PA 06/02 Soil Analysis Follow-Up

Hey Everyone!
There were a few questions asked during yesterdays workshop that we didn’t get to cover. Please see my answers below. If I missed a question feel free to reach out.

On the Geotechnical report what is the difference between Depth in Feet and Elevation in Feet? Depth in Feet = overall distance from starting point of sample. Elevation in Feet = Measurement above sea level

Is Sand Stable or Unstable for foundations?
Sand is unstable as a primary soil for foundations. It is especially unstable in seismic areas due to liquification. ( Liquefaction is when a soil behaves like a liquid, such as when seismic “S” waves cause vibrations during earthquakes. Loose and uncompacted granular soils such as sand and sandy (non-plastic) silts are the most susceptible to liquefaction.)

What is the difference between a Boring and A CPT?
"Soil Boring: a technique used to survey soil by taking several shallow cores out of the sediment. It is used when a drilling jacket or jack-up rig is to be supported on the soil. Conventional soil boring was used to determine the subsurface soil profile and static soil properties.
Cone Penetration Test (CPT): an in-situ test that is used to identify the soil type. In this test a cone penetrometer is pushed into the ground at a standard rate and data are recorded at regular intervals during penetration. A cone penetration test rig pushes the steel cone vertically into the ground. The cone penetrometer is instrumented to measure penetration resistance at the tip and friction in the shaft (friction sleeve) during penetration.

When to use each:
Standard boring testing is used in construction projects for the preliminary soil investigation. It’s an inexpensive test, the test can be done quickly, and it’s relatively simple to perform. CPTs are used for detail soil investigation and construction quality control. They are known to have increased accuracy and speed of deployment/results, they show a more continuous oil profile. They do tend to take more skill to perform and can be more expensive then standard boring tests." - Courtesy of past workshop instructor Rebecca Smith

I hope this helps. Let me know if there are any more questions.


thanks Faith! I really enjoyed this last session on Soil analysis and appreciated how thorough you were in reviewing each answer.

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