NMR-Based Investigation on the Wet-Dry Deterioration Characteristics of Gypsiferous Rocks Surrounding Underground Excavations

Repeated wetting and drying is one of the most destructive actions that can induce continuous damage to in-situ rocks in many engineering applications. The situation is exacerbated if the action is coupled with flowing water conditions. In this work, the wet-dry (W-D) deterioration characteristics of gypsiferous rocks surrounding underground excavations were investigated. A series of tests at different W-D cycles with different flow rates (0, 10, and 20 l/h) were conducted on gypsiferous specimens to reveal the deterioration behaviors. The change in rock pore structure was characterized by nuclear magnetic resonance (NMR) method and the deterioration characteristics in its mechanical properties were investigated by the P-wave velocity test. Based on the disturbed state concept (DSC), a W-D deterioration model was established. The results showed that repeated W-D actions led to the formation of visible cracks which enhanced the dissolution of gypsiferous rocks, while the loose particles detached from the rock matrix were carried away by the flowing water, resulting in an uneven diameter reduction in the specimens. The damage of internal micro-porestructure and enlargement of internal pores were induced also by the combined action of the W-D processes and water flow. The feasibility of using the pore structure parameters to characterize the deterioration in the mechanical properties of gypsiferous rocks due to W-D actions at different water flow rates was demonstrated based on the proposed deterioration model. This study can provide a useful reference tool to help the engineering design of tunnels under similar geological conditions.

Automated summary

The study investigated the deterioration characteristics of gypsiferous rocks under repeated wetting and drying actions, revealing visible cracks and enhanced dissolution of the rocks. The internal pore structure and particles detachment were found to be affected by the combined actions of W-D processes and water flow, leading to uneven reduction in specimen diameter. The feasibility of using pore structure parameters to characterize mechanical property deterioration of gypsiferous rocks under different water flow rates was demonstrated based on the proposed deterioration model.