Moisture Variation in Expansive Subgrade Through Field Instrumentation and Geophysical Testing

Abstract

Abstract. Seasonal climatic variations in subgrade soil affect pavement responses and can reduce pavement serviceability. In addition to causing shrinkage and swelling in expansive subgrade, variations in moisture suction may alter the material properties of soil, which ultimately affect pavement performance. The current study monitored the seasonal variation of subgrade moisture content, rainfall, and pavement deformation of a section over State Highway 342, in Dallas, Texas. Moisture sensors were installed at different depths up to 4.5 m. The soil was found to be highly plastic clay (CH) in the selected site. In addition to acquiring real-time moisture data from sensors, geophysical testing was also conducted on the slope of the pavement. Electrical Resistivity Imaging (ERI) was carried out at the slope of the instrumented pavement section to observe the moisture flow at the edge of the pavement. Based on the field monitoring data, moisture variation ranged from 5% to 14%, with higher moisture contents correlating with rainfall events. While moisture sensors provided point information, resistivity imaging yielded a continuous portrayal of subsurface moisture flow. Furthermore, rainfall-associated deformation of the pavement was monitored. Based on the monitored data, it was observed that pavement deformation varied with rainfall. A total deformation of 38 mm was recorded over the monitoring period.

Deformation Modeling of Flexible Pavement in Expansive Subgrade in Texas

“…Finally, the time/day of the year was evaluated for assessing the effect of seasonal variation in pavement deformation. Past literature has shown that seasonal variation is one of the major causes of volumetric variation in pavement subgrade [12,13,19]. The preceeding section about change in resistivity with season authenticates that deformation is dependent upon season/time of the year.…”

“…ERI, as geophysical testing was used to continuously profile the moisture variation beneath the pavement. It also allows the determination of moisture variation beneath the slope beside the pavements [12]. ERI measures the electric potential drop between two locations.…”

“…A forward modeling technique was applied in the Earth Imager 2D software [18] to compute the apparent resistivity values from the field data. The two-dimensional image of the subsurface is developed as a final output with the non-linear least squares optimization technique [12].…”

“…Longitudinal cracking, roughness, and fatigue cracking occur due to alternate cycles of volume expansion and contraction [10]. As moisture fluctuation is most susceptible in the pavement shoulder, it is most vulnerable to swelling and shrinkage resulting in pavement distresses [11,12]. Hence, longitudinal cracking in the pavement shoulder are the most prevalent pavement distress [10,13].…”

Study on Water Characteristic Curve and Shear Characteristics of Typical Unsaturated Silty Clay in Shaoxing

“…In geotechnical engineering practice, permeability coefficient, shear strength, and other relevant indexes describing the behavior of unsaturated soils can be obtained indirectly by using the soil-water characteristic curves [24][25][26][27][28][29][30]. According to the influence of matric suction on the cohesion and internal friction angle of unsaturated soil, many scholars used the Mohr-Coulomb strength failure criterion of saturated soil and the measured shear strength parameters of saturated soil and soil-water characteristic curve to predict the shear strength of unsaturated soil.…”