When constructing any object whether it be a road or foundation the base layer is the most important part of the process. Without a strong and resilient base anything you put on top will be more prone to failure as the shifts and settles.
Another thing to consider is what the soil type is that you are building on. There are three main types of soils; sand, silt, and clay. All three soil types are very different, so it is necessary to have an idea of how the soil types are different.
Sand- Sand is a granular material composed of small rock and mineral particles.
Silt- Silt is a dust like sediment that has been transported from wind or water. Silt is made up of very fine rock and mineral particles and has a very fine and floury feel to it.
Clay- Clay is an organic soil with the highest mineral count of the other soils. Clay is an ideal soil from growing. Clays are considered plastic which makes them challenging to build on.
When considered the different soil types and ease of use when building, sand is the ideal soil. Sand is small rocks, so it is easy for the sand to be compacted very tightly and then not change shape when water or anything else is introduced the soil. With sandy soils being the best, clay soils are the worst soil to build on. Because clay soils are plastic in nature, they are unstable to build on. It is frequent that when a clay soil gets wet the clay particles will change shape temporarily or permanently.
While clay soils are known to be a very challenging soil to build on, the most challenging soils are considered highly expansive clays or high plastic clays. These clay types are very unpredictable and will expand or contract when wet then often change shape when dry. This leads to issues during the construction process because it makes it difficult for the construction team to compact the soil uniformly and have the soil stay in the same shape when the soil dries. It also causes large issues post construction in the event water or another liquid seeps into the soil, this often causes massive failures on the topcoat (i.e. asphalt, concrete, etc) because the base has shifted so much and moved the rigid layer of the topcoat.
Construction with expansive clays is very challenging whether it be for unpaved roads, paved roads, or any other foundational work. While the options are limited for treating the expansive clay soils for an unpaved road the following options would be viable choices.
Treating expansive clays with gravel acts as a layer above the expansive soil to decrease the amount of water going into the soil thus decreasing its theoretical expansion. Treating expansive clay soils with gravel will help decrease the likelihood of the road being inoperable because it is too muddy or rutty, but the treatment will not last forever. Depending on the climate, amount of soil expansion, and use the treatment can last as little as a few weeks and as long as 6 months. While treating the soil with gravel is an easy option that is available to most people, the gravel treatment option can add up as time goes on, making the road maintenance very expensive and volatile.
Polymer base soil stabilization is a very popular method around the globe. When using a polymer soil stabilizer, the polymer essentially acts as a glue and bonds the soil particles together. Polymers are easy to use but require a more application steps, usually including compacting the soil. Polymer soil stabilization is effective for most types of soils but will have a limited lifespan. The type of polymer and soil greatly affects the lifespan of the project but expected lifespan can be 6-18 months. Since the expansive clays are often very fine it can make it challenging for the polymers to bond such small particles together.
The options for paved or covered projects involving expansive clays are a little more mainstream and tried and trued.
Over excavation is a very simple process in which the construction crew removes more, ideally all of the expansive clay soils from the location. The void would then get filled with a stable base coarse(s) ranging from imported sand to Type II aggregate. This option is very common because the soil that could cause all future troubles is being completely removed. The Over Excavation option is often very expensive and time consuming because of the fact that all of the old material needs to be hauled out and the new material needs to hauled in. The costs are not only elevated from the hauling purchasing of the new base coarse material.
Cement or Lime treated base (CTB) is very common in different areas of the world. The process includes introducing a small portion of cement or lime into the native soil, then compact the soil, and let the soil cure with the cement. This process often increases the strength of the soil but also adds a chemical bond to the soil particles which helps decrease the likelihood that the soil will expand or contract down the road. Cement treated base is a method that has been used for decades and refined, thus making it fairly easy to use and expeditious. The one downside to Cement Treated Base is the cost; the cost is usually very high since the amount of cement is so high. The cost fluctuates from region to region depending on the cost of cement and availability but traditionally the cost of using Cement Treated Base can increase the cost by 40% over traditional road construction methods.
Another option for both unpaved and paved roads is Perma-Zyme. Perma-Zyme is a unique soil stabilizer that is enzyme based. Perma-Zyme works by interacting with the clay particles and inducing an electrochemical reaction that permanently bonds to the soil particles together. Unlike other options for remediating the expansive clay soils, Perma-Zyme will last in excess of 10 years when used for unpaved roads and over 30 years when used for paved roads. The longer lifespan is due to the chemical reaction with the clay particles that is naturally take centuries but Perma-Zyme expedites the process into days or weeks.
In applications in which the Perma-Zyme is being used to remediate the highly expansive clays. Perma-Zyme works by bonding each clay particle together in the soil and will bond around all other objects in the soil. During this process the shape of the clay particle is being “locked” and will make the soil impervious so the soil will not be able to take on water thus not expanding or contracting.
Post application of Perma-Zyme, the soil’s strength will improve greatly. Many test results have shown that the R-Value of the soil will increase by 400%. With a strength increase of this magnitude the road design can often be adjusted to decrease the amount of base course or asphalt which will decrease the construction costs exponentially.
It is important that proper steps are taken when constructing with highly expansive clays. There are many tools and products in the market today that can aid in making the process smoother and creating longer lasting roads. When working with highly expansive clays, choosing the right tool for the right job is vital.