scholarly journals Experimental Study on Failure Mechanical Properties of Two Kinds of Seafloor Massive Sulfides

Minerals ◽  
2021 ◽  
Vol 11 (10) ◽  
pp. 1144
Author(s):  
Huan Dai ◽  
Yan Li ◽  
Mengdan Li
Keyword(s):  
Mechanical Properties ◽  
Strain Softening ◽  
Triaxial Compression ◽  
Confining Pressure ◽  
Small Scale ◽  
Peak Strain ◽  
Massive Sulfides ◽  
Splitting Test ◽  
Two Samples ◽  
Significant Difference

Remarkable hydrostatic pressures have a significant effect on the failure mechanical properties of seafloor minerals, which also affects the selection and development of mining excavation tools. In this paper, a Brazilian splitting test and triaxial compression test were adopted to investigate the strength and deformation behavior of two kinds of seafloor massive sulfides (SMS) samples at a small-scale size. Based on the mineralogical characterization of the studied samples, the mechanical properties were preliminarily correlated with their internal structures and mineral compositions. Results indicate that there is a significant difference in the triaxial compression deformation properties between the two kinds of SMS samples and the geotechnical data are controlled by mineral type and composition, including porosity. In general, the triaxial compression process of the two kinds of samples included initial compaction, elastic stage, yield stage, failure stage and residual stage, and shows strain softening characteristics after the peak. With the increase in confining pressure, the strain-softening behavior of the white sample is mitigated and gradually changes into strain-hardening. The peak strength and peak strain of the two samples increased linearly with the increase in confining pressure within the confining pressure range of these tests, and the failure pattern of the specimens also changed from a typical brittle failure to a ductile failure. The results of this study provide data to support further understanding of different kinds of SMS, and are of great significance in the design of efficient SMS exploitation equipment.

scholarly journals Mechanical Modeling of Frozen Coarse-Grained Materials Incorporating Microscale Investigation

2021 ◽  
Vol 2021 ◽  
pp. 1-16
Author(s):  
Shan-Zhen Li ◽  
Liang Tang ◽  
Shuang Tian ◽  
Xian-Zhang Ling ◽  
Yang-Sheng Ye ◽  
...  
Keyword(s):  
Strain Softening ◽  
Triaxial Compression ◽  
Confining Pressure ◽  
Coarse Grained ◽  
Peak Strain ◽  
Compression Tests ◽  
Engineering Structures ◽  
Softening Behavior ◽  
Coarse Grained Material ◽  
Predicted Values

In the cold regions of China, coarse-grained materials are frequently encountered or used as backfilling materials in infrastructure construction, such as dams, highways, railways, and mineral engineering structures. Effects of confining pressure (0.2, 0.5, and 1 MPa) and frozen temperature (−2, −5, −10, and −15°C) on the stress-strain response and elastic modulus were investigated using triaxial compression tests. Moreover, the microscale structures of a coarse-grained material were obtained by X-ray computed tomography. The coarse-grained material specimens exhibited strain-softening and significant dilatancy behaviors during shearing. A modified model considering microstructures of the material was proposed to describe these phenomena. The predicted values coincided well with the experimental results obtained in this study and other literatures. The sensitivity analysis of parameters indicated that the model can simulate the initial hardening and post-peak strain-softening behavior of soils. And the transition of volume strain from contraction to dilatancy can also be described using this model. The results obtained in this study can provide a helpful reference for the analysis of frozen coarse-grained materials in geotechnical engineering.

scholarly journals Study on Mechanical Properties of the Basalt Fiber-Rubber Granular Concrete under Triaxial Stress Condition and Its Application

2020 ◽  
Vol 10 (23) ◽  
pp. 8540
Author(s):  
Duohua Wu ◽  
Zhiwen Li ◽  
Juli Li ◽  
Bo Peng ◽  
Hui Shen
Keyword(s):  
Mechanical Properties ◽  
Strain Softening ◽  
Yield Criterion ◽  
Triaxial Compression ◽  
High Stress ◽  
Basalt Fiber ◽  
Peak Strain ◽  
Compression Tests ◽  
Basalt Fibers ◽  
Supporting Structures

To reduce the failure probability of rigid supporting structures caused by large deformation of deeply buried high-stress soft rock roadways, the mechanical properties and failure features of basalt fiber-rubber granular concrete (BFRGC) are investigated based on triaxial compression tests. The post-peak strain softening equations of BFRGC, based on the Mohr–Coulomb yield criterion, are deduced and then compiled in the finite-difference software (FLAC3D) to simulate the post-peak strain-softening process of BFRGC. Combined with practical engineering, the supporting effects of BFRGC with different proportions are evaluated by FLAC3D. The results of compression tests show that the yield strength of the BFRGC increases significantly when the mass percentage of basalt fiber is 0.4%. Moreover, mixing basalt fibers into both the plain concrete and rubber concrete can effectively restrain the development of the fractures under three-dimensional stress. The numerical results show that when the mass fractions of basalt fibers and rubber particles are 0.4% and 5–10%, respectively, both the plastic zone in the surrounding rocks and the deformation of the rigid supporting structures decrease obviously. It is indicated that the optimal ratio of BFRGC can effectively reduce the stress concentration around the roadway and improve the overall bearing capacity of the supporting structures.

Study on mechanical properties and damage evolution of carbonaceous shale under triaxial compression with acoustic emission

2021 ◽  
pp. 105678952199119
Author(s):  
Kai Yang ◽  
Qixiang Yan ◽  
Chuan Zhang ◽  
Wang Wu ◽  
Fei Wan
Keyword(s):  
Mechanical Properties ◽  
Acoustic Emission ◽  
Water Content ◽  
Damage Evolution ◽  
Damage Assessment ◽  
Triaxial Compression ◽  
Confining Pressure ◽  
Damage Variable ◽  
Natural State ◽  
Carbonaceous Shale

To explore the mechanical properties and damage evolution characteristics of carbonaceous shale with different confining pressures and water-bearing conditions, triaxial compression tests accompanied by simultaneous acoustic emission (AE) monitoring were conducted on carbonaceous shale rock specimens. The AE characteristics of carbonaceous shale were investigated, a damage assessment method based on Shannon entropy of AE was further proposed. The results suggest that the mechanical properties of carbonaceous shale intensify with increasing confining pressure and degrade with increasing water content. Moisture in rocks does not only weaken the cohesion but also reduce the internal friction angle of carbonaceous shale. It is observed that AE activities mainly occur in the post-peak stage and the strong AE activities of saturated carbonaceous shale specimens appear at a lower normalized stress level than that of natural-state specimens. The maximum AE counts and AE energy increase with water content while decrease with confining pressure. Both confining pressure and water content induce changes in the proportions of AE dominant frequency bands, but the changes caused by confining pressure are more significant than those caused by water content. The results also indicate that AE entropy can serve as an applicable index for rock damage assessment. The damage evolution process of carbonaceous shale can be divided into two main stages, including the stable damage development stage and the damage acceleration stage. The damage variable increases slowly accompanied by a few AE activities at the first stage, which is followed by a rapid growth along with intense acoustic emission activities at the damage acceleration stage. Moreover, there is a sharp rise in the damage evolution curve for the natural-state specimen at the damage acceleration stage, while the damage variable develops slowly for the saturated-state specimen.

scholarly journals Researches on the Constitutive Models of Artificial Frozen Silt in Underground Engineering

2014 ◽  
Vol 2014 ◽  
pp. 1-8 ◽  
Author(s):  
Yugui Yang ◽  
Feng Gao ◽  
Hongmei Cheng ◽  
Yuanming Lai ◽  
Xiangxiang Zhang
Keyword(s):  
Mechanical Characteristic ◽  
Stress Level ◽  
Strain Softening ◽  
Triaxial Compression ◽  
High Stress ◽  
Constitutive Models ◽  
Confining Pressure ◽  
Frozen Soil ◽  
Conventional Triaxial Compression ◽  
Shear Process

The researches on the mechanical characteristic and constitutive models of frozen soil have important meanings in structural design of deep frozen soil wall. In the present study, the triaxial compression and creep tests have been carried out, and the mechanical characteristic of frozen silt is obtained. The experiment results show that the deformation characteristic of frozen silt is related to confining pressure under conventional triaxial compression condition. The frozen silt presents strain softening in shear process; with increase of confining pressure, the strain softening characteristic gradually decreases. The creep curves of frozen silt present the decaying and the stable creep stages under low stress level; however, under high stress level, once the strain increases to a critical value, the creep strain velocity gradually increases and the specimen quickly happens to destroy. To reproduce the deformation behavior, the disturbed state elastoplastic and new creep constitutive models of frozen silt are developed. The comparisons between experimental results and calculated results from constitutive models show that the proposed constitutive models could describe the conventional triaxial compression and creep deformation behaviors of frozen silt.

Damage evolution and recrystallization enhancement of frozen loess

2017 ◽  
Vol 27 (8) ◽  
pp. 1131-1155 ◽  
Author(s):  
Zhiwei Zhou ◽  
Wei Ma ◽  
Shujuan Zhang ◽  
Cong Cai ◽  
Yanhu Mu ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Strain Rate ◽  
Damage Evolution ◽  
Deformation Process ◽  
Triaxial Compression ◽  
Confining Pressure ◽  
Recrystallization Process ◽  
Frozen Soils ◽  
Time Deformation ◽  
Pressure Melting

A series of multistage triaxial compression, creep, and stress relaxation tests were conducted on frozen loess at the temperature of −6℃ in order to study the damage evolution and recrystallization enhancement of mechanical properties during deformation process. The effect of strain rate, confining pressure, and hydrostatic stress history in the degradation laws of mechanical properties is investigated further. The strain rate has a significant influence on the stress–strain curve which dominates the evolution trend of mechanical properties. The mechanical behaviors (strength, stiffness, and viscosity) of frozen loess all exhibit evident response for the consolidation and pressure melting phenomenon caused by the confining pressure. The multistage loading tests under different hydrostatic stresses are capable of differentiating the development characteristics of mechanical properties during axial loading and hydrostatic compression process, respectively. The testing results indicated that the recrystallization of the ice particle in the frozen soils is an important microscopic factor for enhancement behaviors of mechanical parameters during the deformation process. This strengthening degree of mechanical properties is determined by temperature, duration time, deformation degree, and stress state during the recrystallization process. The phase transformation led by pressure melting and ice recrystallization is a nonnegligible changing pattern of frozen soils microstructure, which has apparent role in the damage evolution of mechanical properties.

scholarly journals Cracking Behaviors and Mechanical Properties of Rock-Like Specimens with Two Unparallel Flaws under Conventional Triaxial Compression

2019 ◽  
Vol 2019 ◽  
pp. 1-15 ◽  
Author(s):  
Huilin Le ◽  
Shaorui Sun ◽  
Chenghua Xu ◽  
Liuyang Li ◽  
Yong Liu
Keyword(s):  
Mechanical Properties ◽  
Inclination Angle ◽  
Failure Modes ◽  
Shear Failure ◽  
Triaxial Compression ◽  
Confining Pressure ◽  
Critical Value ◽  
Tensile Failure ◽  
Rock Bridge ◽  
Bridge Length

Flaws existing in rock masses are generally unparallel and under three-dimensional stress; however, the mechanical and cracking behaviors of the specimens with two unparallel flaws under triaxial compression have been rarely studied. Therefore, this study conducted comprehensive research on the cracking and coalescence behavior and mechanical properties of specimens with two unparallel flaws under triaxial compression. Triaxial compressive tests were conducted under different confining pressures on rock-like specimens with two preexisting flaws but varying flaw geometries (with respect to the inclination angle of the two unparallel flaws, rock bridge length, and rock bridge inclination angle). Six crack types and eleven coalescence types in the bridge region were observed, and three types of failure modes (tensile failure, shear failure, and tensile-shear failure) were observed in experiments. Test results show that bridge length and bridge inclination angle have an effect on the coalescence pattern, but the influence of bridge inclination angle is larger than that of the bridge length. When the confining pressure is low, coalescence patterns and failure modes of the specimens are greatly affected by flaw geometry, but when confining pressure rose to a certain level, the influence of confining pressure is larger than the effect of flaw geometry. The peak strength of the specimens is affected by flaw geometry and confining pressure. There is a critical value for the bridge length. If the bridge length is larger than the critical value, peak strengths of the samples almost keep constant as the bridge length increases. In addition, as the bridge inclination angle increases, there is an increase in the probability of tensile cracks occurring, and with an increase in the confining pressure, the probability of the occurrence of shear cracks increases.

scholarly journals Influence of Water Pressure on the Mechanical Properties of Concrete after Freeze-Thaw Attack under Dynamic Triaxial Compression State

2019 ◽  
Vol 2019 ◽  
pp. 1-12
Author(s):  
Ruijun Wang ◽  
Yan Li ◽  
Yang Li ◽  
Fan Xu ◽  
Xiaotong Li ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Compressive Strength ◽  
Strain Rate ◽  
Water Pressure ◽  
Mass Loss Rate ◽  
Triaxial Compression ◽  
Ultimate Compressive Strength ◽  
Peak Strain ◽  
Freeze Thaw ◽  
Dynamic Triaxial Compression

This study aims at determining the effect of water pressure on the mechanical properties of concrete subjected to freeze-thaw (F-T) attack under the dynamic triaxial compression state. Two specimens were used: (1) a 100 mm × 100 mm × 400 mm prism for testing the loss of mass and relative dynamic modulus of elasticity (RDME) after F-T cycles and (2) cylinders with a diameter of 100 mm and a height of 200 mm for testing the dynamic mechanical properties of concrete. Strain rates ranged from 10−5·s−1 to 10−3·s−1, and F-T cycles ranged from 0 to 100. Three levels of water pressure (0, 5, and 10 MPa) were applied to concrete. Results showed that as the number of F-T cycles increased, the mass loss rate of the concrete specimen initially decreased and then increased, but the RDME decreased. Under 5 MPa of water pressure and at the same strain rate, the ultimate compressive strength decreased, whereas the peak strain increased with the increase in the number of F-T cycles. This result is contrary to the variation law of ultimate compressive strength and peak strain with the increase in strain rate under the same number of F-T times. With the increase in F-T cycles or water pressure, the strain sensitivity of the dynamic increase factor of ultimate compressive strength and peak strain decreased, respectively. After 100 F-T cycles, the dynamic compressive strength under all water pressure levels tended to increase as the strain rate increased, whereas the peak strain decreased gradually.

Mechanical Properties of Bentonite-Sand Mixtures Under Triaxial Stress Condition

1994 ◽  
Vol 353 ◽  
Author(s):  
M. Umedera ◽  
A. Fujiwara ◽  
N. Yasufuku ◽  
M. Hyodo ◽  
H. Murata
Keyword(s):  
Mechanical Properties ◽  
Shear Strength ◽  
Water Content ◽  
Triaxial Compression ◽  
Confining Pressure ◽  
Strength Properties ◽  
Compression Tests ◽  
Optimum Water Content ◽  
Triaxial Compression Tests ◽  
Optimum Water

AbstractA series of triaxial compression tests is being conducted under the drained condition on bentonite and sand mixtures, known as buffer, in saturated and optimum water content states to clarify the mechanical properties of the buffer.It was found that the mechanical properties of bentonite and sand mixtures are strongly influenced by water and bentonite contents: shear strength in a saturated state is less than that in an optimum water content state; shear strength decreases rapidly with increasing bentonite content. Strength properties are much dependent on confining pressure.

scholarly journals Alternative Local Food Shopping Communities in Hungary

2019 ◽  
Vol 19(34) (2) ◽  
pp. 7-21
Author(s):  
Izabella Bakos ◽  
Anikó Khademi-Vidra
Keyword(s):  
Food Systems ◽  
Consumer Behaviour ◽  
Local Food ◽  
Close Correlation ◽  
Retail Trade ◽  
Local Food Systems ◽  
Small Scale ◽  
Food Shopping ◽  
Two Samples ◽  
Significant Difference

As a result of concerns about the long-term sustainability of globalized retail trade and the stronger presence of health conscious consumer behaviour, governments and groups of conscious consumers worldwide are increasingly focusing on the promotion and development of local food systems and small-scale retail chains and the production of quality local food products to promote the market. In our paper, we would like to give an overview of community-led alternative types of local food systems, with particular attention to shopping community-type consumer and consumer communities. We also describe the main results of our primary research in the population and the shopping community. During the questionnaire we revealed general consumer behaviour and the demand and attitude of local food, the popularity of the customer communities in the settlement of the respondents. In the survey conducted among members of the consumer community, we looked at the analytical areas designated as a target in the population questionnaire for the purpose of comparability and our aim was to explore the sociometrics and lifestyles of communities as well as their community experiences and possible developments. Our hypothesis is that there is a close correlation between the respondents with higher education and income and the preferences of local food. Furthermore, it is assumed that there is a significant difference between the food consumption behaviors of the two samples examined.

scholarly journals SHPB Testing and Analysis of Bedded Shale under Active Confining Pressure

2020 ◽  
Vol 2020 ◽  
pp. 1-8
Author(s):  
Guoliang Yang ◽  
Jingjiu Bi ◽  
Xuguang Li ◽  
Jie Liu ◽  
Yanjie Feng
Keyword(s):  
Mechanical Properties ◽  
Elastic Modulus ◽  
Strain Rate ◽  
Peak Stress ◽  
Confining Pressure ◽  
Dynamic Mechanical Properties ◽  
Dynamic Elastic Modulus ◽  
Peak Strain ◽  
Dynamic Mechanical ◽  
Bedding Angle

Shale gas is the most important new energy source in the field of energy, and its exploitation is very important. The research on the dynamic mechanical properties of shale is the premise of exploitation. To study the dynamic mechanical properties of shale from the Changning-Weiyuan area of Sichuan Province, China, under confining pressure, we used a split Hopkinson pressure bar (SHPB) test system with an active containment device to carry out dynamic compression tests on shale with different bedding angles. (1) With active confining pressure, the shale experiences a high strain rate, and its stress-strain curve exhibits obvious plastic deformation. (2) For the same impact pressure, the peak stress of shale describes a U-shaped curve with an increasing bedding angle; besides, the peak stress of shale with different bedding angles increases linearly with rising confining pressure. The strain rate shows a significant confining pressure enhancement effect. With active confining pressure, the peak strain gradually decreases as the bedding angle increases. (3) As a result of the influence of different bedding angles, the dynamic elastic modulus of shale has obvious anisotropic characteristics. Shale with different bedding angles exhibits different rates of increase in the dynamic elastic modulus with rising confining pressure, which may be related to differences in the development of planes of weakness in the shale. The results of this study improve our understanding of the behavior of bedded shale under stress.

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