Reservoir aggregate

This article gives recommendations for aggregate to be used to store water for infiltration. This is usually called 'Clear stone' at aggregate yards. To see an analysis of Ontario Standard Specifications for granular materials, see OPS Aggregates.

The highest void ratio is found in uniformly graded aggregate, as there are no smaller particles to occupy the inter-particle pores.

Higher permeability is found in larger, angular, uniformly graded aggregate. This is due to larger pore sizes and lower tortuosity.

For advice on decorative surface aggregates see Stone

Gravel used for underdrains in bioretention, infiltration trenches and chambers, and exfiltration trenches should be 20 OR 50 mm, uniformly-graded, clean (maximum wash loss of 0.5%), crushed angular stone that has a void ratio of 0.4.

The clean wash to prevent rapid accumulation of fines from the aggregate particles in the base of the reservoir. The uniform grading and the angularity are important to maintain pore throats and clear voids between particles. (i.e. achieve the void ratio). Porosity and permeability are directly influenced by the size, gradation and angularity of the particles

Gravel with structural requirements should also meet the following criteria:

• Minimum durability index of 35
• Maximum abrasion of 10% for 100 revolutions and maximum of 50% for 500 revolutions

Standard specifications for the gradation of aggregates are maintained by ASTM [https://www.astm.org/Standards/D2940.htm D2940

On-site verification

Steps in conducting a jar test to detect fines in construction materials

Specifying that aggregates for the construction of LID practices must be free from fines is important. But checking that the delivered materials meet specification is essential to reduce problems with construction and longer term performance.

When possible, Construction Managers should observe the offloading of materials to watch for dust clouds. Aggregates or sand for LID construction should not give rise to clouds of dust when dumped.

A simple jar test can be used to gauge the proportion of fines in an aggregate product before acceptance.

Apparatus:

• A large wide-mouthed jar - glass or clear plastic are both fine,
• Tap water, and
• The aggregate to be tested.

Method:

1. Collect approximately 5 cm of material in the jar (or at least two complete layers of 50 mm clear stone),
2. Add water to around 3/4 full,
3. Secure cap and shake,
4. Leave for at least 30 minutes and until the water is clear - plan to run the test overnight when possible,
5. Examine the layer of sediment - if > 3 mm has been washed from 5 cm of product, the material should be rejected,

Note that the sediment may collect on top of, or at the bottom of the construction material.

External references

• Heger, S. (2014). Critical Aspects During System Installation and Inspection General equipment considerations. In PMSA conference. Retrieved from http://www.psma.net/pdf/14/conference-presentations/Keys_to_Installation_(Heger).pdf
• Manitoba. (2010). Onsite Wastewater Management Systems: Field Reference Guide - JAR TEST. Retrieved from http://www.gov.mb.ca/sd/envprograms/wastewater/pdf/jar_test_reference_03_2010.pdf

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A broad category of particulate material used in construction, including sand, gravel, crushed stone, slag, recycled concrete and geosynthetic aggregates, and available in various particulate size gradations.

The slow movement of water into or through a soil or drainage system.

Penetration of water through the ground surface.

Gravel, or crushed stone of various size gradations (i.e., diameter), used in construction; void forming material used as bedding and runoff storage reservoirs and underdrains in stormwater infiltration practices.

The void ratio (e) of a mixture is the ratio of the volume of void-space to the volume of solids. It is closely related to the concept of porosity (n) where porosity is the ratio of the volume of void-space to the total or bulk volume of the mixture. e = Volume of voids/Volume of solids = n/(1-n)

A broad category of particulate material used in construction, including sand, gravel, crushed stone, slag, recycled concrete and geosynthetic aggregates, and available in various particulate size gradations.

Soil particles with a diameter less than 0.050 mm.

The porosity (n) of a mixture is the ratio of the volume of void-space to the total or bulk volume of the mixture. It is closely related to the concept of void ratio (e) where void ratio is the ratio of the volume of void-space to the volume of solids. n = Volume of voids/Total volume of mixture = e/(1+e)

Low Impact Development. A stormwater management strategy that seeks to mitigate the impacts of increased urban runoff and stormwater pollution by managing it as close to its source as possible. It comprises a set of site design approaches and small scale stormwater management practices that promote the use of natural systems for infiltration and evapotranspiration, and rainwater harvesting.

A broad category of particulate material used in construction, including sand, gravel, crushed stone, slag, recycled concrete and geosynthetic aggregates, and available in various particulate size gradations.

Soil, sand and minerals washed from land into water, usually after rain. They pile up in reservoirs, rivers and harbors, destroying fish-nesting areas and holes of water animals and cloud the water so that needed sunlight might not reach aquatic plans. Careless farming, mining and building activities will expose sediment materials, allowing them to be washed off the land after rainfalls.