## 5 Changes in Rock Properties with Increasing Freeze-Thaw Cycle
### Changes in Physical and Mechanical Properties of Rocks
#### 5.3.2 Changes in Rock Strength  
In order to obtain the standardized strengths of the rocks, samples need to be prepared in a standard size, such as core or block samples. The preparation of homogeneous rock blocks or cores is almost impossible due to their inherent heterogeneous properties formed in nature. Especially, the weathered rocks are more difficult to fabricate into homogeneous standardized block or core sizes compared with less-weathered rocks.  
In reality, measurement of rock strength inherently has a high uncertainty because of flaws or small cracks inside the rock and relative orientations between major flaws and loading directions. The extent of weathering, fissures, and the distribution of minerals act as factors introducing uncertainty to rock hardness [25; 26; 27]. Many researchers found the decrease of rock strength reduction with increasing freeze-thaw weathering from different experiments [6; 39; 40; 41; 42]. However, because there are large deviations in rock strength also depending on the sampling location, a large number of repetitive experiments of rocks is required to estimate the general UCS of rocks. Consequently, it is not easy to investigate changes in rocks in their natural state by studying artificial changes in rock strength due to freeze-thaw. However, to minimize the effect of inherent non-homogeneity on rock characteristics of freeze-thaw tests, rock samples with relatively consistent mineral composition and extent of fissures were collected for experiments in this study. Specifically, in order to minimizing uncertainty factors of the uniaxial compression test, we prepared test samples by moulding rocks that were homogeneous and, as far as possible, from nearby locations. Because samples after failure cannot be reused in the uniaxial compression test, we fabricated a large number of samples with similar baseline properties.  
To reduce the uncertainties of UCS, we measured UCSs of three rock specimens for each freeze-thaw cycle and use their average to capture changes in UCS with increasing freeze-thaw cycle. Figure 8 shows the changes in UCS during 900 freeze-thaw cycles of rocks in the study area. UCS measurements were taken from three rock specimens in each group every 150 cycles, and the coloured points on the graph show the mean UCS of the three specimens. As mentioned earlier, due to the high uncertainty in UCS of rock, it is hard to capture clear decrease of UCS with increasing freeze-thaw cycle. The main reason would be the fact that identical rock specimens could not be used in UCS measurement.  
Figure 7: Distribution patterns of samples collected Locations A and B in Ny-Alesund.  
The results show an overall decreasing trend for hardness as freeze-thaw progresses, but there are large deviations in some measurement cycles. These deviations in UCS can be considered the result of inhomogeneity on the inside of the rocks [25; 26; 27]. The UCS of the rocks from Locations A and B decreased from 295 MPa at baseline to 256 MPa (reduction of approximately 13%) and from 227 MPa at baseline to 175 MPa (reduction of approximately 13%), respectively, after 900 cycles. The rocks from Location A showed a decrease in hardness of \(-0.0229\) MPa per freeze-thaw cycle, and the rocks from Location B showed a decrease of \(-0.0318\) MPa per cycle.