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# What Is Backfilling in Mining?
Backfilling refers to the process of refilling an excavated area, often encountered in both construction and mining operations. This guide primarily focuses on backfilling within the mining industry, where it plays a critical role.
In underground mining, backfilling is essential for maintaining structural integrity and safety. The backfill material not only supports the surrounding rock mass but also helps mitigate surface subsidence, reduces ore dilution, and creates a safer working environment. Additionally, using backfill materials can serve as a method to manage potentially hazardous waste, reducing surface environmental impacts by storing these materials underground.
(Note: "Backfilling" is sometimes written as "back filling.")
## Types of Backfill
Backfill typically comprises waste materials leftover after extracting the desired mineral, often called tailings. Below are common types of backfill used in mining:
### Cemented Backfill
Cemented backfill involves mixing tailings and waste rock with cement. This mixture is poured into voids to stabilize the structure. Cement is particularly effective in binding materials together, though its cost can be prohibitive when large quantities are required.
### Dry Rock Backfill
Dry rock backfill consists of dried tailings, gravel, or surface sand. It is ideal for cut-and-fill mining techniques due to its dry consistency and ease of handling.
### Hydraulic Sand Backfill
Hydraulic sand backfill uses fine sand separated from tailings. The coarser sand is used as backfill and is typically transported into mine voids via hydraulic pumps. Binders can be added if needed to enhance stability.
### Paste Backfill
Paste backfill combines solid tailings with water, cementing agents, and fly ash to create a thick, coagulable substance suitable for backfilling. This method is commonly used in coal mining.
## The Backfilling Process in Mines
The process of backfilling depends heavily on the type of mine, the nature of the tailings, and the location of the stope or void. Heavy machinery is often employed to pump backfill into stopes, especially in deep mines. For shallower mines, gravity-fed methods like dump trucks can be utilized.
At most underground mines, cemented paste is the preferred choice for backfilling stopes. Tailings and binders are typically processed at surface-level facilities before being transported to the mine. Personnel use vacuum disc filters to remove excess water from tailings and weigh hoppers to add binders. High-pressure piston pumps then distribute the final product, while barriers or bulkheads are installed at the stope openings to retain the backfill during curing.
## Hazards Associated with Backfilling
While backfilling offers numerous benefits, it also presents certain risks:
- **Segregation of Backfill:** Fine and coarse particles can separate during curing, leading to uneven distribution.
- **Sloughing of Backfill:** Crusts formed on cured backfill may collapse, affecting newly poured backfill.
- **Borehole Clogging:** Pouring backfill down boreholes can lead to blockages, necessitating new holes.
- **Bulkhead Failure:** Bulkheads or barricades holding backfill may fail under pressure.
- **Pipe Hammering:** Sudden pump shutdowns can cause pipes to bang inside boreholes.
- **Pipeline Burst:** Overpressure or clogs can cause pipelines to burst.
- **Pump Blockage:** Pumps managing binder-rich backfill can become clogged over time.
- **Pipeline Plugging:** Pipes are more prone to clogging when binders are involved.
- **Sump Blockage:** Ventilation sumps can get blocked by backfill, requiring pumping to clear.
- **Pump Failure:** Pumps handling binder-heavy backfill are susceptible to failure.
## Advantages and Disadvantages of Backfill Mining
Backfill mining offers significant benefits but also comes with challenges.
### Benefits of Backfill Mining
- Enhances mine stability and safety.
- Allows extraction of residual minerals in pillars.
- Reduces spontaneous rock bursts.
- Minimizes groundwater contamination.
- Improves mine ventilation.
- Mitigates acid rock drainage.
- Prevents roof collapses during blasting.
- Reduces surface storage needs.
- Minimizes post-closure environmental impact.
- Prevents mine collapse in room-and-pillar mining.
### Drawbacks of Backfill Mining
- Requires costly high-density tailings pumps.
- Needs an independent tailings processing facility.
- Increases manpower and equipment demands.
- Expensive when binders are used.
- Slows down mining operations.
- Raises liquefaction risks in saturated areas.
- Can contaminate groundwater through seepage.
- Dewatering tailings adds to operational costs.
In conclusion, while backfilling is a vital aspect of modern mining, careful planning and execution are crucial to maximizing its benefits while minimizing risks.