# Experimental Study on Mechanical Properties of Highway
## 2 Test Description  
Test equipment. The triaxial test system used in this test is produced by MTS company in Eden City, NC, USA, which mainly consists of the Landmark 370.25 triaxial testing machine, peripheral pressure control system, automatic data acquisition system, and other parts, as shown in Figure 1. The main technical specifications of the equipment are as follows: maximum axial force of 250 kN, maximum axial displacement of \(\pm\)88 mm, frequency range of 0-20 Hz, temperature range of \(-\)40 \({}^{\circ}\)C to +60 \({}^{\circ}\)C (with an error of \(\pm\)0.1 \({}^{\circ}\)C), and measurement accuracy of \(\pm\)0.01-0.03. It automatically collects data such as axial load, axial displacement, peripheral pressure, and time, and the measured data are accurate. Test method. The test soil was taken from a highway foundation in the Northwest China region. Its particle grading is shown in Figure 2, and the basic parameters are shown in Table 2. According to the results of the compaction test, the saturated water content of the specimen was 13.2%. In order to reflect that the soil is in an unsaturated state in engineering practice in Northwest China, the optimal water content was taken as the middle value. It floated up and down, and the final setting of the water content of remolded soil was 6%, 8%, 10%, and 12%. The dry density was taken as 1.9296 g/cm\({}^{3}\) according to 96% compaction. By using a special sample preparation instrument, the density of the sample can be controlled. The sample preparation instrument is composed of a hydraulic jack and a three-axis mold. The size of the three-axis mold is \(\mathcal{O}\)50 mm \(\times\) 100 mm. The density of the sample can be \begin{table}
\begin{tabular}{c c c} \hline \hline
**Author** & **Comments** & **Subgrade Type** \\ \hline [PERSON] et al. [13] & Three kinds of coarse fillers were studied experimentally, and the best filler for a high-speed railway subgrade was determined. & Railway \\ [PERSON] et al. [14] & The process and characteristics of soil temperature field and deformation in the freezing process of high-speed railway subgrade are discussed. & Railway \\  & The time domain and frequency domain response of vertical acceleration of & \\ [PERSON] et al. [15] & Harbin–Jiaxing high-speed railway in thawing period and freezing period & Railway \\  & are studied. & \\ [PERSON] et al. [16] & The frost resistance of railway subgrade filler in cold region was studied. & Railway \\ [PERSON] et al. [17] & Soil stabilizers are used to reinforce highway subgrades. & Highway \\  & The influence of additives on the physical and mechanical properties of highway & Highway \\  & subgrade is studied. & \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Literature comparison list. controlled by weighing the soil with the corresponding weight. The perimeter pressure was selected as 50 kPa, 100 kPa, and 150 kPa, according to the common horizontal stress range of the roadbed. In order to study the effect of the number of freeze-thaw cycles, 0, 1, 3, 5, and 7 freeze-thaw cycles, and three freezing temperatures of \(-5\)\({}^{\circ}\)C, \(-10\)\({}^{\circ}\)C, and \(-15\)\({}^{\circ}\)C were set. The freezing and thawing process was carried out in a cycle of 48h. Firstly, freezing at freezing temperature conditions for 24 h, and then thawing at room temperature conditions (20 \({}^{\circ}\)C) for 24 h. The test program is shown in Table 3.  
The specific test steps are as follows:  
1. [label=(1)]
2. Sieving: According to the specifications, the test specimen diameter should be 50 mm, and the maximum allowable particle size should be 5 mm. Therefore, the rejection method (sieving) was used to remove particles that exceed the size limit. The wet soil was mixed well and placed into a plastic bag, sealed, moisturized, and left undisturbed for about 24 h.
3. Sample making: The prepared wet soil was placed into the sample making mold in three layers.