Triaxial tests measure soil’s shear resistance, important for project planning. Soil samples are placed in a tube with a membrane, dropped into liquid, and squeezed. Test equipment measures pressure on the ground to determine cutoff point. Laboratories follow strict protocols, but results may vary.
A triaxial test measures the soil’s ability to resist shear forces. This can be important in project planning, where soils must meet certain standards to support buildings and other structures. Soil tests can be ordered at the start of a site assessment to determine if a location is appropriate for a project. If the ground does not meet standards, the design may need to be modified with tools such as anchoring buildings into bedrock to provide the necessary support. Alternatively, the project could be moved to a better site.
This test involves placing a soil sample into a tube of rubber or other thin material that creates a membrane. The tube is sealed and dropped into a container filled with liquid. The liquid exerts tension on the material, pressing from all sides. The operator can apply pressure to the container to squeeze out the soil from above. When it begins to sag, it has given in to the pressure and has reached its cutoff point.
Test equipment includes tubes that measure the amount of pressure exerted on the ground. This allows the person performing the triaxial test to quantify the cutoff point. Multiple tests can be used to confirm the result before issuing a formal soil quality opinion. If it sags at low pressure, it may be too slow to support large or unstable structures. Some types of buildings, such as gas refineries, may not be allowed on land due to safety concerns.
Laboratories that perform triaxial testing have several methods to choose from. Some use consolidated soil that has been compacted, while others rely on unconsolidated soil in a sample as close to site conditions as possible. The soil may be either drained or undrained for testing, depending on what is being tested and the desired results. The sample condition is always noted in the triaxial test documentation to provide context for readers who may be curious about how the test was performed.
Site evaluation may include testing by several independent laboratories. If the triaxial test results do not match, technicians can explore the conditions and results to determine the cause of the disparity and develop a plan for a new triaxial test that will hopefully provide a more definitive answer. Laboratories follow strict protocols for all testing to maintain consistency and reliability, but labs may have different or conflicting results due to unique protocols, equipment variations, and other factors.
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