# Experimental Study on Cyclic Shear Performance of the Four-Way Geogrid Reinforcement-Soil Interface
## 2 Materials and Methods  
The test utilized Fujian standard sand as the filler material, with a particle size range of 0.1-4 mm determined through a sieving test. The sand has an effective particle size of \(d_{10}\) = 0.23 mm, a continuous particle size of \(d_{30}\) = 0.44 mm, and a limited particle size of \(d_{60}\) = 0.97 mm. The sand exhibited an uneven coefficient of \(Cc\) = 4.43 and a curvature coefficient of \(Cu\) = 0.83. The specific gravity of the soil particles was found to be \(Gs\) = 2.71. Figure 1 shows the grading curve of the particles. The maximum dry density was determined to be \(\rho_{\text{dmax}}\) = 1.84 g/cm\({}^{3}\), while the minimum dry density was \(\rho_{\text{dmin}}\) = 1.35 g/cm\({}^{3}\). For testing purposes, we used the TGSSXG1515 PP four-way geogrid model manufactured by Shandong Tai'an Luder Company (Tai'an, China). Compared to the standard two-way grating, this geogrid has increased rhombic diagonal ribs that form two new types of nodes (node I and node II), as Figure 2 illustrates. Table 1 presents the grating's structural parameters while Table 2 shows its mechanical parameters. Figure 1: Grain size distribution curve of sand. The large-scale dynamic straight shear instrument used in this paper, as Figure 3 shows, includes an mainframe instrument system, an oil source system, and a data acquisition system. The shear test system consists of a servo, sensor, and auxiliary equipment. The oil source system mainly consists of an oil tank, motor, oil pump, hydraulic valve, and electric control cabinet to provide power for the servo actuator. The data acquisition system consists of a plug-in controller, software, computer, and printer. The straight shearer controls the vertical and horizontal actuators through a computerized closed loop. The vertical actuator is mounted on a crossbeam which is supported and connected by two supports. The lower end of the piston rod of the vertical actuator is connected to a pressure beam, and the upper-side limit frame can be connected under the pressure beam to complete the vertical loading of the specimen. The vertical and horizontal movements of the shear box are recorded by the data acquisition system. The upper shear box is connected to a vertical hydraulic servo with a vertical movement of 150 mm. The lower shear box is longer than the upper one \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Name of Part** & **Length (mm)** & **Width (mm)** & \
\begin{tabular}{c} **Maximum** \\ **Elongation (\%)** \\ \end{tabular} &
\begin{tabular}{c} **Ultimate Tensile** \\ **Strength (kN/m)** \\ \end{tabular} \\ \hline Horizontal rib & 60 & 3 & 6.3 & 17.5 \\ Normal rib & 60 & 3 & 5.7 & 15.5 \\ Diagonal rib & 20 & 2 & 6.2 & 18.2 \\ Node I & 20 & 15 & - & - \\ Node II & 20 & 8 & - & - \\ Node O & 3 & 3 & - & - \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Construct parameters of four-way geogrid. \begin{table}
\begin{tabular}{c c} \hline \hline
**Name of Project** & **Value** \\ \hline Maximum output test force in vertical direction & 60 kN \\ Maximum output test force in transverse direction & 35 kN \\ Accuracy of test force & \(\leq\)\(\pm\)1\% \\ Maximum stroke of horizontal actuator & 150 mm \\ Maximum operating frequency & 5 Hz \\ Internal dimensions of the upper shear box & 405 mm \(\times\) 305 mm \(\times\) 150 mm \\ Internal dimensions of the lower shear box & 305 mm \(\times\) 305 mm \(\times\) 150 mm \\ \hline \hline \end{tabular}
\end{table} 
Table 2: The technical parameters of the dynamic straight shear system. Figure 2: Geogrid construction. (**a**) Four-way geogrid; (**b**) Two-way geogrid. in order to maintain a constant shear area during the shearing process. Table 2 shows the technical parameters of the dynamic straight shear. When conducting the four-way geogrid-soil interface shear test using the system, it is essential to ensure that the geogrid remains tightly secured and its relative position with the lower box remains unchanged.