Dear colleagues,
How can I measure the unconfined compressive strength of the loose materials such as soils, to determine the stress and strain curve? Is there any other way to determien the stress strain relationship instead of unconfined compressive strength?
Thank you
Dear Bekir,
You need to conduct triaxial test to obtain the stress - strain curve for soil with any relative density of sand or clay soil with any consistency. The purpose of getting the stress - strain curve is to obtain the Young's modulus of soil. The Young's modulus (E) of soil can be obtained from correlation b/w 'E' and SPT 'N' value..or it is b/w E and angle of internal friction. You could get lot of literature on these aspects and also in any standard Soil mechanics book..ok all the best..
Bekir,
Unconfined compression test used to be considered a performance test, but currently, it is regarded as an index test by some authors. So, although you may draw a stress-strain curve from them, care must be exercised before using that value in numerical analysis.
Soil modulus depends on several factors: the strain magnitude is one of them, i. e. large strains mobilize low modulus. That being said, you may consider in situ techniques like SASW to asses the low-strain maximum-rigidity of the soil and other tests with larger strains to asses the complete behavior of the material (plus physical variables as moisture, density, grain-size).
However, if you are interested in designing any work that induces more significant deformations in the soil, you will have to execute a sampling and testing program. If you have a very loose granular soil, you may be interested in obtaining samples and try to duplicate the field conditions (moisture, density, void ratio) in the lab to design an improvement treatment, for example, soil compaction.
The compacted state may offer better conditions to perform the lab and field tests to obtain significant resistant and deformation parameters.
Best regards,
stress strain curve may be true and apparent. before actual compaction starts all readings related to strain are apparent and after slight compaction resistance will be true resistance so true curve can be obtained. or other wise before test make specimen with slight compaction
Compact soil to obtain optimum moisture content and prepare a 50mm diameter and 100mm length cylindrical sample at optimum moisture and subject the sample to unconfined compression strength test at a strain rate of 1-2mm/min. You can then measure and obtain your stress-strain curve. Cylindrical samples are encouraged for uniform stress distribution during loading and to avoid stress concentration around the edges (cubes).
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