Numerical simulation of pressure relief stress distribution of diamond beaded rope saw cutting in low permeability coal seam
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2023-09-01 |
| Journal | Geomechanics and Geophysics for Geo-Energy and Geo-Resources |
| Authors | Wang We, Xiaochuan Wang, H. Q. Li, Jincheng Hu, Tianyi Zhang |
| Institutions | Wuhan University |
| Citations | 2 |
| Analysis | Full AI Review Included |
Executive Summary
Section titled âExecutive SummaryâThis analysis focuses on the numerical simulation of stress redistribution achieved by diamond beaded rope saw cutting in low-permeability coal seams, utilizing a novel contact surface modeling approach.
- Core Mechanism: Stress transfer is primarily driven by tangential slip (shear displacement) of the coal body along the closed seam surface, modeled accurately using the Coulomb friction contact theory, distinguishing it from wide hydraulic slots.
- Optimal Orientation: The maximum pressure relief range and amplitude occur when the angle ($\alpha$) between the slit and the maximum principal in-situ stress is 45°. This relationship follows a symmetric âsingle peakâ distribution.
- Geometric Influence: Pressure relief range is positively correlated with both slit length (affecting the advancing direction) and working face length (affecting parallel and vertical directions). These parameters have minimal effect on the maximum pressure relief amplitude.
- Geological Influence: A greater in-situ stress difference ($\Delta\sigma$) significantly promotes pressure relief range and amplitude, especially when the slit angle ($\alpha$) is small (near 45°).
- Surface Condition: The friction coefficient ($\mu$) of the seam surface inhibits pressure relief. A smoother cutting surface (lower $\mu$) is essential for maximizing the effective stress relief.
- Modeling Innovation: The study treats the extremely thin rope saw cut as a group of contact surfaces with negligible spacing, providing a more realistic representation for large-scale geomechanical simulations than traditional rectangular hole models.
Technical Specifications
Section titled âTechnical SpecificationsâThe simulation utilized a large-scale Finite Element Model (FEM) based on the Mohr Coulomb criterion.
| Parameter | Value | Unit | Context |
|---|---|---|---|
| Model Size | 500 x 500 x 500 | m3 | Cube model for large-scale simulation |
| Minimum In-situ Stress ($\sigma_H$) | 10 | MPa | Fixed minimum principal stress |
| Ground Stress Difference ($\Delta\sigma$) Range | 1 to 13 | MPa | Varied parameter ($\sigma_h = \sigma_H + \Delta\sigma$) |
| Optimal Slit Angle ($\alpha$) | 45 | ° | Angle relative to maximum in-situ stress |
| Slit Length ($d_l$) Range | 50 to 225 | m | Varied parameter |
| Working Face Length ($d_w$) Range | 150 to 225 | m | Varied parameter |
| Friction Coefficient ($\mu$) Range | 0.00 to 0.13 | - | Seam surface friction (varied parameter) |
| Coal Seam Thickness | 4 | m | Model geometry (No. 5 coal) |
| Coal Youngâs Modulus (E) | 1.49 | GPa | No. 5 Coal material parameter |
| Coal Internal Friction Angle ($\phi$) | 20 | ° | No. 5 Coal material parameter |
| Pressure Relief Threshold | 10 | % | Minimum amplitude used to define relief range |
| Maximum Displacement (Slotted) | 9.4 | mm | Observed at the center of the slot |
Key Methodologies
Section titled âKey MethodologiesâThe numerical simulation was performed using ABAQUS, integrating analytical solutions for stress distribution around cracks with a specialized contact model.
- Model Setup: A large-scale (500 m cube) Finite Element Model was constructed, applying three-dimensional ground stress conditions.
- Material Definition: The Mohr Coulomb constitutive model was used to define the mechanical properties of the coal seam and the surrounding rock.
- Crack Modeling: The thin diamond beaded rope saw slit was treated as a contact surface with negligible spacing, focusing on the resulting shear displacement field rather than normal displacement (which dominates wide hydraulic slots).
- Contact Physics: The Coulomb friction model was implemented to govern the interaction between the two sides of the slit, characterizing the critical shear stress ($\tau_{crit} = \mu F^n$) required for tangential slip.
- Stress Calculation Framework: The problem was solved using the principle of stress superposition, treating the slotted plane as an infinite plane with a hole subjected to far-field stress, and then applying the inverse surface force (rebound force) to the hole boundary.
- Analytical/Numerical Hybrid Solution: Mindlinâs solution for elastic half-planes under concentrated force was integrated numerically (using Gaussian points and iterative calculation steps) to determine the complex stress distribution around the crack.
- Parameter Variation: Simulations systematically varied five key parameters: slit angle ($\alpha$), slit length ($d_l$), working face length ($d_w$), seam friction coefficient ($\mu$), and in-situ stress difference ($\Delta\sigma$) to quantify their impact on pressure relief range and amplitude.
Commercial Applications
Section titled âCommercial ApplicationsâThe findings provide critical design parameters for optimizing diamond beaded rope saw technology in underground mining and resource extraction.
- Coal and Gas Outburst Prevention: Optimizing the slit angle to 45° relative to the maximum principal stress direction ensures the largest possible pressure relief zone, significantly mitigating outburst risk in low-permeability coal seams.
- Enhanced Permeability: The technology provides a high-efficiency method for stress relief, which is directly linked to increased coal seam permeability, improving the effectiveness of pre-drainage gas extraction.
- Mining Layout Optimization: Engineers can use the established relationships (e.g., positive correlation between working face length and relief range) to design mine layouts that maximize the beneficial stress relief effects based on local geological stress fields.
- Tooling and Material Selection: The strong dependence of pressure relief on the friction coefficient ($\mu$) emphasizes the need for rope saw beads and cutting techniques that produce the smoothest possible seam surface, potentially guiding the selection of bead material and cutting speed.
- Geomechanical Risk Assessment: The simulation methodology offers a validated tool for predicting stress redistribution patterns (the âstar peachâ cross-distribution) in highly stressed rock masses, aiding in the planning of safe excavation sequences.
View Original Abstract
Abstract The diamond bead slit is a practical method for changing the stress distribution of low permeability coal seam and achieving pressure relief and reflection improvement. The stress distribution of coal seam in large scale is not clear due to the influence of diamond bead slit parameters and geological parameters, making it difficult to identify. In this paper, the finite element model with built-in Coulomb friction contact surface is used to simulate the stress distribution in coal with different angles, seam length, working face length, seam friction coefficient and different in-situ stress difference. This investigation is conducted to examine the stress distribution of parallel working face, vertical coal seam, and advance working face. The simulation results show that the mechanism of stress transfer in large scale diamond beaded rope saw cutting coal seam is mainly due to the tangential slip of coal body on both sides of seam surface, forming concentrative zone and pressure relief zone with axial distribution, center symmetry and phase. The pressure relief range and maximum pressure relief range of all three direction present a âsingle peakâ distribution with the change of angel α between slit and maximum in-situ stress, i.e. when α = 45°, both of them are maximum. The slit length mainly affects the stress distribution in the advancing direction of the working face, and the length of working face mainly affects the stress distribution in the direction of parallel working face and vertical coal seam, both of which are positively correlated with the pressure relief range and the maximum pressure relief amplitude. The friction coefficient of seam surface and the difference of in-situ stress affect the relative dislocation of coal body on both sides of seam surface, and they inhibit and promote the pressure relief range and the maximum pressure relief amplitude respectively, and are greatly affected by α . The simulation results above suggest that it is reasonable to select fracture and geological parameters in practical engineering.