You are visiting the web site of the EPSCI Program at the U.S. Dept. of Energy's Ames Laboratory, Ames, IA
General Description
The U.S. Army Engineer Waterways Experiment Station (WES), of Vicksburg, Mississippi, under the sponsorship of the U.S. Army Environmental Center (AEC) has developed a cone penetrometer system, known as the Site Characterization and Analysis Penetrometer System, or SCAPS. The SCAPS unit has the capability to provide an empirical estimate of the soil stratigraphy, resistivity, and petroleum, oil, and lubricant (POL) contamination via a cone penetrometer system equipped with a variety of sensors. The POL contamination is determined by use of a laser induced fluorescence system incorporated into a cone penetrometer.
The SCAPS Cone Penetration Test (CPT) truck was developed by WES under the sponsorship of AEC. SCAPS development began in 1986, has received field testing, and has been involved in several field demonstrations during the past two years. The objective of the SCAPS is to provide a cost effective and rapid method to determine in-situ soil conditions and detect and delineate POL contaminants for site screening and characterization. The SCAPS utilizes existing tip and sleeve resistance CPT technology to evaluate soil stratigraphy while simultaneously using resistivity or laser induced fluorescence (LIF) to obtain further subsurface information. The SCAPS comprises a twenty ton truck equipped with hydraulic rams used to push the sensor probes into the ground. Data acquisition, processing, and storage are handled via electronic signal processing and an onboard computer system.
The SCAPS unit is designed for use on level to gently sloping terrain with clayey to sandy soils with small gravel sizes. The air-space above the truck must be free of obstructions such as power lines and the subsurface in the immediate vicinity of a CPT push must be free of buried objects such as utilities. The CPT probes will not penetrate boulders, cobbles, rubble, well compacted sediment, or sound bedrock. The unit can be operated in all weather, although weather extremes will impact operations; in particular, cold weather may cause problems with freezing of the grout and steam cleaning water lines and hot weather may cause discomfort to the personnel, particularly when personal protective equipment must be worn.
To avoid damaging probes on subsurface fill material or cobbles, the SCAPS can pre-push a hole with an uninstrumented 'dummy' probe. The dummy probe has no sensing capability, and consists of a cone and push rods which can be pushed to a desired depth to clear a path for the LIF or resistivity probe. SCAPS has a cone which attaches to 1.75 inch diameter rods and a cone which attaches to 1.44 inch diameter rods to push dummy holes. The 1.44 inch dummy rods are smaller in diameter than the sensor rods while the 1.75 inch dummy rods are the same diameter as the sensor rods. A dummy probe is used by pushing the dummy to the desired depth, retracting it, and reinserting a probe with sensors into the same hole and pushing to a greater depth than the maximum depth reached by the dummy probe. All stratigraphic information in the interval penetrated by the dummy probe is lost because the soil material in that interval has been permanently altered. Data taken below the terminal depth of the dummy push are valid.
When the large diameter dummy rod is used the LIF and resistivity data collected in the interval penetrated by the dummy rods are questionable because it is uncertain whether the instrumented probe sensor had good contact with the soil. However, when the small diameter dummy is used, the resistivity data and LIF data collected in the interval penetrated by the dummy rods may still be valid because the smaller dummy rod diameter should allow for good contact between the soil and sensor. Because of the cohesive nature of clays, the hole may remain open after the rods are removed, but sandy material may collapse into the hole as the push rods are removed. Accordingly, even a sensor probe push following a small diameter dummy pre-push should be viewed with some caution.
The SCAPS unit offers several environmental impact benefits. First, the CPT is less intrusive than conventional drilling because the CPT hole is relatively small and there are no drill cuttings to dispose of. Secondly, a high pressure steam cleaning unit mounted below the truck decontaminates the push rods as they are removed from the ground. Accordingly, gross contamination of the rods is removed prior to handling by the operations personnel. The cleaning water is captured in drums for proper disposal. Lastly, a trailer mounted grout pumping system allows grouting of the CPT hole through a port in the cone tip as the penetrometer probe and push rods are withdrawn. A Portland cement slurry was used to grout in each sensor probe hole as the probe was withdrawn from the ground. The grout minimizes vertical cross contamination between subsurface soil units via the CPT hole. Dummy probe push holes which were not used for a sensor probe push were grouted by filling the hole with dry Portland cement from the surface.
The soil in the near vicinity of the cone and push rods is permanently altered as a push proceeds. Because the soil is altered near the CPT hole, a resistivity probe and laser probe cannot be performed in the same hole. Accordingly, wherever a LIF and resistivity push are performed at the 'same location', the truck must be moved several feet or more so that the tests are actually carried out in undisturbed soil.
On-site demonstration by contractor
Please e-mail comments to: epsciwebkeeper@ameslab.gov.
Last Modified: 1 January 2002 by dave eckels
Expedited Site Characterization: etd/technologies/projects/esc/technologies/cptlif.html