Section 264 — Midslope Rockfall Attenuator

Description

264.01This work consists of installing midslope rockfall attenuators.

Material

264.02Conform to the following Subsections: High -strength low- alloy structural steel 717.01(b) Hollow- core self -drilling anchors 722.07(a) Midslope rockfall attenuator materials 710.10 Non-shrink grout 701.04(b)(2) Rockfall protection hardware 717.01(f) Rockfall protection nuts and washers 717.01(g) Structural carbon steel 717.01(a) Threaded bar ground anchors 722.07(c) Water for cementitious materials 725.01(a) Wire rope 709.03 Wire rope anchors 722.07(b)

Construction Requirements

264.03Qualifications . Provide an on- site supervisor with experience installing midslope rockfall attenuator systems, and drill operators with experience installing ground anchors. At least 30 days before starting rockfall protection work, submit the following for approval:

(a)On-site supervisor. A résumé describing experience on at least five projects installing midslope rockfall attenuator systems on steep slopes within the past 5 years. Include project names, locations, and contact information for project owners;

(b)Drill operators. A résumé describing experience installing at least 1000 linear feet of ground anchors on steep slopes within the past 3 years. Include project names, locations, and contact information for project owners ;

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

(d)Cable net panel and wire mesh backing suppliers. Include the following:

(1)Evidence showing the manufacturer has at least 5 years ’ experience manufacturing the specified products used in similar system applications and capacities. Include details of the manufacturer’s testing procedures and certification of a QA program.

(2)A list of at least 5 past projects with similar site conditions where attenuators were installed using the supplier’s cable nets and steel fabric material. Include owner names and contact information.

264.04Submittals. At least 30 days before starting midslope rockfall attenuator work, submit the following according to Subsection 104.06:

(a)Materials .

(1)A list with brochures and data sheets for system appurtenances to be used including the cable nets and wire mesh backing, anchors, support system, lacing wire rope, wire mesh fasteners, anchor bars, wire rope anchors, grout, wire rope, clips, thimbles, ferrules, steel rings , and other fastening hardware ; and

(2)Drawings for temporary yokes or load frames used for anchor proof testing. Include load cells, test jack and master gauges, and calibr ation data performed by an independent testing laboratory within 90 days of the submittal for each device used. Recalibrate each device that experiences damage or has been involved in an uncontrolled fall.

(b)Equipment .

(1)List equipment to be used for rockfall protection work, including equipment capacities and intended uses; and

(2)Identify the manufacturer of the cable tension meter that will be used during installation of the midslope rockfall attenuator. Provide documentation that the cable tension meter has be en calibrated by an independent testing laboratory within 90 days of use on the project. Manufacturer’s calibration with same certification requirements will be accepted in place of independent certification for new instruments. Provide an identification number for e ach component (or a set such as sheaves used as a unit).

(c)Work p lan.

(1)A description of safety procedures minimizing exposure to hazardous and potentially hazardous conditions to the public, construction personnel, and equipment. Include temporary rockfall mitigation measures, special designs, and installation procedures deemed necessary to safely perform the rockfall protection work ;

(2)A list of materials, devices, and equipment used, and the methods that will be incorporated to protect existing facilities (underground, on the ground surface, and above -ground) and minimize impacts to the environment according to Section 107;

(3)A list of materials, equipment, and the methods for drilling, installing, grouting, and testing ground anchors, including the mix design for grouting operations; and

(4)Procedures for attaching cable net panels with wire mesh backing to upper support ropes, adjacent steel fabric panels, and other temporary and permanent supports. I nclude methods and equipment for delivering and placing on the designed slope locations.

264.05General. Do not order materials until the applicable material submittals are approved. Before installing midslope rockfall attenuators, complete work required according to Sections 260 , 262, and 267, and other on-slope rock stabilization work as applicable. Perform safety scaling that the Contractor deems necessary according to Section 262. Verify the midslope rockfall attenuator work limits. Perform required scaling, rock bolting and doweling, unlined and lined drain holes in rock, and other on- slope rock stabilization work before connecting the cable net panels with wire mesh backing to the ground anchor and support ropes. If applicable, treat exposed steel surface accord ing to Section 563. Store, handle, and install midslope rockfall attenuator systems without damaging the midslope rockfall attenuator, colored finish, or galvanized finish. Repair galvanized finishes and weathering agents according to Section 563. Replace damaged portions of the midslope rockfall attenuator. Construct the midslope rockfall protection at the locations shown in the plan s or as directed. Construct plates, holes, welds, swivels, and foundations for support posts as shown in the plans. Locate the posts, ropes, and wire rope anchors as shown in the plans. Install the midslope rockfall attenuator system within the required tolerances as shown in the plans for alignment and orientatio n. Construct midslope rockfall attenuators with a maximum top support wire rope length of 160 f eet. If the required installation length is longer than 160-feet, use a connection post and start a new top support wire rope. Install and attach the cable net panels and the wire mesh backing as shown in the plans. Use 9/16-inch wire seaming rope for connecting the net panels to the horizontal top B rope, truncating the seaming rope at each post, and restarting it for the next span between posts as shown in the plans. Connect corner cable K to the end post swivel and at least two cells into the cable net fabric at a connection. Use a 9/16-inch wire rope for corner cable K. Repair damaged galvanizing after erection according to Subsection 563.12(b) . Set the bottoms of attenuator net fabric panels as directed according to the geologic conditions.

(a)Foundations. Excavate and prepare new foundations according to Section 209. Use the post foundation shown in the plans. Space posts at 40 feet or less. Provide a proposed layout in plan between new post alignments that shows the angles in the vertical and horizontal alignment between posts and layout a profile showing the ground surface elevation and top attenuator support rope elevation for approval. If threaded ground anchor bars cannot be inserted into the drill holes due to caving conditions, use a hollow- core self -drilling ground anchor with a sacrificial drill bit to advance the anchor into the ground as shown in the plans. Orient the hollow -core anchor bars as shown in the plans. Determine the required anchor length necessary to provide a minimum axial pullout capacity of 30- kips for each self - drilling anchor. Fully encapsulate each ground anchor in either non- shrink grout or minor concrete according to Section 601.

(b)Wire rope tightening. At every midslope rockfall attenuator post, tighten C ropes and F ropes until they are taut. A taut rope is defined as one that has the values shown in Table 264 -1 as measured by a tension meter. Tighten C ropes and F ropes before loading and tightening the B rope. Tighten the B rope to ensure that when the rope is loaded with the attenuator net, the vertical sag between posts is 12 to 18 inches from horizontal. Table 264-1

Wire Rope Tension Meter Values

Rope F or C Vertical

Angle (degrees) Minimum Allowable Rope Tension (lbf) 30±2 370 45±2 550 50±2 to 60±2 770 Calibrate the cable tension meter at no more than a 180 -day interval, or at any lesser time, due to site-specific conditions, wear, or abuse of any component.

264.06Testing Anchors. Sample each grout batch used to construct anchors and submit required samples to an independent testing laboratory for 3- day and 7- day compressive strength testing. Submit results and samples for verification testing. Verify the wire rope anchor capacities by conducting axial pullout tests on every 103- kip capacity anchor, and 25 percent of the 58- kip capacity anchors as selected by the CO. Provide a pullout test load that is 60 percent of the ultimate wire rope anchor capacity shown in the plans. For pullout proof testing, an anchor is acceptable when it sustains the specified capacity fo r 10 minutes with no loss of load. Test against a temporary yoke or load frame with no part of the yoke or load frame within 3 feet of the anchor. If a wire rope anchor fails during testing, test all wire rope anchors. Replace failed wire rope anchors. Com plete wire rope anchor testing before connecting system components to the anchors. Verify that the 1¼- inch diameter hollow -core self -drilling ground anchors provide at least 30- kip axial pullout capacity for each anchor. Conduct the axial pullout test on at least one ground anchor, as selected by the CO, from each foundation where hollow -core self -drilling ground anchors are used. Provide a pullout proof test load that is 60 percent of the minimum pullout strength requirement. An anchor is acceptable when i t sustains the specified capacity for 10 minutes with no loss of load. Test against a temporary yoke or load frame with no part of the yoke or load frame within 3 feet of the anchor or the other four ground anchors associated with that post foundation if already installed. If a hollow -core self-drilling ground anchor fails, test all anchors associated with that post foundation. Modify and replace failed ground anchors and then retest. Complete anchor testing before constructing the remaining portion of the foundation. Replace failed ground anchors.

264.07Acceptance. See Table 264-2 for sampling, testing, and acceptance requirements. Material for midslope rockfall attenuator will be evaluated under Subsections 106.02 and 106.03. Submit a production certification for wire ropes and anchor tendons. Construction and erection of midslope rockfall attenuator will be evaluated under Subsecti ons 106.02 and 106.04. Drain holes in rock will be evaluated under Section 267. Minor concrete will be evaluated under Section 601. Rock bolts and dowels will be evaluated under Section 260. Slope scaling and safety scaling will be evaluated under Section 262. Treating exposed steel surfaces, treating galvanized steel field cuts, and repairing damaged galvanizing will be evaluated under Section 563.

Measurement

264.08Measure the Section 264 pay items listed in the bid schedule according to Subsection 109.02 and the following as applicable: Measure the midslope rockfall attenuator by the square yard of covered area of the installed cable net panel with wire mesh backing portion of the system on the slope, excluding ove rlaps and areas trimmed off.

Payment

264.09The accepted quantities will be paid at the contract price per unit of measurement for the Section 264 pay items listed in the bid schedule. Payment will be full compensation for the work prescribed in this Section. See Subsection 109.05 . Table 264-2 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

Production

Non-shrink

grout (701.04(b)(2) ) Measured & tested for conformance (106.04 ) Flow – ASTM C939 1 per mix design Source of

Material Yes, if

requested Within 24 hours after completion of test

Compressive

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

Proof test for

anchors Measured & tested for conformance (106.04 ) Deformation – Subsection

264.06Subsection

264.06Installation No Within 24 hours after completion of test