Section 256 — Permanent Ground Anchors
Description
256.01This work consists of providing and installing permanent drilled and grouted ground anchors.
Material
256.02Conform to the following Subsections:
Anchor tendons
Galvanized coatings High -strength low- alloy structu Neat hydraulic cement grout Steel pipe 722.02 717.07 ral steel (bearing plates) 717.01(b) (3) 701.04(a) 717.06
Construction Requirements
256.03Qualifications . Provide an engineer or geologist, drill foreperson, and drill operators with experience installing permanent ground anchors. At least 30 days before starting permanent ground anchor work , submit the following for approval:
(a)Drill foreperson . A résumé for each drill foreperson describing at least 2 years’ experience supervising construction of ground anchors of similar lengths and scope to those shown in the plans and in similar geotechnical conditions described in the geotechnical report. Include experience as the direct supervisor responsible for on- site construction operations;
(b)Drill operator. A résumé for each drill operator describing at least 1 year’s experience in the construction of ground anchors;
(c)Professional engineer or geologist. A résumé for a professional engineer or professional geologist with at least 5 years’ experience in the design and construction of ground anchors to log ground anchor installation ; and
(d)Geotechnical engineer or geologist. If applicable, a résumé for a geotechnical engineer or engineering geologist working under the direct supervision of the professional engineer or professional geologist described in Subsection 256.03(c) , to log ground anchor installation. Include at least 2 years ’ experience in the design and construction of ground anchors.
256.04Submittals. At least 30 days before starting ground anchor work, submit the following according to Subsection 104.06:
(a)Start date and schedule;
(b)Method of excavation and ground anchor construction sequence to ensure site safety and maintain slope stability;
(c)Plan and profile drawings showing contractor -located buried utilities according to Subsection 107.02(d) and locations of ground anchors relative to those utilities;
(d)Ground anchor types, sizes, horizontal and vertical spacings, total length and depths, installation angles from horizontal, ultimate tendon strengths for the range of material to be encountered, proposed drill hole diameter and the minimum bond zone length for factored design loads shown in the plans. Include calculations for minimum bond zone lengths;
(e)Tendons, couplers, bearing plates, facing items, and additional hardware with the manufacturer’s SDS, product data sheets, specifications; (f) Manufacturer’s recommendations for tendon and hardware handling, storing, assembly, and working temperature ranges; (g) Grout type, mix design, mixing equipment, placement procedures, and 7 -day grout compressive strength test results; (h) Procedures and material for repairing corrosion protection coatings in the field;
(i)Drilling methods and equipment;
(j)Drill hole diameters to achieve the specified pullout resistance;
(k)Alternative drilling and grouting methods (such as grout additives or pressure grouting);
(l)Additional material needed to achieve required bond capacities (such as grout socks and post -grout tubes); (m) Methods to ensure borehole stability during excavation and grout placement;
(n)Ground anchor testing methods and equipment including type and capacity of reaction load system, drawings, supporting calculations for structural components of the ground anchor load test apparatus, and calculations for soil bearing and settlement below the reaction frame; and
(o)Identification number and calibration te st certification for each jack, pressure gauge, and electronic load cell. Clearly indicate the serial number of each component of the testing assembly on calibration graphs. Submit results from calibration tests conducted by an independent testing laborato ry within the previous 60 days.
256.05Tendon Fabrication.
(a)General. Size tendons to ensure:
(1)The design load is no more than 60 percent of the minimum ultimate tensile strength of the tendon; and
(2)The maximum test load is no more than 80 percent of the minimum ultimate tensile strength of the tendon. Use the anchor tendon type shown in the plans. Protect anchors and the anchor head assembly against corrosion using Class I Corrosion Protection as recommended in PTI, Guide Specification for Post - Tensioning Materials .
(b)Bond length. Determine the bond length necessary to develop the design load shown in the plans. Do not use a bond length less than the minimum bond length shown in the plans. Provide corrosion protection of the tendon bond length with a cement grout cover. Where encapsulation of the tendon is required, protect the tendon bond length from corrosion by encapsulating it in a grout -filled corrugated plastic or deformed steel tube or with a corrosion protection coating according to ASTM A775, A934, A153 or A143. Place the grout inside the tube either before or after the tendon is placed in the drill hole. Centralize the tendon within the tube with at least ⅛ inch grout cover.
(c)Centralizers. Use spacers along the tendon bond length of a multi -element tendon to separate each of the individual elements of the tendon. Use centralizers to ensure at least ½ inch of grout cover over the tendon bond length or tendon bond length encapsulation as appropriate. Use centralizers that do not impede the free flow of grout up the bore hole. Position centralizers no more than 5 feet from the top of the tendon bond length, no more than 12 inches from the bottom of the tendon bond length, and with center -to-center spacing of no more than 10 feet. Centralizers are no t required on hollow -stem -augured tendons if the ground anchor is grouted through the auger and the hole is maintained full of a grout with a slump less than 9 inches during extraction of the auger.
(d)Unbonded length. Provide the unbonded length as shown in the plans.
(1)If the drill hole is grouted in one operation, provide corrosion protection of the unbonded length with a PVC sheath filled with corrosion -inhibiting grease, corrosion- inhibiting grout, or a heat-shrinkable tube internally coated with an elastic adhesive. If grease is used under the sheath, coat the unbonded tendon length, fill spaces between individual elements of multi -element tendon with grease, and provide measures to prevent grease from escaping at the ends of the sheath. If the sheath is gr out filled, provide a separate bond- breaker along the unbonded length of the tendon.
(2)If a grease -filled sheath corrosion protection is provided and the drill hole above the bond length is grouted after the ground anchor is locked off, grout the tendon insi de a second sheath. Where restressable ground anchors are used, provide restressable anchorage compatible with the post-tensioning system provided. If multi- element tendons are used, properly seat the wedges according to the manufacturer’s recommendations for the post -tensioning system provided.
(e)Bearing plates. Size the bearing plates according to the manufacturer’s specifications and ensure:
(1)The bending stresses in the plate do not exceed the yield strength of the steel when a load equal to 95 percent of the minimum specified ultimate tensile strength of the tendon is applied; and (2) The average bearing stress of the bearing plate is no more than recommended in the PTI, Guide Specification for Post- Tensioning Materials . Weld trumpet to bearing plate. Make the inside diameter of the trumpet at least the size of the hole in the bearing plate. Make the trumpet long enough to accommodate movements during stressing and testing. For multiple or single element tendons with encapsulation over the unbounded length, make the trumpet at least 24 inches beyond the structural fascia and soil backslope interface. Fill the trumpet of restressable ground anchors with corrosion -inhibiting grease. Provide a permanent Buna-N synthetic rubber seal between the trumpet and the unbonded length corrosion protection. Fill the trumpets of non -restressable ground anchors with grout after anchor load lock- off is accepted. Provide a 12- inch minimum tightly -fitting temporary seal between the trumpet and the unbonded length corrosion protection.
256.06Handling and Storing Material. Protect ground anchors and tendons from corrosion during the storage, fabrication, and handling before insertion in the borehole. Provide proper care to avoid prolonged exposure to the elements and to avoid mechanical or physical damage which would reduce or impair the future ability of the components to resist corrosive conditions encountered during the service life. Replace tendons exhibiting abrasions, cuts, welds, weld splatter, corrosion, or pitting. Repair or replace tendons exhibiting damage to encapsulation or sheathing. Degrease the bond length of tendons and remove solvent residue before installation.
256.07Installation.
(a)Drilling. Drill ground anchor holes within 12 inches of the required location. Drill the longitudinal axis of the drill hole parallel to the longitudinal axis of the tendon. Install the ground anchor within 3 degrees of the required inclination from horizontal. Install the ground anchor with a horizontal angle within 3 degrees of a line drawn perpendicular to the plane of the structure. Do not extend ground anchors beyond the right -of-way or easement limits as shown in the plans. Do not damage existing utilities in the project site. Insert the tendon in the drill hole to the required total length without driving or forcing. If the tendon cannot be completely inserted, remove the tendon and clean or redrill the hole to allow insertion. Provide a professional engineer or professional geologist to observe advancement of ground a nchors. Record material types, drilling depth of condition and material changes, drilling down- force pressure, production rates, and estimated water flows encountered during drilling. Submit drill logs to the CO at the end of each shift.
(b)Grouting .
(1)Equipment. Use a positive displacement grout pump equipped with a pressure gauge able to measure pressures of at least 150 pounds per square inch or twice the required grout pressure, whichever is greater. Provide a secondary pressure capability of at least 1000 pounds per square inch to clean out grout or dirt blockages in hoses, tremie tubes, or casings. Use a high speed, high shear grout mixer with a minimum operating speed of 1500 revolutions per minute to produce a well-mixed grout that is free of lumps or other indications of prior cement hydration. Provide holding tanks with a variable speed high- efficiency paddle that maintains a thoroughly mixed grout for pumping.
(2)Procedures. Grout tendons into drill holes using a neat hydraulic cement grout placed in on e continuous operation. Inject the grout from the lowest point of the drill hole. The grout may be placed either before or after insertion of the tendon. Record the quantity of the grout and the grout pressure for each ground anchor. Control the grout pres sures to avoid excessive heaving or fracturing. Inject grout within 45 minutes of adding the cement to the water or within 15 minutes after mixing when the ambient temperature is 90 °F or higher. Do not allow the grout temperature to exceed 90 °F. Except as indicated below, the grout above the top of the bond length may be placed at the same time as the bond length grout, but do not place it under pressure. Do not place grout at the top of the drill hole in contact with the back of the structure or the bottom of the trumpet. Use pressure grouting for grout protected tendons anchored in rock. After sealing the drill hole, pressure inject grout until a 50- pound per square inch grout pressure at the top of the drill hole is maintained for 5 minutes.
(c)Finishing. After grouting of tendon is complete, fill the grout tube with grout if it will remain in the hole. Wait at least 3 days before loading the tendon. Extend the corrosion protection surrounding the unbonded length up beyond the bottom seal of the trumpet or 12 inches into the trumpet if no trumpet seal is provided. Trim the corrosion protection surrounding the tendon so it does not contact the bearing plate of the anchor head during testing and stressing. Place the bearing plate and anchorhead so the axis of the tendon is within three degrees of perpendicular to the bearing plate and the axis of the tendon passes through the center of the bearing plate without bending the tendon. If grout protected tendons or corrosion protection coated encapsulations are used, electronically isolate the bearing plate, anchorhead, and trumpet from the surrounding concrete, soldier pile, or metallic element embedded in the structure. Place trumpet grease during construction. Place trumpet grout after the ground anchor has been t ested and stressed. Completely cover anchorages permanently exposed to the atmosphere with a corrosion-inhibiting grease or grout. Inspect the trumpet and anchorage grout levels 24 hours after initial grout placement. If needed, refill the trumpet or anchorage with grout.
256.08Testing and Stressing.
(a)Testing equipment. Conform to the following:
(1)Dial gauges. Use two dial gauges that can measure to 0.001 inch and has sufficient travel to measure the theoretical elastic elongation of the total length at the m aximum test load without resetting, accounting for elongation in both the bonded and unbonded zones. Align the gauges parallel to the axis of the anchor or pile and support the gauges independently from the hydraulic jack, ground anchor, or reaction frame.
(2)Hydraulic jack, pressure gauge, and load cell. Apply test loads with a hydraulic jack and measure with a calibrated pressure gauge and electronic load cell. Use a hydraulic jack and pressure gauge with a pressure range no more than twice the anticipated m aximum test pressure and calibrated as a unit by an independent firm within 90 days of the start of work. Use a pressure gauge graduated in 100 -pound per square inch increments or less. Use a jack with ram travel sufficient to allow testing without resetting.
(3)Reference gauge. Calibrate the reference gauge with the test jack and pressure gauge. Keep the reference gauge at the project site. (4) Reaction frame. Provide a reaction frame designed by a professional engineer to meet the requirements of the site, resis t the maximum test loads, and prevent excessive deformation of the bearing surface.
(b)Stressing. Place testing equipment over the ground anchor tendon to ensure the jack, bearing plates, load cells, and stressing assembly are axially aligned with the tendon and the tendon is centered within the equipment. Do not apply loads greater than 80 percent of the minimum ultimate tensile strength of the tendon. Place the reference pressure gauge in series with the pressure gauge, jack, and load cell 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 ground anchor movement to the nearest 0.001 inch with respect to an independent fixed reference point. Re pump 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. Monitor the pile during stressing of ground anchor tendons. Immediately stop the test if the pile deflects more than 1 inch inward. Provide certified calibrations for torque wrenches, hydraulic jacks, and related equipment dated no more than 90 days before use on the project. Verify the calibration of torquing or jacking equipment upon request.
(1)Performance tests. Performance tests include the installation of the sacrificial ground anchor. The CO will designate locations for sacrificial ground anchors for performance tests. Test according to Tables 256-1 and 256-2. Table 256-1
Performance Test Load Sequence
Test
Sequence Test Load Increment
AL(1) 0.25FDL(2) 0.50FDL(2) 0.75FDL(2) 1.00FDL(2) (Load -Hold Test) Adjust to
Lock -Off
Load
1 Yes Yes – – – – 2 Yes Yes Yes – – – 3 Yes Yes Yes Yes – – 4 Yes Yes Yes Yes 10 minutes(3) – 5 Yes – – – – Yes
(1)AL = Alignment load (no greater than 5 percent of F DL (0.05FDL) applied to the ground anchor before setting the movement recording devices. Zero dial gauges after the first setting of AL).
(2)FDL = Factored design load.
(3)Hold the load to within 2 percent and measure and record the ground anchor movement during the load-hold test at 1, 2, 3, 4, 5, 6, and 10 minutes. When t he ground a nchor movement between 1 minute and 10 minutes exceeds 0.04 inch, maintain the maximum test load an additional 50 minutes and record the movement at 20, 30, 40, 50, and 60 minutes.
(2)Proof tests. Test according to Tables 256-2 and 256 -3. Table 256-2
Proof Test Load Sequence
Test
Sequence Test Load Increment
AL(1) 0.25FDL(2) 0.50FDL(2) 0.75FDL(2) 1.00FDL(2) (Load -Hold Test) Adjust to
Lock -Off
Load
1 Yes Yes Yes Yes 10 minutes(3) – 2 Yes – – – – Yes
(1)AL = Align ment load. See alignment load note in Table 256-1 .
(2)FDL = Factored design load.
(3)Hold the load to within 2 percent and measure and record the ground anchor movement during the load-hold test at 1, 2, 3, 4, 5, 6, and 1 0 minutes. When the ground anchor movement between 1 minute and 10 minutes exceeds 0.04 inch, maintain the maximum test load an additional 50 minutes, recording movement a t 20, 30, 40, 50, and 60 minutes.
(c)Lock -off. Adjust the load to the specified lock- off load shown in the plans and transfer the load to the anchorage device. After transferring the load and before removing the jack, measure the l ift-off load. If the load is not within 10 percent of the specified lock -off load, reset the anchorage and remeasure the lift -off load. Repeat as necessary.
256.09Test Results and Reporting. Identify each ground anchor with a letter and a number based on the row and level respectively. Submit a plan sheet of the wall elevation with the proposed ground anchor identification methodology showing the row letter and level number. Plot the ground anchor movement versus the maximum load for each test sequence as shown in Tables 256 -1 and 256-2 and plot the residual movement of the tendon at each alignment load versus the highest previously applied load. Provide preliminary results to the CO for each ground anchor 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 ground anchor head movement versus load, the A -line, and the B -line. The A -line is defined as 0.8 multiplied by the theoretical free test length elastic elongation. The B- line is defined as the theoretical free test length elastic elongation plus 0.50 multiplied by the theoretical bonded length elastic elongation. Allow 5 days for the CO to conduct a review of the data and approve ground anchor installation. Replace ground anchors with unacceptable performance or proof test results. Do not retest failed ground anchors unless post-grouting has been performed.
256.10Acceptance. See Table 256-3 for sampling, testing, and acceptance requirements. Material for ground anchors will be evaluated under Subsections 106.02 and 106.03. Submit a production certification for the ground anchor material. Construction of ground anchors will be evaluated under Subsections 106.02 and 106.04. Installed ground anchors will be evaluated based on one of the following performance or proof test results:
(a)After a 10 -minute hold, the ground anchor carries the maximum test load with less than 0.04 inch of movement between 1 and 10 minutes and th e total movement at the maximum test load exceeds 80 percent of the theoretical elastic elongation of the unbonded length.
(b)After a 60 -minute hold, which is only conducted after 10- minute hold test fails, the ground anchor carries the maximum test load with a movement rate that does not exceed 0.08 inch per log cycle of time and the total movement at the maximum test load exceeds 80 percent of the theoretical elastic elongation of the unbonded length.
Measurement
256.11Measure the Section 256 pay items listed in the bid schedule according to Subsection 109.02 and the following as applicable: Do not measure linear footage or quantity of sacrificial ground anchors. Do not measure failed performance tests. Do not measure anchors that failed proof testing.
Payment
256.12The accepted quantities will be paid at the contract price per unit of measurement for the Section 256 pay items listed in the bid schedule. Payment will be full compensation for the work prescribed in this Section. See Subsection 109.05 . Table 256-3 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
Source
Aggregate
quality (fine) (703.01 ) Measured & tested for conformance (106.04 & 105) Quality – AASHTO M 6 1 per material type Source of material Yes Before producing –
Mix Design
Neat
hydraulic cement grout(1) (701.04(a) ) Measured & tested for conformance (106.04 ) Flow – ASTM C939 1 per mix design " Yes, if requested " –
Compressive
strength (7-day) – AASHTO T 106 ASTM C109 " " " " –
Production
Performance
test ground anchor Measured & tested for conformance (106.04) Deformation – Subsection
256.08(b)(1) 5% or 3 minimum Installation No 5 days –
Proof test
ground anchor " " – Subsection
256.08(b)(2) Each anchor " " " –
(1)Make grout cubes for testing from random batches of grout as directed. Normally, strength testing for permanent ground anchors will not be required as system performance will be measured by load holding each anchor. Grout cube testing will be required if a dmixtures are used or irregularities occur in anchor testing.