Impact of land–climate interaction on thermo-hydro-mechanical based stability assessment of varved glacial slopes

The increasing average global temperatures are transforming the permafrost regions into seasonally frozen areas, thereby pushing the active layer deeper into the ground and leading to a rise in inexplicable glaciatic geohazards. Although the glaciated Himalayan regions of India are becoming more vulnerable to such events, cold region geotechnical studies remain nearly unattended. This research attempts to evaluate the complex consequences of hydrological changes on the stability of slopes and water balance through numerical modeling using the finite element (FE) technique. The real-time climate data from Tawang, Arunachal Pradesh, is chosen which prevalently experiences sub-zero temperatures in the eastern Himalayan belt. In accordance to various thermal regimes and hydrological conditions common to this region, this study effect of only rainfall water infiltration (RW), water infiltration from both rain and snowmelt (RW + SW), and the complementary influence water migration due to soil temperature gradient [T(RW + SW)] on the slope stability, water infiltration, and runoff dynamics of sloping terrain. Numerical assessment of the stability of both homogeneous and multi-couplet varve slope profiles are carried out. The influence of Red soil-Black soil (RS-BS) laminae (2, 4, 8 and 16 in numbers) as well as the slope inclination (25°–45°) on the hydrogeological response of the layered slopes are delineated. It is conclusively understood that stability of slopes, water infiltration and runoff are strongly influenced by surficial soil couplet directly interacting with the atmosphere; expectedly, the slope inclination angle and the number of laminae also plays substantial role in the stability and temporal dynamics of pore-water pressure within the slopes. Slopes with RS as the topmost layer are found to evidently fail earlier than those with BS as the topmost layer; for the latter case, the area of soil involved in slope failure is comparatively lesser. In any sequential arrangement, the area of soil involved in slope failure increases with the increase in laminae. Slopes with RS as the topmost layer are observed fail quicker under the freeze–thaw phenomenon. The time to the onset of slope failure is found to be comprehensively linked with the time to attain the maximum cumulative net infiltration.