Dynamic Monitoring of Mudstone Swelling During Water Absorption Via Point Cloud Features

Abstract

This study focuses on Jurassic red-bed mudstone, a prevalent geomaterial in Sichuan Basin infrastructure projects, particularly the Chengdu-Wanzhou high-speed railway. Known for its water sensitivity, this mudstone undergoes swelling deformation and fissure development upon moisture exposure, posing risks to track stability, slope integrity, and foundation resilience. Traditional monitoring methods, reliant on single-point diatometers, are limited by their inability to capture 3D deformation dynamics and are hindered by contact-induced boundary constraints, low data efficiency, and lack of full-field analysis capabilities. To address these challenges, an innovative 3D dynamic monitoring system integrating an improved capillary rise test with oblique photogrammetry is introduced. This system comprises a custom capillary water absorption apparatus, a hemispherical multi-camera array for full-field coverage, and a Raspberry Pi-based data acquisition unit. High-frequency imaging throughout capillary water absorption enables multi-view 3D reconstruction, generating time-series point cloud models for spatiotemporal deformation analysis. Key findings reveal a three-stage capillary water absorption process, with axial height growth transitioning from rapid (0–148 min) to metastable (148–306 min) and stable (306–501 min) phases, accompanied by decreasing water absorption rates. Fissure networks evolve from sporadic microcracks to a reticular pattern, exhibiting axial and radial heterogeneity influenced by boundary conditions. Swelling-induced displacement fields show spatial anisotropy, with radial expansion on lateral surfaces and axial uplift on top surfaces, reaching maximum displacements of 5.39 mm and 2.86 mm, respectively. Non-uniform swelling induces a 1.64° surface rotation, indicating substantial shear and torsional strains. Volumetric swelling reaches 7.15%, correlated with fissure density, while surface roughness evolves heterogeneously, reflecting differential stress zones. This research provides a comprehensive framework for understanding water-rock interactions in red-bed mudstone, supporting risk assessment and mitigation strategies for swelling-induced geological hazards.