Research on the pressure relief law of diamond beaded rope saw cutting seam - a numerical investigation

At a Glance

Metadata	Details
Publication Date	2024-04-23
Journal	Geomechanics and Geophysics for Geo-Energy and Geo-Resources
Authors	Jianguo Zhang, Xiaochuan Wang, Zhaolong Ge, Man Wang, Wei Wang
Institutions	Wuhan University, Shenhua Group (China)
Citations	2
Analysis	Full AI Review Included

Executive Summary

This numerical investigation validates the use of diamond beaded rope saw (DBRS) cutting as an effective pressure relief method for high-outburst risk, low-permeability coal seams.

Model Validation: A finite difference model (FLAC3D/UDEC) based on Superimposed Beam Theory and Coulomb friction contact was successfully validated against laboratory test data, confirming its applicability for simulating stress distribution during DBRS cutting.
Pressure Relief Mechanism: DBRS cutting creates a continuous slot, generating deformation space that releases strain energy and redistributes internal stress, effectively mitigating the gas lock effect common in low-permeability seams.
Inclination Impact: Pressure relief efficacy increases significantly with coal seam inclination. Relief amplitude rose from 1.9% (0° horizontal) to 18.2% (45° inclination), driven primarily by enhanced tangential sliding along the contact surface.
Hardness Dependence: Soft coal (Bulk Modulus E = 1.0 GPa) showed superior pressure relief (6.9% amplitude) compared to hard coal (E = 5.0 GPa, 6.3% amplitude), as soft coal allows for greater deformation and stress redistribution.
Slit Dynamics: Stress relief occurs between the leading and trailing edges of the slit, while a localized stress concentration zone consistently forms immediately ahead of the advancing slit tip.
Geometric Influence: Increasing the working face length expands the pressure relief range along the face direction but slightly reduces the relief amplitude in the central area.

Technical Specifications

Parameter	Value	Unit	Context
Numerical Model Size (L x W x H)	500 x 500 x 300	m	Overall simulation domain
Coal Seam Thickness	2.5	m	Model geometry
Roadway Section (W x H)	3 x 2	m	Model geometry
Working Face Lengths Tested (L_w)	150, 200, 250	m	Geometric variable analysis
Slit Advancing Distances Tested (d)	50, 100, 250, 350	m	Temporal variable analysis
Max Pressure Relief Amplitude (45° Inclination)	18.2	%	Stress reduction result (Fig. 21)
Pressure Relief Amplitude (Soft Coal)	6.9	%	At 15° inclination, middle of slit
Pressure Relief Amplitude (Hard Coal 2)	6.3	%	At 15° inclination, middle of slit
Soft Coal Bulk Modulus (E)	1.0	GPa	Lithologic parameter (Table 4)
Hard Coal 2 Bulk Modulus (E)	5.0	GPa	Lithologic parameter (Table 4)
Contact Normal Stiffness (k_n)	1.0	GPa	Coulomb friction model setting
Contact Tangential Stiffness (k_s)	1.0 x 10^-5	GPa	Coulomb friction model setting
Initial Stress (Monitoring Position)	1.05	MPa	After roadway excavation
Max Stress Concentration (Horizontal Seam)	1.15	MPa	At slit tip (9.5% increase over initial)

Key Methodologies

The study utilized a verified numerical approach combining classical mechanics theory with advanced finite difference modeling to analyze stress evolution during DBRS cutting.

Model Setup: A large-scale 3D finite difference model (500m x 500m x 300m) was constructed using FLAC3D/UDEC software, simulating five distinct rock strata layers (Basic Roof, Immediate Roof, Coal Seam, Immediate Floor, Basic Floor).
Theoretical Foundation: The mechanical behavior of the layered rock mass above the slit was modeled using the Superimposed Beam Theory to calculate load distribution and deflection.
Slit Interface Modeling: The cutting seam was simulated as a contact surface governed by the Coulomb Friction Contact Surface Model. This model allowed for normal embedding, tangential slip, and separation, crucial for replicating the stress release mechanism.
Parameter Assignment: Contact parameters were set to reflect the unbonded nature of the slit: high normal stiffness (1.0 GPa) to prevent excessive penetration, and very low tangential stiffness (1.0 x 10^-5 GPa) and zero internal friction angle to allow slip.
Simulation Process: The simulation proceeded in two phases: (1) Initial stress state establishment after roadway excavation, and (2) Seam cutting propulsion, advancing the slit incrementally (50m, 150m, 250m, 350m).
Sensitivity Analysis: The model systematically investigated the influence of four primary engineering factors on stress distribution: coal seam inclination (0° to 45°), working face length (150m to 250m), coal hardness (Soft, Hard 1, Hard 2), and slit advancing distance.
Data Extraction: Stress distribution was analyzed using nephograms of the minimum principal stress (σ₁) and monitoring lines placed at various distances above and below the slit to quantify pressure relief amplitude and range.

Commercial Applications

This research provides critical engineering data supporting the widespread adoption of DBRS technology in high-risk underground environments.

Coal Mine Disaster Prevention: Direct application in mitigating high gas and high ore pressure risks in deep, low-permeability coal seams, replacing complex and costly protective layer mining techniques.
Permeability Enhancement: The stress relief and micro-fracturing induced by DBRS cutting enhance coal seam permeability, significantly improving the efficiency and yield of Coal Bed Methane (CBM) extraction.
Inclined Seam Exploitation: Provides validated guidelines for optimizing DBRS cutting parameters (e.g., inclination angle) to maximize pressure relief in geologically complex, inclined strata, which are often difficult to treat with conventional methods.
Mining Equipment Design: The findings on stress concentration at the slit tip and the required cutting depth inform the design specifications for next-generation diamond beaded rope saw machinery, ensuring optimal cutting force and durability.
Geotechnical Stress Management: The methodology for modeling stress redistribution via contact surfaces can be adapted for other geotechnical applications requiring controlled stress relief, such as deep tunnel excavation or large underground cavern construction.

View Original Abstract

Abstract As a new technology to mitigate the high outburst risk of the low permeability coal seam, it is essential to delve deeper into the law and mechanism of pressure relief associated with the diamond beaded rope saw slotting. The paper presents a numerical calculation model under small size that is based on the superimposed beam theory and the contact surface model. The model is compared with the experimental results of similar models in the laboratory to verify its applicability for simulating the numerical calculation of stress distribution in coal seam cut by diamond beaded rope saw. The study then goes on to investigate the influence of coal seam inclination, working face length, coal seam hardness, and seam advancing distance on the pressure relief effect of diamond beaded rope saw cutting seam under engineering scale. The mechanism of the diamond beaded rope saw cutting seam is also analyzed. The results indicate that the diamond beaded rope saw effectively reduces pressure in low permeability coal seams, with the impact range extending to the slit area. Additionally, stress concentration was observed at the front of the slit. Increasing the inclination of the coal seam, working face length, and advancing distance of the cutting seam enhances the pressure relief effect of the diamond beaded rope saw. The latter two factors’ influence is reflected in the direction along the working face and the direction of mining advance, respectively. The efficacy of pressure relief through this particular method is comparatively better in soft coal than in hard coal. This research is significant in promoting the widespread application of diamond beaded rope saws in the pressure relief of coal seam cutting.

Tech Support

Original Source

DOI: https://doi.org/10.1007/s40948-024-00798-2

References

2020 - Mechanical properties and stress-strain evolution mechanism of contact interface between upstream silt foundation and New Fill dam