## 4 Results: Monitoring and Slope Stability  
### Site Preparation and Sensor Planning  
The remote monitoring instruments used consisted of: PVT piezometers to monitor changes of the groundwater table with built-in temperature sensor, inclinometers (installed on the middle of the slope) to monitor slope deformations (Figure 11c), dielectric water potential sensors, Decagon MPS-6 (Decagon devices, Pullman, WA, United States) [20], see Figure 11d. The global deformations of the slope were assessed by Radar/Lidar system (Figure 11e). Some of these instruments were connected to a re-programmed datalogger (KISTEC, jinju, Korea) [21] with a data transfer unit, see Figure 11f. The readings were sent to NGI offices using wireless wi-fi router. A good understanding of the causes of slope failure in a cold region is essential to make a proper monitoring plan. In a cold region, the governing factors of slope failure are severe weather conditions, freezing-thawing effects on the slope, an increase of water content, pore pressure, and the rising of groundwater table. The slope stability monitoring should be designed to measure and detect those factors effectively. The following sensors were selected for slope stability monitoring at the identified critical slope, see Table 3:  
Figure 10: (**a**) Temperature distribution in 2017–2018 and (**b**) difference in the factor of safety considering freeze–thaw influence. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Sensors** & **No. of Sensors** & **ID** & **Depth m** & **Locations** \\ \hline \multirow{6}{*}{PVT (Piezometer)} & \multirow{3}{*}{4} & P-1 & 4.5 & Top of the slope \\ \cline{3-5}  & & P-2 & 8.55 & Top of the slope \\ \cline{3-5}  & & P-3 [1] & 5 & Bottom of the slope \\ \cline{3-5}  & & P-4 [1] & 3 & Bottom of the slope \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Planning of sensors on the slope at Oysand. Figure 11: Test slope at \(\mathcal{O}\)ysand Trondheim Norway: (**a**) 37 degree man-made test slope; (**b**) Layers of test slope; (**c**) inclinometer installation; (**d**) MPS-6 sensors; (**e**) Lidar system; (**f**) data logger box. \begin{table}
\begin{tabular}{c c c c c} \hline
**Sensors** & **No. of Sensors** & **ID** & **Depth m** & **Locations** \\ \hline \multirow{4}{*}{Temperature sensors (PVT)} & \multirow{2}{*}{4} & P-1 & 4.5 & Top of the slope \\ \cline{3-5}  & & P-2 & 8.55 & Top of the slope \\ \cline{3-5}  & & P-3 \({}^{1}\) & 5 & Bottom of the slope \\ \cline{3-5}  & & P-4 \({}^{1}\) & 3 & Bottom of the slope \\ \hline Integrated sensor pack (wc, temperature, tilt) & \multirow{2}{*}{2} & I-1 & 1 & Top of the slope \\ \cline{3-5}  & & I-2 & 2 & Halfway down the slope \\ \hline \multirow{4}{*}{Suction sensors (MPS-6)} & \multirow{4}{*}{10} & S-1, S-2 & 0.25, 0.5 & Three-quarters of the way \\ \cline{3-5}  & & S-3, S-4 & 0.5, 0.25 & Halfway down the slope \\ \cline{3-5}  & & S-5, S-6 & 0.5 & Westernmost hole at the top \\ \cline{3-5}  & & S-7, S-8 & 0.7 & Centre hole at the top of \\ \cline{3-5}  & & S-9, S-0 & 1.05 & Easternmost hole at top of \\ \cline{3-5}  & & S-9, S-0 & 1.05 & the slope \\ \hline Lidar/Radar & 1 set & - & - & 10 m distance at the bottom \\ \hline Air temperature, hygrometer & 1 set & - & - & Top of the slope \\ \hline Precipitation measure & 1 set & - & - & Top of the slope \\ \hline \end{tabular} \({}^{1}\) Two out of four PVTs will be installed afterwards.  
\end{table} 
Table 3: _Cont._Integrated sensor packs, including water content sensors, temperature sensors, and inclinometers, were placed at two locations. The dielectric water potential sensors, Decagon MPS-6 with temperature sensors were installed at five locations. The range of soil suction is \(-9\) to \(-100\),\(000\) kPa, resolution was \(0.1\) kPa, and accuracy was \(\pm\)\(10\%\) of reading \(+2\)kPa from \(-9\) to \(-100\) kPa. The temperature range was \(-40\)\({}^{\circ}\)C to \(60\)\({}^{\circ}\)C (resolution \(0.1\)\({}^{\circ}\)C, accuracy \(\pm\)\(1\)\({}^{\circ}\)C).