I live in an area that has an abundance of river rock and a shortage of crushed stone. Can river rock be used in place of crushed stone as a sub base for foundations, roads, etc. or does the smoothness cause problems when it comes to movement, compaction, settling, etc.?

My gut tells me that the "sharp" edges of crushed stone will result in better interlocking when compacted and thus less shifting/movement. However, I don't have any actual evidence/data to back this up.

Searching around the internet suggests that river rock is used predominately for decorative tasks, but most of the resources are also from the US where I believe river rock is significantly less available (more expensive) than crushed stone and it could just be that people only use it decoratively because it is not economical to use it as a sub base.

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    $\begingroup$ River rock is more expensive because there is a very finite supply, and stripping the rock from a river bed destroys the river's ecosystem. On the other hand a stone quarry can mine and crush rock strata that are hundreds of feet thick. For example one of the largest quarries in the UK is mining a limestone bed 1200 feet thick, and produces more than 5 million tons of crushed stone per year. $\endgroup$
    – alephzero
    Aug 21 at 13:56
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    $\begingroup$ Have a look at this link by Shreenath Rao $\endgroup$
    – NMech
    Aug 21 at 19:58
  • $\begingroup$ @NMech That is a great and useful article, but I didn't see any mention of river rock or a comparison of smooth stones vs jagged stones. Did I miss something perhaps? $\endgroup$ Aug 22 at 5:47

Yes, it can be used in foundations and subbases of roadways if the rocks meet property and gradation requirements. However, crushed stone/gravel is often the choice for the base material.

Base course is a layer of the pavement structure immediately beneath the surface course. It typically consists of high quality aggregate such as crushed gravel, crushed stone, or sand that provides a uniform foundation support and an adequate working platform for construction equipment. Base may consist of unbound materials, such as gravel or crushed stone, or stabilized materials, such as asphalt-, cement- or lime-treated materials.

The subbase course is typically a granular borrow that is placed between the base and subgrade. It can be constructed as either a treated or untreated layer. Untreated or unbound aggregate subbase layers are characterized in a manner similar to the subgrade in pavement design. The material quality requirements of strength, plasticity, and gradation for subbase are not as strict as for a base. The subbase course must be better quality than the soil subgrade, the subbase is often omitted if soil subgrades are of high quality.

Depending on site conditions, subgrade improvements may also be performed. However, the role of different base and subbase layers and rationale for using different base types and layering are not well documented as many agencies specify standard or typical base and subbase layers based on historical performance and their own experiences. For example, it is unclear where and why a treated base should be used, or why one type of treated base is preferred over another.


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