# Experimental Study of the Dynamic Characteristics of PVA-Amended Expansive Soils
## 4 Conclusions  
In this study, for PVA-amended expansive soil, we analyzed the effects of different PVA dosages on the shear strength index, stress-strain curve, and shear strength index of expansive soil under varying peripheral pressures through ordinary triaxial tests to determine the optimal PVA dosage. A British GDS Dynamic Triaxial Instrument was used to carry out multistage loading tests on the amended soil to analyze the dynamic characteristics of the soil based on three aspects, namely, the dynamic stress-strain curve of the amended soil, the dynamic modulus of elasticity, and the damping ratio characteristic parameters. The main research conclusions are summarized as follows:  
1. In the ordinary triaxial compression test, the effects of the PVA content and circumferential pressure on the stress-strain relationship and shear strength of the improved soil are more obvious. With increasing PVA dosage, the stress-strain relationship curve and shear strength of the improved soil first increase and then decrease, and at a PVA dosage of 3%, the stress-strain curve and shear strength reach a peak; that is, the best improvement effect is obtained. 2. Based on the optimum dosage of PVA-amended expansive soils, the dynamic stress-strain backbone curves for the amended soils exhibit obvious nonlinearity at different frequencies and peripheral pressures. The dynamic stress-strain relationship curve for the modified soil shifts upward with increasing enclosing pressure and frequency. The slope of the stress-strain curve is greater in the early stage of dynamic strain development, the dynamic strain of the soil responds to the stress faster, the specimen force and deformation are stable, and elastic deformation accounts for a greater proportion of the total deformation. As the dynamic strain continues to increase, the slope of the curve decreases, and the connections between the soil particles in the specimen are destroyed. 3. The dynamic elastic modulus of the improved soil decreases gradually and is negatively correlated with increasing dynamic strain. The modulus of dynamic elasticity increases with increasing enclosing pressure and frequency and tends to stabilize with the development of dynamic strain. The initial dynamic elastic modulus increases with increasing enclosing pressure and frequency but is less affected by the frequency. 4. The damping ratio for improved soil increases with the development of dynamic strain. At a dynamic strain of \(\epsilon_{\rm d}\leq 0.4\%\), the growth rate of the damping ratio is small; at a dynamic strain of \(\epsilon_{\rm d}>0.4\%\), the growth rate of the damping ratio first increases and then decreases. The damping ratio decreases with increasing circumferential pressure and frequency. **Author Contributions:** Conceptualization, X.Z. and B.Z. ; methodology, B.Z. ; software, B.Z. and D.Y. ; validation, B.Z. and W.W.; formal analysis, B.Z. and X.L. All authors have read and agreed to the published version of the manuscript. **Funding:** The authors appreciate the funding from the National Natural Science Foundation of China (Grant Nos. 51978248 and 51708190). **Institutional Review Board Statement:** Not applicable. **Informed Consent Statement:** Not applicable. **Data Availability Statement:** The data that support the findings of this study are available from the corresponding author upon reasonable request. The data are not publicly available due to privacy. **Conflicts of Interest:** The authors declare no competing interests.