Underground Paste backfill mining solution
Engineered Subsidence Control for Underground Coal Recovery
Extracting coal beneath villages and infrastructure creates one critical risk: surface subsidence.
Paste filling eliminates it.
Instead of leaving voids to collapse, pump engineered paste, fly ash, coal gangue, cement, water into mined-out areas. The paste consolidates, supports the overburden, and lets you extract safely beneath populated zones.
India’s first commercial coal paste filling project proved it works: SECL Singhali Underground Mine (Chhattisgarh) is extracting 8.4 million tonnes over 25 years with zero surface impact.
John Finlay delivers full system design and EPC contracting, integrating slurry engineering, equipment selection, and operational supervision into a single accountable partnership.
How paste backfill works start to finish
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.
Recover what room-and-pillar left behind
The original remining 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.
Maximize recovery
Pillar recovery rises from 67.8% to 100% no 2 m sacrificial coal rib.
Control subsidence
Cemented paste carries the overburden, controlling strata movement and surface settlement.
Use the waste
Gangue, fly ash and bottom ash become a non-segregating paste, with no tailings dam.
Run in parallel
Mining and backfilling proceed simultaneously on different strips, lifting output.
48 pillars · 8 groups · A-B-C strips
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 strips: IB→VIIIB, then IA→VIIIA, then IC→VIIIC.
Engineered for a 3.25 MPa support body
Design strength is set by strip-pillar stability theory and fixed at 3.25 MPa using the conservative Bieniawski method.
Paste Mix Composition
Recommended paste mix per m³ (~81% solids)
Recommended Paste Mix (per m³)
| 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 |