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SPT, CPT and soil investigation.

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Jorge Rodriguez

on 15 January 2014

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Transcript of SPT, CPT and soil investigation.

Standard Penetration and Cone Penetration Tests.
Jorge J. Rodriguez E.I.T.

Agenda
Standard Penetration Test (SPT)
Cone Penetration Test (CPT)
Advantages and Disadvantages of SPT and CPT Testing.
Data results.
References.
Questions.
Standard Penetration Test (SPT)
One of the most commonly used in-situ tests used by geotechnical firms. Developed in the 1920's (Coduto).
In 1958, it was standarized as ASTM D1586 ( Standard Test Method for Standard Penetration Test (SPT) and Split Barrel Sampling of Soils).
Procedure:
Drill an exploratory boring (2.5 to 8 in.)
Insert a split-spoon sampler into the boring. Attached the split spoon with steel rods to a 140 lb. hammer.
Using either rope or automatic mechanism, raise the hammer to a height of 30 in. and allow it to fall into the steel rod. Record the total of blows per 6 in. interval until the split spoon sampler has reached a penetration of 18 in.
Compute the N value as the sum of blow counts for the last 12 in. of penetration of the split spoon sampler. The number of blows on the first 6 in. interval is not included in the total sum as a result of soil disturbance during the drilling process and also loose soil falling from the sides of the boring onto the bottom. If any of the 6 in. interval reaches a blow count of 100, the process should stop immediately (ASTM 1586-11).
Remove the split spoon sampler and collect the soil inside for further testings.
Repeat the process using a new split spoon sampler.
Cone Penetration Test (CPT)
Standard Penetration Test (SPT) [cont.]
Cone Penetration Test (CPT) [cont.]
Advantages and Disadvantages:
CEGR5278
Dr. Rajaram Janardhanam

References
ASTM D1586-11, "Standard Test Method for Standard Penetration Test (SPT) and Split Barrel Sampling of Soils".
ASTM D3441-05, "Standard Test Method for Mechanical Cone Penetration Tests of Soil".
Braja M. Das, Principles of Foundation Engineering, Seventh Edition, Pag. 81-89, 98-107.
Coduto, Donald P., Foundation Design Principles and Practices, Second Edition, Pag. 115-131.
Questions?
Preguntas?
Quaestiones?
Domande?
Wèndí?
Saval?
Perguntas?
Shitsumon?
Another in-situ test method eveloped in the 1930's
Standarized as ASTM D3441 in 1974 ( Standard Test Method for Mechanical Cone Penetration Tests of Soil).
CPT tests give the engineer the opportunity to retrieve the changes in soil stratigraphy as a function of depth.
Uses two types of cones: mechanical cone and electric cone.
The geotechnical properties retrieved using this test are: side friction, cone resistance, friction ratio and pore pressure.
Procedure:
A CPT rig is placed at the site of investigation.
A hydraulic ram pushes the cone into the ground using the weight of the rig as a reaction until it reaches the desired depth.
A software equipment is able to manage en retrieve side friction, cone resistance, friction ratio and pore pressure throughout the whole depth.
SPT:
Soil sample can be recovered for additional testing.
Larger margin of error. Needs more correlation equations to minimize the errors due to procedure.
Relies strictly on blow counts in order to make soil classification.

CPT:
Tip resistance, side friction, pore pressure and friction angles can be determined right after collecting the in-situ data.
Gives a better idea on soil stratigraphy.
No soil samples are recovered.
Poor test for soils with high gravel content.
Tends to be more expensive due to use of special rig at the site.
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