Thermally assisted fracturing of ancient rock surfaces due to environmental effects: The case of the Valley of the Kings (Egypt) and Langoren Island

Temperature fluctuations from climatic cycles can induce thermo-mechanical fatigue, impacting the stability of rock masses, specially in shallow bedrocks and slopes. This research investigates the mechanism driving fatigue at two distinct environments: Långören Island in Finland and the Valley of the Kings in Egypt.

Installed monitoring systems at these locations continuously track rock slabs subjected to temperature cycles. The sensors recorded annual deformation ratios of 0.04 mm/°C for Finland and 0.05 mm/°C for Egypt, indicating cumulative fatigue effects over time. Limited literature on deformation ratios complicates comprehensive comparisons. Mechanical and thermal conditions were documented through geological mapping and laboratory tests, while 2D finite-difference numerical models were developed using FLAC®. For Långören Island, a linear correlation between measured and simulated data yielded an R² of 0.85, with a slope of 0.5 and an intercept of 0.45 mm, indicating the need for further calibration. In contrast, the Valley of the Kings model achieved a slope of 0.85 and a lower intercept of 0.001 mm, with a similar correlation (R² = 0.80), suggesting a better match between measured and simulated data. Despite the similar R² values, the shorter study period at Långören Island likely led to greater data scatter, affecting the overall fit, whereas the longer-term monitoring at the Valley of the Kings allowed for refined modeling of site-specific factors.

In the Valley of the Kings, observed conditions and the site’s complex geometry prompted the development of a thermo-mechanical model in FLAC3D®. A calibrated 3D model was used to explore transient conditions from April 2018 to March 2019, with a 156 different variations used including localized plasticity to account for inelastic displacements recorded through July 2023. The simulations correlated with measurements, yielding an R² of 0.90, a slope of 0.65, and intersection of 0.3 mm for the first 12 months from April 218 to March 2019.

A conceptual approach using Goodman’s diagram, related mean and alternating deviatoric stresses to assess fatigue failure. A novel thermo-mechanical fatigue criterion based on crack initiation stress thresholds of 11.4 MPa for the Valley of the Kings predicts further crack growth due to thermal fluctuations. This framework can be applied to various scenarios involving natural rocks and concrete structures subjected to environmental temperature changes, linking material properties to fatigue failure mechanisms. Understanding thermal fatigue is crucial to preserving natural cliffs and rock built infrastructure of cultural significance, ultimately improving rock engineering design resilience to safeguard for the future.