Section 260 — Rock Bolts and Dowels

Description

260.01This work consists of providing and installing rock bolts and dowels.

260.02Definitions.

(a)Rock bolt. Fully grouted, deformed steel bars that are post -tensioned , installed entirely in rock, and actively reinforce a rock mass.

(b)Rock dowels. Fully grouted, deformed steel bars that are untensioned , installed entirely in rock , and passively reinforce a rock mass.

Material

260.03Conform to the following Subsections: Non-shrink grout 701.04(b)(2) Rock bolts and rock dowels 722.03 Water for cementitious materials 725.01(a)

Construction Requirements

260.04Qualifications. Provide an on- site drill foreperson and drill operators with experience installing and testing rock bolts and dowels. A t least 21 days before starting rock bolt and dowel work, s ubmit the following for approval:

(a)Drill foreperson . A résumé for the drill foreperson describing f ive projects wi thin the past 5 years that the drill foreperson has completed with at least 3000 linear feet of rock bolts and dowels installed according to similar contract requirements ;

(b)Drill operators. A résumé for each drill operator describing three projects within the past 5 years that each drill operator has completed safely and satisfactorily with at least 1000 linear feet of rock bolts and dowels installed according to similar contract requirements ; and

(c)Rope supported laborers. A r ésumé for rope supported laborers conforming to Subsection 262.02.

260.05Submittals. At least 21 days before starting rock bolt and dowel work, submit the following according to Subsection 104.06:

(a)Proposed construction sequence and schedule;

(b)Proposed drilling methods and equipment;

(c)Proposed drill hole diameter and the minimum bond zone length for design loads shown in the plans. Design minimum bond zone lengths according to PTI, Recommendations for Prestressed Rock and Soil Anchors ;

(d)Proposed rock bolt and dowel type, couplers, bearing plate, washers (flat and beveled), nut, stressing anchorages, centralizers, and bond breakers (if applicable) with specifications including manufacturer’s data sheets, and brochures. Include manufacturer’s verification for the bearing plate thickness for the specified rock bolt and dowel capacities;

(e)Manufacturer’s recommendations for bar and hardware handling, storing, and working temperature ranges;

(f)Non-shrink cement gr out type, mix design, 3- day and 7- day compressive strength test results, placement procedures, manufacturer’s SDS and brochures, and mixing equipment for each of the following stages of non-shrink cement grouting:

(1)Two-stage grouting. Means for determining the level of primary (first -stage) grout in the hole;

(2)Single- stage grouting. Fabrication details for proposed bond- breaker in the free stressing zone including corrosion inhibiting compounds, if applicable;

(g)Manufacturer certification for corrosion -resistan t bar coating and procedures and material for repairing corrosion protection coatings in the field;

(h)If open joints, seams, or loose material is encountered, the methods, equipment, and materials used to control excessive grout injection volumes; (i) Details for placing, stressing, and testing rock bolts and dowels. Schedule of a test installation to demonstrate rock bolt and dowel installation, testing equipment, and procedures. The proposed rock bolt stressing equipment, setup, and procedures that will be used for the performance and proof testing;

(j)If required, a detailed procedure for placing the anchor head assembly (bearing plate and nut) below the exposed rock surface or for removing the anchor head assembly following final lock- off without impacting the bar design load. Include details for a countersink or flush -cut with a colored grout patch, if applicable;

(k)Special installation methods (such as upwardly inclined rock bolts and dowels, techniques for constructing bearing pads, grouting across open joints and debris- filled discontinuities) if applicable;

(l)Identification number and calibration test certification for each jack, pressure gauge, and electronic load cell to be used for testing. Clearly indicate the serial number of each component of the t esting assembly on calibration graphs. Submit results from calibration tests conducted by an independent testing laboratory within the previous 90 days; and

(m)Report documentation examples including installation and testing report formats.

260.06Rock Bolt and Dowel Fabrication.

(a)General. Fabricate rock bolts and dowels according to PTI, Recommendations for Prestressed Rock and Soil Anchors . Deliver rock bolts and dowels to the job site in bulk lengths and field cut to the appropriate lengths after drilling fo r each rock bolt and dowel. Do not precut rock bolts and dowel steel bars at the factory. Size bars to ensure:

(1)The design load does not exceed 60 percent of minimum ultimate tensile strength of the bar; and

(2)The maximum test load does not exceed 80 percent of the minimum ultimate tensile strength of the bar.

(b)Couplers. Couple only fully- grouted anchors. Couple sections together only if the design length exceeds the standard commercially available bar lengths. Use couplers with a center stop to ensure equal le ngth of thread connects each section. Do not use couplings that interfere with the flow of grout.

(c)Anchorage. For the stressing anchorage, use a steel bearing plate, washers (flat hardened, beveled or, spherical, as required), and a nut that can develop 95 percent of the minimum ultimate tensile strength of the bar.

(d)Centralizers. For cement grouted rock bolts and dowels, place centralizers along the bar at 10- foot centers, with at least one centralizer per rock bolt or dowel. Locate the lowermost centralizer within 12 inches of the end. Use centralizers of sufficient strength to support the bar in the drilled hole and provide at least 0.5 inch of grout cover around it. Do not place centralizers on the bond breaker.

260.07Handling and Storing Material. Handle and store bars according to ASTM A767 and D3963 guidelines and the manufacturer’s recommendations. Repair or replace bars with damage to corrosion protection coatings as required by ASTM A767 and D3963. Handle, transport, and store hardware material according to the manufacturer’s recommendations. Protect finishes from abrasions that remove the darkened color. Repair minor damages to epoxy coated, galvanized, and weathered surfaces. Repair galvanized finishes according to Section 563.

260.08Installation. Before installing rock bolts and dowels, complete on- slope rock stabilization work as applicable. Perform safety scaling that the Contractor deems necessary according to Section 262. If applicable, treat exposed galvanized steel surfaces according to Section 563. Provide and install rock bolts and dowels with a minimum design capacity as shown in the plans.

(a)Drilling. Provide equipment able to drill stra ight, uniform -diameter holes no larger than 4 inches in diameter. Do not use water or drilling slurry. Drill rock bolt and dowel holes to the minimum depths shown in the plans, and within 6 inches of the required location. Adjust total bolt and dowel lengt hs to address existing subsurface conditions encountered. Unless otherwise shown in the plans, drill rock bolts and dowels perpendicular to rock faces or inclined slightly downward (0 to 5 degrees) from the axis perpendicular to the rock face. Size drill h ole diameters to provide at least 0.5 inch of grout cover around bars. Clean drill holes of cuttings, sludge, and debris. If rock bolts and dowels cannot be installed in a drilled hole, re -drill the hole. Do not use hand drills to advance holes unless approved.

(b)Grouting. Install rock bolts or dowels no more than 24 hours after completing drill holes. Orient reinforcement no more than 5 degrees outside of the specified angle. Complete first -stage grouting no more than one week after rock bolt and dowel installations. Tension each rock bolt and dowel no more than one week after completing first stage grouting. Complete second stage grouting no more than 3 days after successful post tensioning, wherever two -stage grouted rock bolts are installed. Use positive displacement grout pumps according to Subsection 256.07(b)(1) . Install steel bars and grout according to the manufacturer’s recommendations. Incorporate an acceptable bond breaker where rock bolts are grouted in a single stage. Where grouting rock bolts in two stages, completely fill the minimum bond zone length under stage one, and after successful post tensioning of the bolt fill the free -stressing (unbonded) length with grout under stage two. Control grout pressures to avoid ground heaving or fracturing, and fill grout tube with grout when it will remain in the hole. Flush surplus water and diluted grout from lines before injection and replace leaky fittings before continuing grouting operations. Clean excess grout off rock surfaces, rock bolts and dowels, and bearing plates. Perform QC of the grout by performing minimum compressive strength tests, and submit test results to the CO. Record the quantity of injected grout and the grout pressure for each installation. Notify the CO of grout quantity overruns including the reason for the overrun and proposed actions to minimize future overruns. Obtain approval for alternative grouting methods.

(c)Bearing plate installation. Install bearing plates so at least t hree- quarters of the plate’s surface is in contact with a rock face. If rock faces are irregular or unsound, chip out surrounding rock or construct an approved bearing pad. Ensure that the rock bolt or dowel axis is within 20 degrees of being perpendicular to the bearing plate and that the bar passes through bearing plate center without bending. Use beveled washers where the bar axis is more than 5 degrees from the bearing plate perpendicular. Allow at least 6 inches of bolt and dowel length beyond the nut and washers. Use over - sized bearing plates as approved where rock surfaces are weak or highly weathered. After load -testing and acceptance, tension and lock -off the rock bolts, place the second stage of non- shrink grout in the entire free stressing length, and remove excess grout from rock faces and anchorage assembly hardware. Ensure the bar is fully encapsulated in grout to the collar of the hole. Check grout levels through key-holes the day after grout filling and fill the annulus space with grout as needed using a tremie tube. Repeat grout level checks and grout filling procedures until a fully grouted annulus space is achieved.

260.09Rock Bolt Testing, Stressing, and Finishing. Conduct testing of tensioned and untensioned rock bolts according to PTI, Recommendations for Prestressed Rock and Soil Anchors . If applicable, trim the corrosion protection surrounding the free stressing length of the bar so it does not contact the bearing plate during testing and stressing. For single stage cement grouted rock bolts, tension the bar after the bond zone grout is set and attain s sufficient pull -out strength. For two -stage cement grouted rock bolts, tension the bar after the bond zone grout is set and attain s sufficient pull- out strength and before the free stressing length is grouted.

(a)Performance tests. Before starting production bolting, design rock bolts and construct test bolts for each rock type according to the approved submittal drawings. Do not start production bolting for a rock type until the CO approves the constructed test bolt, rock bolt design, and construction methods for that rock type. Perform at least two successful performance tests for each different rock unit, anchor type, and proposed drilling -installation -grouting method before starting produc tion rock bolt installation. Performance tests may be required on bolts shown in the plans, or in sacrificial locations, if reasonable access for inspection is not provided according to FAR Clause 52.246- 12 Inspection of Construction. Use a calibrated hol low-ram hydraulic jack and gauge with graduations of 200 pounds per square inch or less to tension rock bolts. Tension rock bolts to 133 percent of the design load, and maintain the tension at least 10 minutes, and no more than 60 minutes if needed, with a maximum load tolerance of 200 pounds per square inch. Apply loads and record extensions under loads with a tool that can measure to 1 mil. Conduct loading according to Table 260-1. The Design Load (DL) during the testing is as sh own in the plans. The alignment load (AL) is the minimum load required to align the testing apparatus and should not exceed 10 percent of the DL. Table 260-1

Performance Test Loading Schedule

Load Hold Time

AL Obtain reading

0.25DL Obtain reading 0.50DL Obtain reading 0.75DL Obtain reading 1.00DL Obtain reading 1.20DL Obtain reading 1.33DL Obtain reading " 1 minimum " 2 minimum " 3 minimum " 4 minimum " 5 minimum " 6 minimum " 10 minimum " 60 minimum (if needed)

AL Obtain reading

DL Lockoff

Submit rock bolt test results to the CO for further analysis. Rock bolts are acceptable when the following conditions are met:

(1)The total elastic movement obtained at the maximum test load exceeds 80 percent of the theoretical elastic elongation of the free stressing length;

(2)The total elastic movement obtained at the maximum test load does not exceed the theoretical elastic elongation of 100 percent the free stressing length plus 50 percent of the bond length plus the jack length;

(3)The rock bolt carries the maximum test load with a creep rate less than 0.04 inch from the 1-minute reading to the 10- minute reading, or 0.08 inch per log cycle of time from the 6 -minute reading to the 60- minute reading; and

(4)The CO approves submitted test results in wri ting. Perform additional performance tests if installations fail to meet the test criteria.

(b)Proof testing. Proof test each rock bolt by tensioning bolts applying and maintaining 133 percent of the design load for 10 minutes. Rock bolts are acceptable when no loss of load occurs during the proof test. Replace failed rock bolts at no additional cost to the Government and document the expected reasons for failure to address and rectify deficiencies in the rock bolt installation methods used for given site cond itions. Adjust rock bolt installation methods as approved before installing additional rock bolts. After rock bolts are acceptable, lower the tension and lock off the load at 100 percent of the design load with a nut and a flat or beveled washer as needed to ensure that the nut is flush against the bearing plate. Grout the remaining portion of the rock bolt no more than 72 hours after re -tensioning and lock off.

(c)Finishing. Trim completed rock bolt ends to within 6 inches of the rock face. Treat field cuts, repair damages to galvanization, and repair and finish exposed steel surfaces according to Section 563.

260.10Rock Dowel Lift -Off Testing and Finishing. Test rock dowels according to PTI, Recommendations for Prestressed R ock and Soil Anchors . Test only fully grouted dowels. Conduct at least two successful lift -off tests for each different rock unit, anchor type , and proposed method of drilling, installation, and grouting. Gradually load lift -off test reinforcements to 60 percent of the minimum ultimate tensile strength of the dowel bar and monitor the pressure gauge to verify the anchor is holding the design load for at least 10 minutes. Test 5 percent of the remaining dowels if the anchors do not pull out. Replace the dowel and conduct lift -off tests on remaining rock dowels when pressure gauge drops are due to anchorage movements. Apply 100 foot- pounds of torque to ensure proper seating against the rock face. Trim completed rock dowel ends to within 6 inches of the rock face.

260.11Drilling Logs, Test Results, and Reporting. Submit drilling logs and test results to the CO for review. Maintain daily records of rock bolt and dowel work including the following:

(a)Drawings depicting the location of each anchor on post -scaled photographs, noting anchor designation, date drilled, general drilling logs that note the drilling conditions and materials encountered, the location of significant drilling changes (geologic contacts, voids, or open fractures), dates of grouting operations, total anchor length, bonded length, free stressing length, grout mix, grout volume, average grout pressure, hole diameter, size of bar, bar inclination, and installation comments. Submit as -built drawings according to Subsection 104.06(c) .

(b)Performance and proof test data forms, including the anchor designation, bonded length, free stressing length, stressing length, date of stressing operation, signature of stressing operator or inspector, required elongation and associated gauge pressure, actual elongation and associated gauge pressure, identification numbers of jacking equipment, comments, and a table including incr emental jack pressure, jack load, and movement.

260.12Acceptance. See Table 260-2 for sampling, testing, and acceptance requirements. Material for rock bolts and dowels will be evaluated under Subsections 106.02, 106.03, and 106.04. Construction of rock bolts and dowels will be evaluated un der Subsections 106.02 and 106.04. Grouting will be evaluated under Subsections 106.02 and 106.04. Safety scaling will be ev aluated under Section 262. Treating exposed surfaces and repairing galvanized surfaces will be evaluated under Section 563.

Measurement

260.13Measure the Section 260 pay items listed in the bid schedule according to Subsection 109.02 and the following as applicable: When measuring rock bolts and dowels by the linear foot, measure from the trimmed steel end to 6 inches from the slope face. Do not measure rock bolts and dowels that failed testing.

Payment

260.14The accepted quantities will be paid at the contract price per unit of measurement for the Section 260 pay items listed in the bid schedule. Payment will be full compensation for the work prescribed in this Section. See Subsection 109.05 . Table 260-2 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

Non-shrink

grout (701.04(b)(2) Measured & tested for conformance (106.04) Flow – AASHTO C939 1 per mix design Source of material Yes, if requested Before producing –

Compr essive

Strength (3 -day & 7-day) – ASTM C109 1 per mix design Source of material Yes, if requested Before producing –

Production

Non-shrink

grout (701.04(b)(2) ) Measured & tested for conformance (106.04) Compre ssive Strength (3 -day & 7-day) – ASTM C109 1 set from each batch of grout Source of material Yes, if requested Within 24 hours after completion of test –

Performance

test for rock bolts

Measured &

tested for conformance (106.04) Deformation – Subsection

260.09(a) Subsection

260.09(a) Installation No Within 24 hours after completion of test –

Proof test for

rock bolts Measured & tested for conformance (106.04) Deformation – Subsection

260.09(b) Each bolt Installation No Within 24 hours after completion of test –

Lift-off test

for rock dowel Measured & tested for conformance (106.04) Deformation – Subsection

260.10Subsection

260.10Installation No Within 24 hours after completion of test –