINTEF's UCS database of Iddefjord granite). A second attempt was executed in a procedure where the triaxial tests were run with several loading steps, starting the procedure with zero confinement. The results obtained by this test procedure complied better with the UCS values that can be obtained from the database of the NTNU/SINTEF's laboratory (database of the UCS obtained by conventional uniaxial test). The test procedure carried out for testing in this paper follows in principle the triaxial test Type II, described in ISRM's recommendations [2] with one deviation as the triaxial test procedure applied here starts with zero confinement. After the first step (the zero-confinement step), the triaxial test continued with several confinement levels. In this paper, the selected confinement levels were \"Step-0 MPa\", \"Step-2 MPa\", \"Step-5 MPa\", \"Step-10 MPa\", \"Step-15 MPa\", and \"Step-20 MPa\". The range and levels of confinement were selected based on experience obtained from extensive testing on Iddefjord granite and cover the complete behaviour of the Iddefjord granite (non-linear in the lower confinement and more linear in the higher confinement range). The following concerns related to the test procedure must be considered:  
* In \"Step-0 MPa\" in this test, the indication of corresponding peak strength is accurately monitored with no or minimum disturbance to the sample. This is achieved by high-frequency readings with clear and continuous plotting of the stress-strain curve, \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline \multirow{2}{*}{**Sample**} & **Diameter** & **Height** & **Weight** & **Density** & **Sound Travel** & **V\({}_{\text{p}}\)** & **n\({}_{\text{e}}\)** & **Schmidt** & **Converted** \\  & **(mm)** & **(mm)** & **(g)** & **(kg/m\({}^{3}\))** & **Time** (ms)** & **(\%)** & **(\%)** & **Hammer** & **R\({}_{\text{n}}\)(L)** \\ \hline A & 48.39 & 124.06 & 598.95 & 2625 & 23.8 & 5213 & 0.44 & 74 & 54 \\ B & 48.35 & 119.21 & 576.50 & 2634 & 24.3 & 4906 & 0.44 & 63 & 45 \\ C & 48.34 & 119.20 & 576.71 & 2636 & 24.2 & 4926 & 0.44 & 63 & 45 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Some additional measurements for the samples. strict control of the speed of loading (based on the axial or radial strain rate), and an experienced operator;
* In principle, three loading steps after \"Step-0 MPa\" are sufficient but in our tests, five loading steps were used with selected confinement levels. The purpose of the five loading steps and the selected confinement levels is (a) to have more points for constructing the peak strength envelope, and (b) to observe the rock behaviour in a wide range of confinement. All tests were controlled by an axial strain rate of 240 micro-strains per minute. From our experience with this rock, it is known that the sample is hard and brittle. Thus, the rate of 240 \(\mu\epsilon/\)min was selected so that laboratories could have enough time to observe and catch the peak loads in every step. A lower rate can be used but it will cause the test to be time-consuming. The rate of 240 \(\mu\epsilon/\)min is good for the purposes.