Everyone has heard horror stories associated with clay soils. All you need to do is attempt to dig a hole with a shovel to realize how hard it gets when dry, and feel it stick to your boots like a pair of concrete shoes after it rains. Similar reactions happen to your trenchless equipment while advancing underground. Clay is not an ideal soil type for construction since it is highly reactive to moisture. It is soft and sticky when wet, and hard when dry. If you don’t know much about the soil you are working within, it could spell bad news for your trenchless project.

Identification is Key

It is important to properly identify the ground conditions along the alignment. While it would be wonderful if everyone had a professional to interpret the geotechniFigure 1: Reactive clays can expand and stick to trenchless equipment causing extreme loads. cal profile prior to the project starting, most seasoned professionals understand that soil investigating is never really done until the project is finished. Fortunately, there are relatively simple ways to determine if your soil is “reactive” or “non-reactive”. If no geotechnical report is available, simply break off a golf ball size clump of damp clay and roll it between your hands. If you can roll it into the thickness of a pencil without crumbling, the ground is going to be reactive and swell. If you can continue to form an even longer spaghetti-like noodle without it crumbling, it will be even more reactive with water.

Industry Solutions

Understanding how a properly designed drilling fluid works with an adequate delivery system for your clay type is very important. Since clay particles can be 1000X smaller than sand, clay particles will have substantially more surface area per volume for water to contact. Certain types of clay molecules have negatively charged locations on their surface that can attract water molecules like a magnet. As additional water is added to clay, the layer of water continues to grow around the clay molecule. This phenomenon causes the clay particles to separate and swell. In some cases, such as mixing Wyoming bentonite for a slurry, this process is a desired result as porosity increases, yet permeability remains low.