Soil classification tests are methods of determining the physical and engineering properties of soils, such as moisture content, specific gravity, grain size distribution, Atterberg limits, and shear strength. These tests are important for geotechnical design and construction, as they help to identify the soil types, behavior, and reactivity on a site. Soil classification tests can be divided into two categories: field tests and laboratory tests. Field tests are performed on site using simple tools and visual observation, while laboratory tests are performed in a controlled environment using specialized equipment and procedures.
Some of the common field tests are:
- Visual inspection: This involves examining the soil color, texture, structure, odor, and consistency by hand or with a pocket knife.
- Pocket penetrometer: This is a device that measures the unconfined compressive strength of cohesive soils by pushing a calibrated spring-loaded piston into the soil sample.
- Torvane shear: This is a device that measures the shear strength of cohesive soils by applying a torque to a thin metal blade inserted into the soil sample.
- Dynamic cone penetrometer: This is a device that measures the penetration resistance of soils by dropping a hammer on a cone-shaped tip attached to a rod that is driven into the soil.
- Standard penetration test: This is a test that measures the penetration resistance of soils by driving a split-barrel sampler into the soil using a hammer and a drill rig.
Some of the common laboratory tests are:
- Moisture content: This is a test that measures the amount of water in a soil sample by weighing it before and after drying it in an oven.
- Specific gravity: This is a test that measures the ratio of the weight of a soil sample to the weight of an equal volume of water, using a pycnometer or a gas jar.
- Grain size distribution: This is a test that measures the percentage of soil particles of different sizes, using sieves or a hydrometer.
- Atterberg limits: These are tests that measure the water content at which a soil changes from a solid to a plastic state (plastic limit), and from a plastic to a liquid state (liquid limit), using a casagrande apparatus or a cone penetrometer.
- Shear strength: These are tests that measure the resistance of a soil to failure under shear stress, using a direct shear box, a triaxial cell, or a vane shear apparatus.
There are various soil classification systems that are used to group soils based on their properties and behavior. One of the most widely used systems is the Unified Soil Classification System (USCS), which divides soils into four major categories: coarse-grained soils, fine-grained soils, organic soils, and peat. The USCS further subdivides these categories based on the grain size distribution, plasticity, and organic content of the soils. The USCS uses symbols and names to identify the soil groups, such as GW for well-graded gravel, CL for low-plasticity clay, OL for organic silt, and PT for peat.