- Cone penetration test
The cone penetration test (CPT) is an in situ testing method used to determine the geotechnical engineering properties of soils and delineating soil stratigraphy. It was initially developed in the 1950s at the Dutch Laboratory for Soil Mechanics in Delft to investigate soft soils. Based on this history it has also been called the "Dutch cone test". Today, the CPT is one of the most used and accepted in situ test methods for soil investigation worldwide.
The test method consists of pushing an instrumented cone, with the tip facing down, into the ground at a controlled rate (usually 2 centimeters/second). The resolution of the CPT in delineating stratigraphic layers is related to the size of the cone tip, with typical cone tips having a cross-sectional area of either 10 or 15 cm², corresponding to diameters of 3.6 and 4.4 cm.
History and development
The early applications of CPT mainly determined the soil geotechnical property of bearing capacity. The original cone penetrometers involved simple mechanical measurements of the total penetration resistance to pushing a tool with a conical tip into the soil. Different methods were employed to separate the total measured resistance into components generated by the conical tip (the "tip friction") and friction generated by the rod string. A friction sleeve was added to quantify this component of the friction and aid in determining soil cohesive strength in the 1960s (Begemann, 1965). Electronic measurements began in 1948 and improved further in the early 1970s (de Reister, 1971). Most modern electronic CPT cones now also employ a pressure transducer with a filter to gather pore water pressure data. The filter is usually located either on the cone tip (the so-called U1 position), immediately behind the cone tip (the most common U2 position) or behind the friction sleeve (U3 position). Pore water pressure data aids determining stratigraphy and is primarily used to correct tip friction values for those effects. CPT testing which also gathers this piezometer data is called CPTU testing. CPT and CPTU testing equipment generally advances the cone using hydraulic rams mounted on either a heavily ballasted vehicle or using screwed-in anchors as a counter-force. One advantage of CPT over the Standard Penetration Test (SPT) is a more continuous profile of soil parameters, with CPTU data recorded typically at 2cm intervals.
Additional in situ testing parameters
In addition to the mechanical and electronic cones, a variety of other CPT-deployed tools have been developed over the years to provide additional subsurface information. One common tool advanced during CPT testing is a geophone set to gather seismic shear wave and compression wave velocities. This data helps determine the shear modulus and Poisson's ratio at intervals through the soil column for soil liquefaction analysis and low-strain soil strength analysis. Engineers use the shear wave velocity and shear modulus to determine the soil's behavior under low-strain and vibratory loads. Additional tools such as laser-induced fluorescence, X-ray fluorescence, soil conductivity/resistivity, membrane interface probe and cameras for capturing video imagery are also increasingly advanced in conjunction with the CPT probe.
An additional CPT deployed tool used in Britain, Netherlands, Germany, Belgium and France is a piezocone combined with a tri-axial magnetometer. This is used to attempt to ensure that tests, boreholes, and piles, do not encounter unexploded ordnance (UXB) or duds. The magnetometer in the cone detects ferrous materials of 50 kg or larger within a radius of up to about 2 m distance from the probe depending on the material, orientation and soil conditions.
Standards and use
CPT for geotechnical applications was standardized in 1986 by ASTM Standard D 3441 (ASTM, 2004). ISSMGE provides international standards on CPT and CPTU. Later ASTM Standards have addressed the use of CPT for various environmental site characterization and groundwater monitoring activities. Particularly for geotechnical soil investigations, CPT is gaining popularity compared to standard penetration testing as a method of geotechnical soil investigation by its increased accuracy, speed of deployment, more continuous soil profile and reduced cost over other soil testing methods. The ability to advance additional in situ testing tools using the CPT direct push drilling rig, including the seismic tools described above, are accelerating this process.
- "Cone Penetration Testing in Geotechnical Practice"; T. Lunne, P.K. Robertson and J.J.M. Powell. Blackie Academic & Professional. London.
- De Reister, J., 1971, "Electric Penetrometer for Site Investigations"; Journal of SMFE Division, ASCE, Vol. 97, SM-2, pp. 457-472.
- Begemann, H. K. S, 1965, "The Friction Jacket Cone as an Aid in Determining the Soil Profile"; Proceedings, 6th ICSMFE, Montreal, Quebec, Canada, Vol I, pp.17-20.
- Meigh, A.C., 1987 "Cone Penetration Testing - Methods and Interpretation", CIRIA, Butterworths.
- ASTM, 2004, "Standard Method of Deep Quasi-Static Cone and Friction-Cone Penetration Tests of Soil"; ASTM Standard D 3441, ASTM International, West Conshohocken, PA, 7 pp.
- ASTM D-5778 "Standard Test Method for Performing Electronic Friction Cone and Piezocone Penetration Testing of Soils".
- International Reference Test Procedure for CPT and CPTU - International Society of Soil Mechanics and Geotechnical Engineering (ISSMGE) (http://www.issmge.org)
- Mayne, Paul; Auxt, Jay A.; Mitchell, James K.; Yilmaz, Recep (October 4-5, 1995). "U.S. National Report on CPT". Proceedings, International Symposium on Cone Penetration Testing, Vol. 1 (CPT '95). Linköping, Sweden: Swedish Geotechnical Society. pp. 263-276. http://geosystems.ce.gatech.edu/Faculty/Mayne/papers/CPT%2095%20US%20Report.pdf. Retrieved 2011-09-26.
Topics in geotechnical engineering Soils Soil properties Soil mechanics Geotechnical investigation Laboratory tests Field tests Foundations Retaining walls Slope stability Earthquakes Geosynthetics Instrumentation for Stability Monitoring
Wikimedia Foundation. 2010.
Look at other dictionaries:
Standard penetration test — The standard penetration test (SPT) is an in situ dynamic penetration test designed to provide information on the geotechnical engineering properties of soil. The test procedure is described in the British Standard BS 1377 9:1990 and ASTM D1586.… … Wikipedia
Cone Penetrometer — The Cone Penetrometer apparatus is an alternative method to the Casagrande Device in measuring the Liquid Limit of a soil sample (See:Atterberg Limits). It is usually considered to be a more scientific approach because it is based less upon human … Wikipedia
Cone — This disambiguation page lists articles associated with the same title. If an internal link led you here, you may wish to change the link to point directly to the intended article … Wikipedia
Fall cone test — The Fall cone test apparatus is an alternative method to the Casagrande Device in measuring the Liquid Limit of a soil sample (See:Atterberg Limits). It is usually considered to be a more scientific approach because it is based less upon human… … Wikipedia
Drucksondierung — Die Drucksondierung (Cone Penetration Test, CPT) ist ein Sondierverfahren zur Baugrunderkundung, bei dem ein Messkopf mit kegelförmiger Spitze mit konstanter Geschwindigkeit über ein Gestänge in den Boden gedrückt wird. Gemessen wird im… … Deutsch Wikipedia
Geotechnical engineering — [ Boston s Big Dig presented geotechnical challenges in an urban environment.] Geotechnical engineering is the branch of civil engineering concerned with the engineering behavior of earth materials. Geotechnical engineering includes investigating … Wikipedia
Angle of repose — For the Wallace Stegner novel, see Angle of Repose (novel). For the friction angle between two solid objects, see Friction. For the Sleepytime Gorilla Museum song of the same name, see In Glorious Times. Angle of repose The angle of repose or,… … Wikipedia
Hydrometer — Not to be confused with Hygrometer. Hydrometer from Practical Physics Schematic drawing of a hydrometer. The lower the densi … Wikipedia
Geotechnical investigation — Geotechnical investigations are performed by geotechnical engineers or engineering geologists to obtain information on the physical properties of soil and rock around a site to design earthworks and foundations for proposed structures and for… … Wikipedia
Deep foundation — A deep foundation installation for a bridge in Napa, California, United States … Wikipedia