scholarly journals Experiment and Mechanism Investigation on Freezing-Thawing of Sandstone with Different Water Contents

2021 ◽  
Vol 2021 ◽  
pp. 1-11
Author(s):  
Guilei Song ◽  
Longxiao Chen ◽  
Kesheng Li ◽  
Deng Zhang ◽  
Junhao Xu ◽  
...  
Keyword(s):  
Acoustic Emission ◽  
Water Content ◽  
Shear Failure ◽  
Freezing Temperature ◽  
Emission Characteristics ◽  
Underground Engineering ◽  
Empirical Formulas ◽  
Splitting Failure ◽  
Acoustic Emission Test ◽  
Water Contents

Freezing-thawing cycles seriously affect the safety of underground engineering in cold regions. At present, most research studies focus on the effect of number and freezing temperature on freezing-thawing cycles. As another important factor, the mechanism of rock mass water content affecting freezing-thawing is less studied. This paper studied the influence of the water content on mechanical property, microstructure, and acoustic emission characteristics of sandstone. The results indicated that the uniaxial compressive strength (UCS) and elastic modulus (E) of sandstone after 20 freezing-thawing cycles decreased as the water content increased. However, the decreasing rate of UCS gradually decreased, while the decreasing rate of E gradually increased. Furthermore, the empirical formulas of UCS and E about water content were obtained. The porosity and plasticity of sandstone after 20 freezing-thawing cycles increased as the water content increased. The empirical formulas of UCS and E about water content were obtained. The porosity and plasticity of sandstone after 20 freezing-thawing cycles increased as the water content increased. The decreasing trend of UCS with porosity was the same as that of UCS with water content. The failure form of sandstone gradually changed from splitting failure to shear failure. The results of the acoustic emission test showed that the stress-strain curves combined with acoustic emission ring counting could reveal the damage evolution process of sandstone during loading.

scholarly journals Mechanical Properties and Acoustic Emission Characteristics of Karst Limestone under Uniaxial Compression

2018 ◽  
Vol 2018 ◽  
pp. 1-14 ◽  
Author(s):  
Jianxun Chen ◽  
Qingsong Wang ◽  
Jiaqi Guo ◽  
Yanbin Luo ◽  
Yao Li ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Acoustic Emission ◽  
Water Content ◽  
Uniaxial Compression ◽  
Wave Velocity ◽  
Brittle Failure ◽  
Shear Failure ◽  
Testing Machine ◽  
Natural State ◽  
Saturated State

Firstly, I-RPT ultrasonic detector was used to test the wave velocity of karst limestone with different initial microstructure and water content. Then, RMT-150B rock testing machine and DS2-16B acoustic emission system were used to test the acoustic emission (AE) under uniaxial compression. Mechanical properties and AE characteristics were obtained during rock failure. The detailed relationship between stress-strain and AE characteristics was studied in this paper. Research results indicated the following: (1) For samples with many primary fissures and defects, wave velocity in dry state was larger than that in its natural state. From natural state to saturated state, the wave velocity tended to increase. For samples with good integrity, wave velocity increased with increasing of water content. (2) In the dry state, the samples presented tension failure. In saturated state, the samples presented tension-shear failure. For samples with cracks and good integrity, samples showed brittle failure. For samples with many corrosion pores which showed ductile damage under natural and saturated state, the spalling phenomenon was enhanced under saturated state. (3) With increasing of water content, the peak stress and AE peak reduced dramatically. In brittle failure, AE peak could be considered a sign of failure. In ductile failure, AE activity decreased gradually with the decrease of stress. (4) The mechanical properties and AE characteristics corresponding to four main fracture propagation types were also discussed.

ANALYSIS OF EMPIRICAL COMPRESSION INDEX EQUATIONS USING THE WATER CONTENT

2017 ◽  
Vol 4 (1) ◽  
Author(s):  
Amir W. Al-Khafaji ◽  
Krishnanand Y. Maillacheruvu ◽  
Melissa Hoerber
Keyword(s):  
Water Content ◽  
Empirical Models ◽  
Soil Types ◽  
Data Sets ◽  
Regression Equations ◽  
Compression Index ◽  
Empirical Formulas ◽  
Wide Range ◽  
Compression Data ◽  
Water Contents

This paper proposes a new method to evaluate the reliability of published empirical formulas in terms of accuracy and applicability to different soil types. Different empirical models are proposed to properly approximate the compression index for a wide range of water contents and soil types. They were developed using a unique technique and a substantial number of published regression equations and compression data. Familiar empirical equations were examined for their reliability in predicting the compression index of clay for any water content. A comparison was made between available and newly-proposed empirical formulas using combined regression data sets compiled independently by several authors. The newly proposed empirical compression index equations are applicable to a wide range of clay soils, and in validating other published relationships. The degree of scatter and variations in the computed compression index values are minimized for any water content.

Experimental Study on Acoustic Emission Characteristics of Splitting Damage Processes for Different Ages of Concrete

2011 ◽  
Vol 105-107 ◽  
pp. 976-980
Author(s):  
Yan Wang ◽  
Sheng Xing Wu ◽  
Shuo Chen ◽  
Yao Wang ◽  
Bao Long Wei
Keyword(s):  
Acoustic Emission ◽  
Gradual Increase ◽  
Damage Mechanism ◽  
Strength Development ◽  
Early Age ◽  
Emission Characteristics ◽  
Related Research ◽  
Splitting Failure ◽  
Early Age Concrete ◽  
Damage Processes

A total of 18 specimens’ damage processes of concrete under split load in 1d, 3d, 5d, 7d, 14d and 28d ages are monitored by acoustic emission (AE) technique and corresponding typical AE characteristics are summarized. The results show that splitting tensile strength of concrete and the number of AE hits are both showing a gradual increase with the growth of age. During the process of splitting failure of concrete specimens in 14d and 28d, AE hits in higher duration and amplitude are collected, It shows that the older concretes tends to release more energy, at last, AE parameters which are in higher correlation with the development of mechanical properties for early age concrete are given. Related research conclusions can provide the foundation for the research of strength development and damage mechanism of early age concretes.

scholarly journals Acoustic Emission Waveform Analysis of Sandstone Failure with Different Water Content

Geofluids ◽  
2021 ◽  
Vol 2021 ◽  
pp. 1-10
Author(s):  
Hongru Li ◽  
Manchao He ◽  
Rongxi Shen ◽  
Yingming Xiao ◽  
Tai Cheng
Keyword(s):  
Acoustic Emission ◽  
Water Content ◽  
Rock Failure ◽  
Waveform Analysis ◽  
Energy Index ◽  
Hilbert Huang Transform ◽  
Energy Mechanism ◽  
Influence Of Water ◽  
Ae Signal ◽  
Water Contents

Previous studies have shown that water can reduce the acoustic emission (AE) energy and other parameters during rock failure. However, the fracture mechanism of rock can be better reflected by analyzing the AE waveform. Therefore, this paper conducted experiments of uniaxial compression on sandstone samples of various water contents and collected AE signals simultaneously. Analyses of fast Fourier transform (FFT) and Hilbert-Huang transform (HHT) were performed on the AE waveform when the sample failed. The results show that as the water content increases, the frequency and intensity of the AE signal will decrease. The influence of water on the intensity of the AE signal is greater than that on the frequency. Through the analysis of the energy mechanism of rock failure, it is pointed out that the frequency and intensity of AE signal are closely related to elastic energy index W ET and burst energy index K E . The research results have guiding significance for the monitoring of rockburst.

scholarly journals Experimental Study on Mechanical Properties and Acoustic Emission Characteristics of Water Bearing Sandstone under Stable Cyclic Loading and Unloading

2020 ◽  
Vol 2020 ◽  
pp. 1-15
Author(s):  
Xinzhan Qin ◽  
Yu Zhou ◽  
Manchao He
Keyword(s):  
Mechanical Properties ◽  
Acoustic Emission ◽  
Cyclic Loading ◽  
Water Content ◽  
Coal Mines ◽  
Surrounding Rock ◽  
Emission Characteristics ◽  
Cyclic Loading And Unloading ◽  
Loading And Unloading ◽  
Pumped Storage

Due to the adjustment of energy structure, a large number of coal mines are abandoned. Considering the environmental and economic effects, many experts proposed to use the abandoned mine cavern as the reservoir of the pumped storage power station. Furthermore, considering the long-term effects of repeated pumping and drainage and hydrodynamic pressure on the surrounding rock in coal mines, a large amount of sandstone was collected from the Ruineng coal mine in Yan’an city to carry out a series of laboratory tests. Through uniaxial compression testing of rock samples with different water content rates, combined with acoustic emission (AE) analysis, the strength softening and macrodeformation characteristics are obtained, and the influence of water content on acoustic emission characteristics is clarified. The mechanical properties of water bearing rock under cyclic loading and unloading experiments with varying upper limits are obtained using a triaxial test system, and the precursory information of rock failure is captured, providing significant guidance for stability analysis and instability warning for surrounding rock in pumped storage power stations.

scholarly journals Shear Behavior and Anisotropy Characteristics of the Fracture Morphology of Sandstone with Different Water Contents

Geofluids ◽  
2020 ◽  
Vol 2020 ◽  
pp. 1-8 ◽  
Author(s):  
Changang Du ◽  
Lulu Sun ◽  
Botao Qin ◽  
Jiang Xu ◽  
Yixin Liu
Keyword(s):  
Water Content ◽  
Shear Failure ◽  
Shear Fracture ◽  
Failure Process ◽  
Three Dimensional ◽  
Fracture Morphology ◽  
Jointed Rock ◽  
Direct Shear Tests ◽  
Initiation And Propagation ◽  
Water Contents

Hydromechanical coupling in rock masses is an important issue for many rock mechanics and hydrogeology applications. The change of a water-bearing state will induce the fracture of the intact rocks and further accelerate the shear slip instability of the sheared surface. To investigate the weakening effect of water content on the mechanical properties of a rock mass, laboratory direct shear tests combined with three-dimensional analysis of sheared surfaces were carried out on sandstone samples with different water contents. The variogram parameters, sill and range, were applied to quantify the morphology of shear fracture surfaces, to reflect the shear failure process of the intact rock, and to provide a basis for resliding instability of jointed rock. It was determined that the sill represents the height of the fluctuation body in the fracture surface and the range represents the single fluctuation body and may reflect the frequency of fluctuations. The test results revealed that the increase in water content had a clear weakening effect on the shear strength and deformation behavior of rock, especially under saturated conditions. Moreover, the distribution of water in the samples directly affected the crack initiation and propagation and characteristics of the fracture morphology.

scholarly journals Experimental Study of Creep Acoustic Emission Characteristics of Coal Bodies around Boreholes under Different Moisture Contents

Energies ◽  
2021 ◽  
Vol 14 (11) ◽  
pp. 3103
Author(s):  
Tianjun Zhang ◽  
Zhiqiang Ling ◽  
Mingkun Pang ◽  
Yukai Meng
Keyword(s):  
Acoustic Emission ◽  
Water Content ◽  
Water Saturation ◽  
Axial Strain ◽  
Transient Strain ◽  
Influence Of Water ◽  
Creep Transient ◽  
Coal Rock ◽  
Saturated Water Content ◽  
Water Contents

Water content is an important factor in the deformation-destruction process of coal bodies. To analyze the influence of water on the creep acoustic emission (AE) characteristics of coal rock surrounding a borehole, we conducted graded loading creep AE tests of single-hole specimens with different water contents (0%, 4%, 8% and water-saturation) under uniaxial loading. The findings include the following: the water content affects the creep mechanical properties of the coal body around a borehole. The creep transient strain and steady-state strain increased exponentially with rising water content; the saturated specimen showed the highest increase, reaching 44.5% and 28.6%, respectively. The specimen water content affected the cumulative ringing count (CRC) and the axial strain during creep. The axial strain increased with rising water content, the CRC increased linearly with rising axial strain. The higher the water content, the greater the CRC rise. At different stress levels, the CRC in the 4%, 8% and saturated water content specimens changed by 43%, 53% and 74%, respectively. The AE ringing rate showed a pattern of grow–decline–stabilize at each creep stage. The AEs decreased significantly with the rising water content and the creep curve lagged behind the AE data. This paper provides guidelines for gas extraction, borehole maintenance and AE detection.

scholarly journals Experimental Study on Normal Frost-Heave Force Generated from Loess upon Freezing considering Multiple Factors

2019 ◽  
Vol 2019 ◽  
pp. 1-9
Author(s):  
Zai-kun Zhao ◽  
Tie-hang Wang ◽  
Xin Jin ◽  
Yu Zhang
Keyword(s):  
Experimental Study ◽  
Water Content ◽  
Freezing Temperature ◽  
Frost Heave ◽  
Dry Density ◽  
Force Model ◽  
Test Results ◽  
Multiple Factors ◽  
Water Contents ◽  
Good Agreement

An experimental study on the normal frost-heave force generated by loess was conducted by subjecting loess with various water contents and densities to different temperature conditions. The experimental results show that the interaction of the three factors has a significant effect on the normal frost-heaving force. Normal frost-heave force increases exponentially with an increase in dry density and linearly with a reduction in the freezing temperature or an increase in water content; of these factors, dry density has the greatest influence on frost-heave force, followed by water content then temperature. A frost-heave force model is developed that includes overall consideration of the interactions of water content, density, and temperature based on fitting of the test results. The value calculated with the model is in good agreement with values measured in verification tests, indicating that the model has high accuracy and can provide scientific guidance for engineering design in loess areas.

scholarly journals Study on Characteristics of Energy Storage and Acoustic Emission of Rock under Different Moisture Content

2021 ◽  
Vol 13 (3) ◽  
pp. 1041
Author(s):  
Chuanming Li ◽  
Nan Liu ◽  
Wanrong Liu ◽  
Ruimin Feng
Keyword(s):  
Acoustic Emission ◽  
Energy Storage ◽  
Water Content ◽  
Elastic Limit ◽  
Test System ◽  
Natural State ◽  
Uniaxial Compression Test ◽  
Sound Emission ◽  
Underground Engineering ◽  
Rock Samples

In order to study the energy storage and sound emission characteristics of rocks under different water content, uniaxial compression test, cyclic loading, unloading test and sound emission test were carried out using RMT-150B rock mechanics test system and DS5 acoustic emission system. The results show that the total strain energy of saturated rock samples and the area of hysteresis loop are the largest in the same period number, which indicates that the presence of water can reduce the elastic limit of rock samples, making the rock very easy to deform and even damage. Acoustic emission tests show that the damage energy of water-bearing rocks is small. The higher the water content, the smaller the peak damage energy. The bending energy index WET of the rock sample under saturated and natural state is smaller than that under dry state, which further indicates that the presence of water can reduce the elastic limit of the rock and soften it. The results can provide a basis for the prediction of underground engineering construction and rock failure instability.

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