Evaluating the hydraulic behavior of sandy fouled ballast: A case study from Inner Mongolia, China

This study examines the hydraulic behavior of sandy fouled ballast from Wuhai-Jilantai railway in Inner Mongolia, China, with a focus on its response to variable wetting and drying conditions influenced by climate change. The material characteristics were investigated, and it was classified as poorly-graded gravel (GP) according to the Unified Soil Classification System (USCS). This classification indicated that the material consisted primarily of gravel and sand with few fine particles. Large-scale infiltration column tests were conducted to assess the hydraulic properties, simulating precipitation rates of Wuhai (8 mm/hr) and Marsa Matruh (43 mm/hr). The results showed that under Wuhai conditions, saturation levels reached 49.3 % at the column top and 75.8 % at the bottom. In contrast, the ballast was fully saturated under Marsa Matruh’s precipitation rate. The saturated hydraulic conductivity, determined using constant head permeability tests, was measured at 1.06*10⁻⁵ m/s. Saturation levels after drainage were 39 % and 97 % at the column top and bottom, respectively. Then, a notable increase in evaporation rates facilitated by enhanced ventilation compared to applying high temperatures only. Unimodal and bimodal models were applied for understanding the Soil-Water Characteristic Curve (SWCC) and hydraulic conductivity. This research uncovers previously unreported heterogeneity in sandy fouled ballast and demonstrates the efficacy of bimodal models, providing a superior fit and more accurate prediction of hydraulic behavior, underscoring the critical role of sophisticated modeling techniques in predicting the impacts of climate variability on railway infrastructure.