Geotechnical tests analyze a number of soil characteristics including density, draining capacity, moisture and particle content. Soil generally consists of dirt, minerals, and rocks, along with water and air. Some areas have soil that contains clay or sand. Environmental engineering services evaluate the soil composition of a particular site before construction begins, which determines the condition of the ground under various circumstances. Environmental and weather conditions that might cause soil expansion and contraction or ground shifting are some of the factors a geotechnical test analyzes.
Before spending millions of dollars and hundreds of man-hours building a structure, landowners need to know whether the ground can support the proposed building. Soft, air-filled ground may cause more structural settling than desired, causing premature cracking throughout a building. Areas with heavy rainfall followed by periods of intense heat might have soil movement that could potentially ruin a building foundation. When developing barriers or walls along a body of water, engineers require a series of evaluations that determine what structures might prevent landslides, soil erosion, or slope instability.
The geological engineer not only performs testing on visible topsoil but also analyzes the layers below ground level by taking bore samples and digging pits or trenches. Technicians might perform some tests on-site while others require laboratory evaluation. The geotechnical test, called the sieve analysis, examines the size and number of various particles in the soil. The hydrometer analysis determines the amount of silt particles that are too small for sieve testing. These tests might provide information for general soil classifications or be used to determine if soil composition is suitable for use in concrete mixing.
Many tests determine moisture content and the effects of moisture on soil. A liquid limit geotechnical test analyzes the amount of moisture required before soil becomes liquid while the linear shrinkage test determines the amount of shrinkage wet land exhibits after being exposed to extreme drying conditions. The hydraulic conductivity test evaluates water flow through clay and sandy soils to predict land settling and its possible effects on structures. The moisture content in clay soils when changing from semisolid to plastic is determined by the plastic limit test.
Some tests evaluate the overall strength of the ground. The compaction geotechnical test, for example, evaluates the density and moisture content of compacted soil to determine whether a location can adequately support heavy structures. The California bearing ratio test analyzes soil density and compaction by using penetrating instruments that apply varying amounts of direct force. The shear test evaluates the strength of sand containing soils where contractors might build levees or retaining walls.