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Dynamic Cone Penetration (DCP) testing is used to measure the strength of in-situ soil and the thickness and location of subsurface soil layers.
It is similar to CPT in that a metal cone is advanced into the ground to continuously characterize soil behavior. However, unlike in CPT, where the cone is driven into the ground at a constant rate by varying amounts of force, in DCP, the cone is driven by a standard amount of force from a hammer, and how far the cone moves with each blow is used to determine the soil density and properties at that level.
In DCP testing, the pushing force is applied by manually dropping a single or dual mass weight (called the hammer) from a fixed height onto the push cone unit. The resulting downward movement is then measured. Unlike CPT systems, basic DCP equipment is hand-portable and may be limited to test depths of3-4 feet: this makes it a good choice for shallow testing applications such as road bed construction and maintenance. Since DCP is essentially hand-powered, it is cheaper and more portable than CPT equipment, but the possibility of human error makes it trickier to obtain consistent and accurate data.
Historically, one of the largest difficulties associated with DCP has been obtaining accurate depth difference measurements with a hand rule after each blow of the hammer. As you can imagine, taking these measurements by sight and recording them by hand can be slow, finicky work. Plus, to measure the total depth, the sum of these measurements is calculated, so it is easy to accumulate a troublesome amount of error if each measurement is even slightly off.
Fortunately, handheld electronics technology has alleviated these issues to a great extent. Vertek's Handheld DCP System uses a smartphone app and a laser rangefinder to automatically count blows and measure, record and plot depth. From the smartphone, this data can be easily graphed in the field and transferred to a computer or client for reporting and analysis. Automatic data collection saves time, increases accuracy, and means that the test can be efficiently completed by one person.
To further increase the repeatability and efficiency of DCP testing, fully automated (ADCP) systems are available. ADCP rigs can be mounted on lightweight trailers, commercially available trucks, or ATVs. Automated tests are both faster and more consistent than their manual counterparts, and also decrease physical labor for the operator.
The Dynamic Cone Penetration Test provides a measure of a material’s in-situ resistance to penetration. The test is performed by driving a metal cone into the ground by repeated striking it with a17.6 lb (8 Kg)weight dropped from a distance of2.26 feet (575 mm). The penetration of the cone is measured after each blow andis recorded to provide a continuous measure of shearing resistance up to5 feet below the ground surface. Test results can be correlated to California Bearing Ratios, in-situ density, resilient modulus, and bearing capacity.
The Cone Penetrometer Test (CPT) is a method used to determine the geotechnical engineering properties of soils and delineating soil stratigraphy. It was initially developed in the1950s 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 soil 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 (controlled between1.5 -2.5 cm/s accepted). 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 either10 or15 cm², corresponding to diameters of3.6 and4.4 cm.
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