Coal Pillar Recovery via Segmented Mining and Cemented Backfill
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Solution Overview
Problem
Current room-type coal pillar recovery methods in China are inefficient, costly, and pose safety and environmental risks due to low recovery rates and high investment requirements, particularly for coal pillars with an aspect ratio greater than 0.6.
Innovation Solution
An internally injected replacement support method that divides coal pillars into reserved and pre-mined sections, fills the gap with cemented material, and stabilizes it to support the overburden, allowing for safe and efficient recovery of coal resources while reducing environmental impact.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If traditional recovery methods (splitting and pocket/wing recovery) are used, then operation simplicity is maintained, but resource recovery rate and mechanization degree are low
Solution Approach 1:
The coal pillar is divided into a reserved coal pillar and a pre-mined coal pillar, allowing the pre-mined portion to be recovered through simple gap mining while the reserved portion maintains structural integrity. This segmentation enables high recovery rates without complex operations.
Solution Approach 2:
The coal pillar is pre-divided into reserved and pre-mined sections before recovery begins. The pre-mined coal pillar is extracted first through the reserved gap, enabling efficient mechanized recovery while the reserved portion remains in place to provide ongoing support.
2Productivity
If filling recovery methods (casting/filling or comprehensive mechanized filling) are used, then resource recovery rate and mechanization degree improve, but filling material costs and equipment input costs increase
Solution Approach 1:
Instead of filling the entire goaf with expensive materials, only the reserved coal pillar gap is blocked with minimal filling material to enable cemented backfill injection. The pre-mined coal pillar goaf is left open for efficient coal removal, significantly reducing filling material requirements and costs.
3Productivity
If room-type coal pillars are left after mining, then production efficiency is high and management is simple, but mine safety and ecological environment are threatened
Solution Approach 1:
The coal pillar is segmented into reserved and pre-mined portions. The reserved coal pillar maintains structural support for mine safety, while the pre-mined portion is recovered to eliminate safety hazards and improve resource utilization.
Solution Approach 2:
The aspect ratio criterion (greater than 0.6) is used to determine which coal pillars are suitable for this recovery method. By changing the parameter from absolute size to aspect ratio, the method can be applied to various coal pillar dimensions while ensuring safety and efficiency.
4Strength
If the reserved coal pillar width is increased to ensure roof stability, then roof support strength improves, but coal resource recovery rate decreases
Solution Approach 1:
The coal pillar is pre-divided into reserved and pre-mined sections with optimized width proportions. The reserved gap width is calculated to provide sufficient support while maximizing the pre-mined portion for recovery. This preliminary division optimizes both support strength and recovery rate.
Solution Approach 2:
The aspect ratio (greater than 0.6) serves as a critical parameter to determine coal pillar suitability for this method. By using this parameter, the system optimizes the balance between reserved pillar width for support and pre-mined width for recovery across different geological conditions.
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 enables safe, efficient, and cost-effective recovery of coal pillars with an aspect ratio greater than 0.6, supporting overburden strata, preventing water leakage, and reducing fire and spontaneous combustion risks, thus enhancing resource recovery and environmental safety.
Implementation Method 1
injecting a cemented filling material into a goaf surrounded by the reserved coal pillar for filling
Data Source
AI summary
An internally injected replacement support room-type coal pillar recovery method is provided. During the recovery, the room-type coal pillars with an aspect ratio greater than 0.6 are divided into two parts: reserved coal pillars and pre-mined coal pillars. After the mining of the pre-mined coal pillars, a cemented filling material is injected into a goaf surrounded by the reserved coal pillars, and is stabilized to replace the coal pillars for support, and the reserved coal pillars are recovered. A mechanical model of the reserved coal pillars in a support overburden stage is established based on the Winkler beam theory, to obtain displacement and stress conditions of a roof of the reserved coal pillar in a support stage. A theoretical reserve-width of the reserved coal pillars is obtained according to a first strength theory of the roof and a criterion of ultimate strength of the reserved coal pillars.