Aggregate produced in a crushing and screening plant waits in the stockyard until it reaches the customer. The quality achieved at the plant’s screens and crushers can easily be lost in the stockyard: fractions can mix, coarse and fine particles can separate (segregation), and material can be contaminated with soil and mud. In addition, not knowing stock quantities accurately makes production planning and financial reporting difficult.
In this guide we cover stockpiling methods, preventing segregation and contamination, stockyard design, inventory measurement and safety in stockpile tunnels.
Stockpiling Methods
| Method | Description | Advantage / Disadvantage |
|---|---|---|
| Conical pile from a fixed conveyor | Material falling to a single point from the conveyor head forms a conical pile | Simple; but coarse particles roll to the toe, causing segregation |
| Radial stacking conveyor | The conveyor slews around a pivot and forms an arc-shaped stockpile | High capacity, layered stockpiling possible, segregation can be reduced |
| Telescopic conveyor | A conveyor whose length and height vary | Layered, controlled stockpiling, minimal segregation |
| Layered stockpiling with a loader | Material is spread in thin layers by loader | Reduces segregation; but the machine can crush and contaminate the material |
| Enclosed silos and bins | Material is held in an enclosed structure | Protection from dust and rain; high investment |
| Reclaim via a stockpile tunnel | Tunnel and feeders under the pile | Reclaim without loaders, blending; safety risks |
What Is Segregation and How Is It Prevented?
Segregation is the separation of particles of different sizes within the same fraction during stockpiling. In a conical pile, coarse particles roll to the toe while fines stay in the centre. As a result, when the loader takes material from different points of the pile, the grading of the product going to the customer changes. This is a major cause of quality complaints, especially for products with a wide size range (e.g. 0–31.5 mm sub-base, 0–5 mm sand) and for concrete and asphalt aggregates.
- Reduce drop height: Use telescopic chutes, rock ladders or height-adjustable conveyors.
- Stockpile in layers: Move the radial conveyor along its arc to build thin layers.
- Work with narrow fractions: Making wide-range products by blending narrow fractions reduces segregation.
- Loading technique: Train loader operators to take the face of the pile in vertical cuts; taking only from the toe loads coarse material.
- Consider the wind: Wind blows fines out of falling material, creating both segregation and dust.
Preventing Contamination
- Base: The stockyard base should be compacted and preferably surfaced with sub-base, concrete or aggregate. A soil base contaminates material at the bottom of the pile with mud.
- Dividing walls: Use concrete blocks or walls between fractions to stop piles mixing.
- Drainage: The stockyard should be sloped and drained. Standing water causes contamination and raises product moisture.
- Traffic: Stop machines and trucks driving onto piles with muddy wheels.
- Labelling: Mark each pile clearly to prevent tipping onto or loading from the wrong pile.
For approaches to overall product quality see our aggregate quality guide.
Stockyard Design
The stockyard should be planned at the plant design stage together with capacity and dispatch arrangements.
| Design Topic | Point to Note |
|---|---|
| Stock capacity | Seasonal demand fluctuation, product range and plant shutdown periods |
| Pile geometry | The material’s angle of repose, conveyor height and area |
| Traffic flow | One-way truck circulation, weighbridge location, loader manoeuvring space |
| Dust control | Water spraying, windbreaks, covered stockpiles (dust and noise control) |
| Expansion | Space for new products and capacity increases |
For conveyor design and maintenance see our belt conveyor guide, and for feed hoppers our stockpile and feed hopper guide.
Inventory Measurement
Knowing stock quantities accurately is essential for production planning, sales and financial reporting.
- Drone photogrammetry: A three-dimensional model of the piles is built from drone images and their volumes are calculated. It is a fast, safe and repeatable method.
- Laser scanner and GNSS surveys: Volume calculation by ground-based survey.
- Density: To convert volume to tonnes, the pile density (loose bulk density) must be known. This value varies with material, grading and moisture and should be measured periodically.
- Belt scale and weighbridge reconciliation: Losses are identified by comparing the difference between production (belt scale) and dispatch (weighbridge) with the change in stock. For belt scale accuracy see our belt scale guide.
- FIFO: First in, first out can be applied to prevent material that sits for a long time from becoming contaminated or degraded.
Stockpile Tunnels and Reclaim Systems
Stockpile tunnels allow reclaim without loaders by transferring material onto a conveyor through feeders (vibrating feeders, belt feeders) installed under the pile. Blending can also be done by drawing from several feeders at different rates. For feeder selection see our feeder types guide.
Stockpile Tunnel Safety
Stockpile tunnels and piles carry serious risks:
- Voids and bridging in the pile: When a feeder draws material, hidden voids can form inside the pile. A person or machine climbing onto the pile can be engulfed in such a void. Never walk on piles that are being actively drawn down.
- Confined space: The tunnel must have ventilation, lighting, emergency exits and communications; confined space working procedures must be applied.
- Dust: Dust build-up in the tunnel is a respiratory hazard.
- Belt and feeder: Nip points must be guarded, and lockout–tagout carried out before maintenance.
For detailed safety measures see our occupational safety guide.
Field Example
Suppose that a ready-mix concrete customer of an aggregate plant complains about fluctuations in the fines content of 0–5 mm sand. Sieve analyses at the plant show the product is consistent as it leaves the screen. It turns out that the problem arises in the stockyard: sand falling from height off a fixed conveyor segregates in the conical pile, and the loader mostly takes material from the toe. When a telescopic chute is added to the conveyor head and the loader operators are trained, grading fluctuations fall markedly.
Frequently Asked Questions
In which products is segregation most pronounced?
It is more pronounced in products with a wide size range (e.g. 0–31.5 mm, 0–5 mm). Its effect is smaller in narrow fractions.
What should the stockyard base be like?
Compacted, drained and preferably surfaced with sub-base or concrete; a soil base causes contamination.
How reliable are drone stockpile surveys?
With a correct flight plan, ground control points and an up-to-date density value, they give practical and reliable results.
Why is it dangerous to climb onto a stockpile?
Hidden voids can form in piles being drawn from below; a person or vehicle on top can be engulfed in them.
Spare Parts for Stockyard Equipment
| Equipment | Frequently Replaced Parts | Note |
|---|---|---|
| Radial and fixed stacking conveyors | Idlers, belt, scraper blades, pulleys | Should be chosen to withstand wind and outdoor conditions |
| Radial conveyor travel gear | Wheels, bearings, drive motor | Ground evenness affects life |
| Telescopic chutes | Wear liners, chains | Reduce segregation |
| Stockpile tunnel feeders | Vibrator motors, springs, liners | Safe access for maintenance inside the tunnel |
| Tunnel conveyor | Idlers, belt, safety equipment | Pull cord switches and misalignment sensors should be tested |
| Dust suppression systems | Nozzles, pumps, filters | Frost protection in winter |
You can find parts for stacking conveyors and tunnel feeders on our belt conveyor spare parts and feeder spare parts pages. For conveyor idlers and safety equipment, see our conveyor idlers and conveyor safety equipment guides.
Stockyard Audit Checklist
- Is every pile correctly labelled?
- Is there mixing between fractions?
- Is there standing water or mud on the base?
- Are conveyor drop heights under control?
- Are loader operators using the correct loading technique?
- Are the dust suppression systems working?
- Are stockpile tunnel entrances controlled, and is the ban on walking on piles enforced?
- Is the inventory survey up to date?
Glossary
- Segregation: The separation of particles of different sizes within the same fraction.
- Radial stacking conveyor: A conveyor that slews around a pivot and forms an arc-shaped stockpile.
- Stockpile tunnel: A tunnel under the pile from which material is reclaimed by feeders.
- Live stock: The part of the stockpile that can be drawn by gravity through the tunnel feeders.
- Dead stock: The part of the stockpile that can only be reclaimed by loader.
- Loose bulk density: The weight per unit volume of material in the pile; used in inventory calculations.
More Questions
How can the live stock ratio be increased?
Using more feeders along the tunnel and designing the pile geometry accordingly increases the live stock ratio.
When is covered stockpiling needed?
Covered stockpiling is considered for plants close to residential areas where dust control is critical, for products affected by moisture (e.g. dry sand, filler) and in regions with heavy rainfall.
What records should be kept in the stockyard?
Inputs by product (belt scale), outputs (weighbridge), periodic volume surveys and density values should be recorded.
CSP Mühendislik Support
CSP Mühendislik designs and fabricates stacking conveyors, stockpile tunnel feeders and hopper systems and supplies conveyor spare parts. For your idler, pulley, belt and scraper requirements see our belt conveyor spare parts page, and for hopper and feeder parts our hopper spare parts and feeder spare parts pages.
