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. The test method consists of pushing an instrumented cone tip first 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. 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 Direct Push hydraulic rams using screwed-in anchors as a counter-force
(See CPT Anchoring) .
CPT/MIP - Cone Penetration Testing/Membrane Interface Probe
CPT/MIP Investigations give an understanding of soil stratigraphy , hydraulic properties, and the distribution of VOCs with respect to the subsurface architecture. CPT/MIP provides optimal resolution of soil and contaminant properties. The CPT tip resistance and sleeve friction allow definition of soil stratigraphy at high resolution, and the pore water pressure tool measures relative permeability of soil materials. A MIP tool is added to the CPT rod string to provide vertical definition of VOCs. The MIP will volatilize VOCs from soils and groundwater as the tool is pushed into the subsurface. VOC vapors are drawn through a hydrophobic membrane, and carried to the surface via peek tubing with an inert carrier gas to be analyzed with on-site instruments, typically an electron capture detector, photo-ionization detector and flame ionization detector (ECD, PID and FID).
CPT for geotechnical applications was standardized in 1986 by ASTM Standard D3441 (ASTM, 2004). 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 (SPT) as a method of geotechnical soil investigation by its increased accuracy, speed of deployment and reduced cost over other soil testing methods. The ability to advance additional insitu testing tools using CPT and a direct push rig, is accelerating this process.
Zebra 10cm cone with Robertson Chart