## 3 Results  
### \(T_{2}\) Spectra of Saturated Mixtures  
The \(T_{2}\) spectra of kaolinite-quartz and montmorillonite-quartz saturated mixtures are shown in Figure 2. The \(T_{2}\) values corresponding to the peak signal amplitude (\(T_{2P}\)) of kaolinite-quartz and montmorillonite-quartz saturated mixtures were different. The \(T_{2P}\) of kaolinite-quartz mixtures and montmorillonite-quartz mixtures ranged from 7.84 to 11.89 ms and 1.20 to 2.25 ms, respectively. Based on this, the dominant clay mineral could be roughly inferred from the \(T_{2}\) spectrum of saturated mixtures. Besides \(T_{2P}\), the whole \(T_{2}\) spectrum, including the maximum and minimum \(T_{2}\), shifted to the left as the clay content increased. According to Equation (3), the reason why \(T_{2}\) shifted to the left may have been due to the increases in the relaxation coefficient or decreases in the pore diameter of mixtures with increased clay contents. The peak signal amplitude increased as the clay contents increased in mixtures. According to NMR theory, the total area of the \(T_{2}\) spectrum, which is equal to the \(T_{2}\) total signal amplitude (\(A_{t}\)), is proportional to the weight of distilled water in mixtures. The distilled water was used to verify and determine this relationship. The relationship between \(A_{t}\) and the weight of distilled water is shown in Figure 3. The relationship between \(A_{t}\) and the weight of distilled water can be expressed by Equation (12). \[A_{t}=302.6\ \mathrm{m} \tag{12}\]  
Figure 3: The relationship between the \(T_{2}\) total signal amplitude and weight of distilled water. The line is the fitting line of the points. The Equation in the box is the Equation of the line. \(R^{2}\) indicates the correlation coefficient of the Equation. Figure 2: The \(T_{2}\) spectra of kaolinite-quartz and montmorillonite-quartz saturated mixtures. From left to right, curves with different colors and symbols with different shapes indicate \(T_{2}\) spectra of M100, M80, M60, M40, K100, K80, K60, and K40, respectively. According to \(T_{2p}\), \(T_{2}\) spectra could be divided into two groups. The group on the left and right are the \(T_{2}\) spectra of montmorillonite-quartz and kaolinite-quartz saturated mixtures, respectively. Here, \(m\) is the weight of distilled water and the correlation coefficient \(R^{2}\) of Equation (12) was 0.996. This indicated that the water content of mixture can be expressed by the \(T_{2}\) total signal amplitude of the \(T_{2}\) spectrum. The relationship between the \(T_{2}\) signal amplitude per unit weight of dry soil particles (\(A_{uw}\)) and clay content is shown in Figure 4. The \(T_{2}\) signal amplitude per unit weight of dry soil particles can represent the water content of per unit weight of dry soil (\(m_{uw}\)). The \(m_{uw}\) increased with an increase in clay content. The \(m_{uw}\) of montmorillonite-quartz was much bigger than in kaolinite-quartz mixtures. This is mainly because the double-layer structure of montmorillonite can hold more water. The relationships between \(A_{uw}\) and clay contents of kaolinite-quartz mixtures and montmorillonite-quartz mixtures can be expressed by Equations (13) and (14), and the \(R^{2}\) values of Equations (13) and (14) were 0.997 and 0.982. \[A_{um}=0.606 CC+35.22 \tag{13}\]  
\[A_{um}=1.581 CC+25.98 \tag{14}\]  
The geometric mean of \(T_{2}\) (\(T_{2 gm}\)) was defined by Equation (15):  
\[T_{2 gm}=\exp\left(\sum_{T_{2s}}^{T_{2s}}\frac{A_{i}}{A_{t}}\ln(T_{2i})\right) \tag{15}\]  
where \(T_{2s}\) and \(T_{2s}\) were the start and ending points of \(T_{2}\) spectra, respectively, which were \(T_{2s}\) = 0.01 ms and \(T_{2e}\) = 10,000 ms in this study; \(T_{2i}\) represents the individual values of \(T_{2}\); \(A_{i}\) is the cumulative signal amplitude at \(T_{2i}\); and \(A_{t}\) is the total signal amplitude of the \(T_{2}\) spectrum. The \(T_{2 gm}\) values of mixtures in the initial saturated state are shown in Figure 5. The \(T_{2 gm}\) decreased as the clay content increased.