CONTINUOUS FLIGHT AUGER (CFA) PILES QC/QA PROCEDURES. Preferred QC/QA Procedures

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1 Preferred QC/QA Procedures The Federal Highway Administration (FHWA) has provided QC/QA guidance for this technology as noted below. The reference document also contains information about construction techniques, design procedures, and specifications. Chapter 7 of the document contains complete descriptions of QC/QA procedures. A summary of the QC/QA procedures is presented following the reference table below. Publication Title Design and Construction of Continuous Flight Auger Piles Publication Year Publication Number Geotechnical Engineering Circular (GEC) No. 8 Available for Download Yes 1 Construction quality is achieved by meeting established requirements, as detailed in project plans and specifications, including applicable codes and standards. Quality Control (QC) and Quality Assurance (QA) are terms applied to the procedures, measurements, and observations used to ensure that construction satisfies the requirements in the project plans and specifications. QC and QA are often misunderstood and used interchangeably. Herein, Quality Control refers to procedures, measurements, and observations used by the contractor to monitor and control the construction quality such that all applicable requirements are satisfied. Quality Assurance refers to measurements and observations by the owner or the owner's engineer to provide assurance to the owner that the facility has been constructed in accordance with the plans and specifications. QC/QA Guidelines The recommended QC/QA guidelines for Continuous Flight Auger (CFA) Piles are found in FHWA Geotechnical Engineering Circular No. 8 by. Comprehensive QC/QA guidance is provided in Chapter 7, starting on page 160. Other information relating to description of CFA and Drilled Displacement (DD) piles, construction techniques, applications, static capacity analysis, design recommendations, and specifications are in this document also. A summary of recommended QC/QA practices is provided by in section 7.7 on page 191. QC/QA activities are arranged in categories that follow the project delivery sequence: prior to construction, on-site review of contractor s equipment, during drilling, during grout/concrete placement, during reinforcement placement and pile top finishing, and post installation. November 2012 Page 1 of 9

2 The specification in includes guidance for implementing the following QC/QA techniques: Inspection/observation Automated monitoring Concrete/grout testing Load testing Integrity testing These methods are briefly described below. More detailed descriptions are presented by Brown et al. (2007), who recommend the following QC/QA frequencies: Recording of inspection/observation data for each pile installed Automated monitoring for each pile installed 6 samples of concrete/grout for strength testing per 50 cubic yards of material Load tests on 2% of production piles Integrity testing of 20% of production piles Individual QC/QA Methods QC/QA Method: Inspection/Observation According to, an inspection checklist/log should include documentation and verification of the following information: Pile location and plumbness Ground surface elevation Pile toe (bottom) depth/elevation Depth/Elevation of top of grout/concrete Pile length Auger diameter Details of the reinforcing steel (number, size, and grade of longitudinal bars, size and spacing of transverse steel; outside diameter and length of cage); type of centralizer used November 2012 Page 2 of 9

3 CONTINUOUS FLIGHT AUGER (CFA) PILES Flow cone efflux time and volume of grout placed, or slump and volume of concrete placed Theoretical volume of excavation (theoretical diameter = diameter of auger) Depth/Elevation to which reinforcing steel was placed Date/Time of beginning of drilling Date/Time of completion of drilling Date/Time grout or concrete was mixed Date/Time ready-mix grout or concrete truck arrived at project site, and copies of all grout or concrete batch tickets used for the pile construction Date/Time of beginning of grout or concrete pumping Date/Time of completion of grout or concrete pumping Date/Time of placement of reinforcing steel Weather conditions, including air temperature, at time of grout or concrete placement Identification of all grout or concrete samples taken from the pile All other pertinent data relative to the pile installation All readings made by the automated measuring and recording equipment to include as a minimum: Auger rotation vs. depth for every 0.6-meter (2-foot) increment, or less, of auger advancement during the drilling process, and during placement of grout or concrete (if auger is rotated during this placement). Volume of grout or concrete placed vs. depth of outlet orifice for every 0.6-meter (2-foot) increment, or less, of pile placed. Average maximum and minimum pump stroke pressures at ground level for every 0.6- meter (2-foot) increment, or less, of pile placed. Average maximum and minimum pump stroke pressure at or near the auger head for every 0.6-meter (2-foot) increment, or less, of pile placed, if directed by the engineer. The engineer may also specify that torque and crowd force (downward thrust on auger) measurements be made at every 0.6-meter (2-foot) increment, or less, of auger advancement during the drilling process. November 2012 Page 3 of 9

4 C/QA Method: Concrete/Grout Sampling and Testing Representative samples of the grout or concrete mix must be obtained at the project site for QC/QA testing. The ideal location and time to obtain samples for testing is at the point of discharge into the soil and after the mix has been pumped through the lines and the auger, as the properties (especially workability) can be changed by pumping extended distances. Generally, sampling at the point of discharge is not possible and samples are typically obtained from the discharge location into the pump hopper. The three parameters most commonly measured are temperature, workability, and strength. Each of these is discussed below. Temperature Temperature should be checked on every truck as a means of verifying the consistency of the mix. Grout or concrete should not be placed when its temperature falls below 4 C (40 F) or exceeds 38 C (100 F), unless approved procedures for cold or hot weather are followed. Workability Workability is measured using slump testing for concrete and flow cone testing for grout. Workability should be checked on every truck as a means of verifying the consistency of the mix. Slump ranges for concrete in CFA piles should typically be 200 mm ±25 mm (8 inches ±1 inch). Slump measurements should be made according to ASTM C 143 (Standard Test Method for Slump of Hydraulic-Cement Concrete). Workability of grout is tested using a flow cone as specified in ASTM C939 (Standard Test Method for Flow of Grout for Preplaced-Aggregate Concrete) and U.S. Army Corps of Engineers CRD-C These specifications call for a 12 mm (0.5 inches) outlet for the flow cone. Grout mixes used for CFA piles are typically too thick to flow through a cone with this outlet diameter, so it is common practice to modify the above specifications to provide a 19 mm (0.75 inches) opening. Grouts suitable for CFA piles typically have a fluid consistency represented by an efflux time of 10 to 25 seconds when tested with the 19 mm (0.75 inches) opening. Strength Strength testing is performed in the laboratory after collecting and curing samples from the field. For concrete, 150-mm (6-inch) diameter by 300-mm (12-inch) high cylinders (ASTM C 31 November 2012 Page 4 of 9

5 Standard Practice for Making and Curing Concrete Test Specimens in the Field ) should be made from samples of the mix from the field in the same manner as for most other cast-in-place concrete construction, including drilled shaft construction. Samples should be cured and tested according to ASTM C39 (Standard Test Method for Compressive Strength of Cylindrical Concrete Specimens) or the agency s normal procedures. Concrete compressive strength requirements for CFA piles are typically 24 to 31 MPa (3,000 to 4,500 psi) and will be specified according to the project requirements. For grout, 50-mm (2-inch) cubes are most often used for strength testing, (see Figure 7.10) per ASTM C109 (Standard Test Method for Compressive Strength of Hydraulic Cement Mortars). Typical strength requirements for grout are 27.6 to 34.5 MPa (4,000 to 5,000 psi). November 2012 Page 5 of 9

6 QC/QA Method: Automated Monitoring The CFA pile construction equipment should have the capability to record the following parameters during drilling: Auger rotation Depth of the auger injection point Torque delivered to the auger Crowd force During grouting, the following parameters should be automatically recorded: Volume of grout or concrete Maximum and minimum grout or concrete pressure Auger rotation (if rotated) and lifting speed Depth of the injection point Note that manual monitoring of the above information alone is not considered sufficient by. Manual monitoring should be a backup to the automated installation monitoring. November 2012 Page 6 of 9

7 QC/QA Method: Load Testing present a performance-based specification in which the contractor is responsible for computing static resistance, setting pile length requirements for a given design axial loading, and verifying that the performance requirements are satisfied via the use of load tests. Load tests are performed in the pre-production phase to verify that proposed construction procedures are capable of producing the desired performance and on a specified percentage of production piles to verify performance of piles installed during the construction phase. The side shear component is mobilized with relatively small pile vertical displacements relative to the surrounding soil, typically less than 10 mm (0.4 inches). The end bearing component is fully mobilized with larger displacements, typically at a pile tip movement in the range of 5% to 10% of the pile diameter. Driven piles of comparable axial resistance are likely to mobilize the tip resistance at a smaller vertical displacement due to the inherent preloading at the tip that occurs during installation. Consequently, the load-settlement curve from a load test of a CFA pile may appear somewhat softer than that of a typical driven pile, and methods used to interpret ultimate load resistance from load tests on driven piles could be conservative for CFA piles. According to, the results of a test pile installation and testing program should be used to: Establish target drilling penetration rate(s) for the various subsurface conditions on the site Establish pressure/volume relations for placement of grout/concrete. The grout factor (i.e., ratio of the volume of grout/concrete actually used to the theoretical volume for the specified pile size) that is calculated on the test pile(s) ±7.5% should be used for the installation of the production piles Establish target values for torque and crowd force for displacement or partial displacement piles Establish mix design parameters such as grout flow, necessary admixtures, etc. Evaluate design correlations of side and base resistance with the site specific soil parameters November 2012 Page 7 of 9

8 QC/QA Method: Integrity Testing Post-construction integrity testing is best used to verify that the production parameters (penetration speed, grout/concrete pressure and volume, etc.) are appropriate for the site conditions to produce piles with the desired properties and without defects. Types of integrity tests include the sonic echo test, cross-hole sonic logging (CSL), single-hole sonic logging (SSL), and the backscatter gamma test. The sonic echo test is performed by striking the top of the pile with a small instrumented hammer and thereby sending a compressive wave down the length of the pile. The wave is reflected at the toe of the pile and is measured at the surface. In the event that there are any discontinuities or defects in the pile, the wave will be reflected prior to reaching the toe of the pile. Sonic echo testing is recommended for piles less than 30 inches in diameter. CSL is conducted with a source in one tube and a receiver in another. A strong signal measurement with a time that is consistent for strong grout/concrete is an indicator of quality. SSL uses a source and receiver in the same tube and measures the wave speed of the material surrounding the tube. The backscatter gamma test or gamma-gamma logging uses a radioactive source on one end of a probe to emit gamma photons with a detector on the other end. The photon count is calibrated to the grout/concrete density within a radius of about 100 mm (4 in.) around the tube. November 2012 Page 8 of 9

9 References Brown, D.A., Dapp, S.D., Thompson, W.R. and Lazarte, C.A. (2007). Design and construction of continuous flight auger piles. Geotechnical Engineering Circular (GEC) No. 8, U.S. Department of Transportation, Federal Highway Administration, Washington, D.C., 270 p. November 2012 Page 9 of 9