Soil testing (in geotechnical investigations) is a broad term used to describe the various tasks involved in gathering the required information for planning foundations and “earth works”. Structures such as buildings or bridges require a strong and stable foundation to stand on. Geotechnical experts gather
information about the physical properties of rocks and soil from a proposed site to assess the suitability of the particular site. For example, bridges are
meant to support heavy loads such as vehicles or trains. Bridges are built on piles and the foundation should support the load. Swampy areas often have
“loose” soil with high water content and are not ideal for construction. However, soil testing studies would confirm the property of the soil and rocks at a site.
To get adequate information about a site, surface and subsurface investigations must be undertaken. Geologic mapping and direct field studies provide information about the surface. For large projects such as bridges on seas, geophysical methods are used to gather subsurface data. For building constructions and designing foundations for bridges, many methods are available. However, the most common method is the use of boring techniques to get soil or rock samples.
Soil samples provide evidence of what lies beneath the surface. Geology of the area might indicate the age and type of rock one can expect in
the formations. Boring brings up the soil or rock and often the lithology can be established. Rocky sub surfaces act as strong bed rocks. However, soil
testing focuses more on finding out whether the site is suitable for construction or whether there could be potentially dangerous sink holes, mud
slides, or faults. This is done through analysis of the sand grains for grain size, water content, ability to withstand stress and shear, etc.
To test soils or rocks of a site:
- Conduct field or site investigations in situ
- Study associated geological maps
- Gather data from nearby sites
- Use appropriate method to understand subsurface
- Get samples and analyze physical property of soil in the laboratory
- Depending on the results, make a decision
Here are some photographs of the equipment used to gather core samples. The usual tools used include samplers such as augers, Shelby tubes
or pistons. At times, undisturbed samples are required to make a decision. The sampler selected depends on the type of sample required and the rock or soil
property. The photographs show sampler tubes with the core.