Hydraulic Properties of the Subgrade with a Hydrophobic Barrier in Saline Soil Areas: Soil Column Tests and Numerical Analysis

In saline soil areas, the intrusion of moisture and salt into the road or railway subgrades can prompt their decay and consequently impact the infrastructure. This study proposes a novel measure, namely the hydrophobic sand barrier, to mitigate water and salt-induced degradation of the subgrade. Due to the low affinity to water, the hydrophobic sand can retard or even prevent water infiltration and movement in soils, showing its potential use as a hydraulic barrier. To demonstrate its applicability in the subgrade in saline soil region, this paper assesses the hydraulic performance of hydrophobic sand induced by two hydrophobic agents (dichlorodimethylsilane and Tung oil) through soil column test and finite element numerical analysis. The results indicate that both types of hydrophobic sands could retard water infiltration, while the dichlorodimethylsilane induced one had greater resistance to infiltration. The numerical analysis showed that in subgrades with a hydrophobic sand barrier, the distribution of groundwater within the subgrade is related to the type of hydrophobic agent, the thickness of the barrier, and the groundwater level. Therefore, in the design and construction of subgrade, the type of hydrophobic material, the thickness of the hydrophobic sand barrier, humidity field patterns and subgrade height should be comprehensively considered to address the construction feasibility of the subgrade.