The cone penetration test (CPT) is a soil test that collects data as it penetrates the soil using a cylindrical metal rod with a conical tip. The data collected can be used to design pile foundations and evaluate soil seismic classification. A CPT system is required to take measurements using the cone penetrometer, which is mounted on a truck equipped with instrumentation to record data. Additional equipment is required for seismic testing using a seismic cone penetrometer (SCPT) to measure shear wave velocity.
A cone test, usually called a cone penetration test (CPT), is a type of soil test used to collect various types of data. The CPT collects data at regular intervals as it penetrates downward through the soil. The data collected from a conical test can be used to design pile foundations and to evaluate the seismic classification of the soil.
The cone test is so called because the equipment used to dig into the ground consists of a cylindrical metal rod with a pointed, conical tip. Other parts include a movable friction sleeve, a filter element to measure pore pressure, and sensors to measure the various forces acting on the rod. The entire assembly that enters the ground is known as a cone penetrometer or piezocone penetrometer. Penetrometers can be mechanical or electrical, and various cone diameters can be used: common sizes include 0.55 inch (about 1.4 cm), 1.42 inch (about 3.6 cm), and 1.73 inch (about 4.4 cm).
A CPT system is required to take measurements using the cone penetrometer. The rig is a truck specially equipped to carry out conical tests. A hydraulic ram is mounted in the center of the truck bed to push the penetrometer down through the ground. The carriage also contains instrumentation that records the force at the cone tip, the frictional force at the friction sleeve, the pore pressure, and, in some cases, shear wave velocity measurements. A computer in the plant records all the data collected during a test.
To perform a cone test, the hydraulic ram pushes the penetrometer through the soil at a constant rate, usually 0.79 inch per second (about 2 cm per second). Desired measurements are taken in equal increments between 0.20 and 1.97 inches (approximately 0.5 and 5 cm). Sections of rod approximately 3.28 feet (1 meter) long are added as the penetrometer proceeds deeper into the ground. Once the penetrometer has been removed from the ground, the hole is filled as required by local regulations.
Additional equipment is required to perform a seismic assessment with a cone test. Seismic testing requires a special type of penetrometer called a seismic cone penetrometer (SCPT), which measures the velocity of shear waves. The setup for a seismic test also includes a plate which contains a release device. Test personnel hit the plate with sledgehammers to generate seismic waves. The computer used to collect the data may function like an oscilloscope, a device that collects shear wave data.
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