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.

scholarly journals Elastic-Plastic Threshold and Rational Unloading Level of Rocks

2019 ◽  
Vol 9 (15) ◽  
pp. 3164 ◽  
Author(s):  
Ming Ji ◽  
Hongjun Guo
Keyword(s):  
Stress Level ◽  
Triaxial Compression ◽  
Confining Pressure ◽  
Confining Stress ◽  
Elastic Plastic ◽  
Conventional Triaxial Compression ◽  
Confining Pressures ◽  
Pressure Increment ◽  
Loading And Unloading ◽  
Plastic Transformation

During loading and unloading test, various rocks manifest different stress values of elastic-plastic transformation. This study proposes to include axial pressure increment ratio in the conventional triaxial compression test to evaluate different variables (nominal elastic modulus, nominal Poisson’s ratio, strain, and energy). The relationships among various factors including variables, the stress level of initial confining stress and axial pressures, were analyzed by analyzing the stress–strain plot record obtained from testing various rocks. The extreme value point of the deformation parameter, also known as the elastic-plastic threshold, was analyzed. In addition, the elastic-plastic thresholds were later used as unloading points during the unloading tests. Under the same confining condition, different rocks demonstrated different unloading levels. Furthermore, a linear correlation was observed between unloading levels and changing confining pressures, and the gradient is mainly related to the types of rocks. During the unloading tests of rocks, the rational unloading level is recommended to be no higher than the stress level at the elastic-plastic threshold under the corresponding confining pressure.

Effect of particle size and strain conditions on the strength of crushed basalt

1983 ◽  
Vol 20 (4) ◽  
pp. 706-717 ◽  
Author(s):  
Mosaid Al-Hussaini
Keyword(s):  
Particle Size ◽  
Stress Level ◽  
Level Density ◽  
Triaxial Compression ◽  
Volumetric Strain ◽  
Confining Pressure ◽  
Strain Diagram ◽  
Compression Tests ◽  
Cohesionless Soils ◽  
Lower Shear

This paper describes the results of an investigation carried out to study the influence of particle size, stress level, density, method of consolidation, and strain conditions on the strength and compressibility of crushed basalt. All specimens were prepared at medium or high density, consolidated isotropically or under K0 consolidation, and sheared under effective confining pressure ranging from 443 to 2297 kPa. The material used in the test program had a straight line grain size distribution with maximum particle size ranges from 0.63 to 76.2 mm and minimum particle size equivalent to No. 30 U.S. standard sieve size:The tests indicated that an increase in the particle size (i.e., gradation) increases the strength and decreases the axial and the volumetric strain at failure. The study indicated further that the crushed basalt under triaxial compression has a lower shear strength than when sheared under plane strain conditions. Particles crushed were significantly influenced by the stress level and gradation and to a lesser degree by density of material. Keywords: cohesionless soils, density (mass/volume), shear tests, stress–strain diagram, compression tests, rockfill dams.

Statistical damage model with strain softening and hardening for rocks under the influence of voids and volume changes

2010 ◽  
Vol 47 (8) ◽  
pp. 857-871 ◽  
Author(s):  
Wen-Gui Cao ◽  
Heng Zhao ◽  
Xiang Li ◽  
Yong-Jie Zhang
Keyword(s):  
Constitutive Model ◽  
Strain Softening ◽  
Triaxial Compression ◽  
Damage Model ◽  
Damage Threshold ◽  
Model Parameters ◽  
Volume Changes ◽  
Conventional Triaxial Compression ◽  
Damage Constitutive Model ◽  
Statistical Damage

With regards to the composition of natural rocks including voids or pores, deformation behavior is strongly affected by variation in porosity. By using a statistical damage-based approach, the characteristics of strain softening and hardening under the influence of voids and volume changes are investigated in the present paper. Suppose that a rock consists of three parts: voids, a damaged part, and an undamaged part. The effects of voids and volume changes on rock behavior are first analyzed through determination of the porosity and an associated damage model is then developed. Later, a statistical evolution equation describing the influence of the damage threshold on the propagation condition of rock damage is formulated based on measurement of the mesoscopic element strength. A statistical damage constitutive model reflecting strain softening and hardening behavior for rocks loaded in conventional triaxial compression is further developed and a corresponding method for determining the model parameters is also provided. Theoretical results of this proposed model are then compared with those observed experimentally. Finally, several aspects of the present constitutive model, which affect the relevant behavior of rocks, are particularly discussed.

Constitutive models of frozen soil

2000 ◽  
Vol 37 (4) ◽  
pp. 811-816 ◽  
Author(s):  
Ping He ◽  
Yuanlin Zhu ◽  
Guodong Cheng
Keyword(s):  
Failure Process ◽  
Constitutive Models ◽  
Confining Pressure ◽  
Frozen Soil ◽  
Damage Development ◽  
Soil Particles ◽  
Whole Process ◽  
Pressure Melting ◽  
Stress States ◽  
Relationship Of

The constitutive models on viscoelastoplasticity and the damage to frozen soil presented in this paper can be used to analyze the relationship of stress and strain, under complicated stress states, and damage development and the failure process of the internal structure of frozen soil. The models successfully predict the whole process of creep, including the failure stage. Both strengthening and weakening effects of confining pressure, namely increasing the friction force between soil particles and decreasing the frozen force between ice and the soil particles due to pressure melting of ice, are considered in the constitutive models.Key words: viscoelastoplasticity, damage development, constitutive model, frozen soil.

Mechanical and cracking behavior of granite containing two coplanar flaws under conventional triaxial compression

2018 ◽  
Vol 28 (4) ◽  
pp. 590-610 ◽  
Author(s):  
Yan-Hua Huang ◽  
Sheng-Qi Yang
Keyword(s):  
Triaxial Compression ◽  
Three Dimensional ◽  
Damage Threshold ◽  
Confining Pressure ◽  
Crack Coalescence ◽  
Failure Behavior ◽  
Shear Cracks ◽  
Cracking Behavior ◽  
Conventional Triaxial Compression ◽  
Triaxial Compressive Strength

Flaws widely exist in rock mass, which significantly influences the strength and failure behavior of rock. The study of the flaw effect on the mechanical and cracking behavior is important to predict the unstable failure of fractured rock engineering. However, three-dimensional crack propagation behavior of real rock containing preexisting flaws under triaxial compression has been rarely studied. To increase the understanding of crack coalescence behavior, a series of laboratory conventional triaxial compression experiments were carried out on granite specimens containing two coplanar three-dimensional flaws. On the basis of experimental results, the effects of flaw angle and confining pressure on the strength properties of granite specimens were analyzed. As the flaw angle increased from 30° to 60° and the confining pressure increased from 0 to 30 MPa, the triaxial compressive strength and crack damage threshold of granite specimen increased. The cohesion and internal friction angle of preflawed granite specimen increased with increasing flaw angle. And then, X-ray micro-CT scanning technique was used to investigate the internal fracture characteristic of granite specimen. Four typical crack coalescence modes were identified in this experiment, i.e. no coalescence, two types of indirect coalescence, and shear coalescence. Under uniaxial compression, cracks from the tips of the flaws led to the specimen failure under tension, while under higher confining pressure, shear cracks and antiwing cracks were dominant.

Experimental Study on the Strain Softening Behavior of Plate Anchors in Clay Under Cyclic Loading

2014 ◽  
Author(s):  
Long Yu ◽  
Qi Zhou ◽  
Jun Liu
Keyword(s):  
Cyclic Loading ◽  
Bearing Capacity ◽  
Stress Level ◽  
Strain Softening ◽  
High Stress ◽  
Offshore Structures ◽  
Pullout Capacity ◽  
Softening Behavior ◽  
Plate Anchors ◽  
High Stress Level

Many geotechnical designs require knowledge of soil uplift resistance where the foundation must withstand tensile forces, such as wind loading on transmission towers, wave action on offshore structures, and buoyancy forces on buried pipelines. Most existing researches on the bearing capacity of plate anchors are limited to static analyses. The effects of offshore cyclic loading on the bearing capacity of plate anchors are not very clear. The ultimate pullout capacity of plate anchors in clay may decrease as the accumulated plastic shear strain grows due to the strain-softening of clay under cyclic loading. In this study, 1 g model tests were carried out to estimate the softening behavior of plate anchors including one low stress level case and two high stress level cases. PIV (Particle Image Velocimetry) technique was used to investigate the soil flow mechanism of the anchor at low stress level. Numerical analyses are carried out to simulate the large deformation behavior of the anchor at high stress level under cyclic loading.

Analysis on Bolt Supporting Mechanism for Roadways Driving along next Goaf Based on Triaxial Compression Test

2012 ◽  
Vol 594-597 ◽  
pp. 1159-1162
Author(s):  
Sheng Zhong ◽  
Yong Jie Yang ◽  
Min Wang
Keyword(s):  
Mechanical Test ◽  
Triaxial Compression ◽  
Confining Pressure ◽  
Test System ◽  
Deformation Characteristics ◽  
Compression Tests ◽  
Conventional Triaxial Compression ◽  
Strength And Deformation ◽  
Rock Mechanical Test ◽  
Triaxial Compression Tests

Conventional triaxial compression tests of coal specimens are carried out by MTS815 servo-controlled rock mechanical test system, and the strength and deformation characteristics of coal under different confining pressure are analyzed. On that basis, bolt supporting mechanism of surrounding rocks of roadways driving along next goaf is studied.

Research on Post-Peak Characteristics of Elastic-Plastic Strain-Softening Model Based on Mohr-Coulomb Strength Criterions

2011 ◽  
Vol 261-263 ◽  
pp. 1439-1443
Author(s):  
Shao Qing Niu ◽  
Shuang Suo Yang ◽  
Lei Cui
Keyword(s):  
Rock Mass ◽  
Strain Softening ◽  
Triaxial Compression ◽  
Dynamic Change ◽  
Confining Pressure ◽  
Strength Parameters ◽  
Underground Engineering ◽  
Coulomb Failure ◽  
Confining Pressures ◽  
Damage Extent

Considering the characteristic that rock mass can transform from brittleness to plasticity and the dynamic change of post-peak strength parameters of the rock mass, the invariability of elastic modulus and poisson's ratio, constitutive model of rock mass could be described with the characteristic that strength parameters obey different Mohr-Coulomb failure criterions under different plastic strains. This model may reflect the post-peak subsequent characteristics of rock mass and the fact that rock mass can transform from brittleness to plasticity with the increase of confining pressure. Numerical calculation is applied to simulate the triaxial compression test under different confining pressures and underground engineering example, which proves that this model has the characteristic of reflecting the damage extent of surrounding rock.

Experimental Investigation on Triaxial Rheological Mechanical Properties of Biotite Granitic Gneiss

2011 ◽  
Vol 90-93 ◽  
pp. 311-316
Author(s):  
Yu Zhou Jiang ◽  
Rui Hong Wang
Keyword(s):  
Rheological Properties ◽  
Stress Level ◽  
Rock Specimen ◽  
Testing Machine ◽  
High Stress ◽  
Linear Acceleration ◽  
Confining Pressure ◽  
Granitic Gneiss ◽  
Confining Pressures ◽  
Rheological Experiments

In order to know about the rheological properties of typical biotite granitic gneiss in Xiaowan Hydropower Project, triaxial rheological experiments with biotite granitic gneiss were carried out on the rock servo-controlling rheological testing machine. As a result the typical complete rheological curve of the biotite granitic gneiss indicates that when the stress level is low, the rheological deformation of rock specimen is not obvious; when in high stress conditions, the rock mass rheological properties are very significant with large rheological deformation, including three typical rheological phases. The rheological deformation decreases with the increase of the confining pressure, and at the same time the rheological rate of rock specimen changes with the change of stress level. In low stress state, the corresponding rheological rate of the rock specimen incarnated as the rheological rate attenuation stage and the rheological rate uniform stage, while once the stress level exceeds the long-term strength of rock specimen, the rheological rate would first decreases and then keep at a constant value, and finally it will trend to follow the non-linear acceleration law. The rupture form of the low-intensity biotite granitic gneiss specimen is the main crack surface which causes the damage of rock specimen, and finally generated by the expansion and transfixion of the crack in the initial cavern flaw. The rheological deformation and rupture form of rock specimen in different confining pressures are not exactly the same.

scholarly journals Experimental Investigation of Energy Evolution in Sandstone Failure during Triaxial Unloading Confining Pressure Tests

2019 ◽  
Vol 2019 ◽  
pp. 1-11 ◽  
Author(s):  
Rui Yang ◽  
Depeng Ma ◽  
Yongjie Yang
Keyword(s):  
Elastic Energy ◽  
Triaxial Compression ◽  
High Stress ◽  
Confining Pressure ◽  
Energy Evolution ◽  
Compression Tests ◽  
Sandstone Sample ◽  
Pressure Tests ◽  
Unloading Confining Pressure ◽  
Sample Damage

The deformation and failure of sandstone samples are closely related to energy changes in the material. To explore the energy evolution during the process of sandstone sample damage, loading and unloading tests with different test paths were conducted. The results show that more energy is stored and consumed before the stress reaches its peak, while after the peak stress, more energy is released and consumed. Energy dissipation increases internal cracking, leads to sample damage and lithologic deterioration, and reduces the bearing capacity of the sample. During triaxial unloading of the confining pressure, the higher the initial unloading confining pressure, the more the elastic energy stored, and the more the energy released when the sandstone sample fails, resulting in more severe damage. Therefore, during the excavation of high-stress rock masses, large amounts of elastic energy stored in sandstone can be rapidly released, leading to rock burst disasters. Additionally, during triaxial unloading confining pressure tests, the damage in sandstone when the sample is close to failure increases more rapidly than that during conventional triaxial compression tests because of the unloading effect of the confining pressure. This phenomenon also illustrates that the failure of sandstone induced by unloading is more sudden than that induced by loading.

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