# Experimental Study of Influence of Plant Roots on Dynamic Characteristics of Clay
## 2 Experimental Materials with Tested Material
### Experimental Procedure  
To investigate the influence of plant roots in the 1-5 m clay layer on the dynamic properties of soil, three different confining pressures (100 kPa, 200 kPa, and 300 kPa) were applied. The root mass density of clay is generally low, ranging between 0 and 0.03 g-cm\({}^{3}\)[27]. Therefore, the dynamic shear modulus and damping ratio of clay were tested under five different root mass density conditions (0%, 1%, 1.5%, 2%, 2.5%, and 3%).  
The experimental plant selected was Cynodon dactylon, a common local herbaceous plant. It is a widely distributed grass species native to tropical and subtropical regions, including Africa, Asia, and southern Europe. It is now widely cultivated globally, especially in warm climates such as the southern United States, China, India, and Australia. Its chemical composition is primarily cellulose and minerals, with fiber components mainly  
\begin{table}
\begin{tabular}{c c c c c} \hline
**Coefficient of** & **Curvature** & **Plasticity** & **Liquid Limit** & **Plasticity** \\
**Uniformity** & **Coefficient** & **Limit** & **Ludic Limit** & **Index** \\ \hline
14.29 & 1.11 & 22.87\% & 41.63\% & 18.76 \\ \hline \end{tabular}
\end{table}
Table 1: Physical parameters of soil.  
Figure 3: Resonance column test system.  
consisting of cellulose, hemicellulose, and lignin. Due to its strong drought resistance, it is often used for slope protection and soil and water conservation [28].  
The resonant column specimens were cylindrical, with a diameter of 50 mm and a height of 100 mm. Due to specimen size limitations, Cynodon dactylIon roots with a diameter of 0.5-1 mm and a length of 8-10 mm were selected. The specimen soil was dried at 108 \({}^{\circ}\)C for 8 h and then prepared with a dry density of 1.65 and a water content of 12%. To thoroughly mix Cynodon dactylIon roots with the soil, the soil and roots were evenly divided into five portions by weight, as required by the standard [25]. The mixture was layered into the mold in 20 mm layers, as shown in Figure 4.  
In the installation process of the resonant column test, it is crucial to start by covering the specimen with latex film and securing it onto the base of the resonant column, ensuring airtightness. Next, place the top cap, install the drive system, and connect the drive disk to the specimen's top cap. Install the accelerometer, connect the coils, and safeguard the coil wires. Mount the top disk/LVDT on the top of the resonant column. After completing the installation of all components, double-check the magnet positions in the coils and make necessary adjustments to ensure the safety of all wires. Lastly, install the glass cover to complete the assembly of the entire testing apparatus. Careful execution of this process, involving detailed operations and precise adjustments, is crucial for ensuring the accuracy and reliability of the experiment, as depicted in Figure 5. In the preliminary experiments, fine-grained soils such as clay exhibited significant damping effects at low frequencies (<30 Hz), but the damping ratio gradually stabilized as the frequency increased. Testing in the 30 Hz to 150 Hz range captures the damping trend of clay while also providing stable damping ratio data. The testing conditions included undrained and unconsolidated soil samples subjected to applied confining pressures. Upon reaching a stable confining pressure, the twist resonance test was conducted using GDS RCA (v 1.0.0) software. In the test, an input voltage was applied, and a frequency sweep was performed within the range of 30-150 Hz. This procedure provided data on resonance voltage amplitude and resonance frequency, allowing for the calculation of parameters such as dynamic shear modulus based on these values. After completing the twist resonance test, the testing apparatus automatically transitioned to the damping test mode, with the resonance frequency as a parameter for the damping test. These steps were repeated until all the necessary tests were completed, as outlined in reference [29].  
Figure 4: Test specimen.