Investigation of morphological features and mechanical behavior of jointed limestone subjected to wet-dry cycles and cyclic shear in drawdown areas of the Three Gorges Reservoir

Abstract

Reservoir drawdown induces cyclic water level fluctuations, exposing geomaterials in drawdown areas to repetitive wet-dry cycles and cyclic shearing forces. Understanding the deterioration mechanisms of geomaterials under these conditions is crucial for ensuring the long-term stability of the geomaterials in drawdown areas. This study systematically explores the deterioration mechanisms of jointed limestone from the Three Gorges Reservoir region under these dual effects. Employing three-dimensional white light scanning and EDS (energy dispersive spectroscopy) technology, the morphological and chemical evolution of rock joints was quantitatively characterized. The modified JRC-JCS (joint roughness coefficient-joint wall compressive strength) model was utilized to predict shear strength. The findings reveal that with the increase of wet-dry cycles and cyclic shears times, the surface of joints becomes progressively smoother, and the deterioration rate of shear strength gradually decreases. Cyclic shear primarily damages micro-protrusions, while wet-dry cycling affects both protruding and recessed areas through the dissolution of soluble mineral crystals. Compared with other typical model, the modified JRC-JCS model demonstrated better accuracy in predicting shear strength. The findings reveal the deterioration mechanisms of geomaterials in drawdown areas, providing essential insights for assessing the long-term stability of jointed rock mass in these regions.