# Effects of Freeze-thaw Cycles on the Mechanical Properties and Microstructure of a Dispersed Soil
## 2 Materials and Methods
### Testing Methods
#### 2.3.2 Identification of Dispersibility of the Soil Samples  
As a particular type of soil, the dispersibility of dispersed soils cannot be determined by using a single traditional index or test; it is generally necessary to use a variety of identification tests to perform a comprehensive determination. In this research, the soil sample dispersion characteristics were assessed through the pinhole, crumb, and double hydrometer techniques. To ensure the robustness of the obtained results, concurrent assessments were conducted for each of the aforementioned tests. The procedures for each test are elucidated as follows.  
The pinhole test is a reliable method for clay dispersion identification. In the pinhole test, the soil specimens were compressed into cylindrical samples measuring \(\Phi\) 37 mm \(\times\) 38.1 mm. Before the test, a small cone was pushed into the top of the piece, and a 1 mm pinhole was formed by penetrating each sample with a needle (Figure 2g). The pinhole test was then performed under the pressure of a 50 mm water head, and distilled water was used. During the test, the liquid flow through the pinhole was measured for a certain period, and the color and turbidity of the liquid flow were observed. The pinhole diameter of the piece after erosion was measured using a graduated scale to determine the change in the pinhole size of the samples prior to and following the test. Finally, the soil samples were classified into different dispersibility classes according to the pinhole effluent's final pore diameter, final flow rate, and turbidity [29].  
The crumb test, which involves observing the degree of crumb formation in soil samples immersed in stagnant water, was conducted to assess the samples' dispersibility. In the crumb test, a 15 mm sided cube was submerged in a beaker filled with 250 mL of distilled water. A timer was initiated to monitor the alterations in the soil samples when placed in water. Throughout the actual test, the beaker remained undisturbed. The outcomes of the crumb test were utilized to categorize the soil's dispersibility classes [30].  
The test procedure and data processing for the UCS test in this study were performed according to the guidelines outlined in GB/T50123-2019 [22]. The experiments were carried out utilizing a YYW-2 strain-controlled pressure instrument (Figure 2c). At least three soil samples with a size of \(\Phi\) 39.1 mm \(\times\) 80 mm were prepared for each freeze-thaw cycle stage to guarantee the precision of the experiment. The unconfined compressive strength of each soil sample was determined from the shape of the stress-strain curve. To visually assess the impact of freeze-thaw cycles on the strength and stiffness of the soil samples, we used the strength decline percentage (_SDP_) and modulus decline percentage (_MDP_) to evaluate the soil samples [31]. The variations in the strength decline percentage (_SDP_) and modulusdecline percentage (_MDP_) under different numbers of freeze-thaw cycles were determined according to Equations (1) and (2), respectively:  
\[SDP=\frac{q_{u0}-q_{un}}{q_{u0}}\times 100\% \tag{1}\]  
\[MDP=\frac{E_{0}-E_{n}}{E_{0}}\times 100\% \tag{2}\]  
_SDP_ and _MDP_ represent the percentage reduction in strength and elastic modulus, respectively, after undergoing n freeze-thaw cycles. The parameters \(q_{un}\) and \(q_{u0}\) represent the unconfined compressive strength values of the soil after undergoing n freeze-thaw cycles and before any exposure to freeze-thaw cycles, respectively. Similarly, \(E_{n}\) and \(E_{0}\) indicate the modulus values after n freeze-thaw cycles and prior to any freeze-thaw cycle exposure.