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

2016 ◽  
Vol 2016 ◽  
pp. 1-12 ◽  
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.

scholarly journals The Critical Indicator of Red-Bed Soft Rocks in Deterioration Process Induced by Water Basing on Renormalization Group Theory

2021 ◽  
Vol 11 (17) ◽  
pp. 7968
Author(s):  
Chang Xia ◽  
Cuiying Zhou ◽  
Fengxian Zhu ◽  
Zhen Liu ◽  
Guangjun Cui
Keyword(s):  
Renormalization Group ◽  
Group Theory ◽  
Soft Rock ◽  
Renormalization Group Theory ◽  
Silty Mudstone ◽  
Soft Rocks ◽  
Multi Scale ◽  
Unit Model ◽  
Deterioration Process ◽  
Red Bed

The internal damage of red-bed soft rock induced by water is pervasive. The accumulation, growth, and localization of damage is a multi-scale process that can lead to significant strength loss in red-bed soft rock. Yet, research on the critical state of deterioration process considering multi-scale failure is limited due to high degree of system freedom. Renormalization group theory is an effective approach to find critical point of phase transition in a disordered system. To apply renormalization group theory in red-bed soft rocks, this article firstly analyzed their microstructures. Then, the granular unit model and stripy unit model are proposed to describe the self-similar characteristics of red-bed soft rocks. The calculation results based on renormalization group theory are consistent with the experimental results. The critical reductions of strength induced by water are 60% in light-yellow silty mudstone and 80% in grey silty mudstone. In addition, the critical state of damage propagation caused by stress is also studied and the analytical solution is derived. Results show that the renormalization group theory can effectively couple the micro damage and strength deterioration which provides guidance to the engineering.

scholarly journals A Synthetic Material to Simulate Soft Rocks and Its Applications for Model Studies of Socketed Piles

2017 ◽  
Vol 2017 ◽  
pp. 1-8 ◽  
Author(s):  
Can Mei ◽  
Qing Fang ◽  
Haowei Luo ◽  
Jiangang Yin ◽  
Xudong Fu
Keyword(s):  
Soft Rock ◽  
Convincing Evidence ◽  
River Sand ◽  
Soft Rocks ◽  
Model Studies ◽  
Strain Behavior ◽  
Manufacturing Procedure ◽  
Rock Specimens ◽  
Concrete Hardening ◽  
Compressive Tests

A detailed manufacturing procedure of a synthetic soft rock is presented, as well as its applications on the laboratory experiments of socketed piles. With the homogeneity and isotropy of the simulated soft rock, the influence of different variables on the bearing performance could be investigated independently. The constituents, cement, gypsum powder, river sand, concrete-hardening accelerator, and water, were mixed to form the specimens. Both uniaxial and triaxial compressive tests were conducted to investigate the stress-strain behavior of the simulated soft rock. Additionally, the simulated soft rock specimens were used in model pile tests and simple shear tests of the pile-rock interface. Results of the simulated soft rock in both the uniaxial and triaxial compressive tests are consistent with those of natural soft rocks. The concrete-hardening accelerator added to the mixtures improves the efficiency in laboratory investigations of soft rock specimens with a curing time of 7 days. The similarities between the laboratory tests and the field observations provide convincing evidence to support its suitability in modeling the behavior of soft rocks.

scholarly journals Properties of Crushed Red-Bed Soft Rock Mixtures Used in Subgrade

2016 ◽  
Vol 2016 ◽  
pp. 1-8 ◽  
Author(s):  
Huayan Yao ◽  
Shanpo Jia ◽  
Wenning Gan ◽  
Zhenhua Zhang ◽  
Kunlin Lu
Keyword(s):  
Moisture Content ◽  
Resilient Modulus ◽  
Soft Rock ◽  
Road Construction ◽  
Absorption Capacity ◽  
Test Results ◽  
Soft Rocks ◽  
Red Bed ◽  
Compaction Degree ◽  
Physical And Mechanical Characteristics

Slaking red-bed soft rocks are widely distributed in the south of Anhui Province, China, and several highways will go through this area. It is important to evaluate their physical and mechanical characteristics for the purpose of using this kind of soft rocks as materials for road construction. In this paper, the compacting tests, the resilient modulus tests, the California bearing ratio (CBR) tests, and permeability tests have been carried out on crushed red-bed soft rock mixtures. The test results showed that, for a given degree of compaction, the resilient modulus decreases linearly with the increase of moisture content. For a given moisture content, the resilient modulus and CBR values increase linearly with the increase of compaction degree, while the soaking swelling, water absorption capacity, and permeability coefficient decrease linearly. In other words, the strength and water stability are enhanced with the increase of the degree of compaction. The results demonstrate that the crushed red-bed soft rock mixtures can be directly used as materials for the highway construction by taking corresponding measures.

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

2021 ◽  
Author(s):  
Kai Huang ◽  
Bo Kang ◽  
Fusheng Zha ◽  
Yunfeng Li ◽  
Qing Zhang ◽  
...  
Keyword(s):  
Mineral Content ◽  
Microstructural Analysis ◽  
Soft Rock ◽  
Sample Surface ◽  
Mineral Dissolution ◽  
Slope Instability ◽  
Large Particles ◽  
Durability Index ◽  
Argillaceous Siltstone ◽  
Red Bed

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.

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

2019 ◽  
Vol 7 (5) ◽  
pp. 155 ◽  
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.

scholarly journals Quantitative Precursory Information of Weak Shocking Failures of Composite Soft Roof

2019 ◽  
Vol 2019 ◽  
pp. 1-10
Author(s):  
Lihua Wang ◽  
Zenghui Zhao ◽  
Zhongxi Tian ◽  
Wei Sun
Keyword(s):  
Deformation Rate ◽  
Soft Rock ◽  
Western China ◽  
System Failures ◽  
Soft Rocks ◽  
Mine Roadway ◽  
Strong Body ◽  
And Control ◽  
Precursory Information ◽  
Bearing System

To reveal the mechanism of weak roof shocking in mine roadway arranged in weakly consolidated soft rock strata commonly observed in western China, a bearing system of composite roof composed of weakly consolidated soft rocks and coal layers was proposed. Then, theoretical analysis and numerical calculation were applied for instability failures of the mass bearing system with strong body and weak body. Eventually, precursory information and criteria of instability failures of the bearing system were developed. The main conclusions obtained are as follows: (1) as the elastic energy released at the postpeak failure stage of weak body contributes to system failures, the equivalent stiffness for system failures consists of the stiffness of strong body and the deterioration stiffness of weak body at softening stage; (2) during the loading process of the two-body system, isochronous sudden jumps of the deformation rate in either body can be regarded as the precursory information of weak impact failures; (3) the frequency of sudden jumps of deformation rate is significantly related to the stiffness, indicating that weak impact failures are readily observed in composite soft roof as stiffnesses of weakly consolidated soft rocks and coal seam are close to each other. This study provides references for prevention and control of weak shocking disasters of composite roofs in western China.

Strain softening of siltstones in consolidation process using a constant strain-rate loading system

2020 ◽  
Author(s):  
Nana Kamiya ◽  
Feng Zhang ◽  
Weiren Lin
Keyword(s):  
Strain Rate ◽  
Mechanical Behavior ◽  
Strain Softening ◽  
Constant Strain Rate ◽  
Soft Rock ◽  
Consolidation Process ◽  
X Ray ◽  
Soft Rocks ◽  
Loading System ◽  
Strain Rate Loading

<p><span>The mechanical behavior of soft rocks is dominated by the mechanical properties of the rock itself. Because soft rocks have different physical properties to hard rocks, it is essential to understand the mechanical behavior of soft rocks when tunnels and huge structures are constructed in these. Strain softening is the mechanical behavior of soil and rock materials and is important in understanding soft rock foundation. To investigate the mechanical behavior of siltstone, a sedimentary soft rock, we performed the one-dimensional consolidation tests (hereafter called K0-consolidation test) using a constant strain-rate loading system. We also took high-resolution X-ray CT images of the test specimens before and after the consolidation tests to observe the consolidation deformation. Using Quaternary siltstones distributed in the Boso Peninsula, central Japan as specimens, strain softening in the consolidation process was confirmed in some formations using two test machines at Kyoto University and Nagoya Institute of Technology. </span></p><p><span>All specimens yielded and the consolidation curves showed over- and normal-consolidation areas. Some specimens’ stress decreased suddenly at increasing strain just before yielding, which can be regarded as a real strain softening because no strain localization could be confirmed within specimens. The stress at the time of the softening differed even for specimens taken from the same formation. Furthermore, the micro-focus X-ray CT images indicated that the specimens had no macro cracks inside. This suggests that strain softening is not due to brittle failure in local areas but due to the softening of the framework structure of the siltstone itself. The samples used in this study are siltstone taken from the Quaternary forearc basin, whose development is related not only to consolidation but also tectonic effects such as horizontal compaction accompanied by plate subduction. Therefore, it is possible that the strain softening confirmed in this study reflects the micro cracks and internal structure that developed during siltstone formation.</span></p>

Research on Shear Creep Property of Soft Rock in Dam Foundation

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.

scholarly journals Comparative Analysis of Thermomechanical Properties and Thermal Damage Constitutive Models of Three Soft Sedimentary Rocks

2020 ◽  
Vol 2020 ◽  
pp. 1-11
Author(s):  
Wenhua Zha ◽  
Weixing Shao ◽  
Suqin Yao ◽  
Qiang Chen ◽  
Denghong Chen
Keyword(s):  
Elastic Modulus ◽  
Thermal Damage ◽  
Sedimentary Rocks ◽  
Soft Rock ◽  
Peak Stress ◽  
Thermomechanical Properties ◽  
Stress Strain ◽  
Soft Rocks ◽  
The Difference ◽  
Sandy Mudstone

In order to study the difference in thermomechanical properties of soft sedimentary rocks of different coal measures, three types of soft sedimentary rocks, sandstone, sandy mudstone, and mudstone, which are common in deep mines, are tested using the RMT-150B rock mechanics test system and GD-65/150. Uniaxial compression experiments were conducted on three kinds of soft rock-cement mixed specimens at 25°C～55°C multistage temperature in an environmental chamber. The difference of important parameters such as stress-strain curve, peak stress, and elastic modulus was analyzed and compared. The results show that (i) in the test temperature range, the stress-strain curves of the three types of soft rocks at different temperatures are roughly divided into four stages: compaction, elasticity, yield, and failure. The proportion of deformation in the compaction stage to the total deformation decreases gradually with the increase of temperature. (ii) When the temperature is lower than 40°C, the yield stage is shorter, and the peak stress and elastic modulus of the three types of soft rocks decrease significantly with the increase of temperature. (iii) Above 40°C, the decreasing trend of peak stress and elastic modulus curve decreases, and the yield stage becomes more and more obvious. The decreasing rate of elastic modulus of sandstone is 0.041 GPa/°C; the decreasing rate of peak stress is 0.193 MPa/°C, the decreasing rate of sandy mudstone is 0.022 GPa/°C and 0.124 MPa/°C, and the decreasing rate of mudstone is 0.020 GPa/°C and 0.051 MPa/°C. (iv) The rationality of the established thermal damage constitutive model of sedimentary soft rock was verified.

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