## 3 Results and Discussion
### Acoustic-Assisted UCS Experiments  
Experimental series A, i.e., acoustic-assisted UCS experiments, consists of a total of 14 UCS experiments conducted on different rock types present in the Kizildere geothermal field (Table 2). Table 8 presents an overview of the static elastic parameters obtained from the UCS experiments. The axial stress-strain relationships for all UCS tests performed are shown in Figure 4.  
The laboratory results clearly indicate that limestone sample TS2-SZL2 is the stiffest material assessed; the steep axial stress-strain slope between 0.2-0.3% strain yields a high Young modulus (E) of 52.9 GPa. On the other hand, it is apparent that the tested siltstone cores are the weakest, i.e., softest, samples studied. The very gentle axial stress-strain slopes (E = 3.8 GPa) suggest that the material underwent a relatively substantial amount of deformation before rock failure occurred. Figure 4: Axial stress–strain behaviour from the 14 UCS experiments performed. For some UCS tests, unloading cycles were also performed. For the limestone samples (black trends in bottom graph): note the variation in ultimate strength and stress–strain slope due to heterogeneity as a result of diagenesis. \begin{table}
\begin{tabular}{c c c c c c c c c c c c c c c} \hline \hline
**UCS** & \multicolumn{6}{c}{**Experiment**} \\ \hline Type & \multicolumn{2}{c}{Calcstic} & \multicolumn{2}{c}{Mandle} & \multicolumn{2}{c}{Limestone} & \multicolumn{2}{c}{Quartz} & \multicolumn{2}{c}{Stitstone} & \multicolumn{2}{c}{Quartz} & \multicolumn{2}{c}{TDS2-} & \multicolumn{2}{c}{TDS2-} & \multicolumn{2}{c}{TDS2-} \\ Code & TDD2- & TDI2- & TDI2- & TDI- & TDI- & TSD2- & TSD2- & TDD20- & TDD20- & T- & T- & T- & T- & T- & T- \\ Climate strength & & CS4 & CS5 & M2 & M3 & SZ12 & SZ14 & SZ15 & QZ-1 & TDD20- & QZ-2 & T- & B1-3 & QMS1 & \\ (MPa) & 44.4 & 45.6 & 57.0 & 51.1 & 145.4 & 72.5 & 43.7 & 82.0 & 48.3 & 88.8 & 15.5 & 14.5 & 75.4 & 22.2 \\ Static Young modulus & 22.2 & 26.5 & 40.1 & 29.5 & 52.9 & 33.9 & 27.9 & 35.0 & 38.5 & 38.0 & 3.8 & 3.8 & 43.1 & 10.5 \\ Static rotation (\(\cdot\)) & 0.14 & 0.14 & 0.17 & 0.14 & 0.9 & 0.19 & 0.09 & 0.11 & - & 0.17 & 0.27 & 0.23 & 0.18 & 0.16 \\ Bulk modulus (GPa) & 10.3 & 2.3 & 20.3 & 13.7 & 80.2 & 18.2 & 11.3 & 15.0 & - & 19.2 & 2.8 & 2.3 & 22.4 & 5.1 \\ Shear modulus (GPa) & 9.7 & 11.6 & 17.1 & 12.9 & 19.0 & 14.2 & 12.8 & 15.8 & - & 16.2 & 1.5 & 1.5 & 18.3 & 4.5 \\ \hline \hline \end{tabular}  
* During this experiment the extensence chain, used to monitor the radial strain, failed. Hence, the static Poisson ratio, and indirectly the bulk and shear moduli, could not be obtained.  
\end{table} 
Table 8: Static elastic parameters obtained from the UCS experiments. The steep axial stress-strain trend, at strain values of >0.2%, related to limestone sample TS2-SZL2, suggests that the material experienced relatively little axial deformation prior to failure at \(\sigma_{1}\) = 145.4 MPa. This implies a somewhat more brittle-like behaviour of the particular limestone core compared to the other rock samples. The latter is supported by the post-failure fracture pattern observed in the sample (Figure S1 in Supplementary Materials). Figure S1 indicates axial splitting for the limestone and quartzite cores, an indication of brittleness, whereas the other rock samples (marble, calcschist, quartzschist, mudstone, and siltstone) show a clear shear failure pattern. The degree of axial splitting amid the limestone and quartzite cores differs and appears to be related to their porosity: presence of axial splitting patterns increases with decreasing porosity. The results shown in Table 8 and Figure 4 reveal large variations among the three limestone samples assessed. Though all limestone cores were drilled from the same block, large discrepancies in static elastic parameters are observed. Most probably, a high level of heterogeneity, due to diagenesis processes and the presence of fossils, within the limestone yields different axial stress-strain relationships for the three samples investigated.