scholarly journals The Scale Effect of Coarse-Grained Materials by Triaxial Test Simulation

2021 ◽  
Vol 2021 ◽  
pp. 1-13
Author(s):  
Xiaotao Ai ◽  
Guangjin Wang ◽  
Xiangyun Kong ◽  
Bo Cui ◽  
Bin Hu ◽  
...  
Keyword(s):  
Scale Effect ◽  
Triaxial Test ◽  
Failure Process ◽  
Deformation Modulus ◽  
Peak Stress ◽  
Friction Angle ◽  
Confining Pressure ◽  
Coarse Grained ◽  
Strength Parameters ◽  
And Migration

The scale effect is an unavoidable problem in the laboratory test of coarse-grained materials. By combining the self-developed cellular automaton program with laboratory experiments, a method of simulating the triaxial test of coarse-grained materials was proposed in this paper, and a triaxial test numerical specimen that can characterize the discontinuous, nonuniform, and heterogeneous characteristics of bulk geotechnical materials was established. The parallel grading method was adopted to create six grading curves for numerical simulation based on one in situ grading curve. The failure process and the scale effect on the strength and deformation of coarse-grained materials were analyzed and discussed. The results showed that under the same confining pressure, the peak stress and initial deformation modulus E i increased with the increase of the maximum particle size d max , while the degree of shear shrinkage and Poisson’s ration υ decreased. As the confining pressure increased, the scale effect of coarse-grained materials would be magnified. If particle breakage and migration were assumed to be neglected, the internal friction angle φ and d max would be roughly proportional, the cohesive force c fluctuated with the increase of d max , and the empirical relations between d max and c and φ were established, respectively, which provides a reference for estimating the actual shear strength parameters of coarse-grained materials on-site. The research results can provide a way of thinking for the study of the scale effect of coarse-grained materials and also have certain reference significance for inferring the strength parameters of the original-graded coarse-grained materials.

scholarly journals Macro-Micromechanical Properties of Sandy Pebble Soil of Different Coarse-Grained Content

2018 ◽  
Vol 22 (1) ◽  
pp. 65-71
Author(s):  
Junfu Lu ◽  
Di Li ◽  
Xiaoqiang Xue ◽  
Shenlin Ling
Keyword(s):  
Internal Friction ◽  
Triaxial Test ◽  
Large Scale ◽  
Strain Curve ◽  
Friction Angle ◽  
Confining Pressure ◽  
Discrete Element ◽  
Internal Friction Angle ◽  
Coarse Grained ◽  
Research Results

Sandy pebble stratum is a typical discrete particle unstable stratum, mainly consisting of sand and pebble. However, the effect of coarse-grained content on the stability of stratum is not clear. This paper defined the sandy pebble soil of different coarse-grained content in Chengdu City, Sichuan Province, China as the research object. Research on macro-mesomechanical properties of sandy pebble soil of different coarse-grained content was carried out using the method combining the indoor large-scale triaxial test of coarse-grained soil with the discrete element numerical triaxial test. The research results showed that the stress-strain curve of sandy pebble soil exhibited strain softening with the increase of coarse-grained content; when the confining pressure was the same, the stress peak increased and the strain when the peak was reached decreased gradually with the increase of coarse-grained content. It revealed the functional relationship between coarse-grained content and mechanical indexes of sandy pebble soil such as internal friction angle and cohesion. The internal friction angle and cohesion of sandy pebble soil linearly increased with the rise of coarse-grained material; it proposed the particle discrete element micro parameters of sandy pebble soil of different coarse-grained content, including contact modulus, friction coefficient, particle stiffness ratio, contact bond strength. The research results provided the theoretical support for the new design and construction of sandy pebble stratum project. 

Stability Analysis of Dam Slope by Double Safety Factors of Dynamic Local Strength Reduction Method

2015 ◽  
Vol 744-746 ◽  
pp. 593-596
Author(s):  
Yuan Meng
Keyword(s):  
Internal Friction ◽  
Reduction Method ◽  
Failure Process ◽  
Friction Angle ◽  
Strength Reduction ◽  
Internal Friction Angle ◽  
Material Strength ◽  
Strength Reduction Method ◽  
Strength Parameters ◽  
Local Strength

When calculating the dam slope failure process, traditional strength reduction method doesn't consider the difference of decay rate between cohesion and internal friction angle and discount the strength parameters for all elements. This paper uses two different reduction factors for material strength parameters, slope cohesion and internal friction angle. Based on the yield approach index criterion, we change the reduction region in time and put forward a double safety factor of dynamic local strength reduction method for engineering analysis of dam slope stability.

Test of Dynamic Strength Characteristics of Lishi Loess

2013 ◽  
Vol 303-306 ◽  
pp. 2902-2907 ◽  
Author(s):  
Nian Qin Wang ◽  
Xiao Ling Liu ◽  
Bo Han ◽  
Bo Tao Liu
Keyword(s):  
Stress Relaxation ◽  
Dynamic Stress ◽  
Peak Stress ◽  
Confining Pressure ◽  
Dynamic Strain ◽  
Soil Consolidation ◽  
Strength Parameters ◽  
Loading Test ◽  
Loess Slope ◽  
Effective Strength

Lishi loess is an important component of loess slope. To explore the structure and strength change characteristics of Lishi loess caused by shock (vibration) action, and to reveal the mechanism of loess slope catastrophe, the dynamic triaxial test was performed by using equivalent sine wave under strain controlling. The results show that:① There is an obvious stress relaxation phenomenon during the same cyclic loading test, the degree decreases with the increasing of dynamic strain and confining pressure. And the influence of dynamic strain variation on stress relaxation degree is less under high confining pressure than under low confining pressure;② Under a confining pressure of 40kPa, within 1% strain ranges, the needed dynamic stress to reach the specified strain is just 0.01kN, and the peak stress decreases with the augmentation of dynamic strain, when peak stress increases to 0.204kN, the sample is destructed; Under a confining pressure of 90kPa, soil radial particles are closely spaced, within 2% strain ranges also only a dynamic stress of 0.01kN is needed to reach the specified strain, and with the increase of dynamic strain, the samples are destructed when dynamic strain increases to 0.267kN. The dynamic failure stress of Lishi loess increases gradually with the increase of confining pressure, and the linear regression equation is бd=0.0011б3+0.1590, the correlation coefficient is 0.9944. ③According to Mohr-Coulomb failure criterion, the strength parameters of Lishi loess in somewhere of the north of shaanxi are C=30.33kPa，φ=14°. Under the dynamic shearing action, the dynamic effective strength parameters are obviously less than static effective strength parameters, this indicates that the soil consolidation effect reduced and the particles displaced and occluded each other.

scholarly journals Experimental Studies of Scale Effect on the Shear Strength of Coarse-Grained Soil

2022 ◽  
Vol 12 (1) ◽  
pp. 447
Author(s):  
Shuya Li ◽  
Tiancheng Wang ◽  
Hao Wang ◽  
Mingjie Jiang ◽  
Jungao Zhu
Keyword(s):  
Particle Size ◽  
Shear Strength ◽  
Internal Friction ◽  
Scale Effect ◽  
Friction Angle ◽  
Coarse Grained ◽  
Test Results ◽  
Maximum Particle Size ◽  
Maximum Particle ◽  
Coarse Grained Soil

Shear strength is an essential index for the evaluation of soil stability. Test results of the shear strength of scaled coarse-grained soil (CGS for short) are usually not able to accurately reflect the actual properties and behaviors of in situ CGS due to the scale effect. Therefore, this study focuses on the influence of the scale effect on the shear strength of scaled CGS, which has an important theoretical significance and application for the strength estimation of CGS in high earth-rock dam engineering. According to previous studies, the main cause of the scale effect for scaled CGS is the variation of the gradation structure as well as the maximum particle size (dmax), in which the gradation structure as a characteristic parameter can be expressed by the gradation area (S). A total of 24 groups of test soil samples with different gradations were designed by changing the maximum particle size dmax and gradation area S. Direct shear tests were conducted in this study to quantitatively explore the effect of the gradation structure and the maximum particle size on the shear strength of CGS. Test results suggest that the shear strength indexes (i.e., the cohesion and internal friction angle) of CGS present an increasing trend with the improvement of the maximum particle size dmax, and thus a logarithmic function relationship among c, φ, and dmax is presented. Both cohesion (c) and internal friction angle (φ) are negatively related to the gradation area (S) in most cases. As a result, an empirical relationship between c, φ, and S is established based on the test results. Furthermore, a new prediction model of shear strength of CGS considering the scale effect is proposed, and the accuracy of this model is verified through the test results provided by relevant literature. Finally, the applicability of this model to different types of CGS is discussed.

Numerical Simulation of Triaxial Tests for Coarse-Grained Soil Considering the Initial Fabric of Samples Grain

2010 ◽  
Vol 143-144 ◽  
pp. 873-878
Author(s):  
Guang Jin Wang ◽  
Xiang Yun Kong ◽  
Yi Lei Gu ◽  
Chun He Yang
Keyword(s):  
Numerical Simulation ◽  
Internal Friction ◽  
Random Distribution ◽  
Friction Angle ◽  
Internal Friction Angle ◽  
Coarse Grained ◽  
Triaxial Tests ◽  
Strength Parameters ◽  
The Relationship ◽  
Coarse Grained Soil

The strength parameters of granular coarse-grained soil are the critical factor that affects the stability of ultra-high dump. The soil particles of different size have no sorting and random distribution, which leads to the initial fabric of sample grain uncontrolled in the laboratory test of coarse-grained soil, therefore, only relying on the laboratory testing is difficult to obtain the reliable strength parameters of coarse-grained soil. Based on Cellular Automata method, combining the laboratory triaxial tests of coarse-grained soil developed the HHC-CA model which generated the coarse-grained soil samples of different initial fabric of grain to characterize the heterogeneous and random distribution of coarse-grained soil grain group. Then by means of FLAC3D, conducting triaxial numerical simulation tests of coarse-grained soil and discussing the relationship between the gravel contents of samples shear band and samples and internal friction angle. Moreover, the shear strength model for different coarse-grained contents is established. Numerical simulation results indicated that the relationship between internal friction angle of coarse-grained soil and gravel contents of samples shear band were increasing function in the same size grading. According to the increasing of samples gravel contents, the internal friction angle might reduce, but the mean internal friction angle significantly increased with the increment of samples gravel contents.

Study on Particle Breakage of Coarse-Grained Soil Based on Large-Scale Triaxial Test

2014 ◽  
Vol 937 ◽  
pp. 585-589
Author(s):  
Fu Yong Chu
Keyword(s):  
Power Function ◽  
Triaxial Test ◽  
Large Scale ◽  
Confining Pressure ◽  
Particle Breakage ◽  
Plastic Work ◽  
Coarse Grained ◽  
Earth Dam ◽  
Relationship Of ◽  
Coarse Grained Soil

Using large-scale shearing device, isotropiclly consolidated-drained triaxial test under different confining pressures are performed for overburden material of ShuangJiangKou earth dam which relative density is 0.8. The relationship between particle breakage of coarse-grained soil and input plastic work under loading and between particle breakage and confining pressure and between particle breakage and strength of coarse-grained soil. The results show that the particle breakage of coarse-grained soil and the input plastic work under loading is closely related. The particle breakage of coarse-grained soil increase with the input plastic work and there is a relationship of power function between Bg andWp. the increase of confining pressure will lead to the increase of particle breakage of coarse-grained soil, and there is a relationship of power function between Bg and. the increase of particle breakage of coarse-grained soil will lead to the decrease of strength of coarse-grained soil, and a relationship of linear between Bg andφ.

Influence Factor on Dilatancy of Coarse-Grained Soil Based on Large-Scale Triaxial Test

2014 ◽  
Vol 919-921 ◽  
pp. 687-692 ◽  
Author(s):  
Fu Yong Chu
Keyword(s):  
Relative Density ◽  
Triaxial Test ◽  
Large Scale ◽  
Confining Pressure ◽  
Coarse Grained ◽  
Earth Dam ◽  
Triaxial Shear Test ◽  
Overburden Material ◽  
Confining Pressures ◽  
Coarse Grained Soil

Abstract：Using large-scale shearing device, K0 consolidated-drained triaxial test and isotropiclly consolidated-drained triaxial test under different confining pressures are performed for overburden material of ShuangJiangKou earth dam which relative density is 0.9. And meanwhile, isotropically consolidated-drained triaxial test under different confining pressures are also performed for overburden material of ShuangJiangKou earth dam which relative density is 0.8. The difference of strength and deformation between under under K0-consolidation condition and isotropic consolidation condition and between under different relative density, and the influence of confining pressure, relative density and consolidation condition on the dilatancy of coarse-grained are analyzed. The results show that the strength of K0 consolidated-drained triaxial shear test is slight greater than that obtained by isotropically consolidated-drained test. The strength of coarse-grained soil increases with increase of relative density.The volume strain value of isotropically consolidated-drained triaxial shear test is bigger than that of K00 consolidated-drained test, and the volume strain value decreases with the decreases of relative density. The dilatancy of coarse-grained soil decreases with the increase of confining pressure, and increases with the increase of static lateral pressure coefficient.

scholarly journals Mechanical Characteristics of Coal and Rock in Mining under Thermal-Hydraulic-Mechanical Coupling and Dynamic Disaster Control

2021 ◽  
Vol 2021 ◽  
pp. 1-12
Author(s):  
Haifeng Ma ◽  
Lingjie Wang ◽  
Xin'gang Niu ◽  
Fanfan Yao ◽  
Kexue Zhang ◽  
...  
Keyword(s):  
Elastic Modulus ◽  
Temperature Gradient ◽  
Coal Mine ◽  
Coal Sample ◽  
Deformation Modulus ◽  
Peak Stress ◽  
Confining Pressure ◽  
Peak Strain ◽  
Lateral Expansion ◽  
Mechanical Coupling

In order to reduce the risk of coal and rock dynamic disasters in the coal mine production process, the coupling mechanics characteristics of coal and rock produced in the process of coal mining in the Dingji Coal Mine are taken as the research object, and the experimental study on the deformation characteristics and the variation rule of mechanical parameters of raw coal under multifield coupling (temperature, gas, and stress coupling) was carried out. The results show that the elastic modulus, peak strain, and peak stress of raw coal samples under the thermal-hydraulic-mechanical coupling have the same change law in the test temperature range and all of them show a linear decreasing law as the temperature increases. Under the same temperature gradient increasing condition, the elastic modulus, peak strain, and peak stress show a nongradient decreasing trend as the temperature increases. Both the deformation modulus and the lateral expansion coefficient show a linear increase as the temperature increases, while the deformation modulus and the lateral expansion coefficient show a nongradient increase trend as the temperature increases under the same temperature gradient increasing condition. Under the action of the thermal-hydraulic-mechanical coupling, unloading confining pressure obviously accelerated the yield process of the coal sample, and the confining capacity of confining pressure on transverse strain of the coal sample decreased. To prevent the occurrence of coal and gas outburst, it is necessary to take specific prevention measures according to the change law of triaxial compression mechanics of a raw coal specimen under the action of the thermal-hydraulic-mechanical coupling.

scholarly journals Elastoplastic constitutive behavior and strain localization of a low-porosity sandstone during brittle fracturing

2021 ◽  
Author(s):  
Shihuai Zhang ◽  
Pei Guo ◽  
Shunchuan Wu
Keyword(s):  
Constitutive Model ◽  
Yield Surface ◽  
Strain Localization ◽  
Pure Shear ◽  
Failure Process ◽  
Frictional Coefficient ◽  
Peak Stress ◽  
Confining Pressure ◽  
Elastoplastic Behavior ◽  
Confining Pressures

We investigated the elastoplastic behavior and strain localization of the Zigong sandstone (porosity: 6.5%) during brittle fracturing based on two series of axisymmetric compression experiments. The experiments were conducted under various confining pressures (σ3 = 0 ~ 80 MPa). For each confining pressure, the sandstone specimens were deformed under constant axial and circumferential strain rates, respectively. When σ3 < 60 MPa, the sandstone first undergoes stable deformation in the post-peak stage and then loses its stability. Before the emergence of instability, the mechanical behavior is hardly affected by the controlling method. When the confining is larger, the sandstone manifests a stable failure process during the whole loading stage. The observed elastoplastic behavior was described by a two-yield surface constitutive model established in the framework of generalized plastic mechanics. The proposed constitutive model incorporates two quadratic yield functions, as well as two linearly independent plastic potential functions, to honor the shear yield and volumetric dilatancy, respectively. Via the return mapping algorithm, the proposed constitutive model was verified by comparing the numerical results with experimental results. In addition, the two-yield surface constitutive model, which is equivalent to the model proposed by Rudnicki and Rice,1 was applied to localization analysis. Assuming that the onset of localization occurs at peak stress, frictional coefficient μ and dilatancy factor β were determined from experimental data. The variations of both plastic parameters predict the transition of localization mode from pure dilation bands under uniaxial compression to pure shear bands at high confining pressures, which is consistent with the experimental observations.

Experimental Study of Triaxial Test of Gravel Soil in Yili's First Coal Mine

2011 ◽  
Vol 347-353 ◽  
pp. 60-65
Author(s):  
De Jun Meng ◽  
Zhong Hui Sun ◽  
Bo Yang Dou ◽  
Peng Fei Han ◽  
Yan Bing Wang
Keyword(s):  
Moisture Content ◽  
Triaxial Test ◽  
Friction Angle ◽  
Confining Pressure ◽  
Test Machine ◽  
Strength Index ◽  
Gravel Soil ◽  
Moisture Conditions ◽  
The Relationship ◽  
Water Contents

The strength of gravel soil of Yili’s First Mine in different water contents was studied by multifunction static and dynamic triaxial test machine. The results show that （1）The yield limit decreases with the increasing of water content under steady confining pressure, and the greater the confining pressure, the greater the yield point of its axial in the same moisture conditions. （2）The expansion becomes into contraction with increasing moisture content. （3）Strength index of gravel soil becomes smaller with the increase of moisture content. The relationship between friction angle and water contents is . And the relationship between cohesion (or bite force) and water contents is . The results provide a theoretical basis for shaft design and construction of Yili’s First Mine.

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