You’re a civil engineer and you need to test soil. What’s the best tool for the job?

1 Soil samplers

When performing soil testing, one of the first steps is to collect soil samples from different depths and locations of your site. To do this, you need to use a soil sampler. These devices come in various shapes and sizes, depending on the type and consistency of the soil. The most common ones are the split-spoon sampler, the Shelby tube sampler, and the auger sampler. The split-spoon sampler is a hollow metal tube that is driven into the soil by a hammer and then split into two halves to retrieve the soil core. It is suitable for cohesive and granular soils that are not too hard or dense. The Shelby tube sampler is a thin-walled metal tube that is pushed into the soil by a hydraulic piston and then pulled out with the soil core inside. It can be used for soft and clayey soils that need to preserve their structure and moisture content. The auger sampler is a spiral-shaped metal blade that is rotated into the soil by a drill and then lifted out with the soil auger attached. This type of sampler works best for loose and sandy soils that are easy to penetrate and mix.

2 Soil sieves

Once you have collected your soil samples, analyzing their particle size distribution is necessary in order to measure how coarse or fine the soil is. To accomplish this, soil sieves are used to separate the particles into different size fractions by passing them through a series of mesh screens with different openings. Depending on the amount and type of soil being tested, these sieves can be either hand-operated or machine-operated. Standard sieves are circular metal frames with wire mesh screens that have standard openings ranging from 4.75 mm to 0.075 mm, and they are used for coarse-grained soils with more than 50% of particles larger than 0.075 mm. On the other hand, a hydrometer is a glass device that measures the specific gravity of a soil-water suspension and is used for fine-grained soils with more than 50% of particles smaller than 0.075 mm. After placing the suspension in a glass cylinder and stirring it to disperse the particles, the hydrometer is inserted into the cylinder and the reading is taken at different time intervals to determine the percentage of particles that have settled at different depths.

3 Soil testers

Once you have determined the particle size distribution of your soil samples, you should perform more tests to measure other soil properties and characteristics, such as moisture content, density, compaction, shear strength, compressibility, and permeability. To do this, you can use soil testers which are either field-based or laboratory-based, depending on the accuracy and complexity of the test. For example, a moisture meter is a device that measures the water content of the soil by using electrical resistance, capacitance, or microwave techniques. Additionally, a Proctor compaction tester measures the maximum dry density and optimum moisture content of the soil by compacting it in a cylindrical mold with a standard hammer. Lastly, a direct shear tester measures the shear strength of the soil by applying a horizontal force to the upper half of a soil sample while holding the lower half fixed. There are many more available tools for testing soil as a civil engineer; however, soil testing is an essential skill that can help you design safe and sustainable structures and infrastructures that can withstand natural and man-made forces.