THE COUPLED THERMO-HYDRO-MECHANICAL NUEMRICAL ANALYSIS FOR THE ESTIMATION OF ACTIVE ZONE AND FREE-FIELD HEAVE IN EXPANSIVE NATURAL CLAY AND BEDROCK-Paper

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The study presents a fully coupled thermo-hydro-mechanical (THM) model to estimate the active-zone depth and free-field heave or shrinkage of expansive clay and bedrock under changing climate conditions. Unlike many earlier numerical approaches, the model accounts for temperature effects and couples heat transfer, liquid-water and vapor movement, and soil deformation.<br /><br />Implemented in COMSOL Multiphysics, the model uses the van Genuchten formulation for soil-water retention and hydraulic conductivity, and an elastic form of the Extended Barcelona Model to represent swelling and shrinkage. It was applied to a one-dimensional soil profile at a Colorado Front Range residence, using ten years of meteorological data and properties for high-plasticity clay fill over Mancos Shale.<br /><br />Simulated changes in suction, temperature, and deformation diminished with depth, indicating an active zone approximately 6–8 m deep. Seasonal responses were strongest near the surface and negligible at greater depths. The analysis suggested that the drilled piers extended sufficiently below the active zone to resist uplift; heave of the slab-on-grade was a more likely cause of the observed cracking and distress.<br /><br />For comparison, the study used VOLFLO software to estimate movements under extreme wet and dry conditions. Its predicted shrinkage and swelling fell within the range of deformation calculated by COMSOL. Overall, the results indicate that strongly coupled THM modeling can capture climate-driven behavior in expansive soils and provide useful estimates of active-zone depth and free-field movement. The authors note that the approach showed promising results for assessing expansive-soil effects on infrastructure.

Keywords

thermo-hydro-mechanical model

expansive clay

active zone depth

soil swelling

soil shrinkage

van Genuchten

Extended Barcelona Model

COMSOL Multiphysics

Mancos Shale

free-field heave