Soil suction and temperature measurements in a heavy haul railway formation

Abstract

Transportation foundations around the world exist predominantly in an unsaturated state. Support for the adoption of unsaturated soil mechanics in routine geotechnical engineering is ever-increasing. However, the measurement and characterization of soil suction is a potentially significant barrier thereto. To this end, the efficacy of various measurement techniques was investigated, with the aim to characterize the temporal variation in soil suction and temperature within the formation layers of a heavy haul railway formation. Tensiometers, fixed-matrix soil-water matric potential sensors and capacitance-type volumetric water content sensors were installed within the formation layers of a railway track and monitored for a period of 18 months. The average suction measured over the observational period was 25.6, 12.7, 3.5 and 4.2 kPa for the special subballast, subballast and two subgrade layers respectively. Suctions reached a minimum of 0 kPa at the end of the rainfall season across all layers and reached a maximum, ranging between 10 and 60 kPa across all layers at the end of the dry season. Soil temperatures for the observational period varied between 10 and 22 °C and displayed seasonality in-phase with the monitored air temperatures. The special subballast layer (uppermost layer) showed the greatest variation in both suction and temperature and is the layer which experienced the greatest stress changes as a result of seasonal variations in rainfall and air temperature.