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Geotechnical Engineering Circular (GEC) No. 8
Design And Construction Of Continuous Flight Auger Piles
Final
April 2007

Chapter 8: Guide Construction Specifications For Continuous Flight Auger (CFA) Piles

Contractor Performance Based Specifications of CFA Piles
English Units (Metric Units)
(With Commentary)

Commentary: Owner-controlled design specifications can vary in the amount of design performed by the Owner's Design Engineer and the amount performed by the CFA Pile Contractor. This guide specification is set up for the Owner-controlled design (Standard Design) method wherein the Owner provides preliminary plans showing the pile design loadings, footing/cap design, and pile layout for each footing/cap location. The Owner also provides related design criteria and requirements, subsurface data, rights-of-way limits, utility locations, site limitations, construction material and testing specifications, and required Contractor working drawing/design and construction submittals and review requirements. The CFA Pile Contractor designs the individual piles and pile cap connections and selects the CFA construction method and equipment. The CFA Pile Contractor prepares a preliminary CFA pile design and a firm cost proposal based on the Owner's preliminary plans and specifications. Once the contract is awarded, the selected CFA Pile Contractor prepares detailed CFA pile design calculations and working drawings and submits them to the Engineer for review.

8.1 Description

This work shall consist of constructing CFA piles as shown on the contract plans and approved working drawings and as specified herein. The CFA Pile Contractor is responsible for furnishing all design, materials, products, accessories, tools, equipment, services, transportation, labor and supervision, and manufacturing techniques required for design, installation and testing of CFA piles and pile cap connections for this project.

The CFA Pile Contractor shall design and install CFA piles, including selection of the CFA pile type, diameter, length, pile cap connection, and installation means and methods that will provide the load capacities indicated on the project plans, without damage to existing nearby structures. A minimum diameter will be specified and a minimum length may be specified. The CFA pile load capacities shall be verified by load testing as required, and the pile integrity will be verified by pile integrity tests as required. All piles must meet the test acceptance criteria specified herein.

The imperative mood is used within this specification; for example, when it says, "submit three copies", the CFA Pile Contractor shall submit three copies" is implied.

Sections of this specification are referred to in the text, for example, as "(8.)1.1" to facilitate locating them in this Chapter 8 and allow future renumbering them once the specification is modified according to the Owner's needs.

8.1.1 Definitions

CFA Pile: any foundation that is made by rotating a hollow-stem auger into the ground to the specified pile depth. Grout or concrete is injected through the auger shaft under continuous positive pressure, as the auger is being withdrawn, in order to exert a positive upward pressure on the earth-filled auger flights as well as lateral pressure on the soil surrounding the placed grout or concrete column. Reinforcing steel, as specified, is inserted into the column of fluid grout or concrete following the completion of grout or concrete placement. CFA piles as defined herein include: a) traditional continuous flight auger piles; b) drilled displacement piles intended to install a cast-in-place pile with full displacement and minimal soil spoil; and, c) partial displacement piles which may displace some soil but not act as a full displacement pile.

Commentary: Many contractors and equipment builders have patented various components of the drilling system for various types of CFA piles, most typically some part of the tooling. As defined within this specification, these various types of piles are all within the broader category of CFA pile; therefore, they would not be considered as "proprietary systems" for bidding purposes. All of the CFA pile systems are generally similar in installation techniques and performance.

CFA Pile Contractor: the firm responsible for performing the CFA pile work.

Design Engineer: the Licensed Professional Engineer that designs the CFA piles. The person must meet the experience requirements in Section (8.)1.6.2.

Engineer: the Owner's project engineer, project manager, or other representative.

Inspector: the Owner's field representative on the project site.

Owner: agency responsible for the project.

Plans: drawings provided by the Owner for bidding purposes.

Project Manager: an employee of the CFA Pile Contractor supervising the work and that has a minimum of three years experience with CFA projects of similar size and scope.

Working Drawings: drawings submitted by the CFA Pile Contractor. This would include the detailed pile designs.

8.1.2 Related Specifications

Commentary: Engineer to specify all related specifications from the applicable standard specifications.

8.1.3 Reference Codes and Standards

The following publications form a part of this specification to the extent indicated by the references. The latest publication as of the issue date of this specification shall govern, unless otherwise indicated.

AASHTO Standard Specification for Highway Bridges, current Edition, including current interim specifications.

State Department of Transportation (DOT) Standard Specifications, current Edition, including interim specifications.

Commentary: Engineer to note any additional publications to be referenced.

8.1.4 Available Information

Available information developed by the Owner, or the Owner's duly authorized representative, include the following items:

  1. Plan Set(s) __________, Project No. __________, prepared by __________, dated __________. The plans include the preliminary CFA pile size and length developed for the project, as well as plan view, profile, and typical cross sections for the proposed CFA pile locations.

    Commentary: The Owner should provide preliminary design information for the Contractor as part of the bidding package. The complete list of items will vary according to project and local procedures, but will generally include:

    1. plans showing the pile design loadings, minimum pile diameter, minimum reinforcement, pile to footing/cap connection design, and pile layout for each footing/cap location. In some cases, the plans may include a minimum pile tip elevation.
    2. design criteria and requirements, such as minimum safety factors and maximum allowable vertical and horizontal displacements.

    Refer to Chapter 6 of FHWA Geotechnical Circular No. 8 "Augered Cast-in-Place and Continuous Flight Auger Piles" for detailed guidance on plan information to provide on the preliminary plans.

  2. Geotechnical Report No.(s)__________, Project No. __________, prepared by __________, dated __________, included or referenced in the bid documents, containing the results of exploratory borings, observation pits, or other site investigation data obtained in the vicinity of the proposed CFA pile locations.

    Commentary: The subsurface conditions expected can significantly impact the CFA Pile Contractor's choice of procedures, methods, equipment, the bidding process, and contract administration. A geotechnical investigation report should be included in the contract special provisions. This report provides information to bidders of the subsurface conditions and will reduce the potential for differing site conditions construction claims and disputes. By including the geotechnical investigation report in the contract special provisions, it becomes a legal part of the contract documents.

8.1.5 Project Site Survey

Before bidding the work, the CFA Pile Contractor shall review the available subsurface information and visit the project site to assess the site geometry, equipment access conditions, and locations of existing structures and above-ground facilities.

The CFA Pile Contractor is responsible for field locating and verifying the locations of all utilities shown on the plans prior to starting the Work. The CFA Pile Contractor shall notify the Engineer of any utility locations different from those shown on the plans that may require relocation of foundation elements or modification to the structure design.

Commentary: Many public owners have standard specifications or procedures for handling utilities on a project, so this section may not apply or can be modified to include reference to the applicable State DOT specification/procedure. As with any foundation system, the location of active and abandoned underground utilities can have a significant impact on the installation of CFA piles.

Prior to the start of any CFA pile construction activity, the CFA Pile Contractor and the Engineer shall jointly inspect the site to observe and document the pre-construction condition of the site, existing structures, and utilities.

8.1.6 CFA Pile Contractors Experience and Submittal of Experience

Commentary: The quality of CFA piles is highly dependent upon the skill of the CFA Pile Contractor and the specific crew that is assigned to the project. It is essential that the CFA Pile Contractor is competent to perform the work at hand either through providing documentation of successful completion of prior projects of a similar nature to the project being bid, or by directly demonstrating his or her competence by installing a demonstration pile that does not contain defects and has been constructed to at least the diameter and depth shown on the plans.

8.1.6.1 Experience Requirements

Listed below are potential CFA Pile Contractors to design, furnish, and install CFA piles for the Owner, based on previous CFA Pile Contractor experience submittals verified and accepted by the Owner:

  1. Contractor Name, Mailing Address, Contact Name, Phone Number
  2. Contractor Name, Mailing Address, Contact Name, Phone Number
  3. Contractor Name, Mailing Address, Contact Name, Phone Number

If the CFA pile work is bid as a subcontract item to a prime contract, the Prime Contractor shall name the intended CFA Pile Contractor at least __________ calendar days prior to the beginning of the work for review.

8.1.6.2 Experience Requirements and Submittal

The CFA Pile Contractor shall be experienced in the construction and load testing of CFA piles and shall provide documentation of a minimum of three projects performed in the two-year period preceding the bid date in which CFA piles were installed successfully under subsurface and project conditions similar to those of the current project. The CFA Pile Contractor shall also provide documentation that the designated job site supervisor (foreman or crew chief) has had a minimum of three years of experience in supervision of the installation of CFA piles. Drill rig operators shall be documented to have a minimum of three years experience installing CFA piles.

The CFA Pile Contractor shall assign a Project Manager to supervise the work that has a minimum of three years experience with CFA projects of similar size and scope. The CFA Pile Contractor shall not use consultants or manufacturers' representatives to satisfy the Project Manager requirements of this section. This person may also be the Design Engineer if the Project Manager/Design Engineer is an employee of the CFA Pile Contractor. A Design Engineer that is a Consultant cannot be the Project Manager.

The CFA piles shall be designed by the Design Engineer, a Professional Engineer licensed in the State of __________ experience in the design of at least three successfully completed CFA pile projects over the past five years with CFA piles of similar capacity to those required for the project. The Design Engineer may be either an employee of the CFA Pile Contractor or a separate Consultant Design Engineer meeting the stated experience requirements.

Five copies of the completed project reference list and personnel list shall be submitted by the CFA Pile Contractor at least __________ calendar days before the planned start of CFA pile construction. The project reference list shall include a brief project description with the project Owner's name and current phone number and load test reports. The personnel list shall identify the CFA Pile Contractor, Project Manager, drill rig operators, and job site supervisor to be assigned to the project. The personnel list shall contain a summary of each individual's experience and be complete enough for the Engineer to determine whether each individual satisfies the required qualifications. The Engineer will approve or reject the CFA Pile Contractor's qualifications within __________ calendar days after receipt of a complete submission.

The work shall be performed by the personnel listed on the submittals. If personnel changes need to be made during the course of the project, work shall be suspended until the replacement personnel are approved by the Engineer. Additional time required due to incomplete submittals, unacceptable submittals, or obtaining approval of replacement personnel will not be cause for a time extension or delay claims. All costs associated with incomplete, replacement, or unacceptable submittals shall be borne by the CFA Pile Contractor.

8.1.7 CFA Pile Design Requirements

The CFA piles shall be designed to meet the specified loading conditions as shown on the contract plans and approved working drawings. The piles shall be designed using the Service Load Design (SLD) procedures contained in Chapters 5 and 6 of FHWA Geotechnical Circular No. 8, "Augered Cast-in-Place and Continuous Flight Auger Piles".

The required geotechnical safety factors/strength factors for SLD shall be in accordance with the FHWA circular, unless otherwise specified. Estimated soil/rock design shear strength parameters, unit weights, applied foundation loadings, special corrosion protection requirements, known utility locations, easements, rights-of-way, and other applicable design criteria will be as shown or listed on the plans, other contract documents, or specified herein. Structural design of any individual CFA pile element not covered in the FHWA manual/circular shall be by the SLD method in conformance with appropriate articles of the most current Edition of the AASHTO Standard Specification for Highway Bridges (i.e., 17th Edition as of 2007), including current interim specifications.

8.1.7.1 CFA Pile Design Submittals

At least 60 calendar days before the planned start of CFA pile construction, submit complete design calculations and working drawings to the Engineer for review and approval. Include all details, dimensions, quantities, ground profiles, and cross-sections necessary to construct the CFA piles. Verify the limits of the CFA pile structures and ground survey data before preparing the detailed working drawings.

The working drawings and calculations shall be signed and sealed or stamped by the CFA Pile Contractor's Design Engineer or by the consultant Design Engineer (if applicable), previously approved by the Engineer. If the CFA Pile Contractor uses a consultant Design Engineer to prepare the design, the CFA Pile Contractor shall have overall contractual responsibility for both the design and construction.

Submit __________ sets of the working drawings with the initial submission. Drawing sheet size shall be __________ by __________ set will be returned with any indicated corrections. The Engineer will approve or reject the CFA Pile Contractor's submittal within __________ calendar days after receipt of a complete submission. If revisions are necessary, make the necessary changes and resubmit __________ revised sets. When the drawings are approved, furnish __________ and a Mylar sepia set of the approved drawings. The CFA Pile Contractor will not be allowed to begin CFA pile work until the submittal requirements are satisfied and found acceptable by the Engineer. Changes or deviations from the approved submittals must be re-submitted for approval. No adjustments in contract time or delay or impact claims will be allowed due to incomplete submittals.

8.1.7.2 Design Calculations

Design calculations shall include, but not be limited to, the following items:

  1. A written summary report which describes the overall CFA pile design.
  2. Applicable code requirements and references.
  3. CFA pile structure critical design cross-section(s), including soil/rock strata, piezometric levels, and location, magnitude and direction of applied loads.
  4. Design criteria, including soil/rock shear strengths (friction angle and cohesion), unit weights, unit skin friction values, and unit end-bearing values. Any additional subsurface borings, laboratory work, or other subsurface data collected for the design shall also be included.
  5. Safety factors used in the design.
  6. Seismic design earthquake acceleration coefficient or other seismic design criteria applicable for the geographic area of the project.
  7. Design calculation sheets (both static and seismic) with the project number, CFA pile structure location, designation, date of preparation, initials of designer and checker, and page number at the top of each page. Provide an index page with the design calculations.
  8. Design notes including an explanation of any symbols and computer programs used in the design.

If applicable, requirements for items 2, 5, and 6 will be outlined in the bid package.

8.1.7.3 Working Drawings

The working drawings shall include all information required for the construction and quality control of the piling. Working drawings shall include, but not be limited to, the following items unless provided in the contract plans:

  1. A plan view of the CFA pile structure(s) identifying:
    1. A reference baseline datum.
    2. The offset from the construction centerline or baseline to the face of the CFA pile structure at all changes in horizontal alignment.
    3. Beginning and end station of CFA pile structures.
    4. CFA pile locations with center-to-center pile spacing.
    5. Right-of-way and permanent or temporary construction easement limits, location of all known active and abandoned existing utilities, adjacent structures or other potential interferences.
    6. The centerline of any drainage structure or drainage pipe behind, passing through, or passing under the CFA pile structure.
    7. Subsurface exploration locations shown on a plan view of the proposed CFA structure alignment with appropriate reference base lines to fix the locations of the explorations relative to the CFA structure.
  2. An elevation view of the CFA pile structure(s) identifying:
    1. CFA pile locations and elevations with vertical and horizontal spacing; and
    2. Existing and finished grade profiles both behind and in front of the CFA pile structure.
  3. General notes for constructing the CFA piles including construction sequencing or other special construction requirements.
  4. Horizontal and vertical curve data affecting the CFA pile structure and control points, including match lines or other details to relate CFA pile structure stationing to centerline stationing.
  5. A listing of the summary of quantities.
  6. CFA pile typical sections including spacing, diameter, reinforcing bar sizes, locations, and details; centralizers and spacers; and connection details to the substructure footing/pile cap.
  7. Typical details of verification and proof load test piles, including reaction systems.
  8. Details, dimensions, and schedules for all CFA piles and reinforcing steel.

Commentary: Submittals procedures shall be coordinated with Owner procedures.

Revise the drawings when plan dimensions are changed due to field conditions or for other reasons. Within __________ calendar days after completion of the work, submit as-built drawings to the Engineer. Provide revised design calculations signed by the approved Design Engineer for all design changes made during the construction of the CFA piles.

8.1.8 Construction Submittals

At least 60 calendar days before the planned start of CFA pile construction, submit complete construction submittals to the Engineer for review and comment. The Engineer will review and comment on the CFA Pile Contractor's submittal within __________ calendar days after receipt of a complete submission. If revisions are necessary, make the necessary changes and resubmit. The CFA Pile Contractor will not be allowed to begin CFA pile work until the submittal requirements are satisfied and found acceptable by the Engineer. Changes or deviations from the approved submittals must be re-submitted for approval. No adjustments in contract time or delay claims will be allowed due to incomplete submittals.

8.1.8.1 Pile Installation Plan

The CFA Pile Contractor shall use the Pile Installation Plan to demonstrate, to the satisfaction of the Engineer, the dependability of the equipment, techniques, and source of materials to be used on the project. Reference to successful completion of projects with similar pile sizes in similar soil conditions using the proposed equipment and procedures should be included. The components of the plan shall meet the requirements contained in this specification. This plan shall include, but not be limited to, the following items:

  1. List and sizes of proposed equipment, including drilling rigs, augers and other drilling tools, pumps for grout or concrete, mixing equipment, automated monitoring equipment, and similar equipment to be used in construction, including details of procedures for calibrating equipment as required;
  2. Step-by-step description of pile installation procedures;
  3. A plan of the sequence of pile installation;
  4. Target drilling and grouting parameters (along with acceptable ranges) for pile installation, including auger rotation speed, drilling penetration rates, torque, applied crowd pressures, grout pressures, and grout volume factors;
  5. Details of methods of reinforcement placement, including support for reinforcing cages at the top of the pile and methods for centering the cages within the grout or concrete column;
  6. Mix designs for all grout or concrete to be used on the project, including slump loss vs. time curves and strength development vs. time curves for mixes with fly ash and/or slag;
  7. Equipment and procedures for monitoring and recording auger rotation speed, auger penetration rates, auger depths, and crowd pressures during installation;
  8. Equipment and procedures for monitoring and recording grout or concrete pressures and volumes placed during installation;
  9. Contingency plans for equipment failures during drilling or grouting operations (grout pump, monitoring equipment, etc.);
  10. Procedures for protecting adjacent structures, on or off the right-of-way, that may be adversely affected by foundation construction operations, including a monitoring plan as required in Section 3.1; and
  11. Other required submittals shown on the plans or requested by the Engineer.

Commentary: A clearly written pile installation plan can be very effective in reducing misunderstandings between the Engineer and the CFA Pile Contractor and can form the basis for solving potential problems before they occur, thus keeping the project on schedule and minimizing claims. In reviewing the CFA Pile Contractor's submittal, the key information regarding the equipment that should be scrutinized is:

  1. the rated capacity and boom lengths of the drill rig;
  2. the torque, rotational speed, and crowd capacity on the drilling machine;
  3. the horsepower of the hydraulic power unit used to turn the auger; and
  4. the positive displacement piston-ball valve pump, pump stroke displacements, engine horsepower and pump pressures of the grout pump to be used.

Most CFA piling installed in the United States in the last 30 years has utilized crane-mounted drilling equipment. Crane-mounted rigs have no means of applying crowd onto the auger, and thereby have limited ability to control the rate of penetration and the potential for soil mining, i.e., removal of excess soil during drilling. Crane-mounted rigs should be approved only for non-caving soil conditions after careful consideration of the amount of control the equipment provides on the applied downward pressure and penetration rate during drilling. Conversely, hydraulic rigs provide drilling control systems that allow the use of partial or full displacement piles, allowing more flexibility for the CFA Pile Contractor's installation means and methods to achieve the desired pile capacity. The selection of equipment is ultimately the responsibility of the CFA Pile Contractor.

Stiff soils or large diameter piles (more than 18 inches [0.45 m]) require special consideration in sizing equipment. The minimum torque supplied should be 30,000 ft-lb (41 m-kN), and the equivalent crowd capacity should be at least 5,000 lb (22 kN). However, this minimum may not be sufficient in many circumstances. The Contractor's plan for sequence of installation should preclude the installation of piles that are within six diameters of each other, center to center, prior to the time that the first pile installed is fully set.

8.1.8.2 Conformance Testing Plan

Along with the Pile Installation Plan, a specific plan for completing a testing program as outlined in the bid package shall be submitted by the CFA Pile Contractor to the Engineer for review. The program shall consist of pre-production static load tests, production static and/or rapid and/or dynamic load tests, and post-installation integrity tests in sufficient quantities to provide the data necessary to demonstrate that the installed piles meet the load and deflection criteria established in the project plans with an appropriate factor of safety. The complete installation process and equipment used during the pre-production test pile program should be used to install the production piles.

The pre-production test program establishes the baseline parameters for construction of production piles. Verification load tests and structural integrity tests during construction will be used to verify that the CFA Pile Contractor is producing acceptable piles. Pile testing methods and frequencies shall meet the requirements contained in Sections (8.)3.11 and (8.)3.12 of this specification and the appropriate sections of the State DOT Standard Specifications.

The conformance testing program shall meet the requirements as indicated in the bid package and shall include a list of the automated measuring and recording equipment to be utilized during construction. The minimum requirements for automated measuring and recording equipment are contained in Section (8.)3.4 of this specification. The submitted list should include type of equipment, manufacturer, data to be collected, current calibration records, and sample data records.

Sampling and testing of materials used on the project shall also be included in the conformance testing plan. The requirements for materials testing in the State DOT Standard Specifications shall be listed, as well as the requirements for grout or concrete testing included in Section (8.) 3.2 of this specification.

The Conformance Testing Plan will clearly indicate the QA/QC tasks to be performed by the CFA Pile Contractor or its representative, the Inspector, or both.

Commentary: The intent of the Conformance Testing Program is to assure the Owner that the piles have been installed as designed by the CFA Pile Contractor and that they meet the required load performance criteria. The use of automated measuring and recording equipment provides a means of monitoring each pile for conformance to the installation criteria.

8.1.9 Pre-Construction Meeting

A pre-construction meeting will be scheduled by the Engineer and held prior to the start of CFA pile construction. The Engineer, prime Contractor, CFA Pile Contractor, Inspectors, excavation Contractor, and Geotechnical Instrumentation Specialist (if applicable) shall attend the meeting. Attendance is highly recommended. The pre-construction meeting will be conducted to clarify the construction requirements for the work, to coordinate the construction schedule activities and identify contractual relationships and delineation of responsibilities among the prime Contractor and various Subcontractors. Main aspects involving multiple subcontractors may include those pertaining with excavation for CFA pile structures, anticipated subsurface conditions, CFA pile installation and testing, CFA pile structure survey control, and site drainage control.

8.2 Materials

All materials shall conform to the pertinent item requirements in the relevant State DOT Standard Specifications, or as otherwise noted.

Notes:
  1. Type III Portland cement shall not be used when the air temperature for the 12 hours following batching will exceed 60° F (15° C).
  2. Type B fly ash shall not be used in conjunction with Type II Portland cement.
  3. All admixtures must be approved by the __________ specified in Item __________. Admixtures shall be stored in accordance with Item __________, Concrete Admixtures.
  4. Reinforcing steel item includes the requirements and the assemblies of reinforcing steel.
Portland cement (Types I, II, & III)Item __________ (Hydraulic Cement), ASTM C 150
WaterItem __________ (Portland Cement Concrete) AASHTO T 26
Fine and coarse aggregateItem __________ (Portland Cement Concrete), ASTM C 33, ASTM C 87-90, ASTM C 227-90, ASTM C 289-94, ASTM C 295-90, a ASTM C 586-92
Mineral admixtures (Fly Ash)Item __________ (Concrete Admixtures) ASTM C 618 Class C or F
Water reducing admixturesItem __________ (Concrete Admixtures) ASTM C 494, ASTM C 1017
Fluidifier (fluidizer)Item __________ (Grout Admixtures) ASTM C 937, CRD-C 619
Reinforcing steelItem __________ (Reinforcing Steel), ASTM A 615, ACI 315
Grout flow testing (flow cone)ASTM C 939, CRD-611-94
Grout cube samplesASTM C 109
Grout cube testingASTM C 109, ASTM C 942
Concrete slump testingItem __________ (Portland Cement Concrete), ASTM C143
Concrete cylinder samplesItem __________ (Portland Cement Concrete), ASTM C31
Concrete cylinder testingItem __________ (Portland Cement Concrete), ASTM C 39

Commentary: The appropriate sections of each State DOT Standard Specifications should be included under the materials section. A complete generic materials section cannot be provided herein considering the vast combinations of materials and control methods used by individual State DOTs. Some general guidance on grout and concrete is provided in Sections (8.)3.2 and (8.)3.3 of this specification.

8.3 Construction Requirements

8.3.1 Site Preparation and Protection of Adjacent Structures
8.3.1.1 Site Preparation

Muck, organics, soft clay, or other unsuitable materials encountered within 5 ft (1.5 m) of the ground surface, such material shall be removed or otherwise treated to prevent problems with pile top construction. Excavation of unsuitable surface material and backfilling shall be completed to the Engineer's satisfaction, or as required in the contract documents, prior to the construction of CFA piles. Should more than 5 ft (1.5 m) of unsuitable surface material be encountered, the CFA Pile Contractor shall advise the Engineer immediately and proceed with work as directed by the Engineer. Should the CFA Pile Contractor suspect that any soils that are excavated are contaminated by hydrocarbons, refuse, or other environmentally hazardous material, he or she shall contact the Engineer immediately and proceed with work as directed by the Engineer.

Commentary: Unsuitable materials should generally be removed to their full depth, or to a depth of 5 ft (1.5 m), whichever is less. The excavation is typically backfilled with soil having a plasticity index of 20 or less compacted to at least 95% of its maximum dry density, as specified by ASTM D 698 (AASHTO T 180), at within 2% of optimum moisture content.

8.3.1.2 Protection of Adjacent Structures

The CFA Pile Contractor shall be solely responsible for evaluating the need for, design of, and monitoring of measures to prevent damage to adjacent structures or underground utilities, on or off the right-of-way. These measures shall include, but are not limited to, selection of construction methods and procedures that will prevent over-excavation and excessive migration of grout through the ground, monitoring and controlling the vibrations from construction activities (including placement of casings, sheet piling, shoring and similar ancillary features), and protecting utilities.

Structures located within a horizontal distance equal to the planned length of the pile shall be monitored for vertical and horizontal movement in a manner approved by the Engineer within an accuracy of 0.01 in. (0.3 mm). Monitoring of adjacent structures will be done by an independent party working for the CFA Pile Contractor and approved by the Engineer. A monitoring plan, including the locations of measurement points and the frequency of recording measurements shall be submitted to the Engineer for approval as part of the CFA Pile Installation Plan. Monitoring shall begin with a base-line measurement recorded no more than 10 calendar days prior to construction of the pile, any shoring, or similar ancillary features. In addition to monitoring for movement, the condition of the adjacent structure, including cracks and crack widths, before and after construction of the CFA piles, shall be documented by visual inspection, photographs, and/or video. Structures owned by Owner shall be monitored for movement but need not be monitored for condition unless called for on the plans.

As soon as any movements are detected in adjacent structures, the CFA Pile Contractor shall stop construction, notify the Engineer, and take any immediate remedial measures required to prevent damage to the adjacent structures. The CFA Pile Contractor and the Engineer shall then review the current installation procedures. If revisions to the installation procedures are deemed necessary, the CFA Pile Contractor shall submit a revised installation plan for approval by the Engineer before resuming work.

Commentary: The installation of CFA piles can result in large settlement of the ground surface if the rate of rotation of the auger is high relative to its rate of penetration or over-rotation, especially in loose sandy soils. This action can promote settlement and damage to existing structures near the location of the pile installation. In some soils, the pumping of grout can result in the fracturing of the ground, the traveling of grout in the ground a considerable distance horizontally under pressure, which can lift the ground surface and structures (including buried conduits) founded nearby. Careful monitoring of the movements of adjacent structures and changes in the condition of such structures is necessary in order for the CFA Pile Contractor to know when their procedures are producing ground movements in order and when immediate corrective action needs to be taken during the pile installation. If a soil susceptible to densification is encountered, the penetration rate should be increased or the rate of rotation of auger be reduced. Condition surveys are needed for the evaluation of the effect of the construction process on the serviceability of adjacent structures by the Engineer.

8.3.2 Grout or Concrete

The grout or concrete property requirements listed to follow in this section shall be determined from samples taken during CFA pile construction as described in Section (8.)3.2.4.

Commentary: CFA piles have traditionally been constructed in the United States with sand-cement grout. Construction of CFA piles with concrete is now routinely accomplished in the United States and abroad, and has proven to produce acceptable piles when properly specified and constructed. The specifications herein allow for the use of either grout or concrete; however, once a mix design is established through the pile test program it should not be altered.

As a guide for strength development, grout and concrete meeting these specifications typically attains 30 % and 70 % of their 28-day compressive strength after 3 and 7 days of curing, respectively. Both grout and concrete mixes may contain pozzolanic additives. The most commonly used is fly ash (ASTM C 618-94; however, finely ground silica flume and blast furnace slag (ASTM 989-94) can also be used. The use of pozzolanic additives results in lower permeability of the hardened concrete and tends to retard the set time of the cement paste, thereby increasing the time that the grout or concrete remains workable. As a consequence of providing a more workable mix, materials such as fly ash, silica flume, and/or slag will probably severely retard the early strength gain of the grout mix, typically until about 10 to 14 days of age. In all cases, the submitted mix design should include strength development vs. time information.

Each DOT will likely have local mix designs that are preferred for CFA pile construction (or drilled shafts produced by the wet method), based on performance of local cements and aggregates. Concrete mix design for CFA pile construction should be given special attention. Desirable properties are fluidity, compaction under self weight, resistance to segregation, and controlled set time. Specific guidance on slump and aggregate gradation are provided below.

8.3.2.1 Mix Design - Grout

The grout shall consist of a mixture of Portland cement fly ash, water, fine aggregate (sand), fluidifier, and if necessary, retarder, which shall be proportioned and mixed so that the grout will exhibit the following properties:

  1. All solids shall remain in suspension in the grout without excessive bleed-water.
  2. The grout shall be tested for fluid consistency (using a flow cone) in accordance with the modifications made to either ASTM C 939 or the U.S. Army Corps of Engineers specification CRD 611-94 (USACE, 1994), as described below, and shall be obtained as described in Section (8.)3.2.4. Either of these specifications is herein required to have the flow cone outlet modified from a ½ in. (12 mm) diameter outlet to a ¾ in. (19 mm) diameter outlet. A range of acceptable fluid consistency (expressed as eff1ux time per standard volume as described in the cited specifications) shall be established, and must meet the approval of the Engineer.
  3. The grout shall not exhibit shrinkage in excess of 0.15 % in the vertical direction, as tested in accordance with ASTM C 1090, and shall be housed in a 100 % humidity room at a temperature of 68° F to 74° F (20° C to 23° C), or as otherwise specified by the Engineer.
  4. Grout samples recovered for strength testing, as described in Section (8.)3.2.4, shall exhibit a minimum compressive strength of __________ 28 days after casting, as required by the design.
  5. The submitted mix design shall include curves of viscosity loss versus time. In addition, grout shall be designed so as to maintain the range of acceptable fluid consistency for a period of at least 2 hours or longer, if required by the project-specific pile installation plan.
  6. Strength development versus time curves/data shall be provided, with data for times beyond 28 days as required for mixes that include fly ash, silica flume, or slag.

Commentary: The grouts used in CFA pile production are typically too thick to flow effectively from the standard ½ in. (12 mm) outlet. The flow cone specified by the U.S. Army Corps of Engineers (CRD 611-94) may be modified by simply taking out the removable ½ in. (12 mm) diameter orifice that extends out the bottom of the device to leave a ¾ in. (19 mm) diameter opening, while a flow cone would need to be custom fabricated to the ASTM C 939 specification with the modified outlet diameter. Grouts acceptable for CFA pile construction typically have a fluid consistency represented by an eff1ux time of 10 to 25 seconds when tested in accordance with the modifications described herein.

Checking the grout flow is considered a quality control tool valued primarily for the purpose of quickly indicating whether the grout currently being tested will most likely conform with grout samples meeting the specified design requirements furnished previously on the project. Should any piles be found inadequate in subsequent testing, a record of grout flow may be valuable in identifying other suspect piles, which may then be subject to further testing at the discretion of the Engineer.

8.3.2.2 Mix Design - Concrete

The concrete shall consist of a mixture of Portland cement, fly ash, water, coarse aggregate, fine aggregate (sand), water reducers, and if necessary, retarder, which shall be proportioned and mixed so that the concrete will exhibit the following properties:

  1. All solids shall remain in suspension in the concrete mix without excessive bleed-water.
  2. Concrete samples recovered for slump testing as described in Section (8.)3.2.4, shall exhibit a slump of 8 in. ± 1 in (200 mm ± 25 mm) when tested in accordance with ASTM C 143.
  3. Concrete samples recovered for strength testing, as described in Section (8.)3.2.4, shall exhibit a compressive strength of __________ 28 days after casting, as required by the design.
  4. The submitted mix design shall include curves of slump loss versus time.
  5. Strength development versus time curves/data shall be provided for mixes that include fly ash, silica flume, or slag.

Commentary: Concrete mix designs appropriate for drilled shafts constructed by the wet method are generally acceptable for use in CFA pile construction, with the notable exception that CFA pile construction may require a greater degree of workability. Greater workability is needed to allow for the concrete to be pumped through the delivery lines and auger, and subsequent insertion of the required reinforcing steel to planned elevation after placement of the concrete. Accordingly, the coarse aggregate for CFA pile construction is typically limited in size to no greater than ⅜ in. (9.5 mm). Consideration should be given to the benefit of well rounded aggregate (i.e., pea-gravel).

Slump requirements are based on providing the necessary quality of workability for uniform and proper placement throughout the duration of CFA pile construction. A slump range of 8 in. ± 1 in. (200 mm ± 25 mm) is suggested. Sampling frequencies for slump measurement are recommended in Section (8.)3.2.4

High workability is achieved with proper aggregate gradations, water-cement ratios and appropriate admixtures such as water reducing, with retarding admixtures, and air entraining agents. Angular crushed aggregates are harder to work than similar sized rounded aggregates. To insure against segregation, the sand/cement content should be high compared to the coarse aggregate content. Fly ash can be used to replace some of the Portland cement in many situations, but may result in slower strength development.

8.3.2.3 Field Operations
  1. All oil, rust inhibitors, residual drilling slurries and similar foreign materials shall be removed from holding tanks/hoppers, stirring devices, pumps and lines, and all other equipment in contact with the grout or concrete before use.
  2. All grout or concrete used shall be batched at a State approved facility, and delivered to the project site. The addition of water at the project site is permitted only with prior approval by the Engineer and only to the extent that the water-cementitious material ratio does not exceed the ratio of the approved design mix.
  3. If agitated continuously, the grout or concrete may be held in the ready mix truck for up to 2.5 hours if the air temperature is not greater than 68° F (20° C), or up to 2 hours if the air temperature is between 68° and 100° F (20° and 38° C) if other than Type III Portland cement is used. Grout or concrete shall not be placed if the air temperature exceeds 100° F (38° C) or is less than 39° F (4° C) unless approved procedures for hot (over 100° F [38° C]) or cold weather (less than 39° F [4° C]) placement are followed. Grout or concrete designed with retarders to extend the holding time or placement temperature range shall be placed in accordance with the mix design parameters.
  4. A screen with a mesh with openings no larger than ¾ in. (19 mm) for grout, or 4 in. (100 mm) for concrete shall be used between the delivery point from a ready mix truck and the pump, to remove large particles or cement clumps that can clog the grout or concrete injection system.
  5. The grout or concrete pump shall be a positive displacement pump with a known volume per stroke that is capable of developing peak pressures of at least 350 psi (2,400 kPa) at the pump. The pump shall be sized appropriately to the pile size such that a smooth, continuous delivery of grout or concrete can be maintained while limiting the pressure variations (particularly the pressure drop) felt by the pile due to the pump strokes. The CFA Pile Contractor shall provide the Engineer with the value of the volume of grout or concrete delivered by each stroke of the pump and shall demonstrate to the Engineer that the actual volume delivered by each stroke of the pump is within 3% of the value provided. The volume per stroke shall be recalibrated when the Engineer suspects that the grout or concrete delivery performance has changed.
  6. Automatic measurements shall be made and recorded during the pile construction process as described in Section (8.)3.4 of this specification. All inspection records shall be made as described in Section (8.)3.10 of this specification.
  7. The minimum value of grout pressure at the pump outlet or at the top of the auger that is required on the approved working drawings or approved pile installation plan shall be maintained for all grout or concrete placement operations throughout the project.
8.3.2.4 Grout or Concrete Sampling and Testing

Grout or concrete samples for strength testing shall be taken from the discharge at the delivery trucks prior to pumping. Concrete samples shall be cylinders 6 in. (150 mm) diameter by 12 in. (300-mm) high, or sized appropriately for maximum aggregate size according to ASTM C 39. Grout samples shall be 2 in. (50 mm) cubes and shall be subjected to a 10% increase in required compressive strength as compared to cylinder samples.

The CFA Pile Contractor, Testing Agency, or qualified party specified in the contract documents shall make no less than six (6) such samples for each 50 yd3 (38 m3) of grout or concrete placed. No less than six (6) such samples shall be made per working day, or less than six (6) such samples for each mix of grout or concrete produced by the supplier. Concrete or grout cylinders (or alternatively cubes for grout) shall be cured and tested in accordance with the State DOT specifications.

The samples will be tested by __________ (Agency's name) for unconfined compressive strength. As a minimum, two (2) samples shall be tested at seven days after sampling; two (2) samples shall be tested at 28 days after sampling; and two (2) samples will be held in reserve. Those samples tested at 28 days after casting shall exhibit a minimum compressive strength as specified in Section (8.)3.2.1 for grout or Section (8.)3.2.2 for concrete.

A grout sample shall be obtained from every truck, and shall be tested for fluid consistency (flow cone) and temperature prior to discharging into the pump hopper. The grout sample shall exhibit the fluid consistency as specified in Section (8.)3.2.1. Alternatively, if a concrete mix is used, a concrete sample shall be obtained from every truck, and shall be tested for slump and temperature prior to discharging into the pump hopper. The concrete sample shall exhibit the slump as specified in Section (8.)3.2.2. Additional samples may be required at the discretion of the Engineer at any time during the grout or concrete placing process to ensure that consistent fluidity/slump is being achieved.

Commentary: Often smaller sized cylinder samples of grout are used and are typically either 3 in. (75 mm) diameter by 6 in. (150 mm) high, or 2 in. (50 mm) diameter by 4 in. (102 mm) high. Smaller sized cylinder samples for grout should only be permitted with prior approval by the Engineer. If the samples are cast using a method or sample different than that used for the mix design, a relationship between the compressive strengths obtained by the methods will need to be established.

The type of and frequencies for grout or concrete testing listed in this section are recommended as a minimum requirement. The Engineer may choose to increase the type or frequency of testing in the project specifications or at any time during the construction of the CFA piles. For non-critical foundations, only the Engineer may choose to relax the frequency of grout and concrete sampling and testing.

Some State DOTs have standard test procedures and/or frequencies that are not included in the specification when done by State personnel. In such cases, the State DOT should reference their testing manual/procedures and that the testing will be performed by State personnel.

8.3.3 Auger Equipment

The auger flights shall be continuous from the top of the auger to the bottom tip of the cutting face of the auger, with no gaps or other breaks. Gaps in the flighting are allowed only where auger sections are joined and may not exceed 1 in. (25 mm). The length of any auger brought to the project site shall be such that the auger is capable of installing a pile to a depth that is 20% greater than the depth of the pile shown on the approved working drawings. The auger flighting shall be uniform in diameter throughout its length, and the outside diameter of the auger shall be at least 97% of the design diameter of the pile. Only single helix augers shall be used. The hollow stem of the auger shall be maintained in a clean condition throughout the construction operation. In order to facilitate inspection, the leads shall be clearly marked every 1 ft (0.3 m) along its length so that such marks are visible to the unaided eye from the ground.

Commentary: The requirements contained in this section are a minimum requirement for CFA piles. The CFA Pile Contractor may propose to use alternative equipment subject to the approval of the Engineer through the Installation Plan submittal process. In general for CFA piles, continuous flight augers that continuously remove soil during drilling are the common type of auger or drilling tool used. Consideration of augers or drilling tools that provide full or partial displacement of the soil during drilling should also be made.

The bottom of the auger flights and the cutting teeth attached thereto shall be constructed geometrically so that the bottom of the pile will be as flat as feasible. The grout or concrete injection port shall be fitted with a means of sealing it against ingress of water and soil during drilling.

The auger shall be guided at the ground surface by a guide connected to the leads of the CFA piling rig. If the auger is over 40 ft (12 m) long, it shall also be guided by a guide to be located approximately half the length of the auger above the ground-surface guide. Where CFA piles are installed with hydraulic, fixed mast installation platforms, and the stem to which the auger is fixed has an outside diameter 10 in. (250 mm) or greater, a guide above the ground surface is not required. The leads that carry the rotary unit that power the auger should be restrained against rotation by an appropriate mechanism.

The piling rig shall be capable of penetrating the ground without drawing surrounding soils laterally into the pile bore, as is described in Section 3.5. It shall be capable of installing a pile to a depth at least 20% greater than the depth of the piles shown on the approved working drawings.

8.3.4 Automatic Measurement and Recording Equipment

As a minimum, the following automatic measurements shall be made and recorded during the drilling operation:

  1. auger rotation;
  2. depth of the auger injection point;
  3. torque delivered to the auger; and
  4. crowd force (downward thrust on auger).

All measurements shall be referenced to (or plotted against) the depth of the auger injection point. This shall be accomplished with a rotational position indicator on the auger head system and an electronic position indicator on the crane line or boom holding the auger. Torque and thrust load cells shall be positioned on the auger head system.

As a minimum, the following automatic measurements shall be made and recorded during the grouting or concreting operation:

  1. volume of grout or concrete;
  2. maximum and minimum grout or concrete pressure;
  3. auger rotation (if rotated); and,
  4. depth of the injection point.

All measurements shall be referenced to (or plotted against) the depth of the auger injection point. This shall be accomplished with electronic flowmeters and electronic pressure transducers placed in the grout or concrete pressure line, an electronic position indicator on the crane line or boom holding the auger, and a rotational position indicator on the auger system.

Calibration shall be made on all measuring and recording equipment at the beginning of the project that will demonstrate that the values indicated by the measuring and recording equipment are within 3% of the values indicated. Calibrations shall be performed in accordance with the equipment manufacturer's specifications. All measuring and recording equipment shall also be recalibrated when the Engineer suspects that the drilling and grouting or concreting performance has changed.

Commentary: Automated measuring and recording equipment provide real time evaluation of each pile on a project. Piles that have installation records out of specification or that otherwise appear abnormal can be selected for integrity tests or verification load tests to determine if they should be accepted or rejected.

8.3.5 Drilling

The CFA Pile Contractor shall perform the drilling required for the piling, through whatever materials are encountered, to the dimensions and elevations required by the CFA Pile Contractor's design, as shown on the approved working drawings. Drilling shall not commence until sufficient supply of grout or concrete is present on the project site to complete the pile. The drilling parameters (auger rotation speed, penetration rates, crowd, torque, etc.) for the production piles shall be within the ranges established in the Pile Installation Plan, as verified by the pre-production testing program. The same procedures used to install the test piles shall be used to install production piles.

The center of any pile shall be within 3 in. (75 mm) of the location shown on the approved working drawings in a horizontal plane (i.e., plan-view). The completed pile shall be plumb to within 2%, if vertical, or shall be installed to within 2% of its design batter, as determined by the angle from the vertical, if planned as a batter pile. Any pile in violation of these tolerances will be subject to review by the Engineer and may be rejected or replaced at the CFA Pile Contractor's expense.

Adjacent piles within six diameters, center to center, of each other shall not be installed until it can be demonstrated by the CFA Pile Contractor that the grout or concrete in the first pile installed is fully set. The grout or concrete should have set enough such that the integrity of the existing pile will not be compromised if drilling the new pile causes mining of soil away from the existing pile.

The auger shall not be extracted from the ground at any time during the construction of a pile in such a way that would result in an open unsupported borehole or inflow of water into the pile borehole. It should become necessary to raise the auger and subsequently re-insert the auger during the pile construction process, the depth of the pile shall be increased and/or other additional measures shall be required as directed by the Engineer.

The auger shall be advanced into the ground at a continuous rate and at a rate of rotation that prevents excess spoil from being transported to the ground surface. The rate of penetration shall be established as a part of the test pile program. Automated monitoring equipment shall be used to verify this target rate of penetration is maintained during construction of production piles.

Pile termination criteria, including refusal criteria, if applicable, will be established during the pre-production test pile program. If refusal is encountered before planned depth is achieved, rotation of the auger shall be stopped, and the CFA Pile Contractor shall inform the Engineer. The CFA Pile Contractor and Engineer shall evaluate the installation data and determine if the established termination criteria have been met, or if other action is required to complete the pile. If an obstruction is encountered and it does not allow the pile to be completed in the planned location, the CFA Pile Contractor shall notify the Engineer and the Design Engineer in order for the Engineer and Design Engineer to determine remedial action.

Commentary: The penetration rate should generally be maintained such that the auger advances a depth equal to or greater than the pitch of the auger for every 1.5 to 2 revolutions for cohesionless soils, or 2 to 3 revolutions for cohesive soils. Loose cohesionless soils are more susceptible to mining by the auger flights, and generally call for the more stringent guideline. The intent of this provision is that the piles be constructed to a consistent standard as reflected in the results of the test pile program, and that soil mining be avoided.

In general, refusal is defined as a rate of auger penetration of less than 1 ft/minute (0.3 m/minute) with equipment that is appropriate for the project. If correlated with soil boring information, refusal may provide an indication that a strong layer has been reached, but should not be used as the sole criteria for setting pile tip levels for conventional CFA piles. Refusal criteria may be used to set pile tip levels for drilled displacement piles, based on the criteria established and verified to achieve capacity during the pile load testing program.

8.3.6 Placement of Grout or Concrete

The placement of grout or concrete shall commence within 5 minutes after the auger has achieved the planned depth. Grout or concrete shall be pumped through the hollow-stem auger with sufficient pressure (as measured at the top of the auger) as the auger is withdrawn to completely form the pile and fill any soft or porous zones surrounding the pile.

At the beginning of grout or concrete placement the sealing device (plug, or bottom cover plate at the tip of the auger) shall be removed by the application of grout or concrete pressure, or with a central reinforcing bar. As pumping begins, the auger shall be lifted from 6 to 12 in. (0.15 to 0.3 m) to facilitate removal of the sealing device. Care shall be taken to ensure that the auger is lifted only within this specified range to initiate the flow of grout or concrete, and that water inflow and soil movement at or near the base of the auger are minimized. After withdrawing the auger to initiate the flow of grout or concrete, the tip of the auger should be re-inserted to at least the original depth.

The technique and equipment used to initiate and maintain the grout or concrete flow shall be such that a pile of the full design cross-section is obtained from the maximum depth of boring to the final pile cut-off level. The grout or concrete shall be supplied to the pile at a rate during auger withdrawal that ensures that a continuous monolithic shaft of at least the full specified cross-section is formed, and is free from soil inclusions or any grout or concrete segregation.

The auger shall be extracted at a smooth, steady rate while continuously pumping. If rotation of the auger occurs during auger extraction, it shall be positive, i.e. in the same direction as during drilling.

Satisfactory coordination of auger withdrawal with pumping is indicated by maintaining a positive pressure in the grout at the auger tip, and a sufficient volume or pressure of grout or concrete to fill the pile (with a small oversupply of volume). Satisfactory coordination shall be verified using automated monitoring equipment.

The volume of grout or concrete placed as a function of depth shall be measured and recorded at intervals not exceeding 2 ft (0.6 m) using automated monitoring equipment. The magnitude of minimum oversupply (or grout volume factor) appropriate for the site conditions shall be established during the pre -production test pile program and maintained during production pile construction. Inadequate volume pumped over a depth interval of 5 ft (1.5 m) is a basis for rejection of the pile.

Commentary: Typical grout volume factors range from 1.15 to 1.2 (i.e., 15% to 20% oversupply). In general, a grout volume factor of 1.15 is considered to be a minimum value. Grout factors greater than 1.5 suggest that soil mining or other undesirable installation effects may be occurring. There may be some cases where grout factors greater than 1.5 are acceptable, particularly if integrity and proof tests indicate that the pile meets the performance requirements and if pre-production piles showed similar results.

The grout/concrete volume factor of the pile shall be within 7.5% of the target volume factor established in the Pile Installation Plan as modified by the results of the pre-production test pile program. Production piles installed outside of this range shall be considered unacceptable piles as listed in Section (8.)3.13.

If placement of grout or concrete is suspended for any reason, such as equipment failure, the pile will need to be re-drilled. The pile may be re-drilled in the same location if the grout or concrete is still fluid enough for the drill rig to penetrate. If the concrete or grout has set, the pile will need to be re-drilled in a new location. The Pile Installation Plan and working drawings will need to be revised by the CFA Pile Contractor to reflect the changes and submitted to the Engineer for approval prior to re-drilling the pile.

Commentary: During grouting, the auger should be pulled with either no rotation or slow continuous rotation in the direction of drilling. A static pull with no rotation can help maintain a static condition at the base of the auger against which the grout/concrete pressure acts. Some contractors prefer to slowly rotate the auger during withdrawal in order to minimize the risk of having the auger flight stick. In addition, some augers have an off-center discharge plug at the base and slow rotation may help to avoid concentrating the distribution of the grout and pressure to an off-center location within the hole. If rotation is used it must be very slow so that the auger does not tend to conduct the soil on the auger flights to the surface ahead of the auger.

The intent of this provision is that the piles be constructed with grout/concrete volumes consistent with the standard as reflected in the results of the pre-production test pile program. The production piles should be installed at the same grout volume factor (within an acceptable range) that was used for the pre-production test pile installation. A pile which is not completed with adequate volume of grout or concrete may be re-drilled at the CFA Pile Contractor's discretion, and this fact recorded on the pile record. The acceptance of a re-drilled pile is at the Engineer's discretion.

8.3.7 Pile Head Finishing and Protection

Immediately upon completion of placement of the fluid grout or concrete, the CFA Pile Contractor shall remove all excess grout or concrete and spoil from the vicinity of the top of the excavation and place a suitable temporary device within the top of the excavation, extending both above and below the ground surface by at least 1 ft (0.3 m) to keep surface spoil from entering the grout or concrete column before it sets. Immediately upon placement of this temporary device, the CFA Pile Contractor shall remove any and all loose soil that has fallen into the grout or concrete column using the tools and methods contained in the approved Pile Installation Plan, and before the grout or concrete begins its initial set. The temporary device shall be removed without disturbing the natural soil surrounding the top of the pile once the grout or concrete has set.

8.3.8 Reinforcing Steel Placement

Any required reinforcing steel shall be placed as shown on the plans by lowering the steel into the grout or concrete column while it is in a fluid state. The reinforcing steel shall be free of oil, soil, excessive rust or other deleterious material. The reinforcing steel shall be centered in the excavation by means of plastic or cementitious spacers placed at sufficient intervals along the pile and at sufficient intervals around the steel to keep the steel centered. Metallic spacers shall not be permitted. Centralizer types and spacing are subject to approval by the Engineer. If cages of reinforcing steel are called for on the approved working drawings, the longitudinal bars and lateral reinforcement (spiral or horizontal ties) shall be completely assembled and placed as a unit. Where spiral reinforcement is used, it shall be tied to the longitudinal bars at a spacing not to exceed 1 ft (0.3 m) unless otherwise shown on the plans. Welding of reinforcement is permitted only if weldable reinforcing steel is specified as part of the approved design.

The reinforcing steel shall not be spliced except at locations that are shown on the plans, and the reinforcing steel shall be free of any permanent distortion, such as bars bent by improper pickup. If a pile is required by the Engineer to be lengthened after the steel has been cut and cages have been assembled, the schedule of reinforcing steel (both longitudinal and lateral) shall be extended to the required depth by splicing. Splices should be as close to the bottom of the reinforcing cage as possible. Splicing by welding shall not be permitted unless weldable reinforcing steel is specified as part of the approved design.

The reinforcing steel shall be placed in the grout column immediately after screening the grout or concrete and before the grout or concrete begins to set. The steel may be lowered into the grout or concrete by gravity or pushed gently to final position by hand. The reinforcing steel shall not be vibrated, driven, or otherwise guided into position by mechanical means.

The reinforcing steel shall be held in position at the ground surface within the fluid grout column by supports appropriate for the reinforcement used, which shall remain in place until the grout reaches its initial set, or 24 hours, whichever is longer.

Commentary: If the soil profile contains considerable dry or moist sand, it is critical that the cage be placed as soon as possible after placement of grout or concrete, in less than 10 minutes if possible, because the grout or concrete will begin to set very quickly under such conditions. Steel spacers should not be permitted as they may greatly accelerate corrosion of the reinforcing steel, particularly above the ground water table. Centering guides made of steel, such as a wire "basket" or "football" tied at the base of single-rod reinforcement may be used. The time for initial set will vary according to mix design. Mixes with significant amounts of retarders or fluidifiers may require longer than 24 hours to reach initial set under certain conditions (cold weather, for example). The installation plan should include requirements for the duration of reinforcement support.

8.3.9 Pile Cut-Off

The CFA Pile Contractor shall cut off the tops of piles and square with the pile axis at the elevations indicated on the approved working drawings, by removing fresh grout or concrete from the top of the pile or by cutting off hardened grout or concrete down to the final cutoff point at any time after initial set has occurred. The finished top of pile shall be no more than 1 in. (25 mm) below or 3 in. (75 mm) above the elevation shown on the approved working drawings.

8.3.10 Inspection and Records

The CFA Pile Contractor shall maintain accurate records for each pile constructed. Similar records will be maintained by the Engineer. These records shall show:

  1. Pile location;
  2. Ground surface elevation (reference grade for pile length);
  3. Pile toe (bottom) depth and elevation;
  4. Elevation of top of grout or concrete;
  5. Pile length;
  6. Auger diameter;
  7. Details of the reinforcing steel (number, size, and grade of longitudinal bars, size and spacing of transverse steel; outside diameter and length of cage);
  8. Flowcone efflux time and volume of grout placed or slump and volume of concrete placed
  9. Theoretical volume of drilled hole (theoretical diameter = diameter of auger);
  10. Depth to which reinforcing steel was placed;
  11. Date/Time of beginning of drilling;
  12. Date/Time of completion of drilling;
  13. Date/Time grout or concrete was mixed;
  14. 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;
  15. Date/Time of beginning of grout or concrete pumping;
  16. Date/Time of completion of grout or concrete pumping;
  17. Date/Time of placement of reinforcing steel;
  18. Weather conditions, including air temperature, at time of grout or concrete placement;
  19. Identification of all grout or concrete samples taken from the pile;
  20. All other pertinent data relative to the pile installation; and
  21. All readings made by the automated measuring and recording equipment to include as a minimum:
    1. Auger rotation verses depth for every 2 ft (0.6 m) increment, or less, of pile advancement during the drilling process, and during placement of grout or concrete (if auger is rotated during this placement);
    2. Volume of grout or concrete placed versus depth of outlet orifice for every 2 ft (0.6 m) increment, or less, of pile placed;
    3. Average maximum and minimum pump stroke pressures at ground level for every 2 ft (0.6 m) increment, or less, of pile placed;
    4. Average maximum and minimum pump stroke pressure at or near the auger head for every 2 ft (0.6 m) increment, or less, of pile placed, if directed by the Engineer; and
    5. Additionally, the Engineer may also specify that torque and crowd force (downward thrust on auger) measurements be made for every 2 ft (0.6 m) increment, or less, of pile advancement during the drilling process.

These data shall be provided to the Engineer within 24 hours of the completion of the pile. Data collected by automated measuring and recording equipment shall be provided in numerical or graphical form.

8.3.11 Testing

Any testing of CFA piles shall conform to the pertinent item requirements in the relevant State DOT's Standard Specifications. If the relevant Standard Specifications do not refer to load testing for CFA piles specifically, the specifications for load testing of deep foundations may be used.

Commentary: A discussion of testing programs and procedures is contained in Chapter 7 of the FHWA "Geotechnical Circular No. 8 - Augered Cast-in-Place and Continuous Flight Auger Piles". The scope of the testing program for all structures will depend on many factors, including the anticipated loads and the quantity of piles to be installed on the project. For structures that are often referred to as "non-critical structures", such as sound barrier walls, overhead signs, and light/signal pole foundations, the Engineer may not require the same frequency of testing as for bridges and other structures. For example, a qualified contractor that consistently demonstrates proper installation techniques may not need to perform a load test for a lightly loaded pile for a "non-critical" structure. Monitoring records during construction and post-construction integrity testing may provide sufficient confidence for the Owner that the piles will carry the design load.

8.3.11.1 Pre-Production Testing

Piles installed for pre-production testing (including any reaction piles required for static load testing) shall include all construction, monitoring, and inspection requirements of production piles. The results of the installation and testing will be used to:

  1. Establish target drilling penetration rate for the various subsurface conditions on the site;
  2. Establish pressure/volume relations during placement of grout/concrete. The grout factor ±7.5% calculated for the test pile(s) shall be used for the installation of the production piles;
  3. Establish target values for torque and downward thrust or crowd for displacement or partial displacement piles;
  4. Establish mix design parameters such as grout flow, necessary admixtures, etc; and
  5. Evaluate design correlations of side and base resistance with the site specific soil parameters. Revision of the design by the CFA Pile Contractor may result from these tests, subject to approval by the Engineer.

All of the parameters listed above that are established during the pre-production test pile program will be used to install the production piles.

Commentary: In past practice, the pre-production test program was primarily a load test program which demonstrated that the contractor could properly install a test pile and achieve the desired load capacity of the pile. The intent of the pre-production testing program in this specification is to install test piles to establish and/or verify installation criteria as well as load capacity. The results of the pre-production test program will then be used during production pile installation to ensure that the CFA Pile Contractor is consistently installing acceptable piles (i.e. the production pile is the same as a test pile).

Pre-production load tests will generally consist of a single or multiple static load tests, depending on the number of piles to be installed, the range of design pile capacities and the variation of subsurface conditions at the site. For very large projects, pre-production testing may include a single static load test supplemented with several piles tested by the rapid or dynamic load test methods outlined in Section (8.)3.11.2. Performing rapid or dynamic tests during the pre-production testing program will allow these methods to be calibrated against static load tests results prior to production pile installation. The CFA Pile Contractor and the Engineer will be able to best determine the appropriate quantity and level of pre-production testing based on the project conditions.

Since a major advantage of CFA piles is speed of installation, the pre-production load test program may be performed concurrent to the start of production piles to reduce additional mobilization or delay costs. This may be sufficient for small to medium sized projects. The ability to modify the design based on the results of the load test may be limited in this case.

8.3.11.2 Verification Load Testing

Verification tests shall be performed on a minimum of 2% of production piles (and more as required by the Engineer) to demonstrate that the installed production piles meet the established load-deflection criteria. Verification tests can be performed using static load tests, rapid load tests (RLT), or dynamic load tests (DLT). Combinations of the various test methods may also be used as appropriate for the project. RLT and DLT test methods shall conform to the State DOT Standard Specifications or be otherwise approved by the Engineer.

Commentary: A single pre-production test only demonstrates the performance of the test pile. Performing verification tests periodically throughout production pile installation will verify that the pile installation techniques continue to provide adequate pile capacities. The use of RLT (such as Statnamic ™ or Fundex systems) or DLT (drop hammer) can often allow testing a large number of piles more efficiently, in terms of time and cost when compared to static load test methods. Calibrating the RLT or DLT tests with static load tests during the pre-production test program may reduce delays associated with analyzing the test data during pile production.

8.3.12 Integrity Testing

Post-installation integrity tests shall be performed on a minimum of 20% of the production piles. Such tests include, but are not limited to, sonic echo tests, impulse-response tests, cross-hole sonic tests, and backscatter gamma tests. Specific integrity test requirements are outlined in the bid documents. Test methods shall conform to the State DOT Standard Specifications or be otherwise approved by the Engineer.

The CFA Pile Contractor shall install access tubes (of a design that is acceptable to the Integrity Testing Firm) to accommodate those tests that require access to the interior of the CFA pile. These tubes shall be secured to the reinforcing steel and capped prior to placing the steel cage in the fluid grout. The piles that will include the access tubes shall be noted on the approved working drawings and in the test program.

The CFA Pile Contractor shall engage an independent Consultant, acceptable to the Engineer, to perform integrity tests and to report the results, with interpretations, to the CFA Pile Contractor and the Engineer.

Commentary: Post-installation integrity tests are valuable in establishing that a CFA Pile Contractor's procedures are producing acceptable piles on any given project. The most reliable of the post-installation integrity tests for identifying anomalies within the pile are those that use down-tube instruments, such as the cross-hole sonic (CSL) test, single-hole sonic test (SST), the backscatter gamma test, and the fiber-optic television camera test. These tests all require that the CFA Pile Contractor attach appropriate access tubing to the reinforcing steel prior to placing the steel in the grout column. They also require interpretation, which should be performed by independent, experienced, and qualified specialty consultants. It is not always possible to determine whether an anomalous reading is a defect within the pile. The final decision on acceptability of the pile must be made by the Engineer, based on construction records, the post-installation integrity test expert's report, and upon the Engineer's analysis of the possible effect on foundation performance of the potential defect.

In order to be effective, access tubes for sonic or backscatter gamma testing should be distributed evenly circumferentially around a reinforcing cage at a frequency of approximately one for every 1 ft (0.3 m) of cage diameter. It is advisable that tubes used for cross-hole sonic tests consist of Schedule 40 steel, because such tubes will remain bonded to the grout. Polyvinyl chloride (PVC) tubes do not ordinarily remain bonded to the grout beyond a few days after grout takes its initial set, and debonding will render the cross-hole sonic tests ineffective. PVC tubes should be used only for backscatter gamma testing unless cross-hole sonic tests will be performed within 72 hours of casting the grout.

The necessary frequency of post-construction integrity testing should be outlined in the owner's bid package. In situations when the Owner has little experience with CFA piles, a particularly difficult project is at hand, or the project or site conditions give reason to expect problems with pile integrity, integrity testing of more than 20% of production piles may be required. A typical reasonable approach for load-bearing piles is to subject the first 10 to 15 piles to be constructed to integrity tests to establish that the contractor's construction practice at the site is adequate. Thereafter, the frequency of such tests can be set to meet the 20% criteria, can be reduced, or perhaps eliminated if the construction records for the remaining production piles are similar to those of the initial piles that were subjected to integrity tests.

8.3.13 Unacceptable Piles

Unacceptable piles are defined as piles that do not meet the project performance criteria with regard to load carrying capacity and deflections. The following items constitute construction conditions would be considered a basis for pile rejection:

  1. Piles that are tested using post-installation integrity testing methods and are judged by the Engineer to be unacceptable.
  2. Piles subjected to a verification load test where the test indicates the load capacity of the pile does not meet the design load and deflection criteria with an appropriate factor of safety.
  3. Piles for which the data from the automated measuring and recording equipment, other recording methods, or the Inspector's records indicate that a defective pile has been installed due to an inadequate penetration rates, grout/concrete volume factors or pressures, or other pile installation parameters that do not meet the criteria established by the pre-production test program.
  4. Piles out of position at the ground surface or not within the plumbness or batter limits defined in Section (8.)3.5.
  5. Piles in which the top of pile elevation is outside the limits shown on the approved working drawings and described in Section (8.)3.9.
  6. Piles in which the grout or concrete strength, and/or grout or concrete factor is less than as designed.
  7. Piles in which the reinforcing steel was not inserted as designed.
  8. Piles that exhibit any visual evidence of grout or concrete contamination, excessive settlement of grout/concrete, structural damage, or inadequate consolidation of grout/concrete (honeycombing).

Unacceptable piles shall be replaced or repaired at the CFA Pile Contractor's expense, as directed by the Engineer.

Commentary: In addition to the above list, there may be incidents that cause a pile to be unacceptable, such as when lateral communication occurs between piles, or when excessively large grout takes occur. The action taken by the CFA Pile Contractor, Inspector, and Engineer will vary depending on the circumstances. The soil conditions, design load, and other design factors will need to be considered before the pile is rejected or the CFA Pile Contractor is allowed to repair or replace the pile. Options include, but are not limited to, abandoning the pile, switching from grout to concrete, or allow the pile to be grouted to the best of the CFA Pile Contractor's ability and then re-drill the pile after the grout has had its initial set. Judgment on the part of the Engineer and the Design engineer will need to be exercised.

8.4 Measurement

CFA pile foundations shall be measured as per pile. Pre-production testing will be measured as a lump sum. Integrity tests and verification load tests will be measured on a per pile basis.

8.5 Payment

The work performed and materials furnished in accordance with this Item and measured as provided under Section (8.)4 ("Measurement") will be paid for at the unit prices bid under the payment categories listed below.

Payment categories:

  1. Per pile accepted by the Engineer.
  2. Per pile placed with access tubes for down-hole integrity testing accepted by the Engineer.
  3. Per pile for integrity testing on a production pile.
  4. Per pile for rapid load test on a production pile.
  5. Per pile for dynamic load test on a production pile.
  6. Lump sum for pre-production test program as approved by the Engineer.

The quantities to be paid will be the quantities in each category shown on the approved working drawings and as accepted after installation by the Engineer, unless specific changes are required in writing by the Engineer. Unit prices that are bid will apply to the extension of any pile to a depth up to 120% of the depth for that pile that is shown on the approved working drawings when such an increase in depth is required by the Engineer. For such purposes, the length of the pile shall be measured between the top of the grout or concrete and the bottom of the pile. If increases in depth exceeding 120% of the depth shown on the working drawings are required by the Engineer, or if diameters other than those that are shown on the working drawings are required by the Engineer, the unit prices shall be renegotiated for those piles involved.

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Updated: 04/07/2011
 

FHWA
United States Department of Transportation - Federal Highway Administration