Softening of soft red-bed rocks subjected to rainfall-evaporation cycles is commonly characterized by rapid disintegration and is often accompanied by cracking,resulting in degradation of the mechanical properties of ...Softening of soft red-bed rocks subjected to rainfall-evaporation cycles is commonly characterized by rapid disintegration and is often accompanied by cracking,resulting in degradation of the mechanical properties of the rock,which can lead to slope instability or rockfalls.The microstructural changes in soft red-bed rocks after immersion were imaged,and two-dimensional(2D)images of cracks under water absorption-evaporation conditions were obtained.The dynamics,fractal characteristics,and geometry of the cracks were analyzed using digital image processing and analysis based on morphological algorithms.The results indicate that the faceeface particle bonds become pointeface bonds with numerous micropores with sizes of 1-5 mm.The evolution of cracks generated after water absorption can be divided into four stages:edge crack initiation,crack propagation,crack coalescence forming the main crack,and subcrack segmentation.The evolution of the dynamic characteristics of cracks during water absorption and drying cycles can be effectively described by the crack intensity factor,crack density,and average width.The fractal dimension increases to a stable value with increasing soaking time,whereas drying increases the crack complexity,resulting in fractal dimensions ranging from 1.106 to 1.126.The geometry results indicate that the crack directions are mainly at angles of 30°-70°after soaking and primarily in the range of 50°-60°after 10 drying cycles.The transition of the crack intersection angle from a bimodal to a unimodal distribution suggests that water absorption and drying processes tend to form Y-shaped and T-shaped cracks,respectively.Finally,the evolution of the watererock interface induced by particle dissolution,ion exchange,expansion force,and liquid surface tensionwas used to explain the mechanism of crack evolution related to water entry and evaporation.These results provide a theoretical basis for evaluating the cracking behavior of soft red-bed rocks.展开更多
This paper examines the effect of the microstructure and electrical conductivity(EC)on the swelling ratio and pressure in red-bed mudstone sampled from arid areas in the Xining region in the northeastern Tibetan Plate...This paper examines the effect of the microstructure and electrical conductivity(EC)on the swelling ratio and pressure in red-bed mudstone sampled from arid areas in the Xining region in the northeastern Tibetan Plateau.A series of laboratory tests,including swelling experiments,X-ray diffraction(XRD),and scanning electron microscope(SEM),was carried out for mechanical and microstructural analysis.The coupled influence of the EC and microstructural parameters on the expansion ratio and pressure was investigated,and the weight coefficients were discussed by the entropy weight method.The results revealed an increasing exponential trend in EC,and the maximum swelling speed occurred at an EC of approximately 10μS/cm.In addition,a method for predicting the expansion potential is proposed based on the microstructure,and its reliability is verified by comparing with swelling experimental results.In addition,according to the image analysis results,the ranges of the change in the clay minerals content(CMC),the fractal dimension(FD),the average diameter(AD)of pores,and the plane porosity(PP)are 23.75%-53%,1.08-1.17,7.53-22.45 mm,and 0.62%-1.25%,respectively.Moreover,mudstone swelling is negatively correlated with the plane porosity,fractal dimension and average diameter and is linearly correlated with the clay mineral content.Furthermore,the weight values prove that the microstructural characteristics,including FD,AD,and PP,are the main factors influencing the expansion properties of red-bed mudstones in the Xining region.Based on the combination of macro and micro-analyses,a quantitative analysis of the swelling process of mudstones can provide a better reference for understanding the mechanism of expansion behavior.展开更多
基金funded by the Sichuan Science and Technology Program(Grant Nos.2023YFS0364 and 2024YFHZ0154)the Xizang Science and Technology Program(Grant No.XZ202401ZY0097).
文摘Softening of soft red-bed rocks subjected to rainfall-evaporation cycles is commonly characterized by rapid disintegration and is often accompanied by cracking,resulting in degradation of the mechanical properties of the rock,which can lead to slope instability or rockfalls.The microstructural changes in soft red-bed rocks after immersion were imaged,and two-dimensional(2D)images of cracks under water absorption-evaporation conditions were obtained.The dynamics,fractal characteristics,and geometry of the cracks were analyzed using digital image processing and analysis based on morphological algorithms.The results indicate that the faceeface particle bonds become pointeface bonds with numerous micropores with sizes of 1-5 mm.The evolution of cracks generated after water absorption can be divided into four stages:edge crack initiation,crack propagation,crack coalescence forming the main crack,and subcrack segmentation.The evolution of the dynamic characteristics of cracks during water absorption and drying cycles can be effectively described by the crack intensity factor,crack density,and average width.The fractal dimension increases to a stable value with increasing soaking time,whereas drying increases the crack complexity,resulting in fractal dimensions ranging from 1.106 to 1.126.The geometry results indicate that the crack directions are mainly at angles of 30°-70°after soaking and primarily in the range of 50°-60°after 10 drying cycles.The transition of the crack intersection angle from a bimodal to a unimodal distribution suggests that water absorption and drying processes tend to form Y-shaped and T-shaped cracks,respectively.Finally,the evolution of the watererock interface induced by particle dissolution,ion exchange,expansion force,and liquid surface tensionwas used to explain the mechanism of crack evolution related to water entry and evaporation.These results provide a theoretical basis for evaluating the cracking behavior of soft red-bed rocks.
基金the funding support from National Natural Science Foundation of China(Grant No.42077271)Sichuan Science and Technology Program,China(Grant No.2023YFS0364)Chengdu Science and Technology Program(Grant No.2022-YF05-00340-SN).
文摘This paper examines the effect of the microstructure and electrical conductivity(EC)on the swelling ratio and pressure in red-bed mudstone sampled from arid areas in the Xining region in the northeastern Tibetan Plateau.A series of laboratory tests,including swelling experiments,X-ray diffraction(XRD),and scanning electron microscope(SEM),was carried out for mechanical and microstructural analysis.The coupled influence of the EC and microstructural parameters on the expansion ratio and pressure was investigated,and the weight coefficients were discussed by the entropy weight method.The results revealed an increasing exponential trend in EC,and the maximum swelling speed occurred at an EC of approximately 10μS/cm.In addition,a method for predicting the expansion potential is proposed based on the microstructure,and its reliability is verified by comparing with swelling experimental results.In addition,according to the image analysis results,the ranges of the change in the clay minerals content(CMC),the fractal dimension(FD),the average diameter(AD)of pores,and the plane porosity(PP)are 23.75%-53%,1.08-1.17,7.53-22.45 mm,and 0.62%-1.25%,respectively.Moreover,mudstone swelling is negatively correlated with the plane porosity,fractal dimension and average diameter and is linearly correlated with the clay mineral content.Furthermore,the weight values prove that the microstructural characteristics,including FD,AD,and PP,are the main factors influencing the expansion properties of red-bed mudstones in the Xining region.Based on the combination of macro and micro-analyses,a quantitative analysis of the swelling process of mudstones can provide a better reference for understanding the mechanism of expansion behavior.
