Fractal characteristics of pore structure and nonlinear deterioration mechanism of weakly cemented siltstone under alkaline water effect; [碱水作用下弱胶结粉砂岩孔隙结构分形特征及非线性劣化机理]

Weakly cemented rocks have significant strength decline when exposed to groundwater, frequently resulting in roof weighting anomaly and caving disasters in western coalfields in China. Based on the coal measure geology and hydrological settings of Hami coalfields in Xinjiang Uygur Autonomous Region, the paper investigates the impact of alkaline pH levels and immersion durations on the micro-structure and pore fractal dimension of weakly cemented siltstone using SEM and digital processing techniques, determines the relationship from pore fractal dimension and porosity to uniaxial compressive strength (UCS) and tensile strength, establishing a nonlinear dynamic model to characterize the strength degradation due to alkaline erosion. The results show that: 1) Mineral particles become morphologically rounded and loosened with alkalinity increase, and the enlargement in porosity and pore fractal dimension gradually slows with immersion. 2) The UCS and tensile strength of eroded weakly cemented silt-stone are influenced by the pore structure morphology and distribution, featuring a negative correlation to pore fractal dimension, then to porosity. The rock brittleness is decreased due to alkaline erosion. 3) A nonlinear dynamic model that incorporates pore fractal dimension, porosity, and UCS as descriptors is established utilizing the time series values of these descriptors as specific solutions. The pore fractal dimension, porosity, and UCS calculated via the nonlinear model show a good agreement with experimental results, and the error ranges are 2. 37%-2. 64%, 2. 38%-4. 57%, 3. 48%-8. 12%, respectively. The model is able to assess the porosity and strength parameters of weakly cemented rocks exposed to alkaline erosion over time. © 2024 China University of Mining and Technology. All rights reserved.