The determination of the soil group is carried out at the stage of designing the foundations of buildings and structures. The study of the soil is necessary to determine its ability to withstand the load of the future construction object. Soils are classified into groups according to the nature of structural bonds as follows.
GOST 25100-95 "Classification of soils"
Take several soil samples at different locations on the building site at a depth of up to 5 meters. Determine visually their characteristic features. Look at the soil classifier for the characteristics of each soil group.
Compare the characteristics of soil samples with those given in the classifier. You can easily recognize rocky, coarse and sandy soils. If the sample does not belong to any of these groups, therefore, you have clay soil in your area.
Determine the type of clay soil - it can be sandy loam, loam or clay. Rub some of the sample between your fingers. If it contains a mixture of sand and, up to about 10% clay, and the sample does not roll into a cord when rubbed between the palms, this is sandy loam. If it is a mixture of sand and up to 30% clay, and the sample, when rubbed, rolls into a cord with a diameter of up to 1 cm, it is loam. If the sample is strong enough in the dry state, but plastic in the wet state, it is clay.
If necessary, identify the type of clay soil by the content of sand particles in the sample. So, sandy loam can be sandy loam and silty, loam - light silty and light sandy, heavy silty and heavy sandy. Having determined the soil group, you can start choosing the type of foundation structure for the projected building.