Amendment_0002_31 62 00 MICROPILES - August 7_2025.pdf

DDG(X) LBTS WP4: Shaftline Foundation 1733372

SECTION 31 62 00

MICROPILES

07/13

PART 1 GENERAL

1.1 REFERENCES

The publications listed below form a part of this specification to the extent referenced. The publications are referred to within the text by the basic designation only.

ASTM INTERNATIONAL (ASTM)

ASTM A252 Standard Specification for Welded and Seamless Steel Pipe Piles

ASTM A615/A615M (2012) Standard Specification for Deformed and Plain Carbon-Steel Bars for Concrete Reinforcement

ASTM A706/A706M (2022) Standard Specification for Low-Alloy Steel Deformed and Plain Bars for Concrete Reinforcement

ASTM A722/A722M (2015) Standard Specification for Uncoated High-Strength Steel Bar for Prestressing Concrete

ASTM C109/C109M (2011b) Standard Test Method for Compressive Strength of Hydraulic Cement Mortars (Using 2-in. or (50-mm) Cube Specimens)

ASTM C144 (2011) Standard Specification for Aggregate for Masonry Mortar

ASTM C150 Standard Specification for Portland Cement

ASTM C494/C494M (2013) Standard Specification for Chemical Admixtures for Concrete

ASTM D1143/D1143M (2007; E 2009) Piles Under Static Axial Compressive Load

ASTM D3689 (2007; E 2013; R 2013) Standard Test Methods for Deep Foundations Under Static Axial Tensile Load

ASTM E74 (2018) Standard Practices for Calibration and Verification for Force-Measuring Instruments

U.S. FEDERAL HIGHWAY ADMINISTRATION (FHWA)

FHWA NHI-05-039 (2005) Micropile Design and Construction

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August 7, 2025

1.2 BASIS FOR BIDS AND PAYMENT

1.2.1 General

Base bids on the number, size, and length of micropiles as detailed on the contract drawings. The allowable design load for the 9.625 inch diameter micropiles is 60 tons compression.

Final dimensions and installation procedures for production piles shall be based on test pile installation and results of load testing program.

Adjustment in contract price will not be made for altering the pile dimensions or installation procedures to achieve the specified pile capacity.

1.2.2 Unit Price

For unit price bid, see Price Schedule.

1.2.2.1 Micropiling

Payment will be for completed and accepted micropiles, measured on a per linear foot basis. Payment will be by the contract unit price for furnishing labor, materials, tools, equipment, and incidentals for doing the work involved with installing the micropiles.

1.2.2.2 Micropiling Pre-Production Verification Pile Load Test

Payment will be made for costs associated with verification load testing of pre-production micropiles, including material and labor for fabricating, furnishing and designing load frames; calibrating load cells and hydraulic jacks; furnishing specified test equipment; installing strain gauges; placing and removing test loads and test equipment;

recording, reducing and submitting test data measured on a per each basis. No payment will be made for rejected pile load tests.

1.2.2.3 Micropiling Proof Load Test of Production Pile

Proof load testing of production micropiles, including material and labor for fabricating, furnishing and designing load frames; calibrating load cells and hydraulic jacks; furnishing specified test equipment; installing strain gauges; placing and removing test loads and test equipment;

recording, reducing and submitting test data measured on a per each basis. No payment will be made for rejected pile load tests.

1.3 SUBMITTALS

Government approval is required for submittals. When used, a designation following the "G" designation identifies the office that will review the submittal for the Government. Submit the following in accordance with Section 01 33 00 SUBMITTAL PROCEDURES:

SD-01 Preconstruction Submittals

Contractor Experience; G

Evidence of previous micropile drilling and grouting experience for successful installation of a minimum of 50 micropiles in at least 3 projects of similar size and scope to that required by these Contract Documents over the last three years.

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Experience of superintendent to complete the work showing installation of 25 micropiles within the last two years.

Geotechnical Consultant Qualification; G

Micropile Installation Procedure; G

A detailed description of the construction procedure including sequencing, drilling methods and equipment, assembly of casing, grouting procedures and pressures, quality control measurements made to assure consistency between micropiles and consistency in materials used, and means of disposing of excess drilling fluids and grout.

Drilling Procedure; G

Equipment specification including operating dimensions and procedures used to operate indoors and with the available horizontal clearances and vertical overhead clearances at the site.

Load Testing Apparatus; G

Details for load testing including a drawing of the apparatus, location of dial gauges, reference beams, and reaction piles.

Calculations verifying the adequacy of the test apparatus to safely resist a jacking load of at least 3.5 times the micropile design load. Calculations shall be prepared by a Registered Professional Engineer.

Methane Mitigation Plan (MMP); G

Methane gas was encountered while collecting test borings during design (refer to notes in the borings logs). Building 77H will be occupied by the government throughout construction (including during pile installation). The contractor’s safety plan must include methane as a potential hazard that may be encountered during construction. The methane mitigation plan (MMP) at a minimum must include the contractor’s approach for monitoring methane gas during pile installation and actions that will be taken by the contractor if methane is encountered. Contractor and government personnel must be briefed and notified of the plan. The plan must be reviewed and approved by the contracting officer and must be submitted in conjunction with the contractor’s accident prevention plan (APP).

Methane levels must be kept below 1.25% volume in air. If methane levels exceed this limit, construction activities must be paused and ventilation and/or other corrective actions as indicated in the MMP must be used to reduce methane levels below 1.25% volume in air prior to resuming construction activities.

SD-03 Product Data; G

Grout; G

Admixtures; G

Cement; G

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Fine Aggregate; G

Reinforcing Bars; G

Steel Casing; G

SD-06 Test Reports

Pile Load Tests; G

Installation Record; G

Grout; G

SD-07 Certificates

Product Certificates; G

Pipe Casing; G

Calibration of gages; G

SD-11 Closeout Submittals

Micropile Installation Records; G

As-Built Data; G

Actual pile location data must be submitted within two working days after a pile is installed. The Contractor must provide the Contracting Officer with written tabulation indicating the following information: Pile number; Elevation of top of each pile after installation of the cap plate (measured to the nearest 0.05 ft.).; Deviation from design plan location (measured to the nearest 0.01 ft.).

1.4 QUALITY ASSURANCE

1.4.1 Contractor Experience

Evidence of previous micropile drilling and grouting experience for successful installation of a minimum of 50 micropiles in at least 3 projects of similar size and scope to that required by these Contract Documents over the last three years.

Experience of superintendent to complete the work showing installation of 25 micropiles within the last two years.

1.4.2 Load Testing Apparatus

Details for load testing including a drawing of the apparatus, location of dial gauges, reference beams, and reaction piles.

Calculations verifying the adequacy of the test apparatus to safely resist a jacking load of at least 3.5 times the micropile design load. Calculations shall be prepared by a Registered Professional Engineer.

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1.4.3 Calibration of Gages

Calibrate all gages for measuring grout pressure and grout volume before grouting. Calibration of load cell shall conform to ASTM E74.

1.4.4 Geotechnical Consultant Qualification

The services of an independent, registered Professional Geotechnical Consulting Engineer, licensed in the Commonwealth of Pennsylvania, experienced in soil mechanics, micropile design, micropile installation, and conducting static pile load tests shall be hired by the Contractor to observe test pile installation and job pile installation as specified herein. The Geotechnical Consultant shall be independent of the Contractor and shall have no employee-employer relationship with the Contractor which could constitute a conflict of interest.

Engineering services to be provided by the Geotechnical Consultant shall include: micropile foundation analysis and design, verification of the proper construction of the micropile load testing system and micropiles, monitoring of micropile installation, and certification of the micropile verification and proof load test results. The Geotechnical Consultant shall have experience with drilling in subsurface conditions that include methane gas and shall provide corresponding recommendations for micropile construction to be included in the Contractor's methane mitigation plan.

The Geotechnical Consultant shall have experience on at least three similar projects in similar geologic conditions. Submit qualifications of Consultant and scope of services to be performed for the project.

1.4.5 Pre-Construction Conference

After submittals are received and approved, but before micropile construction and/or micropile verification load testing begins the Contracting Officer will hold a pre-construction conference with the Contractor, Geotechnical Consultant, micropile contractor, and all subconsultants involved in the drilling, installation, inspection and testing of micropiles to review the drawings and specifications, work plans, safety plans, and submittals.

PART 2 PRODUCTS

2.1 MATERIALS

2.1.1 Grout

Neat cement or sand/cement mixture with a minimum 28-day compressive strength of 4,000 psi in conformance with ASTM C109/C109M.

2.1.1.1 Admixtures for Grout

Admixtures for Grout: Admixtures shall be in accordance with ASTM C494/C494M. Admixtures that control bleed, improve flowability, reduce water content, and retard set may be used in the grout, subject to the review and acceptance of the Engineer. Admixtures shall be compatible with the grout and mixed in accordance with the manufacturer's recommendations and shall be added during the trial batch testing.

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2.1.1.2 Cement

All cement shall be Portland cement conforming to ASTM C150 Types II, III or V.

2.1.1.3 Centralizers and Spacers

Centralizers and spacers shall be fabricated from schedule 40 PVC pipe or tube, steel, or material non-detrimental to the reinforcing steel. Wood shall not be used. Centralizers and spacers shall be securely attached to the reinforcement; sized to position the reinforcement within 0.4 inches of plan location from center of pile; sized to allow grout tremie pipe insertion to the bottom of the drillhole; and sized to allow grout to freely flow up the drillhole and casing and between adjacent reinforcing bars.

2.1.1.4 Water

Water used in the grout mix shall be potable, clean, and free from substances that may be injurious to cement and steel.

2.1.1.5 Fine Aggregate

Sand shall conform to ASTM C144

2.1.1.6 Pipe Casing

a. Permanent steel casing/pipe shall meet the Tensile Requirements of ASTM A252, Grade 3, modified, with the yield strength shall be a minimum of 80 ksi

b. The pipe shall have an OD of 9.625 inches and shall have a minimum wall thickness of 0.472 inches.

c. Alternative material: "Structural Grade" (a.k.a. "Mill Secondary") steel pipe meeting the above but without Mill Certification, free from defects (dents, cracks, tears) and with two coupon tests per truckload delivered to the manufacturer.

d. Threaded joints shall develop an ultimate load transfer of 175 kips in compression and 80 kips in tension.

2.1.1.7 Reinforcing Bars

Reinforcing steel shall be threaded bars or deformed bars in accordance with ASTM A615/A615M Grade 75, ASTM A706/A706M Grade 80, or ASTM A722/A722M Grade 150, or as specified on the drawings. When a bearing plate and nut are required to be threaded onto the top end of reinforcing bars for the pile top to pile cap anchorage, the threading may be continuous spiral deformed ribbing provided by the bar deformations (e.g., Dywidag or Williams continuous threadbars) or may be cut into a reinforcing bar. If threads are cut into a reinforcing bar, the next larger bar number designation from that shown on the Plans shall be provided. Bar tendon couplers, if required, shall develop the ultimate tensile strength of the bars.

2.2 Product Certificates

Contractor must submit Product Certificates a minimum of 2 weeks prior to

SECTION 31 62 00 Page 6 pile installation.

PART 3 EXECUTION

3.1 Micropile Installation

The Contractor shall submit the specific installation procedures following FHWA NHI-05-039 Guidance for installing the micropiles prior to starting work. Adjustments to the installation procedure based on the load test results shall be resubmitted prior to installation of production piles.

Production piles shall not be installed until successful completion of the load test. Installation of both test and production micropiles shall be performed in the presence of the Government or their qualified representative.

3.1.1 Drilling

The contractor shall determine the specific method of drilling and installation of the specified micropile casing. Drilling equipment and methods shall be suitable for drilling through the subsurface conditions at the site without damage to the adjacent structure. Methods shall be suitable to drill through the conditions to be encountered as indicated in the test borings. Drilling methods and procedures to be employed shall include provisions for monitoring, reporting, andsafely managing methane gas where encountered during micropile construction. Submit a Methane Mitigation Plan (MMP) for review and approval. Casing shall be advanced the full length of the micropile and the drill bit shall be of sufficient size to obtain the minimum diameter shown on the drawings for the full length of the bond zone. The micropile shall be drilled to the minimum length shown on the drawings. Open hole drilling using mineral slurries shall not be permitted.

3.1.2 Grouting

The contractor shall pressure grout the micropile as the casing pipe is extracted to develop the specified bond length shown on the drawings.

Grout shall be pumped to the bottom of the casing through drill stem or tremie tube. After developing the specified bond length the casing shall be reinserted for the indicated plunge length. Grout pressures and volumes shall be measured at the pile head and recorded as the casing is extracted. Grouting shall be performed the same day that the bond length is drilled. The casing shall be left in place to the depth shown on the drawing. Grout shall be placed to fill the casing to the top. Upon completion the casing shall be capped under pressure until the grout has set. Grouting equipment shall be of sufficient size to permit grouting in continuous operation and within one hour of the start of grouting.

Extended grouting periods shall not be permitted without supporting grout strength testing. The contractor shall determine the grout pressure and extraction rate to produce an acceptable pile based on the load testing requirements specified herein. Grouting shall be performed in a manner which does not heave the adjacent floor slab. Two sets of three grout cubes shall be cast and tested per day of work or as requested by the Government. Grout density and viscosity shall be measured at a frequency of one test per pile. Grout sampling and testing shall be the responsibility of the Contractor.

3.2 INSTALLATION RECORD

The contractor shall submit a record for each micropile installed. The

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Micropile Installation Records shall be submitted within one work shift after that micropile installation is completed. Reports shall include all relevant items used as part of the contractor's quality control. At a minimum reports shall include:

1) Micropile #

2) Date

3) Superintendent name

4) Start and stop time of drilling and grouting

5) Casing size, length, and number of joints

6) Drill bit type and size

7) Grouting pressures and volumes

8) Length of hole and bond length

9) Grout density and viscosity

10) Relevant observations or adjustments made during the installation

3.3 TOLERANCES

Micropile construction tolerances are as follows:

1) Center line of piles shall not be more than 3 inches from specified Plan location.

2) Pile shall be plumb within 2 percent of total length Plan alignment.

3) Top elevation of pile shall be plus 1 inch or minus 2 inches maximum from specified Plan vertical elevation.

4) Joint connections shall not permit eccentricities or kink angles.

When micropiles are installed with dimensions outside of the specified tolerances, with grout not conforming to the specified strength, or with any other nonconforming condition, the Contracting Officer will make a determination regarding the proper corrective measures to be taken.

Corrective measures may include the removal and replacement of defective micropiles, the installation of additional micropiles at nearby locations, the modification of the foundation over the micropiles, or other measures the Contracting Officer deems appropriate.

3.4 PILE LOAD TESTS

Perform verification load testing and proof load testing of micropiles at the locations specified herein or designated by the Engineer. Perform compression load testing in accordance with ASTM D1143/D1143M or tension load testing in accordance with ASTM D3689, except as modified herein.

3.4.1 Verification Load Tests

a. Perform pre-production verification pile load testing to verify the design of the micropile system and the construction methods proposed prior to installing any production piles. Two (2) verification test piles shall be constructed in conformance with the drawings.

Verification test piles shall be sacrificial pre-production micropiles, installed at the locations indicated on the drawings. At least one pre-production pile must be tested in compression.

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b. Verification load tests shall be performed to verify that the Contractor installed micropiles will meet the required compression and tension load capacities and load test acceptance criteria and to verify that the length of the micropile bond zone is adequate. The micropile verification load test results must verify the micropile design and installation methods, and be reviewed and accepted by the Engineer prior to beginning installation of production micropiles.

c. The drilling-and-grouting method, casing length and outside diameter, reinforcing bar lengths, and depth of embedment for the verification test piles shall be identical to those specified for the production piles at the given locations. The verification test micropile structural steel sections shall be sized to safely resist the maximum test load.

d. The maximum verification and proof test loads applied to the micropile shall not exceed 80 percent of the structural capacity of the micropile structural elements, to include steel yield in tension, steel yield or buckling in compression, or grout crushing in compression. Any required increase in strength of the verification test pile elements above the strength required for the production piles shall be provided for in the Contractor's bid price.

e. The jack shall be positioned at the beginning of the test such that unloading and repositioning during the test will not be required. When both compression and tension load testing is to be performed on the same pile, the pile shall be tested under compression loads prior to testing under tension loads.

3.4.2 Testing Equipment and Data Recording

a. Testing equipment shall include dial gauges, dial gauge support, jack and pressure gauge, electronic load cell, strain gauges, and a reaction frame. The load cell is required only for the creep test portion of the verification test. The Contractor shall provide a description of test setup and jack, pressure gauge and load cell calibration curves in accordance with the Submittals Section.

b. Design the testing reaction frame to be sufficiently rigid and of adequate dimensions such that excessive deformation of the testing equipment does not occur. Align the jack, bearing plates, and stressing anchorage such that unloading and repositioning of the equipment will not be required during the test.

c. Apply and measure the test load with a hydraulic jack and pressure gauge. The pressure gauge shall be graduated in 25 psi increments or less. The jack and pressure gauge shall have a pressure range not exceeding twice the anticipated maximum test pressure. Jack ram travel shall be sufficient to allow the test to be done without resetting the equipment. Monitor the creep test load hold during verification tests with both the pressure gauge and the electronic load cell. Use the load cell to accurately maintain a constant load hold during the creep test load hold increment of the verification test.

d. Measure the pile top movement with a dial gauge capable of measuring to 0.001 in. The dial gauge shall have a travel sufficient to allow the test to be done without having to reset the gauge. Visually align the gauge to be parallel with the axis of the micropile and support the gauge independently from the jack, pile or reaction frame. Use a

SECTION 31 62 00 Page 9 minimum of two dial gauges when the test setup requires reaction against the ground or single reaction piles on each side of the test pile.

e. The required load test data shall be recorded by the Contractor's Geotechnical Consultant. Contractor shall submit five copies of the verification load test data report developed by the Geotechnical Consultant for the Engineer's review.

3.4.3 Verification Test Loading Schedule

a. Test verification piles designated for compression load testing to a maximum test load of 2.0 times the micropile Design Load shown on the drawings.

b. The verification pile load tests shall be made by incrementally loading the micropile in accordance with the following cyclic load schedule for both compression and/or tension loading:

Step Loading Applied Load Holding Time (min.)

1 Apply AL 2.5

2 Cycle 1 0.15 DL

0.30 DL

0.45 DL

AL

2.5 2.5 2.5

3 Cycle 2 0.15 DL

0.30 DL

0.45 DL

0.60 DL

0.75 DL

0.90 DL

1.00 DL

AL

2.5 2.5 2.5 2,5 2.5

4 Cycle 3 0.15 DL

1.00 DL

1.15 DL

1.30 DL

1.45 DL

AL

2.5 10 to 60 minutes 2.5

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Step Loading Applied Load Holding Time (min.)

5 Cycle 4 0.15 DL

1.45 DL

1.60 DL

1.75 DL

1.90 DL

2.00 DL

1.50 DL

1.00 DL

0.50 DL

AL

2.5 2.5

AL = Alignment Load DL = Design Load

c. Pile top movement shall be measured at each load increment. The load-hold period shall start as soon as each test load increment is applied. The verification test pile shall be monitored for creep at the 1.30 Design Load (DL). Pile movement during the creep test shall be measured and recorded at 1, 2, 3, 4, 5, 6, 10, 20, 30, 50, and 60 minutes. The alignment load (AL)shall not exceed 5 percent of the design load (DL) load. Dial gauges shall be reset to zero after the initial AL is applied.

d. The acceptance criteria for micropile verification load tests are:

1. The pile shall sustain the first compression or tension 1.0 DL test load with no more than 0.5 in. total vertical movement at the top of the pile, relative to the position of the top of the pile prior to testing.

2. At the end of the 1.30 DL creep test load increment, test piles shall have a creep rate not exceeding 0.04 in./log cycle time (1 to 10 minutes) or 0.08 in./log cycle time (6 to 60 minutes or the last log cycle if held longer). The creep rate shall be linear or decreasing throughout the creep load hold period.

3. Failure does not occur at the 2.0 DL maximum test load. Failure is defined as the load at which attempts to further increase the test load simply result in continued pile movement, at a rate greater than 0.03 inches per 1,000 lbs. of load applied , or when a maximum settlement over 2 inches is recorded.

e. The Geotechnical Consultant will provide the Contractor written confirmation of the micropile design and construction within 3 working days after receipt of the verification load test data report. This written confirmation will either confirm the capacities and bond lengths specified on the drawings for micropiles or reject the piles based upon the verification test results.

3.4.4 Verification Test Pile Rejection

If a verification-tested micropile fails to meet the acceptance criteria, the Geotechnical Consultant shall modify the design, the construction procedure, or both. These modifications may include modifying the installation methods, increasing the bond length, or changing the

SECTION 31 62 00 Page 11 micropile type. Any modification that necessitates changes to the structure shall require the Engineer's prior review and acceptance. Any modifications of design or construction procedures or cost of additional verification test piles and load testing shall be at the Contractor's expense. At the completion of verification testing, test piles shall be removed down to the elevation specified by the Engineer.

3.4.5 Proof Load Tests

a. Perform proof load testing of production piles at locations designated on the drawings prior to installation of the remaining production piles in the area of the proof load test.

b Test piles designated for compression proof load testing to a maximum of 1.67 times the micropile Design Load shown on the drawings in accordance with the following schedule:

Step Loading Applied Load Holding Time (min.)

1 APPLY AL 2.5

2 LOAD CYCLE 0.15 DL

0.30 DL

0.45 DL

0.60 DL

0.75 DL

0.90 DL

1.00 DL

1.15 DL

1.33 DL

1.45 DL

1.60 DL

2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 10 - 60 2.5 2.5

3 UNLOAD CYCLE 1.33 DL

1.00 DL

0.75 DL

0.50 DL

0.25 DL

AL

c. Depending on performance, either a 10-minute or 60-minute creep test shall be performed at the 1.33 DL Test Load. Where the pile top movement between 1 and 10 minutes exceeds 0.04-in., the Maximum Test Load shall be maintained an additional 50 minutes. Movements shall be recorded at 1, 2, 3, 5, 6, 10, 20, 30, 50 and 60 minutes. The alignment load shall not exceed 5 percent of DL. Dial gauges shall be reset to zero after the initial AL is applied. The acceptance criteria for micropile proof load tests are:

1. The pile shall sustain the compression 1.0 DL test load with no more than 0.5-in. total vertical movement at the top of the pile, relative to the position of the top of the pile prior to testing.

2. At the end of the 1.33 DL creep test load increment, test piles shall have a creep rate not exceeding 0.04-in./log cycle time (1 to 10 minutes) or 0.08-in./log cycle time (6 to 60 minutes). The creep rate shall be linear or decreasing throughout the creep load

SECTION 31 62 00 Page 12 hold period.

3. Failure does not occur at the 1.67 DL maximum test load. Failure is defined as the load at which attempts to further increase the test load simply results in continued pile movement, with a maximum total settlement of 1.5 inches.

d. Proof Test Pile Rejection - If a proof-tested micropile fails to conform to the acceptance criteria, the Geotechnical Consultant shall review the proof test results and provide recommendations for modification of the micropile design and/or installation procedures.

The Contractor shall immediately proof test another micropile at a nearby location approved by the Engineer. For failed piles, and further construction of other piles, the micropile contractor shall modify the installation methods, when directed by the Engineer.

Modifications may include installing replacement micropiles, incorporating piles at not more than 50 percent of the maximum load attained, postgrouting, modifying installation methods, increasing the bond length, or changing the micropile type, as approved by the Engineer. A new verification test pile will be required prior to constructing any further production piles to confirm that the modifications produce piles meeting the micropile Design Load shown on the drawings.

Any modifications of design or construction procedures, and cost of additional verification test piles, proof load testing, or replacement production micropiles shall be at no additional time or cost to the Administration.

3.5 As-Built Data

Actual pile location data must be submitted within two working days after a pile is installed. The Contractor must provide the Contracting Officer with written tabulation indicating the following information: Pile number;

Elevation of top of each pile after installation of the cap plate (measured to the nearest 0.05 ft.).; Deviation from design plan location (measured to the nearest 0.01 ft.).

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2.2 Product Certificates

3.5 As-Built Data