Disintegration Mechanism and Hydrogeochemical Processes of Red-Bed Soft Rock Under Drying-Wetting Cycle

Abstract Red-bed soft rock in the drawdown area on bank slopes of landslide easily disintegrates upon exposure to water, and its properties experience comprehensive deterioration, which will cause bank slope instability. To better study disintegration mechanism of the red-bed soft rock, a series of laboratory tests were conducted in this paper to investigate the disintegration characteristics, durability and hydrogeochemical process of red-bed argillaceous siltstone under drying-wetting cyclic conditions. Experimental results showed that, with increasing number of drying-wetting cycles, red-bed argillaceous siltstone gradually disintegrated, from initial appearing the cracks on the surface of the samples to large particles gradually breaking up into small fragments. Significant changes in grain size distribution, and the durability index of the samples progressively decreased. Microstructural analysis showed that the size and distribution of pores and cracks in the sample surface significantly increased, such that the sample surface became disordered and complicated. Notable changed in concentrations of ions in the soaking solutions indicated continuous mineral dissolution and loss during the cyclic drying-wetting. Based on the results obtained from the experiment, it is concluded that the disintegration of samples undergoing drying-wetting cycles was the result of the synergistic action of water and temperature. To be specific, the dissolution of calcite, albite, gypsum, montmorillonite and kaolinite during the wetting procedure, which promotes the decrease in mineral content and increases in pores and cracks. The increases in temperature and the dehydration shrinkage of sample during the drying procedure accelerated the disintegration of the samples.

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An Experimental Study on the Water-Induced Strength Reduction in Zigong Argillaceous Siltstone with Different Degree of Weathering

Advances in Materials Science and Engineering ◽

10.1155/2016/4956986 ◽

2016 ◽

Vol 2016 ◽

pp. 1-12 ◽

Cited By ~ 8

Author(s):

Yu-chuan Yang ◽

Jia-wen Zhou ◽

Fu-gang Xu ◽

Hui-ge Xing

Keyword(s):

Rock Strength ◽

Geotechnical Engineering ◽

Soft Rock ◽

Water Softening ◽

Soft Rocks ◽

Weathering Degree ◽

Weathered Rocks ◽

Argillaceous Siltstone ◽

Rock Specimens ◽

Red Bed

The water-softening property of soft rocks is a key problem in geotechnical engineering. A typical red-bed soft rock (the Zigong argillaceous siltstones) with different weathering degree is selected as an example to study the water-softening property and the influence of degree of weathering. A series of mechanical and microstructure tests are carried out to analyze the weathering characteristics and mechanism of the Zigong argillaceous siltstones. The results of mechanical experiments reveal that the water content and the weathering degree of rock specimens both have a weakening effect on the compressive and shear strengths. According to the results of present microstructure tests, the mechanical properties of the Zigong argillaceous siltstones are closely correlated with their physical properties, including internal microstructure and material composition for highly weathered rocks or moderately weathered rocks (in both natural and saturation conditions). Finally, experimental results indicate that the changes of microstructure and internal materials are two main factors that influence rock strength parameters after contacting with water and that these properties reflect the rock weathering degree. In a word, when red-bed soft rocks are encountered in geotechnical engineering, special attention should be paid to presence of water.

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Elastic strains of quartz inclusions and microstructures from pressure solution in garnet reveal orientation and low magnitude of differential stress during subduction metamorphism

10.5194/egusphere-egu21-13793 ◽

2021 ◽

Author(s):

Hugo van Schrojenstein Lantman ◽

David Wallis ◽

Mattia Gilio ◽

Marco Scambelluri ◽

Matteo Alvaro

Keyword(s):

Microstructural Analysis ◽

Strain Analysis ◽

Fluid Phase ◽

Mineral Dissolution ◽

Ultrahigh Pressure ◽

Garnet Growth ◽

Pressure Solution ◽

Differential Stress ◽

Aspect Ratios ◽

Elastic Strains

Determining the stress state during metamorphism is a key challenge in metamorphic petrology as the effect of differential stress on metamorphic reactions is currently debated. Conventional piezometry generally gives stresses that correspond to overprinting deformation rather than to mineral growth of high-grade metamorphism, so an alternative approach is required. Garnetite lenses from the ultrahigh-pressure, low-temperature metamorphic Lago di Cignana unit (Western Alps, Italy) record compaction by a high degree of mineral dissolution in the fluid-rich environment of a cold subduction zone. This work combines microstructural analysis of deformed garnet with elastic strains of quartz inclusions to study the stresses in these metasedimentary rocks.Garnet exhibits abundant evidence for incongruent pressure solution (IPS), most notably as truncated zones that mismatch across grain boundaries, interlocking structures, and shape-preferred orientation (SPO). The gap in garnet compositions represented by overgrown truncated zonation corresponds to undeformed garnet with inclusions of quartz and coesite, indicating that IPS operated during prograde to peak metamorphism. The distribution of aspect ratios in the garnet grain population suggests that pressure solution preferentially affected smaller grains. SPO analysis of many subregions across a garnetite sample reveals a complex distribution, however the local SPO is consistent with the stress orientation expected for local microstructures such as layering, garnet stacks, or fine-grained internal fluid pathways. Locally, two different preferential orientations are observed, interpreted as the result of two subsequent deformation stages under different stress configurations.Quartz inclusions in prograde euhedral garnet, grown on the outer margin of coevally deformed garnetite, were analysed with Raman spectroscopy. Elastic strains obtained for these inclusions are in agreement with predicted strains for entrapment along the prograde P-T path for the Lago di Cignana unit (~1.5&#8211;2.0 GPa; ~450&#8211;500 &#176;C), whereas significant differential stress during entrapment is expected to result in deviating strain components.By combining microstructural analysis of garnet with elastic-strain analysis of quartz inclusions, stress orientations obtained from deformed garnet are combined with the stress magnitude for coeval garnet growth. The results indicate that the garnetite lenses were deformed and metamorphosed under low differential stress of variable orientation during subduction. These results are in agreement with a system where garnet is wet by a fluid phase that allows IPS.&#160;Acknowledgements: This project has received funding from the European Research Council under the H2020 research and innovation program (N. 714936 TRUE DEPTHS to M. Alvaro)

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Influence Mechanism of Different Flow Patterns on the Softening of Red-Bed Soft Rock

Journal of Marine Science and Engineering ◽

10.3390/jmse7050155 ◽

2019 ◽

Vol 7 (5) ◽

pp. 155 ◽

Cited By ~ 3

Author(s):

Zhen Liu ◽

Xinfu He ◽

Cuiying Zhou

Keyword(s):

Quantitative Analysis ◽

Soft Rock ◽

Flow Patterns ◽

Specific Method ◽

Red Beds ◽

Rock Interaction ◽

Red Sandstone ◽

Influence Mechanism ◽

Water Conditions ◽

Red Bed

As a typical representative of red beds, the softening and disintegration of red sandstone when it encounters water is an important cause of initiated engineering disasters. However, research on the softening of this kind of rock has mainly focused on the still water–rock interaction. There is still a lack of quantitative analysis and a mechanistic explanation for the basic experimental study of dynamic water–rock interactions. Therefore, based on the independently developed multifunctional open channel hydraulic test equipment, the still water was used as the reference by designing the saturation test of red sandstone under two typical flow patterns—laminar flow and turbulent flow—and combined with a three-dimensional numerical simulation; specifically, the chemical, physical and mechanical effects of different flow patterns on the softening of red sandstone are discussed, and the mechanism of the influence of different flow patterns on the softening of red sandstone was further revealed. The results show that under different flow patterns, as the flow of water increased, the alkalinity of the circulating solution became stronger, the speed of stabilization of the ion concentration became faster, the development of the microscopic structure of the corresponding rock became higher and the decrease in mechanical strength became greater. The flow state affects the processes of rock softening and breaking by acting on the rock from the three aspects of chemistry, physics and mechanics. The study makes up for the deficiency of the quantitative analysis index of rock softening under dynamic water conditions and further improves the influence mechanism of different flow patterns on soft rock softening in red beds under dynamic water conditions. This research also provides a specific method for the protection of estuarine and coastal bank slopes with rich red-bed soft rock dissection under different flow patterns.

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Experimental study on compressive strength of the red-bed soft rock highway tunnel's surrounding rock

2011 Second International Conference on Mechanic Automation and Control Engineering ◽

10.1109/mace.2011.5988534 ◽

2011 ◽

Author(s):

Jun Liao ◽

Lei Gao

Keyword(s):

Experimental Study ◽

Compressive Strength ◽

Soft Rock ◽

Surrounding Rock ◽

Red Bed

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Research on Shear Creep Property of Soft Rock in Dam Foundation

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.243-249.2744 ◽

2011 ◽

Vol 243-249 ◽

pp. 2744-2747

Author(s):

Yu Wang ◽

Hua Feng Deng ◽

Tao Lu ◽

Zong Yong Zhao

Keyword(s):

Soil Mechanics ◽

Testing Machine ◽

Creep Property ◽

Soft Rock ◽

Shear Creep ◽

Dam Foundation ◽

Creep Characteristic ◽

The Stability ◽

Argillaceous Siltstone

Creep characteristic is one of the most important mechanical characteristics of rock. It controls the stability of rock engineering. Under step load conditon, the shear creep test of argillaceous siltstone which was collected in dam foundation is performed by using the RMT150c rock and soil mechanics testing machine. The shear creep curves under different normal stresses show that the argillaceous siltstone is very significant in creep, which should be considered in the stability analysis of dam foundation. According to the analysis of experimental results, the long-term shear strength parameters are determined to provide reference for engineering survey and design.

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Stability Reinforcement of Slopes Using Vegetation Considering the Existence of Soft Rock

Applied Sciences ◽

10.3390/app11199228 ◽

2021 ◽

Vol 11 (19) ◽

pp. 9228

Author(s):

Chungang Liu ◽

Huanjun Bi ◽

Dong Wang ◽

Xiaoning Li

Keyword(s):

Factor Of Safety ◽

Soil Layer ◽

Soft Rock ◽

Failure Surface ◽

Soil Parameters ◽

Rainfall Condition ◽

Perfectly Plastic ◽

Elastic Perfectly Plastic ◽

Actual Geometry ◽

Red Bed

This study investigates the effectiveness of vegetation reinforcement on the stability of a slope with red-bed soft rock in a slope along the Xining-Chengdu railway, China. Four kinds of vegetation were considered to reinforce the soil and the slope. The rooted soil parameters were determined based on the laboratory tests. A numerical model was developed based on the actual geometry and soil layer distributions. The soils were modeled as elastic perfectly plastic materials and the vegetation reinforcement was represented as addition cohesion of a series of subsoil layers within a given depth. The effectiveness of vegetation on slope reinforcement under both dry and rainfall conditions was investigated regarding this case. The potential failure surface and corresponding factor of safety of the red-bed soft rock slope for those different conditions were analyzed and compared. It has been found that the addition of vegetation increased the safety of slope stability whether the slope is under a dry condition or a rainfall condition, while the increasing proportion of factor of safety due to vegetation reinforcement for this case is very limited. The results and findings in this study are still significant for the practitioner to evaluate the reasonability of vegetation reinforcement.

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Classification of Red-Bed Rock Mass Structures and Slope Failure Modes in South China

Geosciences ◽

10.3390/geosciences9060273 ◽

2019 ◽

Vol 9 (6) ◽

pp. 273 ◽

Cited By ~ 1

Author(s):

Cuiying Zhou ◽

Xu Yang ◽

Yanhao Liang ◽

Zichun Du ◽

Zhen Liu ◽

...

Keyword(s):

Rock Mass ◽

South China ◽

Slope Failure ◽

Failure Modes ◽

Hard Rock ◽

Soft Rock ◽

Red Beds ◽

Rock Falls ◽

Geological Formation ◽

Red Bed

Red beds are Meso–Cenozoic continental sedimentary strata that are mainly composed of gravel stone, sandstone, siltstone, mudstone, and shale and occasionally have interlayers of limestone, halite, and gypsum. As a typical rock mass, red beds are widely distributed throughout South China. In a typical tropical and subtropical continental environment, red beds are the product of multiple sedimentary cycles, which have resulted in complicated rock mass structures that play an important role in rock mass stability. It is thus of great significance to investigate the influence of different rock mass structures on the stability of red-bed slopes. In this paper, the geological formation history of red beds in South China is described. The main features of red-bed rock mass slopes in South China are discussed. The main combinations of inner geomechanical structures comprise: (1) mega-thick soft rock structures; (2) mega-thick hard rock structures; (3) thick hard rock structures with weak intercalation; and (4) soft–hard interbedded structures. In addition, the features of slope failure are analyzed, and four common failure modes are identified from the statistical data: (a) weathering spalling and scouring; (b) rock falls; (c) landslides; and (d) tensile dumping.

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Experimental studies on red bed soft rock used as roadbed filling

2010 International Conference on Mechanic Automation and Control Engineering ◽

10.1109/mace.2010.5535978 ◽

2010 ◽

Author(s):

Daoxiang Wu ◽

Hongjie Liu ◽

Guoqiang Wang

Keyword(s):

Experimental Studies ◽

Soft Rock ◽

Red Bed

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Laboratory Study On Mechanical Response And Failure Mechanism of Red-Bed Soft Rock Under Water-Rock Interaction

10.21203/rs.3.rs-936170/v1 ◽

2021 ◽

Author(s):

Chi Liu ◽

Xiaoli Liu ◽

Huan Sun ◽

Mingyang Wang ◽

Chunlu Wu ◽

...

Keyword(s):

Mechanical Behavior ◽

Mechanical Response ◽

Soft Rock ◽

Failure Characteristics ◽

Mechanical Coupling ◽

Experimental Platform ◽

Multi Level ◽

Fissure Water ◽

Level Loading ◽

Red Bed

Abstract Red-bed soft rock is a geomaterial that displays special deformation and failure characteristics. The stability of red-bed slopes can be negatively impacted by water and stepped excavation disturbance; however, there is limited research regarding the mechanical behavior and failure characteristics of red-bed soft rock under the action of water-rock hydro-mechanical coupling. In this study, to explore the mechanical response and failure mechanisms of red-bed soft rock under coupled water-rock hydro-mechanical action, a visual experimental platform based on digital radiography and a multi-level loading device was constructed. Angiography was used to visualize the rock fracture process by replacing fissure water with a contrast medium. Multi-level loading was applied to cubic red-bed mudstone samples, and acoustic emission signals, stress, flow rate, and digital radiography images were collected during the failure process. An original image processing method based on Hough transform and a convolutional neural network was used to segment and extract cracks from the imagery, and fissure water flow characteristics, rock mechanical response, and crack evolution were analyzed in detail (Liu et al., 2015; Lv et al., 2013, 2014). Results showed that when the Felicity ratio FR was lower than 1.2, water could induce secondary "water-damaged cracks" in the red-bed samples. Study findings were used to highlight the importance of improved early-warning methods for rainfall-induced landslides at an engineering scale. The original experimental platform proposed and evaluated in this study provides a new and powerful tool to investigate the mechanical behavior of different rock types under the action of water-rock hydro-mechanical coupling at a laboratory scale. These findings will facilitate improved disaster prevention strategies for red-bed geological bodies.

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