Study on Mechanical Properties of Cement-Improved Frozen Soil under Uniaxial Compression Based on Discrete Element Method
Abstract
:1. Introduction
2. Experimental Analysis on Uniaxial Compressive Strength of Cement-Modified Frozen Soil
2.1. The Preparation of Test Samples and the Experiment
2.2. Experimental Results and Analyses
3. PFC3D Particle Flow Numerical Simulation
3.1. Model Establishment
3.2. Initial Value Setting of Model Meso-Parameters
3.3. Model Meso-Parameter Calibration
- Adjust the effective modulus of soil particles (emod) and viscous equivalent modulus (pb_emod) to fit and reshape frozen soil, Eσ/2. Adjust the phase strength (pb_tension) and tangential strength (pb_coh) of the soil particle bonding method and fit the peak stress and strain of the reshaped frozen soil. Adjust the soil particle stiffness ratio (kratio) and viscous stiffness ratio (pb_kratio) to fit the post-peak curve shape.
- Adjust the effective modulus of cement particles (emod) and viscous equivalent modulus (pb_emod) to fit and improve frozen soil, Eσ/2. Adjust the phase strength (pb_tension) and tangential strength (pb_coh) of the cement particle bonding method, and fit the peak stress and strain of the improved frozen soil. Adjust the cement particle stiffness ratio (kratio) and viscous stiffness ratio (pb_kratio) to fit the post-peak curve shape.
- Adjust the friction angle (fa) and friction coefficient (fric) to match the failure form in the same way as the sample.
- After adjustment, the above parameters need to be fine-tuned again in order to achieve a similar stress–strain curve.
3.4. Analysis of Numerical Simulation Test Results
3.5. Comparative Analysis of Cracks, Stress Fields and Particle Displacement Fields
4. Conclusions
- In the laboratory test, the order of cement-improved frozen soil in terms of peak strength is: cement soil < remolded frozen soil < 6% cement-modified frozen soil < 12% cement-modified frozen soil < 18% cement-modified frozen soil. With the increase in cement content, the curve changes from “linear elastic deformation-strain strengthening-plastic deformation-tensile failure” to “linear elastic deformation-strain strengthening-tensile shear failure”.
- Under the same loading conditions, the initial location of the cracks in the samples with different cement contents is basically the same, and the increase in cement content can prolong the time of crack occurrence. With the same strain level, the number of cracks in the sample decreases with the increase in cement content.
- The stress field of the sample is in compression at the linear elastic stage, and the tensile stress chain is activated continuously with loading. At the linear elastic stage and strain strengthening state, new compressive stress chains are increasingly activated. For samples with a high cement content, more compressive stress chains are activated and less tensile stress chains are activated; when the activated tensile stress is smaller, the position of the tensile stress activation is differentiated due to different cement contents. When the specimen is damaged, the 6% specimen is mainly damaged by tensile plastic failure, and the 18% specimen is damaged by tensile shear failure.
- The force chains in the stress field are not evenly distributed in the sample, and the coarse pressure force chains only exist on the cement particles. With the progress of loading, the tensile stress first appears in the connection of soil particles. When the pressure force chains of the cement particles in the sample are damaged or the tensile force chains between particles appear, this indicates that the sample is damaged.
- With different cement contents, the development of a particle displacement field is different. The sample with 18% cement content has obvious delamination dislocation, with a smaller deformation in the transverse direction, mainly concentrated in the axial direction, while the 6% sample has no delamination dislocation, and has a larger deformation in the transverse and axial directions.
Author Contributions
Funding
Institutional Review Board Statement
Informed Consent Statement
Data Availability Statement
Conflicts of Interest
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Soil Layer | ρ (kg/m3) | ω0 (%) | e | ωd (%) | ωP (%) | ωL (%) | IP (%) | IL |
---|---|---|---|---|---|---|---|---|
silty clay | 1780 | 36 | 1.13 | 28 | 23.5 | 37 | 14 | 0.86 |
Soil Type | Particle Composition | ||||
---|---|---|---|---|---|
Grit | Powder Particle | Cosmid | |||
grain size/mm | 0.5~0.25 | 0.25~0.075 | 0.075~0.005 | <0.005 | |
comparative content/% | 0 | 13.1 | 61.2 | 25.7 |
Sample (W%-T) | Intensity/MPa | Peak Strength/MPa | Failure Strain/% | Eσ/2/MPa |
---|---|---|---|---|
40-10 | 4.71 | 4.89 | 8.84 | 110.05 |
Sample (W%-I%-day) | Intensity/MPa | Peak Strength/MPa | Failure Strain/% | Eσ/2/MPa |
---|---|---|---|---|
40-18-7 | 2.60 | 2.60 | 1.88 | 97.01 |
40-18-14 | 2.79 | 2.79 | 2.15 | 112.5 |
40-18-24 | 3.26 | 3.26 | 2.04 | 116.43 |
Sample (W%-T-I%-day) | Intensity/MPa | Peak Strength/MPa | Failure Strain/% | Eσ/2/MPa |
---|---|---|---|---|
40-10-6-7 | 5.34 | 5.48 | 19.03 | 159.30 |
40-10-6-14 | 6.35 | 6.63 | 18.00 | 223.97 |
40-10-6-28 | 6.02 | 6.19 | 18.01 | 173.88 |
40-10-12-7 | 5.77 | 6.34 | 10.01 | 175.14 |
40-10-12-14 | 6.19 | 6.82 | 8.12 | 217.20 |
40-10-12-28 | 6.21 | 7.16 | 8.16 | 237.09 |
40-10-18-7 | 6.23 | 9.33 | 9.12 | 183.14 |
40-10-18-14 | 8.89 | 11.34 | 9.03 | 236.25 |
40-10-18-28 | 9.01 | 11.45 | 7.01 | 322.54 |
Particle Name | Article Size Range (mm) | Density (kg/m3) |
---|---|---|
cement | 2.2 × 10−3–2.8 × 10−3 | 3150 |
soil1 | 1.25 × 10−3–1.6 × 10−3 | 1780 |
soil2 | 1.6 × 10−3–2.0 × 10−3 | 1780 |
Keyword | Symbol | Description | Initial Value |
---|---|---|---|
mod | modulus [force/area] | 48 × 106 | |
emod | Effective modulus [force/area] | 48 × 106 | |
kratio | Normal-to-shear stiffness ratio | 1 | |
tension | Tensile strength [stress] | 2.4 × 106 | |
Cohesion | Cohesion [stress] | 1.2 × 106 | |
fric | friction coefficient [-] | 0.5 | |
fa | friction angle [degrees] | 20 | |
pb_emod | bond Effective modulus | 46 × 106 | |
pb_kratio | bond Normal-to-shear stiffness ratio | 1 | |
pb_tension | bond Tensile strength [stress] | 2.4 × 106 | |
pb_coh | bond Cohesion strength [stress] | 1.2 × 106 | |
pb_fric | bond friction coefficient | 0.5 | |
pb_fa | bond friction angle [degrees] | 20 | |
pb_rmul | radius multiplier [-] | 1 |
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Ding, F.; Song, L.; Yue, F. Study on Mechanical Properties of Cement-Improved Frozen Soil under Uniaxial Compression Based on Discrete Element Method. Processes 2022, 10, 324. https://doi.org/10.3390/pr10020324
Ding F, Song L, Yue F. Study on Mechanical Properties of Cement-Improved Frozen Soil under Uniaxial Compression Based on Discrete Element Method. Processes. 2022; 10(2):324. https://doi.org/10.3390/pr10020324
Chicago/Turabian StyleDing, Fei, Lei Song, and Fengtian Yue. 2022. "Study on Mechanical Properties of Cement-Improved Frozen Soil under Uniaxial Compression Based on Discrete Element Method" Processes 10, no. 2: 324. https://doi.org/10.3390/pr10020324
APA StyleDing, F., Song, L., & Yue, F. (2022). Study on Mechanical Properties of Cement-Improved Frozen Soil under Uniaxial Compression Based on Discrete Element Method. Processes, 10(2), 324. https://doi.org/10.3390/pr10020324