Soil Testing Equipment

Referent and Standards Product for Soil Testing Equipment

Cone Penetration Test


Cone Penetrometer Technology (CPT) is a method of providing real-time data for use in characterizing the subsurface, as opposed to older methods of analyzing subsurface conditions in the laboratory. It consists of a steel cone that is hydraulically pushed into the ground at up to 40,000 pounds of pressure. Sensors on the tip of the cone collect data. Standard cone penetrometers collect information to classify soil type by using sensors that measure cone-tip pressure and friction. CPT is often used in conjunction with Hydropunch tests, which use the CPT holes to extract groundwater for laboratory analysis. An innovation of the CPT (i.e., the wireline CPT) allows multiple CPT tools to be interchanged during a single penetration, without withdrawing the CPT rod string from the ground.

Initially developed to collect information about soil characteristics, as sensor technology was developed CPT also became a platform for collecting information about a variety of contaminants. Recent advances in sensor technology have expanded cone penetrometer capabilities to detect the presence of petroleum hydrocarbons. Sensors are being tested or demonstrated for the detection of other organics, compounds, metals, radioactivity, explosives, and soil moisture.

 Cone penetration testing (CPT) is the most versatile device for in situ soil testing. Without disturbing the ground, it provides information about soil type, geotechnical parameters like shear strength, density, elastic modulus, rates of consolidation and environmental properties. Further, as it can be seen as a small scale test pile, it is the best and most cost-effective device to design piled foundations and sheet piles.

Limitations and Concerns

CPT cannot be used at some sites due to high soil density. Most sensors are now used as screening tools that provide initial site characterization data. The data is confirmed by collecting samples that are analyzed in the laboratory. This is due to limitations in sensor technology, and it will likely diminish in importance as the technology improves.

CPT is useful on sites that contain unconsolidated sediments (e.g., soil and clay that are not cemented together). On the other hand, sites with large boulders, rock or cemented layers are difficult to penetrate.
CPT sensors, such as lasers, that require a lens may be hampered by fouling of the lens due to a reaction to dust. Decontamination may be necessary if the CPT comes into contact with contaminated material.

Cone Penetration Tests are conducted to obtain the cone resistance, the side friction and, if there is a piezocone, the pore pressure. The soil type can be determined by analysing these results, the values can also be used in the design of shallow foundations through the estimation of stiffness and shear strength of cohesive soils.
A 60o cone with face area 10cm2 and 150cm2  'friction sleeve' is hydraulically pushed into the ground at a constant speed (ranging form 1.5 to 2.5 cm/s). The force required to maintain this penetration rate, and the shear force acting on the friction sleeve are recorded. The friction ratio (cone resistance / side friction) gives an indication of the soil type.
Cone Resistance qc = Fc / Ac
Side Friction fs = Fs / As
Friction Ratio Rf = fs / qc
Where  Fc = pushing force, Ac = cone plan area, Fs = shear force on friction sleeve, As = area of friction sleeve.

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Penetration Testing

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