A green-mining solution to recover the trapped pillar coal of the 17E panel (G-III seam, Korba area) — lifting pillar recovery from 67.8% to 100% while controlling surface subsidence through engineered paste backfill, in line with NB/T 11433‑2023.
A true side view: the coal seam is a thin horizontal layer sandwiched between sandstone roof and floor. The surface plant mixes waste gangue and ash into a paste, pumps it underground, and fills the voids in stages — so the standing pillars become one solid body and the ground above stays stable. Press Play, or click any stage.
The original re-mining concept recovered only part of the pillar coal through a slow two-pass cycle with 28-day waits. John Finlay's adjusted solution backfills the roadways first to lock the pillars into one ground-support monolith, then extracts every pillar strip — recovering effectively all the trapped coal.
Pillar recovery rises from 67.8% to 100% — no 2 m sacrificial coal rib.
Cemented paste carries the overburden, controlling strata movement and surface settlement.
Gangue, fly ash and bottom ash become a non-segregating paste — no tailings dam.
Mining and backfilling proceed simultaneously on different strips, lifting output.
Looking down on the panel: 48 pillars form 8 groups (I–VIII), each split into A, B and C strips. Extraction runs across all groups before changing strip: IB→VIIIB, then IA→VIIIA, then IC→VIIIC.
Design strength is set by strip-pillar stability theory and fixed at 3.25 MPa using the conservative Bieniawski method.
| Component | kg/m³ | Mass % | Note |
|---|---|---|---|
| Coal gangue | 1,278.7 | 67.3% | < 10 mm |
| Fly ash | 95.0 | 5.0% | fine filler |
| Cement (OPC 425#) | 161.5 | 8.5% | binder |
| Water | 361.0 | 19.0% | — |
| Admixture | 3.8 | 0.2% | flow / set |
| Total | 1,900 | 100% | ~81% solids |
UCS at 3 / 7 / 14 / 28 days. Higher solids and cement dosage drive strength past the 3.25 MPa design line.
Two independent systems run in parallel — coal haulage on the transport gateroad, paste pipeline on the return gateroad.
| System | Equipment | Key specification | Qty |
|---|---|---|---|
| Silos | Cement silo | 220 m³ / 260 t | 1 |
| Silos | Fly-ash silos | 330 m³ & 800 m³ (1,200 t) | 2 |
| Batching | Twin-shaft mixer | MAO 6000/4000, 2×55 kW | 1 |
| Pumping | Industrial paste pump | HBMD150/14, 100–150 m³/h, 14 MPa | 2 |
| Pipeline | Vertical fill pipe | Ø219×18 mm, 16Mn | 200 m |
| Pipeline | Main fill pipe | Ø194×16 mm, quick-flange | 1,125 m |
| Control | PLC central control | SCADA + in-line pressure monitor | 1 |
| Air | Ex screw compressor | 21 m³/min, 0.8 MPa, 132 kW | 2 |
No sacrificial coal rib means pillar recovery reaches 100% against 67.8%. Some paste is re-mined when taking the A/B strips, but the value of the extra coal recovered exceeds that re-mining cost.
Size the upside of going from 67.8% to 100% recovery. All inputs editable.
Indicative only. Extra coal = resource × (100% − 67.8%). Replace with site coal price and verified paste cost for a bankable model.