643Ground Anchors

643.01.01 General. This work consists of constructing ground anchors for retaining walls.

643.01.02 Qualifications. Prepare a project reference list verifying the successful construction completion of

at least 6 permanent ground anchor retaining wall projects during the past 3 years totaling at least 250 ground anchors. Include a brief description of each project including the location, number of anchors, and the Owner’s name, address, and current phone number. Provide a Nevada Registered Professional Engineer, employed by the ground anchoring Contractor and having experience in the construction of ground anchor retaining walls on at least 6 completed projects during the past 3 years, to supervise the work and pr epare submittals. Consultants or manufacturer’s representatives will not be allowed to satisfy the aforementioned requirement. Use an on- site supervisor and drill rig operators having experience installing ground anchors on at least 4 projects over the pas t 2 years. Prepare a personnel qualifications list containing a summary of each individual’s experience and the respective projects.

643.01.03 Submittals. Submit 5 copies of the following information for review and approval at least 30 days

prior to begin ning wall construction:

643.02.01 General. Materials shall conform to the following Sections:

Portland Cement ...................................................................................................................................................................... Section 701 Concrete Curing Materials and Admixtures ................................ .............................................................................................. Section 702 Water ................................ ................................ ....................................................................................................................... Section 722 Fabricate ground anchor tendons from single steel bars conforming to AASHTO M275, or from single or multiple elements of prestressing strands conforming to AASHTO M203 or ASTM A886. Steel bar couplers shall be capable of developing 100% of the minimum specified ultimate tensile strength of the steel bar. Steel strands shall be continuous with no spli ces, unless approved. Provide centralizers at maximum intervals of 3 m (10 ft) with the deepest centralizer located 0.3 m (1 ft) from the end of the anchor and the upper centralizer for the bond zone located no more than 1.5 m (5 ft) from the top of the tendon bond length. Use spacers to separate the steel strands of strand tendons. Spacers shall be placed at maximum intervals of 3 m (10 ft) and may be combined with centralizers. Fabricate centralizers and spacers from plastic, steel, or other material w hich is nondetrimental to the prestressing steel. Wood centralizers or spacers will not be allowed. Design centralizers to support the tendon in the drill hole. Position the tendon so a minimum of 13 mm (1/2 in.) of grout cover is provided and to permit gr out to freely flow around the tendon and up the drill hole. Centralizers are not required on pressure injected anchors installed in coarse grained soils when the grouting pressure exceeds 1 MPa (150 psi), nor on hollow stem -augered anchors when they are grouted through the auger with grout having a slump of 225 mm (9 in.) or less. Stressing anchorages shall be a combination of either a steel bearing plate with wedge plate and wedges, or a steel bearing plate with a threaded anchor nut. The steel bearing and wedge plate may also be combined into a single element. Anchorage devices shall be capable of developing 95% of the specified mi nimum ultimate tensile strength of the prestressing steel tendon. The anchorage devices shall conform to the static strength requirements of Section 3.1.6 (1) and Section 3.1.8 (1) and (2) of the latest edition of the PTI “Post Tensioning Manual.” All of the tendon bond length shall be free of dirt, manufacturers’ lubricants, corrosion- inhibitive coatings, or other deleterious substances. Fabricate trumpets from steel pipe conforming to ASTM A53, Schedule 40. Trumpets shall have a minimum wall thickness of 5 mm (0.20 in.) and shall be a minimum of 38 c m (15 in.) in length. Fabricate bearing plates from steel conforming to A ASHTO M270 Grade 250 (36) minimum or equivalent. Weld the trumpet to the bearing plate and galvanize according to ASTM A153. Design wedges to preclude premature failure of the prestressing steel due to notch or pinching effects under static and dynamic strength requirements of Section 3.1.6 (1) and Section 3.1.8 (1) and 3.1.8 (2) of the latest edition of the PTI “Post Tensioning Manual.” Do not reuse wedges. Provide grout tubes with an adequate inside diameter to enable the grout to be pumped to the bot tom of the drill hole. Grout tubes shall be strong enough to withstand a minimum grouting pressure of 1 MPa (150 psi). Postgrout tubes shall be strong enough to withstand postgrouting pressures. GROUND ANCHORS 643 Bondbreaker shall be fabricated from smooth plastic tube or pipe and shall enable the tendon to elongate during testing and stressing and allow the tendon to remain unbonded after lock -off. The material shall be nondetrimental to the tendon and capable of withstanding abrasion, impact, and bending during handling and installation. Use material resistant to aging by ultra- violet light and resistant to chemical attack from aggressive environments, grout, and corrosion inhibiting compounds. Corrosion inhibiting compound placed in the free length area shall be an organic compound with the appropriate polar moisture displacing, corrosion inhibiting additives and self -healing properties. The compound shall permanently stay viscous and be chemically stable and nonreactive wi th the prestressing steel, the sheathing material, and the anchor grout. Grout shall be neat Type V cement and water and shall be stable (bleed less than 2%), fluid, and provide a minimum compressive strength of at least 21 MPa (3,000 psi) at time of stressing. Admixtures which control bleed, improve flowability, reduce water content, and retard set may be used in the grout subject to review and approval. Accelerators will not be permitted. Expansive admixtures may only be added to the grout used for fill ing sealed encapsulations, trumpets, and anchorage covers. Use admixtures compatible with the prestressing steels. Mix in accordance with the manufacturer’s recommendations.

643.02.02 Corrosion Protection. (a) Tendon Bonded Length Protection. Provide a gr out-filled corrugated

plastic encapsulation for tendon bond length protection. For bars, the prestressing steel shall be grouted inside the encapsulation prior to inserting the tendon into the drill hole. Perform pregrouting of encapsulated tendons on an inclined, rigid frame or bed by injecting the grout from the low end of the tendon. Fabricate tendon bonded length encapsulations from one of the following:

643.03.01 General. Select the type of tendon to be used. Size the tendon so the design load does not

exceed 60%, the maximum test load does not exceed 80%, and the lock -off load does not exceed 70% of the specified minimum tensile strength of the prestressi ng steel. Determine the hole diameter and the bond length necessary to develop the design load specified on the plans. The minimum bond length shall be 4.5 m (15 ft) for strand tendons in rock and 3 m (10 ft) for bar tendons in rock. The minimum bond length shall be 4.5 m (15 ft) for strand and bar tendons in soil. The minimum unbonded length shall be as shown on the plans.

643.03.02 Construction Site Survey . Field locate and verify the location of all utilities prior to starting the

work. Maintain un interrupted service for those utilities designated to remain in service throughout the work. Give notification of any utility locations different from that shown that may require anchor relocations or wall design modification. Prior to start of any wall construction activity, inspect the site to observe and document the pre- construction condition of the site, existing structures, and facilities. During construction, observe the conditions above the wall on a daily basis for signs of ground movement in the vicinity of the wall. Immediately give notification if signs of movements such as new cracks in structures, increased size of old cracks, or separation of joints in structures, foundations, streets, or paved and unpaved surfaces are observed.

643.03.03 Excavation. Coordinate the work and the excavation so the wall is safely constructed. Perform the

wall construction and excavation sequence as shown and according to the approved submittals. Do not excavate above or below the wall steeper than shown on the plans without written approval. Provide survey reference and control points at or offset along the top of wall alignment at approximate 10 m (30 ft) intervals prior to starting wall excavation. Be responsible for providing the necessary survey and alignm ent control during excavation of each lift, locating and drilling each drillhole within the allowable tolerances, and for performing the wall excavation and anchor installation in a manner which will allow for constructing the finish cast - in-place structur al facing to the specified minimum thickness and to the line and grade as indicated. Complete excavation and grading above and behind the wall before commencing wall excavation. Do not over-excavate the original ground behind the wall or at the ends of t he wall, beyond the limits shown. Do not perform excavation that will affect the wall until wall construction starts. GROUND ANCHORS 643 Excavate to the final wall face using procedures that: prevent over excavation; prevent ground loss, swelling, air slaking, or loosening; prevent loss of support for completed portions of the wall; prevent loss of soil moisture at the face; and prevent ground freezing. Give notification immediately if raveling or local instability of the final wall face excavation occurs. Temporarily stabi lize unstable areas by means of buttressing the exposed face with an earth berm or other methods. Suspend work in unstable areas until remedial measures are developed. If sections of the wall are to be constructed at different times, prevent sloughing or failure of the temporary slopes at the end of each wall section. Remove all or portions of cobbles, boulders, rubble, or other subsurface obstructions encountered at the wall final excavation face which protrude into the wall facing. Determine the method of removal of face protrusions, including method to safely secure remnant pieces left behind the excavation face and for promptly backfilling voids resulting from removal of protrusions extending behind the excavation face. Backfill voids, overbreak, or over-excavation beyond the plan wall excavation line resulting from the removal of face protrusions or excavation operations.

643.03.04 Drilling. Select a drilling method to establish a stable hole of adequate dimensions within the

tolerances specified. The drill bit or casing crown shall not be more than 3 mm (1/8 in.) smaller than the specified hole diameter. At the ground surface, locate the drill hole within 300 mm (12 in.) of the location shown. Select drilling equipment and methods suitable for the ground conditions. If encountered, engineered fill may be non- cohesive and require casing during drilling operations. Cobbles and/or boulders may be encountered in the engineered fill. Use of drilling muds such as bentonite slurry to assist in drill cuttin g removal will not be allowed. Air may be used to assist in drill cutting removal. If caving ground is encountered, use cased drilling methods to support the sides of the drillholes. Remove casings prior to, or during, the grouting operation. When drilling through rock, cobbles, boulders, or obstructions, use percussion or other suitable drilling equipment capable of drilling and maintaining stable drillholes through such materials. Clean holes to remove material resulting from the drilling operations and any other material that would impair the strength of the anchors. The use of water for cleaning holes will not be permitted. Do not install anchors in the drilled holes until the holes have been inspected and approval is given. Remove foreign material disl odged or drawn into the holes during construction of the assemblies. Immediately suspend drilling operations if ground subsidence is observed, the wall is adversely affected, or adjacent structures are damaged from the drilling operation. Immediately stab ilize the adverse conditions, make necessary repairs, and modify drilling operations prior to resuming drilling.

643.03.05 Tendon Placement. Place tendons as specified herein and as recommended by the manufacturer.

Inspect each anchor tendon before installation into the drill hole or casing. Repair damage to the corrosion protection system, or replace the tendon if not repairable. Reconnect loose spacers or centralizers to prevent shifting during insertion. Check un- cased drill holes for cleanliness prior to insertion of the tendon. Insert the tendon into the drill hole to the desired depth without difficulty and in a way that prevents damage to the drill hole, sheathing, coating, grout tubes, tendon, or corrosion protection. The bottom end of the t endon may be fitted with a cap or bullnose to aid its insertion into the hole, casing, or sheathing. Do not drive or force partially inserted tendons into the hole. Remove tendons which cannot be fully inserted to the required depth and clean the drill hol e to allow unobstructed installation. Do not extend anchors beyond the right -of-way or easement limits shown. Install anchors to plan location within the following tolerances: Anchor Head Location, deviation in any direction ................................ ............................................................................... 300 mm (12 in.) Anchor Inc lination ................................ ................................ .................................................................................................... ± 3 degrees Anchor Location, deviation from center of drill hole ................................ ................................ ................................ ................ 25 mm (1 in.) Replace anchors which do not satisfy the specified tolerances. Backfill abandoned drill holes with tremied grout. 643 GROUND ANCHORS

643.03.06 Grouting. Use grout equipment which produces a uniformly mixed grout, free of lumps and

undispersed cement, and capable of continuously agitating the mix. Use a positive displacement grout pump equipped with a pressure gauge which can measure at least twice but no m ore than three times the intended grout pressure. Size the grouting equipment to enable the entire anchor to be grouted in one continuous operation. Inject the grout from the lowest point of the drill hole. The grout may be pumped through grout tubes, casing, hollow -stem -augers, or drill rods. Place grout after insertion of the tendon. Record the quantity of the grout and the grout pressures. Control the grout pressures and grout takes to prevent excessive heave or fracturing. After the tendon is installed, the drill hole may be filled in one continuous grouting operation except that pressure grouting shall not be used in the free length zone. The grout at the top of the drill hole shall not contact the back of the structure or the bottom of the trumpet . If the ground anchor is installed in a fine- grained soil using drill holes larger than 150 mm (6 in.) in diameter, place the grout above the top of the bond length after the ground anchor has been tested and stressed. If approved, grouting the entire dr ill hole at the same time may be allowed if it can be demonstrated that the ground anchor system does not derive a significant portion of its load carrying capacity from the soil above the bond length portion of the ground anchor. Utilize pressure grouting techniques if grout protected tendons are used for ground anchors anchored in rock. Pressure grouting requires that the drill hole be sealed and that the grout be injected until a minimum 0.35 MPa (50 psi) grout pressure, measured at the top of the drill hole, can be maintained on the grout for at least 5 minutes. The grout tube may remain upon completion of grouting if the tube is filled with grout.

643.03.07 Anchorage Installation. Install the anchor bearing plate and the anchor head or nut perpendicular

to the tendon, within ± 3 degrees, and centered on the bearing plate without bending or kinking of the prestressing steel elements. Wedge holes and wedges shall be free of rust, grout, and dirt. Clean and protect the stressing tail from dam age until final testing and lock -off. After the anchor has been accepted, cut the stress tail to its final length according to the tendon manufacturer’s recommendations. Perform cutting with an abrasive saw or other approved equipment.

643.03.08 Stressin g Equipment. Use a dial gauge or vernier scale capable of measuring to the nearest

0.025 mm (0.001 in.) to measure the ground anchor movement. The measuring device shall have a minimum travel equal to the theoretical elastic elongation of the total anchor length at the maximum test load and shall have adequate travel so the ground anchor movement can be measured without resetting the device at an interim point. Use a hydraulic jack and pump to apply the test load. Use the jack and a calibrated primary pres sure gauge to measure the applied load. The jack and primary pressure gauge shall be calibrated as a unit within an accuracy of ± 2%. Have the calibration certificate and graph available on site at all times. The calibration shall be traceable to the Natio nal Institute of Standards and Technology or CALTRANS. The calibration shall have been performed within 60 days of the date when the calibration submittals are provided. Do not commence testing until the calibration has been approved. The primary pressur e gauge shall be graduated in 0.7 MPa (100 psi) increments or less. The stressing equipment shall be capable of measuring and maintaining the hydraulic pressure within 0.35 MPa (50 psi). The ram travel shall be at least 150 mm (6 in.). If elongations great er than 150 mm (6 in.) are required, restroking will be allowed. Have a calibrated reference pressure gauge at the site to periodically check the production primary pressure gauge. The reference gauge shall be calibrated with the test j ack and primary pre ssure gauge. GROUND ANCHORS 643 Provide an electrical resistance load cell and readout to be used when performing an extended creep test. Place the stressing equipment over the ground anchor tendon in such a manner that the jack, bearing plates, load cells and stressing anc horage are axially aligned with the tendon and the tendon is centered within the equipment. Select the stressing equipment and determine the sequence of stressing and the procedure to be used for each stressing operation at the planning stage of the project. Use the equipment in strict accordance with the manufac turer’s operating instructions. Provide stressing equipment capable of stressing the whole tendon in one stroke to the specified test load and stressing the tendon to the maximum specified test load within 75% of the rated capacity. Use a pump capable of applying each load increment in less than 60 seconds. The equipment shall permit the tendon to be stressed in increments so that the load in the tendon can be raised or lowered in accordance with the test specifications and allow the anchor to be lift -off tested to confirm the lock-off load.

643.03.09 Load Testing Setup. Dial gauges shall bear on the pulling head of the jack and their stems shall

be coaxial with the tendon direction. The gauges shall be supported on an independent, fixed frame, such as a tripod, which will not move as a result of stressing or other construction activities during the operation. Prior to setting the dial gauges, accurately place the Alignment Load (AL) on the tendon. The magnitude of the AL depends on the type and length of the tendon. Avoid regripping of strands, which would cause overlapping wedge bites or wedge bites on the tendon below the anchor head. Stressing and testing of multiple element tendons wi th single element jacks will not be permitted. Do not begin stressing before the grout has cured for a minimum of 3 days and has reached a minimum compressive strength of 21 MPa (3,000 psi).

643.03.10 Performance Tests. Conduct performance tests on the ground anchors designated on the plans in

accordance with the procedures described below. Conduct all performance tests prior to proof tests. Proof test the remaining ground anchors in accordance with Subsection 643.03.11. Do not apply a load greater than 10% of the design load to the ground anchor prior to testing. Apply the test load simultaneously to the entire tendon. Stressing of single elements of multi -element tendons will not be permitted. Conduct the performance test by incrementally loading and unloading the ground anchor in accordance with the schedule below. Raise the load from one increment to another immediately after recording the ground anchor movement. Measure and record the ground anchor movement to the nearest 0.025 mm (0.001 in.) wit h respect to an independent fixed reference point at the alignment load and at each increment of load. Monitor the load with the primary pressure gauge. Place the reference pressure gauge in series with the primary gauge during each performance test. If the load determined by the reference pressure gauge and the load determined by the primary pressure gauge differ by more than 10%, recalibrate the jack, primary pressure gauge, and reference pressure gauge. At load increments other than the maximum test l oad, hold the load just long enough to obtain the movement reading. Hold the maximum test load in a performance test for 10 minutes. Use a load cell to monitor small changes in load during constant load- hold periods. 643 GROUND ANCHORS Performance Test Schedule Step Loading Applied Load Record and Plot Record and Plot Calculate Elastic Total Movement, δ ti Residual Movement, δ ri Movement, δ ei 1 AL 2 Cycle 1 0.25DL ............................. δt1 AL ................................ ................................ ................... δr1 .............................. δt1 - δr1 = δ e1 3 Cycle 2 0.25DL .............................. δ2 0.50DL ............................. δt2 AL ................................................................................... δr2 .............................. δt2 - δr2 = δ e2 4 Cycle 3 0.25DL .............................. δ3 0.50DL .............................. δ3 0.75DL ............................. δt3 AL ................................................................................... δr3 .............................. δt3 - δr3 = δ e3 5 Cycle 4 0.25DL .............................. δ4 0.50DL .............................. δ4 0.75DL .............................. δ4 1.00DL ............................. δt4 AL ................................ ................................ ................... δr4 .............................. δt4 - δr4 = δ e4 6 Cycle 5 0.25DL .............................. δ 0.50DL .............................. δ5 0.75DL .............................. δ5 1.00DL .............................. δ5 1.2DL .............................. δt5 AL ................................ ................................ ................... δr5 .............................. δt5 - δr5 = δ e5 7 Cycle 6 0.25DL .............................. δ6 0.50DL .............................. δ6 0.75DL .............................. δ6 1.00DL .............................. δ6 1.2DL ............................... δ6 1.33DL ............................ δt6 * AL ................................................................................... δr6 .............................. δt6 - δr6 = δ e6 * Zero reading for creep test. Hold load for 10 minutes while recording movement at specified times. If the total movement measured during the load hold exceeds the specified maximum value then the load hold shall be extended to a total of 60 minutes. AL = Alignment Load, DL = Design Load, δ i = Total movement at a load other than the maximum for cycle i, i = Number identifying a specific load cycle. Adjust the jack as necessary in order to maintain a constant load. Start the load -hold period as soon as the maximum test load is applied and measure and record the ground anchor movement, with respect to a fixed reference at 1, 2, 3, 4, 5, 6, and 10 minutes. If the ground anchor movement between 1 minute and 10 minutes exceeds 1 mm (0.04 in.), hold the maximum test load for an additional 50 minutes. If the load hold is extended, record the ground anchor movement at 15, 20, 30, 40, 50, and 60 minutes.

643.03.11 Proof Tests. Proof test each ground anchor. Do not apply a load greater than 10% of the design

load to the ground anchor prior to testing. Apply the test load simultaneously to the entire tendon. Stressing of single elements of multi -element tendons will not be permitted. Perform the proof test by incrementally loading the ground anchor in accordance with the schedule below. Raise the load from one increment to another immediately after recording the ground anchor movement. Measure and record the ground anchor movement to the nearest 0.025 mm (0.001 in.) with respect to an independent fixed reference point at the alignment load and at each increment of load. Monitor the load with the primary pressure gauge. At load increments other than the maximum test load, hold the load just long enough to obtain the movement reading. Proof Test Schedule Step Load 1 ................................ ......................................................... AL 2 ................................ ................................ ...................... 0.25DL 3 ................................ ................................ ...................... 1.50DL 4 ................................ ................................ ...................... 0.75DL 5 ................................ ................................ ...................... 1.00DL 6 ................................ ................................ ...................... 1.20DL 7 ................................ ................................ ...................... 1.33DL 8 ................................ ................................ .......... Reduce to lock -off load 9 ................................ ................................ .................. AL (optional) 10 .......................................................................... Adjust to lock -off load GROUND ANCHORS 643 Hold the maximum test load in a proof test for 10 minutes. Adjust the jack as necessary in order to maintain a constant load. Start the load- hold period as soon as the maximum test load is applied and measure and record the ground anchor movement with respect to a fixed reference at 1, 2, 3, 4, 5, 6, and 10 minutes. If the ground anchor movement between 1 minute and 10 minutes exceeds 1 m m (0.04 in.), hold the maximum test load for an additional 50 minutes. If the load hold is extended, record the ground anchor movements at 15, 20, 30, 40, 50, and 60 minutes.

643.03.12 Extended Creep Tests. The ground anchors to be creep tested will be selected.

Conduct the extended creep test by incrementally loading and unloading the ground anchor in accordance with step 7 of the performance test schedule in Subsection 643.03.10. At the end of each load increment, hold the load constant for the observ ation period indicated in the schedule below. The times for reading and recording the ground anchor movement during each observation period shall be 1, 2, 3, 4, 5, 6, 10, 15, 20, 25, 30, 45, 60, 75, 90, 100, 120, 150, 180, 210, 240, 270, and 300 minutes as appropriate for the load increment. Start each load- hold period as soon as the test load is applied. In an extended creep test, use the primary pressure gauge and reference pressure gauge to measure the applied load and use the load cell to monitor small changes in load during constant load- hold periods. Adjust the jack as necessary in order to maintain a constant load. Plot the ground anchor movement and the residual movement measured in an extended creep test. Plot also the creep movement for each load hold as a function of the logarithm of time. Extended Creep Test Schedule Load Observation Period, M inutes AL ......................................................................................... --- 0.25DL ................................ ................................ ..................... 10 0.50DL ................................ ................................ ..................... 30 0.75DL ................................ ................................ ..................... 30 1.00DL ................................ ................................ ..................... 45 1.20DL ................................ ................................ ..................... 60 1.33DL ................................ ................................ .................... 300

643.03.13 Ground Anchor Acceptance. A performance tested or proof tested ground anchor with a 10

minute load hold will be considered acceptable if the ground anchor resists the maximum test load with less than 1 mm (0.04 in.) of movement between 1 minute and 10 minutes and the total elastic movement at the maximum test load exceeds 80% of the theoretical elastic elongation of the unbonded length. A performance tested or proof tested ground anchor with a 60 minute load hold will be considered acceptable if the ground anchor resists the maximum test load wi th a creep rate that does not exceed 2 mm (0.08 in.) in the last log cycle of time (between the reading at 6 and 60 minutes) and the total elastic movement at the maximum test load exceeds 80% of the theoretical elastic elongation of the unbonded length. A ground anchor subjected to extended creep testing will be considered acceptable if the ground anchor resists the maximum test load with a creep rate that does not exceed 2 mm (0.08 in.) in the last log cycle of time (between the reading at 30 and 300 minutes) and the total elastic movement at the maximum test load exceeds 80% of the theoretical elastic elongation of the unbonded length. The maximum acceptable test load with respect to creep shall correspond to that where acceptable creep movements are measured over the final log cycle of time. The initial lift -off reading shall be within ± 5% of the designed lock -off load. If this requirement is not met, adjust the tendon load accordingly and repeat the initial lift -off reading. Anchors that do not satisfy the minimum apparent free length criteria shall be either rejected and replaced or locked off at not more than 50% of the maximum acceptable load attained. Submit proposed procedures for obtaining the required remaining load. Regroutable anchors whi ch satisfy the minimum apparent free length criteria but which fail the extended creep test at the test load may be postgrouted and subjected to an enhanced creep criterion. This enhanced criterion requires a creep movement of not more than 1 mm (0.04 in.) between 1 and 60 minutes at test load. Anchors which satisfy the enhanced creep criterion shall be locked off at the design lock -off load. Anchors which cannot be postgrouted or regroutable anchors that do not satisfy the enhanced creep criterion shall be either rejected or locked off at 50% of the maximum acceptable test load attained. Submit proposed procedures for obtaini ng the required remaining load. 643 GROUND ANCHORS In the event that an anchor fails, modify the design and/or construction procedures. The modifications may include, but are not limited to, installing additional anchors, changing the installation methods, reducing the anchor design load by increasing the number of anchors, increasing the anchor length, changing the anchor type, or post -grouting. Submit a description of any proposed modifications for review and approval. Do not implement proposed modifications until receiving written approval.

643.03.14 Anchor Lock- Off. The magnitude of the lock -off load will be specified on the plans. After testing

has been completed, the load in the tendon shall be such that after seating losses, the specified lock -off load has been applied to the anchor tendon. For single or multiple elements of prestressing strands, seat the wedges at a minimum load of 50% F pu. If the lock-off load is less than 50% F pu, use shims under the wedge plate and seat the wedges at 50% F pu. Remove the shims under the wedge plate to reduce the load in the tendon to the desired lock -off load. After transferring the load to the anchorage, and prior to removing the jack, conduct a lift -off test to confirm the magnitude of the load in the anchor tendon. This load is determined by reapplying load to the tendon to lift off the wedge plate, or anchor nut, without unseating the wedges, or turning the anchor nut. METHOD OF MEASUREMENT

643.04.01 Measurement. Ground anchors , performance tests , and extended creep tests will be measured by

the each. BASIS OF PAYMENT

643.05.01 Payment. The accepted quantities, measured as provided above, will be pai d for at the contract

price per unit of measurement for the pay items listed below that are shown in the proposal. Payment will be full compensation for the work prescribed in this Section. Payment will be made under: Pay Item Pay Unit Ground Anchor ................................ ................................ .................................................................................................................. Each Performance Test ................................ ................................ .............................................................................................................. Each Extended Creep Test ................................ ................................ ......................................................................................................... Each SECTION 644 SOIL NAIL RETAINING WALLS DESCRIPTION

644.01.01 General. This work consists of constructing soil nail retaining walls. Perform soil nail construction

concurrently with pneumatically placed concrete mortar as specified in Section 660.

644.01.02 Qualif ications . Prepare a project reference list verifying the successful construction completion of

at least 4 permanent soil nail retaining wall projects during the past 2 years totaling at least 1,000 m2 (1,200 yd2) of wall face area and at least 500 permanent soil nails. Include a brief description of each project with the Owner's name and current phone number. Provide a Nevada Registered Professional Engineer, employed by the soil nailing Contractor and having experience in the construction of permanent soil nail retaining walls on at least 4 completed projects over the past 2 years, to supervise the work. Consultants or manufacturer's representatives will not be allowed to satisfy the aforementioned requirement. Use an on- site supervisor and drill rig operators having experience installing permanent soil nails on at least 4 projects over the past 2 years. Prepare a personnel qualifications list containing a summary of each individual’s experience and the respective projects.

644.01.03 Submit tals. Submit 5 copies of the following information for review and approval at least 30 days

prior to beginning wall construction: