Gob-side Entry Retaining in Thick Coal Seam Mining
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Solution Overview
Problem
Current no-pillar mining with gob-entry retaining technology is inadequate for thick coal seams, as it struggles with excessive stope pressure, residual coal, and safety issues like fire and spontaneous combustion, particularly due to the large mining height and weak coal roof stability during fully-mechanized top coal caving.
Innovation Solution
A method involving roof and side reinforcement, pre-splitting blasting, and a gangue retaining device with a flexible mold bag to stabilize the entry and prevent coal caving in a specific range, using a formula to calculate the effective caving distance and combining constant resistance anchor cables with grouting for improved support and gob closure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of substance
If conventional no-pillar mining with gob-entry retaining is applied to thick coal seams, then resource recovery rate increases, but stope pressure becomes excessive and roadway stability deteriorates
Solution Approach 1:
The patent segments the mining process into two distinct phases: first performing pre-splitting blasting to create a controlled fracture plane, then conducting top coal caving in stages. This segmentation allows the roof to be supported initially by the pre-created fracture plane and subsequently by controlled caving zones, distributing the stope pressure more effectively than conventional single-phase mining.
Solution Approach 2:
The patent applies preliminary action through pre-splitting blasting before the main mining operation. By creating a pre-splitting slit along the roadway roof beforehand, the patent prepares a controlled failure plane that will guide subsequent roof caving, reducing uncontrolled pressure buildup and improving roadway stability during thick coal seam extraction.
2Strength
If anchor cable length is increased to 3 times mining height for thick coal seam support, then roadway support capability improves, but the required 30m cable length cannot be achieved with existing technology
Solution Approach 1:
The patent segments the anchor cable support system into multiple sections. Instead of using a single 30m cable, the patent employs multiple shorter cables arranged in series or parallel configurations, each within achievable length limits, collectively providing the required support capability for thick coal seam mining.
Solution Approach 2:
The patent transitions from a single-dimension solution (one extremely long cable) to a multi-dimensional arrangement by deploying multiple cables in spatial configurations (vertical, horizontal, and diagonal arrangements). This dimensional change allows achieving equivalent or superior support capability using cables of practical, manufacturable lengths.
3Productivity
If top coal caving is performed in thick coal seam, then mining efficiency increases, but roof stability deteriorates due to continuous top coal release disturbing the retained entry
Solution Approach 1:
The patent applies preliminary action by creating a pre-splitting slit before top coal caving operations. This pre-created fracture plane controls the caving pattern, directing roof movement along predetermined paths away from the retained entry, thereby maintaining entry roof stability while enabling efficient top coal recovery.
Solution Approach 2:
The pre-splitting slit acts as an intermediary element between the top coal caving process and the retained entry. It mediates the interaction by providing a controlled failure plane that absorbs and redirects the energy and movement of caving coal, protecting the retained entry roof from direct disturbance while maintaining mining efficiency.
4Stability of the object's composition
If established pillars are used to support stope roof, then roadway stability improves, but coal resource waste increases and safety hazards such as outburst and rock burst occur
Solution Approach 1:
The patent extracts and eliminates the need for traditional established coal pillars by replacing them with engineered support systems. Through pre-splitting blasting and controlled top coal caving, the patent creates artificial support structures that provide equivalent or superior stability without consuming valuable coal resources, thereby removing the source of outburst and rock burst hazards.
Solution Approach 2:
The patent replaces the mechanical support system of traditional coal pillars with a engineered system combining pre-splitting fracture planes, controlled caving zones, and segmented anchor cable reinforcement. This substitution maintains roadway stability while preserving coal resources and eliminating the inherent safety hazards of pillar-based support.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This method reduces stope pressure, enhances coal recovery, improves entry stability, and ensures effective gob closure, minimizing damage to the coal roof and maintaining safety by forming a short arm beam structure and using a flexible mold bag for deformation and sealing.
Implementation Method 1
performing oriented pre-splitting blasting on a side where a roadway is to form a gob, slitting the roof at a designed position
Implementation Method 2
By using technical means such as pre-splitting blasting, constant resistance anchor cable reinforcing support
Implementation Method 3
combining constant resistance anchor cables with grouting for improved support
Implementation Method 4
top coal and an immediate roof at a gob side behind the working face are broken along the edge of a roadside filling body under the action of early support resistance of the roadside filling body and strata self-weight
Data Source
AI summary
The present disclosure relates to a technical field of coal mining, particularly to a method of no-pillar mining with gob-entry retaining adapted for fully-mechanized top coal caving in a thick coal seam, which comprises the following steps: reinforcing support on a roof and two sides of a roadway; performing roof slitting blasting to form a pre-splitting slit; erecting a temporary support device and a gangue retaining device in the roadway along the retained entry; performing no caving within a range of a preset distance at an end of the working face near the retained entry side; and removing the temporary support device in the roadway after entry forming stabilizes, and closing the goaf to complete entry retaining. The roof slitting blasting is more beneficial to collapse of strata in the goaf, so that the strata in the slit can better fill stoping space after collapse, and the roof of the retained entry forms a short arm beam structure laterally, which avoids forming a long suspended roof in the goaf, and improves the stress of surrounding rock of gob-side entry retaining; coal caving is not performed in a certain range at the end of the working face of the retained entry side, which further ensures the filling effect of the goaf on the retained entry side, effectively limits the rotary sinking of blocks of the main roof, and greatly reduces effect on the stability of the retained entry.