Standard Penetration and Cone Penetration Tests.
Jorge J. Rodriguez E.I.T.
Questions?
Preguntas?
Quaestiones?
Domande?
Wèndí?
Saval?
Perguntas?
Shitsumon?
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.
Advantages and Disadvantages:
Agenda
Standard Penetration Test (SPT)
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.
- Standard Penetration Test (SPT)
- Cone Penetration Test (CPT)
- Advantages and Disadvantages of SPT and CPT Testing.
- Data results.
- References.
- Questions.
- 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.
Standard Penetration Test (SPT) [cont.]
Cone Penetration Test (CPT) [cont.]
Cone Penetration Test (CPT)
- 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.
CEGR5278
Dr. Rajaram Janardhanam