Definition - What does Clay Soil mean?
Engineers use geotechnical surveys to reveal the soil types of the ground through, which a trenchless project will run. Clay soil is defined as having more than 40% clay, less than 45% sand and less than 40% silt. Problems associated with clay are the way in which it sticks together and clogs up trenchless equipment.
Trenchlesspedia explains Clay Soil
Using Horizontal Directional Drilling in clay soil can be challenging. Clay tends to clog up the drilling head making it ineffective and the drilling fluid must be carefully controlled to enable the spoil to be kept in suspension and pumped out of the bore. Auger boring is suitable for clay because the helical coils are able to keep moving through the clay and extract it from the bore. The clogging nature of clay creates a resistance to any trenchless method and high levels of torque are required to penetrate this difficult ground condition.