CPT Data

About the Data

CPT data available through this web site were collected by the USGS Earthquake Science Center for miscellaneous field and project investigations. The data consist of processed CPT soundings. Typically, data are posted through this web site when USGS field investigations are completed, but prior to final interpretation and analysis. Interpretations of stratigraphic and geotechnical significance of the soundings are not available at this web site, but may be available in USGS and other technical publications for some soundings following completion of the project study. A partial listing of these publications is compiled under Publications. USGS Open-file Report 2010-1036 contains maps and a brief description of soundings conducted before 2010.

By clicking on the symbol for each sounding as displayed on the map, Adobe PDF format graphic logs of each CPT sounding can be viewed that display friction ratio, tip resistance, sleeve friction, and soil behavior type. The soil behavior type is based on the classification developed by P.K. Robertson and R.G. Campanella, "Guidelines for use and interpretation of the electric cone penetrometer test," published by Hogentogler and Co, Inc, and University of British Columbia in 1984. The soil classification shown on the graphic log is for illustration only and should not be used for interpretative purposes.

Data for each sounding are also available in a simple text file in tab-delimited ASCII format. Each sounding text file includes a header with information about the sounding and 5 tab-delimited columns of text with cone measurements as a function of depth. Most soundings are digitized at a 0.05 m interval, but older soundings may be only 0.10 m. Shear-wave velocity measurements typically are measured at 2 meter intervals.

Locations of soundings were determined with a Global Positioning System (GPS) unit and post-processed to an accuracy of 3 meters. Elevation data were determined from USGS 7.5’ topographical maps. Shear wave travel times were determined from visual inspection of seismic recordings from a one-component horizontally oriented seismometer in the cone.

Data Information for CPT Archives

Description of header information
File Name: CPT sounding number
Date: Date that CPT sounding was conducted
UTM Grid Zone: The zone use for the Universal Transverse Mercator location of the sounding.
UTM-X: Universal Transverse Mercator Easting coordinate of the sounding in meters
UTM-Y: Universal Transverse Mercator Northing coordinate of the sounding in meters.
Datum: The geodetic datum used for the UTM location.
Elevation, m: Ground elevation in meters.
Total Depth, m: Depth, in meters, of CPT sounding
Water Depth, m: Depth, in meters, to ground water as measured directly in the CPT sounding hole following retrieval of the cone.
City: City in which sounding is located.
County: County in which sounding is located.
State: State in which sounding is located
USGS Quadrangle: 7.5’ USGS quadrangle map in which sounding is located.
Cone No.: Serial No. of CPT cone used to collect field data. Assume a 10-ton subtraction cone was used unless "15t," signifying a 15-ton cone, is indicated after the serial number.
Source: Organization (usually USGS) that collected the sounding data
Surface horizontal offset of seismic source to CPT, m: Shortest horizontal distance in meters between the edge of the ground plate used to input the seismic energy to generate the shear wave and the point where the CPT rod enters the ground.
Description of CPT values in tab-delimited format by column
Depth, m: Depth of measurement in meters.
Tip Resistance, MN/m2: resistance of cone tip in meganewtons per square meter.
Sleeve Friction, kN/m2: friction of cone sleeve in kilonewtons per square meter.
Inclination, in degrees: Inclination of cone from vertical in decimal degrees.
S-wave travel time, ms: The time in milliseconds for a vertically propagating shear wave to travel from the ground surface to a horizontally oriented seismometer contained in the cone.