InterPore2026

Heating-induced pore pressure generation and K₀ evolution in low-permeability clayey soils

22 May 2026, 09:35

15m

Oral Presentation (MS16) Complex fluid and Fluid-Solid-Thermal coupled process in porous media: Modeling and Experiment MS16

Speaker

Dr Nuria Sau (CIMNE / UPC)

Description

Thermal loading in low-permeability clayey soils induces complex coupled thermo-hydro-mechanical responses that are critical for energy geotechnical applications. In particular, temperature-induced pore pressure generation and the evolution of the lateral earth pressure coefficient at rest (K₀) play a central role in the performance and stability of systems such as geothermal wells [1], hydrocarbon wells [2], energy piles ([3] and [4]), and, more specifically, in the geological disposal of radioactive waste [5] -the focus of this study. These thermal effects are also relevant in natural hazard contexts, such as rapid and coseismic landslides, where temperature changes can influence pore pressure generation within shear bands ([6], [7], [8]).
This contribution presents laboratory observations on Ypresian clays, a potential host rock for radioactive waste disposal in Belgium. Unlike Boom Clay, Opalinus Clay, and Callovo-Oxfordian claystone, no Underground Research Laboratory exists for in situ testing, highlighting the need for thorough laboratory characterization. In-situ heating experiments confirm that heating low-permeability rocks leads to pore pressure build-up concurrent with dissipation via consolidation. The thermal pressurization primarily stems from the differential thermal expansion between pore fluid and the rock skeleton [9], further influenced by the compressibility of pore fluid and pore volume, which depend on stress and pore fluid temperature ([10], [11], [12]), degree of saturation, permeability, and heating rate. Experimentally, this is quantified by the thermal pressurization coefficient (Λ), expressing the ratio of pore pressure increase to temperature rise (∆u⁄∆T). In relation to the thermal effects, the evolution of the lateral earth pressure coefficient at rest (K₀) under temperature changes on saturated soils has received limited attention in experimental research.
A set of heating pulse tests was conducted using a custom-built, instrumented axisymmetric cell capable of applying thermal loading under constant-volume conditions while independently controlling hydraulic boundary conditions [13]. The device allows continuous measurement of temperatures, pore water pressures, and total stresses at multiple locations along the specimen. The cylindrical specimen tested were retrieved from 335 m depth with bedding planes orthogonal to the cell axis.
The experimental protocol included three sequential stages: hydration, hydro-mechanical loading, and stepwise heating and cooling. Heating was applied from the base in increments up to 80 °C. Each heating step consisted of undrained heating, pore pressure dissipation, and permeability measurement. Cooling steps were performed under both undrained and drained hydraulic conditions. This protocol allowed separation of thermally induced pore pressure, consolidation-driven dissipation, and changes in K₀.
Results show that, under constant volume conditions, the thermal pressurization coefficient increases with temperature -consistent with the findings of [12] and [14]. Effective stress measurements reveal deviations from purely poroelastic behavior above 40 °C, with a slight decrease in vertical effective stress and an increase in horizontal effective stress, leading to a progressive increase in K₀. This behavior may reflect microstructural rearrangements or changes in the apparent overconsolidation ratio induced by thermal loading. Notably, the potential thermal-induced disruption does not appear to significantly affect the water permeability in the direction orthogonal to the bedding planes.