# Experimental Study of the Dynamic Characteristics of PVA-Amended Expansive Soils
## 1 Introduction  
Expansive soil contains many hydrophilic minerals, such as kaolin and illite. It is a kind of high-plasticity clay characterized by fissures, expansions and contractions, and superconsolidations. This soil is particularly sensitive to changes in water content, which is mainly manifested in the following ways: expansion by water absorption and contraction by water loss. Although expansive soil itself has high strength, due to its sensitivity to water content characteristics, expansive soil can be easily deformed, resulting in damage to the integrity of the soil and thus greatly reducing its strength. Moreover, the expansion of soil can lead to adverse effects on any of the abovementioned structures, especially those spanning highways and railways. Road and railway foundations that use expansive soils as fill are prone to settlement, which leads to cracking of the road surface and landslides and subsidence of slopes; these conditions have been described as \"hidden disasters\" [1]. China has one of the widest distributions and largest areas of expansive soils in the world. With the continuous improvement in the transport infrastructure network, landtransport and ground construction will inevitably involve expansive soil areas, and improving expansive soils is crucial for structures in expansive soil areas. The current treatments for expansive soils can be broadly classified into three categories: physical, chemical, and biological improvements. In terms of physical improvement, several scholars [2; 3; 4] have studied the use of polystyrene foam particles to improve the expansion and contraction of expansive soils as well as reduce the expansion rate and expansion pressure. [PERSON] [5] improved expansive soils through the use of water glass, which raises the plastic limit of the soil and lowers the liquid limit and hydrophilic minerals; this results in a decrease in the expansion rate of the improved soil and a corresponding increase in strength. [PERSON] et al. [6] studied the improvement effect of different dosages of silty sand on expansive soil; explored the changes in the expansion force, expansion rate, internal friction angle, cohesion, and other properties of expansive soil with the dosage of silty sand; and verified the feasibility of using silty sand to improve the expansion and mechanical properties of the soil. For chemical improvement, cement and lime are mostly used to improve expansive soils [7; 8; 9]. [PERSON] et al. [10] mixed ultrafine fly ash and cement in expansive soils to obtain the most reasonable amount of fly ash and cement mixture. [PERSON] et al. [11] modified expansive soils with citric acid-treated alkaline oxygen furnace paste, conducted geotechnical performance tests, and observed the microstructure of the modified soils via X-ray diffraction and scanning electron microscopy. [PERSON] et al. [12] used different mixing combinations of polypropylene fibers and lime in expansive soil to study its mechanical properties. [PERSON] [13] and other scholars have made some contributions to the improvement of expansive soils. These researchers used tire rubber powder and cement kiln ash to treat expansive soils. Subsequently, an in-depth analysis of the soil was carried out using scanning electron microscopy, unconfined compressive strength tests, and other tests. This kind of treatment can not only improve the mechanical properties of expansive soil but also effectively solve environmental problems, such as those associated with waste tires. In terms of biological improvement, the emergence of bioenzymes has provided a new way of thinking about the treatment of expansive soils [14] to improve their strength and reduce swelling [15; 16]. [PERSON] et al. [17] conducted experimental studies on the modification of expansive soils using microorganisms and screened for strains that increased shear strength and reduced swelling and linear shrinkage. [PERSON] et al.