Expansive Clays and Soft Soils

What is expansive clay?

Expansive clay soils, also known as heavy or fat clay soils, are characterized by their soft texture containing minerals that undergo significant volumetric changes with seasonal moisture fluctuations. They absorb water, swelling up to ten percent or more when wet, and subsequently crack when dry. As the water content in these soils freezes, this can compound the swelling problem, leading to frost heave issues. These cyclical changes cause shear stresses, increasing lateral and vertical pressures, causing the cracking and buckling of roads and structures. As a result, damages and repairs from expansive clays incur annual costs in the billions. Damages include cracked foundations, floors, basement walls, sidewalks, driveways, and patios but extend to underground infrastructure as well. In fact, compromised underground infrastructure can cause building foundation problems and ruptured pipe lines.

Understanding expansive clay foundation damage

Expansive soils contain swelling clay minerals that are highly prone to absorbing moisture. This can pose a hazard to the foundational support for buildings and structures. The most obvious way damage is caused is by the uplift action due to swelling. 

Moisture absorption varies with the gradation of particles and the clay content. This leads to issues such as lifting and cracking of footings and causes distress in floor slabs. Designing effective methods to stabilize these swelling soils are the key to prevention or to provide damage control.

Soil stabilization methods that restrict foundation movement

To prevent swelling soils from compromising the integrity of foundations and to restrict foundation movement, it’s crucial to control the soil’s moisture content. Moisture levels in expansive soils can change across a large area, fluctuating based on the amount of seasonal precipitation and natural runoff.

NPA geocells [cellular confinement systems] provide a reliable method for stabilizing moisture levels in expansive clay soils. Geocell technology efficiently redistributes and drains moisture away from the foundation and helps maintain a stable moisture level, even under vertical pressure or rainfall.

Structural geocells made from a novel polymeric alloy [NPA] material outperform other geosynthetics with their flexibility, creep, and high-tensile strength. Though not completely impervious to water, sewage and other liquids, the cell walls have perforations to allow natural drainage of the infill material without hindrance.


Muskeg Soils

Prevalent in our northern climate, Muskeg (Peat Bog), are soils rich in peat moss that habitually absorb large amounts of moisture. This results in extremely soft, swamp-like areas that can reach several meters in depth. Characterized by low surface tension, if one stands on muskeg, one could sink a few inches to potentially their full height.

Thus, it is extremely hazardous and nearly impossible to traverse or build over. While muskeg is not considered frost susceptible, its high-water content may allow the upper depths to freeze while still harboring liquid moisture below.

Soft soil.

Problems of traditional design of roads over muskeg [and other soft soils]

A major challenge in geotechnical engineering is to mitigate the effects that building on expansive clays and soft soils have. As soils freeze in sub-zero temperatures, thawing causes runoff. This coupled with heavy summer rain (without proper drainage) impedes construction during summer.

The traditional solution is to excavate and remove the undesirable soil and replace it with high quality aggregate fill. This method is time-consuming and expensive, especially if suitable aggregate needs to be imported. In addition, the depth of the problematic soil will require the equivalent volume of replacement aggregate. The root problem of course, is the resident moisture which will continue to infiltrate the area over time.

Geosynthetic road design solutions

It is possible to build successfully and safely on expansive soils if the moisture content can be reduced and stabilized against rapid fluctuation.

Stratum uses NPA geocells to design structures that conquer expansive clay conditions and other soft subgrades with swelling potential.

Our specialty is building on weak or impassable soils like muskeg, saturated soils, and expansive clays. We specifically apply our expertise to unique projects affected by extreme cold temperatures and are contending with frost heave and cyclical freeze-thaw stresses.

Tough Cell layer

Are you ready to add stability to your projects? Let us know what you need.