Abstract: In order to study the deterioration effect of swelling pressure of Gaomiaozi sodium bentonite under long-term strong alkali- heat action, 24 groups of orthogonal optimization-tests were designed for Gaomiaozi sodium bentonite from Xinghe County, Inner Mongolia. The test conditions were as follows: one NaOH concentration (0.5 mol/L), four alkali-heat temperatures (25, 90, 150 and 210 ℃), six alkali-heat interaction durations (2, 4, 6, 8, 10 and 12 months). X-ray diffraction (XRD) tests were performed on the bentonite after alkali-heat treatment, and constant volume swelling (CVS) experiments were carried out on the bentonite sample with the initial dry density of 1.7 g/cm3 using self-made 2D swelling-apparatus, with the distilled water as an infiltration medium. The results showed that: 1) With the increase of the time and temperature under alkali-heat interaction, the content of montmorillonite, the maximum swelling pressure and the hydration time decreased; 2) The characteristic curve of swelling pressure-hydration time tended to be stable and was independent of the strong alkali-heat condition when the ratio of the maximum radial and vertical swelling pressures was 0.5; 3) A transferring-function of swelling pressure with hydration-time was established on the basis of damaging-factor of swelling pressure and accelerating-factor of aging duration, the model can better predict the experimental data; 4) A total damage increment was mostly attributed to the coupling effect of damage rate of temperature and time under the alkali-heat interaction, additionally, there was an accelerating effect of the degradation characteristic of swelling pressure facilitated by an increasing temperature.

Key words: alkali-heat effect, GMZ Na-bentonite, swelling pressure, degradation effect, alteration function