Soil stabilization is essential to build and maintain infrastructure. In this article, we’ll weigh the pros and cons of 11 soil stabilization methods:
But first, let’s define soil stabilization.
Soil stabilization is the process of changing soil’s physical, chemical, or biological properties to meet an engineering purpose. Engineering purposes include things like strengthening soil or decreasing its water permeability. People stabilize soil for many projects, such as:
Soil stabilizers generally fall into three broad categories—physical, biological, and chemical. Each can improve the load-bearing capacity and durability of the soil, but they all do it in different ways. Let’s take a look.
Physical soil stabilization uses objects or machinery to stabilize soil. Some examples of objects include aggregate and geotechnical textiles, while mechanical soil stabilization includes dynamic compaction, vibratory compaction, and over-excavation.
Aggregates are rocks that humans process to be a certain size. (Since people don’t make the parent rocks, we still consider aggregates as natural soil stabilizers.) Aggregates come in many sizes and classifications. Coarse aggregates are larger, while fine aggregates are smaller.
Different sized aggregates work best for different jobs. For example, quarry spalls are large, coarse aggregates favorable for heavy-traffic areas like construction entrances and over-excavation sites. Type II aggregate is another coarse aggregate that’s smaller than quarry spalls; it’s a good, easy-to-compact subbase for paved roads.
Aggregates are extremely common, so road commissioners and engineers have more information about what aggregate will work best for their project, how much they need, and how much it’ll cost.
Importing and hauling aggregates is expensive. And choosing the wrong size reduces effectiveness. For example, too fine of an aggregate creates too little friction, making wet paved roads slick and dangerous. Finally, aggregates are prone to produce dust, and you’ll have to replace them as they wash away in rain or work themselves into the soil.
Geotechnical textiles are a special type of polymer made from woven cloth and fabric. (More on polymers in a minute.) Engineers use geotechnical textiles to stabilize soil and rocks. You might also hear people call them geotextiles. Common uses for geotechnical textiles include things like:
Geotechnical textiles are generally cost-effective to buy and to lay on the soil. They’re also useful in areas where you need good drainage since water passes through them easily.
Sediment, fungi, rocks, plants, and other matter can clog geotechnical textiles, limiting drainage. Additionally, geotechnical textiles are fabric, so they can rip. Ripped, clogged, or improperly laid geotextiles need to be replaced—which is difficult and expensive when they’re under a road or other structure.
Compaction applies pressure to push soil particles together, creating a stronger surface. Dynamic compaction repeatedly drops weight on soil, while vibratory compaction uses a roller to “shake” soil into place.
Compaction works on most soils, has no curing time, and uses no harmful chemicals. However, soil must maintain optimum moisture content during compaction to get the best results, so you’ll pay for water, water trucks, and truck drivers. Dynamic compaction has lost popularity because it often requires special equipment and disturbs people nearby.
Sometimes soil is too unstable to support infrastructure—and too difficult to stabilize. That's where over-excavation comes in. With over-excavation, equipment operators remove and export unstable soil. They dig down to stable soil or rock, import compatible soil, and backfill the excavated area to the appropriate depth. Some contractors add stabilization products like geotechnical textiles to the imported soil, too.
Over-excavation removes and replaces low quality soils, ensuring infrastructure lasts long-term. It’s expensive due to labor and material hauling.
Chemical soil stabilization uses man-made compounds like cement, lime, polymers, and chlorides.
Cement soil stabilization mixes soil, water, and cement (usually either Portland or blended). Hardened cement binds soil particles together for a stronger surface. This method works well with coarse-grained soils and aggregates, and it’s most common on unpaved roads.
Cement is extremely strong, water-impermeable, chemical-resistant, and weather-resistant. Compared to other soil stabilization products, cement is brittle and prone to cracking. It also requires the right temperature, soil moisture, and mixing process to work properly. And finally, it’s very expensive.
Lime comes from limestone, but it undergoes chemical changes during processing. You might also hear people call it quicklime or calcium oxide. (Hydrated lime is a special type of quicklime.) Lime stabilizes expansive soils like clay by reducing swelling or shrinking. Its most common use is for paved road subbases, to keep the soil from shifting and cracking the pavement.
Lime dries and strengthens soils, reducing construction downtime and over-excavation. Its environmental remediation properties help absorb toxic liquid wastes.
Getting the right mix of lime into your soil takes work and geotechnical testing. Too much, too little, or the wrong quality produces poor results. Lime soil stabilization also impacts the soil’s pH balance, microbes, and nutrient composition—which can be good or bad.
Finally, lime irritates people’s eyes, skin, and lungs. PPE reduces these risks but doesn’t eliminate them. Long-term exposure poses serious health threats.
Polymers are long, repeating chains of molecules that can be natural or man-made. Most work like glue to bind soil particles together and improve load-bearing capacity and tensile strength. Other polymers work more like soap: they lubricate soil to make other soil stabilizers—like compaction—more effective.
Polymers are widely available and work on most coarse soil types. But they’re typically ineffective for fine soils, like clay-based soils.
Synthetic polymers are susceptible to moisture, so they break down over time. Eventually, they need to be replaced. Many synthetic polymers are also environmental hazards. That’s why many people seek alternatives to synthetic polymers like biodegradable, plant-based options.
Magnesium chloride and calcium chloride are best known for dust mitigation. They pull moisture from the air and decrease water evaporation to keep ground surfaces wetter. They also strengthens soil by lubricating aggregates and soil particles. The lubricated particles move more freely, so they can press closer together during compaction, interlocking and sticking together longer.
People sometimes mix calcium chloride with cement to combine both dust suppression and strength. Scientific studies show this method to be effective.1
The biggest perk of chlorides is dust control. They improve visibility and safety. Plus, dust won’t damage nearby property and plants by settling on them. Calcium chloride also lowers the freezing point of water. In cold regions, this helps keep frost from damaging roads.
After it rains, chloride-treated roads need to be reworked to maintain dust control. Most roads need at least two applications per year—especially after the winter in colder climates.
Both magnesium and calcium chloride leach into the environment. Enough chloride kills plants, disrupts waterways, and corrodes people’s vehicles. Additionally, calcium chloride weakens over time, so soil may collapse.
Completely paving a road with asphalt stabilizes soil and solves some maintenance problems unpaved roads have, like washboarding and mud.
When it’s not possible or cost-effective to pave a whole road, some county road departments apply tiny pieces of asphalt called millings to the road’s surface with a bitumen emulsion. A bitumen emulsion is a stabilizer spray that mixes asphalt millings and water to harden soil. It’s an effective option for unpaved roads.
Asphalt is a highly effective soil stabilizer; that's why most major roads are paved! It’s also extremely expensive, which is why many rural counties don’t use it.
Bitumen emulsions are a “happy medium” between paving and not paving. However, bitumen particles can be brittle and environmentally harmful.
Biological soil stabilization uses living organisms to stabilize soil, such as plants. Biochemical soil stabilization relies on enzymes, which are proteins that cause chemical reactions in living organisms and in soil. Let's examine both.
Stabilizing soil with plants is called biological soil stabilization or soil bioengineering. Plant roots weave throughout the soil, reducing erosion.
Plants are live organisms that purify air and water. They house wildlife. They’re often cheaper than other soil stabilizers. And as a bonus, they’re attractive. However, you’re limited on where you can plant biological soil stabilizers—like alongside a road, not in it. Non-native plants may damage local ecosystems. Additionally, plants are weaker than some man-made solutions.
Enzymatic soil stabilizers are an effective, eco-friendly method, and Perma-Zyme has led the charge in this field since the 1970s. The enzymes in Perma-Zyme chemically react with clay and limestone to bond soil particles together. This creates a concrete-like surface that lasts 10 or more years on residential roads with little to no maintenance.
Rural communities use it on both unpaved and paved roads. The mining, solar, agriculture, and recreation industries also use it to strengthen private roads, drilling pads, parking areas, pond linings, walking paths, and more.
Perma-Zyme works in all climates, and it’s strong enough to support all types of traffic. As we mentioned, it's long-lasting, so you'll pay virtually nothing in maintenance costs. And it's 100% organic, non-toxic, and non-hazardous, so it's safe for the workers who apply it and the communities around the treated area.
Application costs more upfront than some soil stabilizers, like chlorides, and treatments may last a shorter amount of time (around five years) for roads that see lots of heavy truck and equipment traffic. But, paying $0 for yearly maintenance quickly makes up for these things.
Sandy and silty soils are incompatible with Perma-Zyme, so you may need to import compatible clay soils, decomposed granite, lime, or aggregate. (Usually importing these materials is still cheaper long-term than many other methods.) And like cement, Perma-Zyme has weather requirements. It works best at 40 degrees Fahrenheit or above, with no rain for three days.
