# Experimental Study of Influence of Plant Roots on Dynamic Characteristics of Clay
## 3 Experimental Results Analysis
### Influence of Plant Root Systems on Soil Shear Modulus
#### 3.1.2 Different Root Mass Density  
The maximum dynamic shear modulus and the dynamic shear modulus-shear strain curves for soils with different root mass densities are presented in Figure 8 and Figure 9, respectively. These graphs reveal that the dynamic shear modulus of all soil specimens amended with roots surpasses that of the native soil. Several factors contribute to this occurrence. Firstly, plant root systems interconnect soil particles, thereby increasing the internal cohesion within the soil [31]. The conceptual diagram of soil-root interaction is shown in Figure 10. Additionally, root systems introduce frictional forces at the interface between the roots and the soil, enhancing the roughness and surface area inside the soil, thereby amplifying inter-particle friction. This effectively enhances the shear strength of the soil [32; 33; 34]. Secondly, the presence of root systems can restrict soil deformations, especially for smaller-scale deformations. Roots constrain the displacement of soil particles, slowing the rate of deformation and enhancing the soil's rigidity [35; 36]. Thirdly, the distribution of root systems can create a network-like structure within the soil, resembling an \"anchoring\" effect. This network enhances the overall structural integrity of the soil [37]. When the soil experiences shear stress, the presence of root systems impedes the sliding of soil particles along the shear planes, resisting shear deformation. This obstruction makes shear deformation in the soil more challenging, leading to an increased dynamic shear modulus [3; 38]. In summary, plant root systems have the capacity to significantly enhance the dynamic shear modulus of the soil. At three different confining pressures, the dynamic shear modulus gradually increases within the range of 0-1.5% g \(\cdot\) cm\({}^{-3}\) root mass density. The dynamic shear modulus peaks at a root mass density of 1.5% g \(\cdot\) cm\({}^{-3}\), after which it begins to decrease. For root mass densities of 2% g \(\cdot\) cm\({}^{-3}\), 2.5% g \(\cdot\) cm\({}^{-3}\), and 3% g \(\cdot\) cm\({}^{-3}\), the dynamic shear modulus in root-reinforced soil remains relatively stable. This signifies that the inclusion of plant root systems can enhance the soil's dynamic shear modulus. Within a specific range of root mass density, an increased reinforcement effect is observed, and plant roots can impede soil shear deformation. However, when the root content surpasses the optimal root mass density, the increase in the network structure reduces the contact area between soil particles, resulting in reduced cohesion. Moreover, the internal friction in the soil increases with higher root density, which can resist relative particle displacement and elevate the dynamic shear modulus. However, this increase in cohesion and shear resistance tends to saturate as root density rises. Additionally, the presence of roots reduces the specimen's porosity, increasing the overall compactness of the soil and, consequently, enhancing the dynamic shear modulus. Nonetheless, when root content exceeds the optimal root mass density, the increasing root mass density leads to a relative decrease in soil quality, resulting in a reduced rate of change in the dynamic shear modulus, which eventually stabilizes at a certain value. With an increase in confining pressure, the overlap of the dynamic shear modulus-shear strain curves for root mass densities of 2% g \(\cdot\) cm\({}^{-3}\), 2.5% g \(\cdot\) cm\({}^{-3}\), and 3% g \(\cdot\) cm\({}^{-3}\) improves. At a confining pressure of 300 kPa, the overall curves become virtually indistinguishable. This indicates that with increasing confining pressure, the dynamic shear modulus curves for high root mass densities gradually converge. At 300 kPa of confining pressure, there is little differentiation among the dynamic shear modulus curves for high root mass densities. The influence of plant root systems on soil dynamic shear modulus weakens as confining pressure increases.