# Study on the Influence of Moisture Content and Void Ratio on the Disintegration of Red Clay
## 3 Microstructure Analysis of Red Clay
### Nuclear Magnetic Resonance Test  
In order to obtain the water molecule existence state and pore size characteristics of reshaped red clay with different structural properties, the distribution of water molecules in the natural state and saturated state of each soil body was detected using the PQ-001-Mini-NMR nuclear magnetic resonance analyzer from Suzhou Newmai Company. The distribution law of water molecules with moisture content and void ratio and the pore structure characteristics of each soil sample were obtained. Nuclear magnetic resonance (NMR) technology is a non-destructive detection technique used to study the content and distribution of hydrogen nuclei in materials. It is characterized by its accuracy, efficiency, and continuity, and the reliability of its test results is very high. The principle can be summarized as follows: First, a main magnetic field is applied to the soil sample to force the hydrogen nuclei to deviate and lose balance. Then, the interference of the main magnetic field is stopped, allowing the proton group to gradually return to equilibrium. The free induction decay (FID) curve of the nuclear magnetic signal is measured, and the transverse relaxation time distribution curve of the soil pore water is obtained through Fourier transformation. The peak area below this curve represents the content of water molecules in the soil sample; that is, the transverse relaxation time  
Figure 3: Scanning electron microscope images of some red clay soil samples. distribution curve can reflect the distribution characteristics of pore water in the rock and soil medium. According to the KST theory:  
\[\frac{1}{T_{2}}=\frac{1}{T_{2B}}+\frac{1}{T_{2S}}+\frac{1}{T_{2D}}=\frac{1}{T_{2B} }+\frac{\rho_{2}S}{V}+\frac{1}{T_{2D}} \tag{3}\]  
In the equation, \(T_{2B}\) represents the free relaxation time, in milliseconds; T\({}_{2S}\) is the surface relaxation time, in milliseconds; \(T_{2D}\) is the molecular diffusion relaxation time, in milliseconds; \(\rho_{2}\) is the transverse relaxation rate, which is related to the physical and chemical properties of the soil particle surface; \(S\) and \(V\) represent the surface area and volume of the pore where the pore water is located, respectively. For pore water in the soil, \(T_{2B}\) is much larger than \(T_{2S}\) and \(T_{2D}\), so the effects of \(1/T_{2B}\) and \(1/T_{2D}\) on T\({}_{2}\) can be ignored; that is,  
\[\frac{1}{T_{2}}=\rho_{2}\cdot\left(\frac{S}{V}\right) \tag{4}\]  
Before conducting nuclear magnetic resonance (NMR) testing, dry red clay samples with initial moisture contents of 24%, 26%, 28%, and 30% were prepared. After being sealed for 48 h, 12 sets of reshaped samples with structural characteristics were compressed. To eliminate the influence of ferromagnetic materials on NMR experiments, a polytetrafluoroethylene ring cutter with an inner diameter of \(\varphi=40\) mm and a height of h = 20 mm was used. The NMR test first tested the samples in their natural state to obtain the presence of water molecules. Then, the former soil samples were saturated for 24 h using the vacuum saturation method, allowing water molecules to fill all the pores. At this point, the NMR results reflect the moisture distribution in the saturated soil samples, indicating the distribution of micro-pores in the soil. Figure 4 and Table 2 show the results of the NMR tests on various saturated red clay samples. When e = 1.0, all soils exhibit a triple-peak structure. The initial T\({}_{2}\) value of the main peak in the nuclear magnetic attenuation curve gradually decreases from 0.0383 ms to 0.0059 ms as the water content increases. The small pore size gradually shifts to the left, and the peak width decreases from 3.5317 ms to 3.0341 ms. The main peak area decreases from 1252.88 to 1202.95, and the volume of small pores slightly decreases as the moisture content increases, indicating a tighter contact between soil particles.