## 3 Experimental Study
### Experiment Procedure  
The tests for thermal conductivity were conducted based on the transient method, ASTM D5334-14, with a needle probe from the East 30 Sensors Company (Pullman, WA, USA). The transient method has the advantage that, owing to its short test duration, the moisture migration in the materials can be minimized compared to that in the steady state method [21]. Figure 2 shows a schematic of the experiment setup [22]. The length of the needle probe was 60 mm and its aspect ratio was larger than 20. The dimensions of the needle probe were sufficient to generate a radial thermal transfer. The needle probe consisted of a heating wire to raise the temperature of the materials and a thermocouple to measure the change in temperature. The heating wire was connected to a DC (direct current) power supply and an average meter. The thermocouple was connected to a data logger for recording the temperature at every second during the tests.  
The specimens were placed in a transparent polyethylene cylinder with a 10.1 cm inner diameter and 9.3 cm height, and the needle probe was inserted vertically into the materials (Figure 2). They were kept in a room at a constant temperature until the temperature in the specimens became stable (\(24\pm 1\,^{\circ}\mathrm{C}\)). After setting up the specimens, heat was generated by heating the wire for 1 min. The curve of temperature change versus time at the natural logarithm scale was plotted using the data measured during the heating process. The linear relationship between temperature and time can be used to estimate the thermal conductivity \(\lambda\) of the specimen using Equation (10):  
\[\lambda=-\ \frac{I^{2}\times R_{m}}{4\pi}\times\frac{\ln\left(\frac{t_{2}}{ T_{1}}\right)}{T_{2}-T_{1}}\times\frac{1}{L}, \tag{10}\]  
where \(\lambda\) is the thermal conductivity of the specimen (W/mK), \(I\) is the electrical current (A), \(R_{m}\) is the electrical resistance of the heated wire (70 \(\Omega\) in this study), \(T_{1}\) and \(T_{2}\) are the temperatures (K) at times \(t_{1}\) and \(t_{2}\), respectively, and \(L\) is the length of the needle (m).  
Through compaction of the specimens, there was an attempt to achieve a uniform density, and as a result, the initial void ratio of the specimens was between 0.600 and 0.609 for all cases (Figure 3). To change the porosity of the samples, and eventually explore the impact of the porosity and the  
Figure 1: Particle size distributions.  
proportion of fine particles on the thermal conductivity during the tests, the specimens were loaded one-dimensionally in the cylinder at 12.5 to 1600 kPa with a constant load incremental ratio (\(LIR=1\)), using a GeoJac automated loading system (Geotechnical Test Acquisition & Control). The loading interval was 30 min, which was determined through preliminary tests (most of the settlements were completed within 2 to 5 min). At the end of each loading step, the thermal conductivity was measured three times at different specimen locations, and the measurements obtained were very close. This paper presents the average of the three measurements.  
Figure 3: \(Cont\).  
Figure 2: Schematic of experiment setup [22] (copyright, 2015, American Society of Civil Engineers).