Soil testing is important in agriculture, construction, and environmental assessments. It includes testing for nutrients, contaminants, compaction, and percolation. Tests are also done to determine the type and depth of foundation required for different buildings and to detect the presence of expansive clay.
Soil analysis is a valuable tool used to help farmers achieve maximum crop yield. In the construction industry, preliminary tests are mandatory in most locations to detect contamination, determine suitability for construction and select the correct type of foundation. The various types of soil testing include testing for contaminants and mineral concentrations, compaction testing, cone testing, consolidation testing, and percolation testing.
Since the nutrients required for plants are different for each species, soil analysis for agricultural purposes involves evaluating the levels of nutrients required for specific crops. Soil composition also varies at different depths, so samples should be taken from the level where the most root activity will occur. Two frequently tested element levels are nitrogen and phosphorus. There are several methods for measuring nitrate and ammonium, the most common forms of nitrogen used by plants. The Bray P1 test is used to check phosphorus levels in acidic soils, while the Olsen Baking Soda Test checks phosphorus levels for alkaline soils.
Many countries have instituted restrictions on building sites that contain potentially toxic or carcinogenic waste, so it is essential to know a property’s history before development. When a site has been used for a purpose that could cause contamination, soil testing should be done before any development. A unique method for testing such substances in situ is a laser-induced fluorescence system. This test uses a truck-mounted sensor that can detect underground petroleum hydrocarbons and uranium. Other methods include soil vapor testing and using pore water samples taken from the designated area.
Before installing underground septic or sewer filtration systems, required soil tests usually include soil percolation and soil profile tests. The percolation test simulates the conditions of a septic system and measures the soil’s ability to absorb liquids. In addition to drilling test holes at the level where the system will be located, you also need to ensure that the water table at the lowest point is two feet (61 m) lower than the level of the septic system. Soil profile tests evaluate the texture of the soil, whether or not it is waterlogged, and the depth of the underlying bedrock.
Soil testing is essential in construction to determine the types and depths of foundations required for different buildings on different sites. Geotechnical soil testing involves drilling into the ground of a proposed site and then performing laboratory tests on samples to determine the composition of the soil. Compaction tests are vital in determining whether clay soils are suitable for building, what type of equipment should be used to compact the soil, and how much compaction is required before pouring the foundation.
One of the most common field tests for studying soft soils is the conical penetration test, developed in Holland in the 1950s. This relatively inexpensive soil analysis method measures resistance and friction against a cone-shaped tool as it is driven into the ground at a constant speed. The main purpose of this test is to predict the vertical capacity of deep foundations and for soil stratigraphy.
Another reason for soil testing is to detect the presence of expensive clay. Expansive clay contains water-absorbing minerals that cause it to swell when wet and contract when dry, resulting in volume changes of up to ten percent. These clays appear worldwide and are the primary cause of damaged foundations. It is possible to build on expansive clay as long as the foundation is constructed to maintain moisture control. In some areas, foundations of pierced expansive clay piers have been used, although the more stable approach appears to be to extend the foundation below the water ripple zone.
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