## 9 Discussion of the Test and Obtained Results  
Even though only three samples have been tested in this research study, still, several interesting observations can be made:  
* Estimating UCS with empirical methods resulted in a very large variation. Based on 32 empirical methods, calculations yielded results ranging from \"\(-40\)\" to \"+330\" MPa (\"-\" means tension, and \"+\" means compression) for the three granite samples in this research with an expected UCS of about 200 MPa. One probable cause could be that each empirical method is suitable within the limitations of the database that was  
Figure 17: Sample C—comparison between triaxial method (linear and non-linear) with other methods as listed in Table 1. The continuous red lines are the \(\pm 15\%\) lines of the “True-UCS”. used to build such empirical formulae. It seems that method (1) produced reasonable estimates compared to the \"True-UCS\" for all three samples in this research. The rest of the methods, including the ANN model, failed to give results for all three samples that fit to the \"True-UCS\";
* On the other hand, the \"Estimated-UCS\" values based on the triaxial test were close to the \"True-UCS\" for all three samples in this research. The error between the \"Estimated-UCS\" based on triaxial tests and the \"True-UCS\" is within 15% (when using linear fitting equations) and within 5% (when using non-linear fitting equations). It is obvious that non-linear fitting equations provided results with much smaller error than the linear fitting for the test in this research. This may be due to the persistent behaviour of the Iddefjord granite;
* The reliability of the \"Estimated-UCS\" based on the results from the triaxial test can be evaluated by studying the behaviour of the tested rock sample and the obtained rock strengths at different confinements. Normally, a better coefficient of determination (R\({}^{2}\)--closer to 1) indicates a more reliable \"Estimated-UCS\";
* The triaxial test performed in this research is triaxial test Type II. The method can also be applied for triaxial test Type III as the strength envelope is built for each individual rock sample. The use of results from triaxial test Type I may reduce the accuracy of the \"Estimated-UCS\" as test Type I is performed on different rock samples, and the inhomogeneity between the samples will have a negative impact on the accuracy of the calculation process;
* It is noted that the triaxial test and the UCS test might be different in the end effects, frictional constraints, alignment of the sample, failure mechanisms, loading rate, and loading path. However, if the triaxial test and UCS test follow a certain standard or method (ISRM's suggested method for example), then the \"Estimated-UCS\" is expected to be comparable to the result from a conventional UCS test. As stated in this study, the NTNU/SINTEF laboratory has a comprehensive UCS database (which was obtained by using conventional UCS tests) for Iddefjord granite. The \"Estimated-UCS\" values obtained from the triaxial test data were compared to the database and found reasonable;
* It is necessary to mention again that the triaxial test procedure in this research study was not conventional. The first stage of the triaxial tests in this research (with zero confinement) was performed to facilitate the comparison between the \"True-UCS\" and \"Estimated-UCS\" on the same sample in order to demonstrate the reliability of the method. In a normal triaxial test Type II, the test will always start with a certain confinement. The zero-confinement step in our test procedure may cause some disturbance to the rock samples before carrying out the subsequent non-zero-confinement steps. This is similar to the limitation of the triaxial test Type II itself--after every testing step, the sample responds with a certain disturbance.