CONE PENETRATION TESTS

Size: px

Start display at page:

Download "CONE PENETRATION TESTS"

Jeffry Blankenship
6 years ago
Views:

1 February 25, 2015 John Doe, P.E. Acme Engineering and Testing 1234 Test Avenue, Suite 204 Lake Wales, FL Re: Sample CPT Soundings Dear Mr. Doe, Direct Push Services, LLC (DPS) was retained by Acme Engineering and Testing to perform cone penetrometer test (CPT) soundings at Coconut Grove located in Parkland, Florida. The purpose of performing the CPT soundings was to provide geotechnical data to evaluate subsurface conditions at the site with respect to soil classification and relative strength. DPS completed the CPT program on February 23, 2015, and the investigation results are enclosed herein. The investigation and data collection was performed in general accordance with the American Society for Testing of Materials (ASTM) Standard D 5778 for performing electronic piezocone penetration testing of soils. During each CPT, continuous measurements of the tip and sleeve resistance were recorded, as well as the tilt angle and pore pressure. Attachment A provides a more complete description of the CPT procedures and analysis employed during the investigation. TESTING APPARATUS The investigation was performed using a track-mounted, self-anchoring Geoprobe 6625CPT to advance an electronic piezocone penetrometer. The piezocone used in the investigation was manufactured by Geosoft, and is equipped to record continuous data during each CPT test. The data recorded by the cone was evaluated using the Geosoft CPT Pro version 5.61 computer program. The piezocones used during the investigation were calibrated in accordance with ASTM D 5778 on October 2, 2014 by Geoprobe, Inc. (tip serial #4873). The tip has a 60 apex angle, and a 1.4 inch diameter. The piezocone is equipped with a sintered bronze fine porous filter, and glycerin (95% pure) was used for de-airing each filter under vacuum prior to each CPT. CONE PENETRATION TESTS The investigation was completed on February 23, 2015 by performing twenty eight CPT soundings. The soundings were completed at the location generally described by Acme. The soundings were advanced to a depth ranging from 32 feet to approximately 47 feet below ground surface (bgs). The CPT test performed at Coconut Grove was completed without complications, interruptions, or interferences that would impact the reliability of the subsurface data collected. Therefore, the testing data and the resulting data evaluations are considered sufficiently reliable and accurate for the sounding locations. The CPT was performed with a continuous push. All of the data recording devices functioned properly, and the tilt angle remained sufficiently vertical during the push. Telephone (863) P.O. Box 3998, Lake Wales, Florida Facsimile (863)

2 John Doe, P.E. February 25, 2015 Page 2 of 2 Direct Push Services, LLC The CPT data is presented in Attachment B. The reported testing data includes soil classification, tip resistance, sleeve friction ratio, pore pressure, and correlated SPT N values. The test were terminated due to the increase in the point resistance on the Geoprobe or when reaching the desired depth. Sincerely, DIRECT PUSH SERVICES, LLC Scott Blackburn General Manager Telephone (863) P.O. Box 3998, Lake Wales, Florida Facsimile (863)

3 Attachment A

4 CONE PENETRATION TESTING DESCRIPTION AND SUMMARY Cone penetration testing is a geotechnical technique designed to evaluate subsurface conditions and geotechnical soil properties. Cone penetrometer tests are a quasistatic penetration test, meaning that the cone is pushed at a slow rate rather than driven with a hammer or rotary drilling. During a cone penetration test (CPT), a cylindrical metal cone is advanced below land surface at a constant and slow rate, normally by a hydraulic press. As the cone is advanced, measurements are made and data is recorded that indicate the various soil properties encountered by the cone. Cone penetration testing is a cost effective and rapid test method when compared to other subsurface testing procedures. The CPT is designed to evaluate subsurface conditions based primarily on the resistance to penetration encountered by the cone tip. Resistance measurements are also recorded for the cone sleeve, or shaft. In the case of piezocones, subsurface pore pressure can also be measured to assist the evaluation of soil types. The CPT can be performed by continuously advancing the cone without withdrawing it from the borehole. This makes a CPT very time-effective when compared to other testing procedures such as Standard Penetration Test (SPT) where the penetrometer must be withdrawn from the borehole at each test interval. CPT can be performed using a variety of different cones. However, cone penetrometers with 60 degree apex angle and a 1.4 inch diameter have generally become the standard tip design. This translates to a cone base area of 1.54 square inches. The rate of tip advancement is also important, and an advancement rate of 0.79 inches (2 centimeters) per second has also become standard. The CPT method has been standardized by the American Society for Testing and Materials (ASTM) under standard designation D ASTM D 5778 sets forth standard procedures for determining cone resistance from electronic friction-cone penetrometers and pore pressure using piezocone penetrometers. Standard data collected during a CPT is the cone resistance and friction sleeve resistance. The cone resistance, or end bearing resistance, is measured by the force required to advance the cone, and is equal to the vertical force applied divided by the cone base area. The friction sleeve resistance, or local side friction, measures the amount of friction on the cone sleeve, and is equal to the shear force applied to the sleeve divided by the sleeve surface area. The CPT data discussed above is commonly used to calculate the corrected total cone resistance, pore water pressure ratio, and friction ratio. The corrected total cone resistance is the tip resistance corrected for pore pressure acting behind the tip, and allows an estimate of the total tip resistance to be made. The pore water pressure ratio is expressed as a percentage, and represents the ratio of excess pore pressure to cone resistance. The friction ratio is the ratio of sleeve resistance to tip resistance measured at a point where the middle of the sleeve and the tip are at equal depths. The CPT provides data that can be used to estimate various subsurface properties including soil type and strength. Piezocone penetrometer tests are highly effective for identifying sand, silt, and clay layers, as well as determining pore pressure. These tests are also moderately effective for determining other geotechnical engineering properties including friction angle, undrained shear strength, density index, constrained modulus, coefficient of consolidation, permeability, horizontal stress, and over consolidation ratios. Telephone (863) P.O. Box 3998, Lake Wales, Florida Facsimile (863)

5 Modern CPTs are performed using cones with electronic circuitry embedded directly in the tips to record subsurface measurements. These measurements can be transmitted directly to the operator for instant computer storage of the data, or stored within the tip for data retrieval at the end of the CPT. By either method, the data collected during the CPT can be recorded on a computer and available for analysis directly following the CPT. Direct Push Services employs the use of CPT Pro (version 5.61) software developed by Geosoft to evaluate the CPT data. Most of the data interpretations are based upon work produced by P.K. Robertson. While it is beyond the scope of this summary to discuss each evaluation performed by the software, descriptions of any reported data are available upon request. Telephone (863) P.O. Box 3998, Lake Wales, Florida Facsimile (863)

6 Attachment B

7 Classification by Robertson 1986 Sand to silty sand (8) Depth: [ft] qc [kgf/cm^2] Rf [%] u2 [lb/in^2] N60 [] Clay (3) Silty clay to clay (4) Clay (3) 35 Silty clay to clay (4) Very stiff fine grained (11) Location: Project ID: Project: Position: Client: X: 0.00 ft, Y: 0.00 ft Ground level: 0.00 Date: 8/4/2015 Page: 1/1 File: Test No.: A Scale: 1 : 76 Fig.: CPT-4 NOVA.cpt

8 Classification by Robertson 1986 Sand to silty sand (8) Clay (3) Depth: [ft] qc [kgf/cm^2] Rf [%] u2 [lb/in^2] N60 [] Silty clay to clay (4) 20 Silty sand to sandy silt (7) 25 Clayey silt to silty clay (5) 30 Silty sand to sandy silt (7) 35 Clayey silt to silty clay (5) Silty sand to sandy silt (7) Location: Project ID: Project: Position: Client: X: 0.00 ft, Y: 0.00 ft Ground level: 0.00 Date: 8/4/2015 Page: 1/1 File: Test No.: A Scale: 1 : 76 Fig.: CPT-11 NOVA.cpt

CPT and MiHpt Programs Bayou Corne 8 AUG 2013

CPT and MiHpt Programs Bayou Corne 8 AUG 2013 Agenda Introduction and purpose of meeting Why CPT and MiHpt Charlie Faust, Tt CPT and MiHpt overview Charlie Faust, Tt Program progress Charlie Faust, Tt