Section 567 — Micropiles

Description

567.01This work consists of providing and installing micropiles.

Material

567.02Conform to the following Subsections: Centralizers and spacers 722.02(e) Chemical admixtures 711.03 Portland cement 701.01(a) Neat hydraulic cement grout 701.04(a) (1) Reinforcing bars 709.01(a) Steel pipes 715.03 Micropile materials 722.06 Water for cementitious materials 725.01(a)

Construction Requirements

567.03Qualifications . Provide a professional engineer, an on- site supervisor, and installation personnel with experience installing and testing micropiles. A t least 30 days before starting micropile work , submit a résumé for each individual describing their experience on at least five micropile projects of similar complexity within the past 5 years for approval . Include project names, locations, and contact information for project owners.

567.04Submittals. At least 30 days before starting micropile work, submit the following a ccording to Subsection 104.06:

(a)Start date;

(b)Micropile construction sequence;

(c)Micropile types, sizes, spacings, depths, installation angles, and ultimate strengths for range of material to be encountered;

(d)Tendons, full moment splices, permanent casing, and additional hardware with the manufacturer’s product data sheets, specifications, catalog cuts, and mill certificates;

(e)Manufacturer’s recommendations for tendon and hardware handling, storing, assembly, and working temperature ranges. Hollow bar micropiles are unacceptable unless shown in the plans or approved;

(f)Grout type, mix design, mixing equipment, placement procedures, and 7- and 28- day grout compressive strengths test results;

(g)Grouting pressure, volume, and location, if post grouting system is used;

(h)Procedures and material for repairing corrosion protection coatings in the field;

(i)Drilling methods and equipment;

(j)Alternative drilling and grouting methods including grout additives;

(k)Additional material needed to achieve requi red bond capacities such as grout socks;

(l)Methods to ensure borehole stability during excavation and grout placement;

(m)Micropile testing methods and equipment. Include type and capacity of reaction load system, drawings, and supporting calculations for struc tural components of the micropile load test apparatus. Include locations for sacrificial micropiles for verification tests; and

(n)Identification number and calibration test certification for each jack, pressure gauge, and electronic load cell. Clearly indica te the serial number of each component of the testing assembly on calibration graphs. Submit results from calibration tests conducted by an independent testing laboratory within the previous 60 days.

567.05Installation. Stage micropile installation to avoid interconnection or damage to piles with uncured grout. Before drilling holes for constructing production micropiles, install verification micropiles for verification load tests. Install verification and production micropiles as follow s:

(a)Drilling. Provide equipment that can drill soil, boulder colluvium and alluvium, and bedrock to anticipated depths. Drill micropile holes to the required diameter and length shown in Table 567-1 and the construction schedule and sequence. If an obstruction prevents the advancement of the pile, abandon the hole and fill the hole with grout. Drill a new hole at an approved location. Remove drill cuttings and other loose debris from the hole. (b) Casing, reinforcing bar, and splicing. Place reinforcing bars with centralizer s shown in Table 567-1. Use centralizers sized to within ½ inch of the drill hole diameter. Construct microp ile splices to the required design strength. Align casing joints and reinforcing bar splices to avoid eccentricity or angles at splices. Locate threaded pipe casing joints at least two casing outer diameters from bar splices. When multiple bars are used, stagger the bar splices by at least 12 inches. If shown in the plans or approved, weld according to Subsection 551.11(a) .

(c)Grouting. Use a positive displacement grout pump according to Subsection 256.07(b)(1) . Place a neat hydraulic cement grout in one continuous operation. Mix admixtures according to the manufacturer’s r ecommendations. Do not use compressed air to directly pressurize the grout. Grout the micropile the same day the micropile hole is drilled. Inject grout from the lowest point of the drill hole until clean, pure grout flows from the top of the micropile. Grout may be pumped through tremie tubes, hollow stem augers, or drill rods. Ensure complete continuity of the grout column during all phases of grouting and casing extraction. Control the grout pressures and grout takes to prevent excessive heave in cohesiv e soils or fractured formations. Grout the entire pile to the design cut -off level. After grouting is complete, fill the grout tube with grout if the tube will remain in the hole. Ensure grout within the micropiles attains the minimum design strength befor e loading. Observe site conditions in the vicinity of the micropile construction daily . Stop operations and notify the CO if:

(1)Ground heave, subsidence, or grout leakage is observed;

(2)Micropile structure is adversely affected; or

(3)Adjacent structures are damaged from drilling or grouting. Table 567-1

Micropile Construction Tolerances

Micropile Attribute Allowable Variance

Center of micropile < 3 in from indicated plan location or pile spacing Pile-hole alignment ±2% of design alignment Top elevation 0 to 1 in above the design vertical elevation Center of reinforcing bar < 0.75 in from pile center

567.06Testing and Stressing.

(a)Testing equipment. Conform to Subsection 256.08(a) .

(b)Stressing. Place testing equipment over the micropile so that the jack, bearing plates, load cells, and stressing assembly are axially aligned with the micropile and the micropile is centered within the equipment. Do not apply loads greater 80 percent of the structural capacity of the micropile. Place the reference pressure gauge in series with the pressure gauge and jack so they need not be unloaded and repositioned during a test. Raise the load from one increment to another. Hold the load just long enough to measure and record the micropile top movement to the nearest 0.001 inch with respect to an independent fixed reference point. Repump the jack as necessary to maintain a constant load. Monitor the load with a pressure gauge. If the load measured by the pressure gauge and the load measured by the reference pressure gauge differ by more than 10 percent, recalibrate the jack, pressure gauge, and reference pressure gauge.

(1)Verification tests. Perform verification tests at the approved locations. Test under tension according to Tables 567 -2 and 567-4 consistent with AASHTO, LRFD Bridge Design Specifications . Table 567-2

Verification Test Load Schedule

Cycle Load Hold Time (Minutes) 1 AL(1) – 0.075 Factored Design Load (FDL) 4 0.15 FDL 4 0.225 FDL 4 0.30 FDL 4 0.375 FDL 4 2 AL(1) 1 0.15 FDL 1 0.30 FDL 1 0.375 FDL 1 0.45 FDL 4 0.525 FDL 4 0.60 FDL 4 0.675 FDL 4 0.75 FDL 4 3 AL(1) 1 0.30 FDL 1 0.60 FDL 1 0.675 FDL 1 0.75 FDL 1 0.825 FDL 4 0.90 FDL 4 0.975 FDL 60(2) 4 AL(1) 1 0.30 FDL 1 0.60 FDL 1 0.90 FDL 1 0.975 FDL 1 1.05 FDL 4 1.125 FDL 4 1.20 FDL 4 1.275 FDL 4 1.35 FDL 4 1.425 FDL 4 1.50 FDL (Maximum test load) 4 1.20 FDL 4 0.90 FDL 4 0.60 FDL 4 0.30 FDL 4 AL(1) 15

(1)No greater than 4 percent of FDL (0.04 FDL) applied to the pile before setting the movement recording devices. Zero dial gauges after the first setting of AL.

(2)Hold the load to within 2 percent and measure and record pile top movement at 1, 2, 3, 4, 5, 6, 10, 20, 30, 50, and 60 minutes. A verification test is acceptable based on one of the following results:

(a)Total vertical movement does not exceed ⅜ inch under 0.75 FDL. If an AL is used, reduce the allowable movement by multiplying by a factor of (0.75 FDL-AL)/0.75 FDL;

(b)Deflection rate is linear or decreasing and does not exceed 0.040 inch per log cycle time from 1 to 10 minutes or 0.080 inch per log cycle time from 6 to 60 minutes under 0.975 times the FDL; or

(c)Slope of the load versus deflection (at end of increment) curve does not exceed 0.025 inch per kip at each test load increment. If the micropile verification is unacceptable, perform another verification test to establish the cause and make design or construction modi fications. These modifications may include installing replacement test micropiles, modifying the installation methods, increasing the bond length, regrouting with pre -placed re- grout tubes, or changing the micropile type. Submit structure modifications req uiring changes and retest the new system as directed. Submit micropile geometry, construction, testing details, and verification test results for approval before installing production micropiles. Remove verification test micropiles to an elevation 24 inches below finished ground level. If construction methods or foundation material change, perform additional verification tests.

(2)Proof tests. The CO will designate production micropiles for proof testing. Test according to Tables 567-3 and 567-4. A proof test is acceptable based on one of the following results:

(a)Total vertical movement does not exceed ½ inch under 0.75 FDL. If an AL is used, reduce the allowable movement by multiplying by a factor of (0.75 FDL -AL)/0.75 FDL;

(b)Deflection rate is linear or decreasing and does not exceed 0.040 inch per log cycle time from 1 to 10 minutes or 0.080 inch per log cycle time from 6 to 60 minutes under 1.00 times the FDL; or

(c)Slope of the load versus deflection (at end of increment) curve does not exceed 0.025 inch per kip under the maximum test load (1.00 FDL.) If a proof- tested micropile is unacceptable, proof test another micropile in the immediate vicinity. Establish the cause and make design or construction modifications for future piles. Submit structure modifications requiring changes for approval. Table 567-3

Proof Test Load Schedule

Load Minimum Hold Time (Minutes) AL(1) – 0.10 Factored design load (FDL) 4 0.20 FDL 4 0.30 FDL 4 0.40 FDL 4 0.50 FDL 4 0.60 FDL 4 0.70 FDL 4 0.80 FDL 4 0.90 FDL 4 1.00 FDL (Load -hold test) 10(2) 0.75 FDL 4 0.50 FDL 4 0.25 FDL 4 AL(1) 4

(1)No greater than 4 percent of FDL (0.04 FDL) applied to the pile before setting the movement recording devices. Zero dial gauges after the first setting of AL.

(2)Hold the load to within 2 percent and measure and record pile top movement at 1, 2, 3, 4, 5, 6, and 10 minutes. If the movement measured between 1 and 10 minutes exceeds 0.04 inch, continue holding the load and mea sure and record pile movement at 20, 30, 50, and 60 minutes.

567.07Test Results and Reporting. Submit preliminary results to the CO for each micropile tested before testing personnel leave the site at the end of each testing day. Submit detailed verification and proof test load and deflection data in a tabular format within 5 days. Submit a graph that plots total micropile top movement versus load, the A -line, and the B -line. The A -line is defined as 0.8 multiplied by the theoretical free test len gth elastic elongation. The B -line is defined as the theoretical free test length elastic elongation plus 0.50 multiplied by the theoretical bond length elastic elongation. Allow 5 days for the CO to conduct a review of the data and approve micropile insta llation.

567.08Acceptance. See Table 567-4 for sampling, testing, and acceptance requirements. Material for micropiles will be evaluated under Subsections 106.02 and 106.03. Submit a production certification with each shipment of structural steel and casing. Construction of micropiles will be evaluated under Subsections 106.02 and 106.04. Reinforcing steel will be evaluated under Section 554.

Measurement

567.09Measure the Section 567 pay items listed in the bid schedule according to Subsection 109.02 and the following as applicable: When measuring production micropiles by the linear foot, measure from the plan top elevation to the approved tip elevation. Do not measure linear footage for verification tes t piles. Do not measure failed verification or proof tests or additional tests to verify alternative micropile installation methods proposed by the Contractor.

Payment

567.10The accepted quantities will be paid at the contract price per unit of measurement for the Section 567 pay items listed in the bid schedule. Payment will be full compensation for the work prescribed in this Section. See Subsection 109.05 . Table 567-4 Sampling, Testing, and Acceptance Requirements

Material or

Product

(Subsection) Type of

Acceptance

(Subsection) Characteristic Category Test Methods

Specifications Sampling

Frequency Point of

Sampling Split

Sample Reporting

Time Remarks

Mix Design

Neat hydraulic

cement grout (701.04(a)(1) ) Measured & tested for conformance (106.04) All − Subsection

567.04(f) 1 per mix design Source of material If requested Before producing −

Production

Neat hydraulic

cement grout (701.04(a)(1) ) Measured & tested for conformance (106.04 ) Density – AASHTO T 121 1 per 5 piles Mixer No Upon completion of test − Flow – ASTM C939 " Point of discharge " " −

Compressive

strength – ASTM C109 1 set of 3 sample(1) Grout plant " " −

Verification test

micropile " Performance – Subsection 567.06(b)(1) All Installation No 5 days −

Proof test

micropile " Performance – Subsection 567.06(b)(2) 1 in 20 & 1 min per substructure unit " " " −

(1)From each grout plant per day of operation or per five micropiles, whichever occurs more frequently.