Attachment B - letdown_fence specifications.pdf

Fence Construction Specifications

Let-Down Under Tension

FENCE SPECIFICATIONS

Let Down Fence Under Tension

1. Clearing

The fence shall be located in the center of cleared right-of-way. A six foot right-of-way on each side of the fence is to be cleared of logs, small trees and brush. Limbs on trees shall be removed to a height of 8 feet on trees used as posts in the fence. Limbs and brush removed from the right-of-way shall be scattered off the right-of-way. All slash must be kept at least 20’ from any game or livestock trails. All stumps on the right-of-way shall not be higher than 3 inches from the ground. All stumps and staubs on the let-down side shall be cut at ground level straight across. All rocks over 4" diameter shall be cleared from the let-down side of the fence if possible.

2. Hazard Trees

All dead trees within 25 feet of the fence line will be felled. Any tree in question will have to be approved by the Forest Service before leaving it. The felled hazard trees will be bucked up to a distance of 6 ft. on either side of the fence and the material removed from the 6 ft. right-of-way on each side of the fence.

The remainder of the felled hazard trees need not be limbed or bucked. If there is a question as to the necessity of falling a specific tree, the contractor shall consult the Forest Service. The fence will be constructed to let-down UPHILL if crossing a slope.

3. Fence Line Location

All fence line locations are flagged with ribbon. Color will be identified to the contractor. Gate locations are flagged in ribbon and marked. Deviations from the flagged line of more than 20 feet will need approval from the Forest Service. The fence is to be built having a slight curvature. See Exhibit 1

4. Construction

Let-Down Fence Details (Exhibit 1)

4.1 Wire Loops

Where steel posts with split larch stays are used, wire loops (top and bottom) shall be 7-8 inches in diameter and made from No. 9 wire. Use of a pigtail or western union splice for the loop will be used. Where trees or rock jacks are used, the loops shall be secured to the upright of the rock-jack or the nailer attached to the tree with enough slack to enable flipping the loop over the stay on the fence and allowing the stay to “let down” to the ground. For trees or rock jacks, the top and bottom loop will be attached to the backside of the tie point. For “T” posts, the top loop and bottom loop will be attached to the stay. In all attachments, the bottom loop will be nailed to the stay to keep the loop in place when let down.

4.2 Line Wires

Three line wires shall be spaced as follows: The bottom wire will be 16-18 inches from ground level, the next two wires shall be spaced at 12 inch intervals above the bottom wire for a total height not to exceed 40 inches.

4.3 Posts

Construction shall be with 5 1/2 foot 1.33 steel T-type posts set approximately 18-20 feet apart.

The spacing may be slightly closer to keep the bottom wire at an acceptable height above the ground line. Live trees or line jacks (see plan R6-16-RM 122.44) may be used in lieu of steel posts. If live trees are used, they must be located within two feet of the established line (an off set must be used to maintain the stretch line, plan R6-16-RM 112.45), be a minimum of 8" dbh and must have a nailer ( "scab" ) attached as shown in R-6-16-RM 121.46. Only Western larch, Ponderosa pine or Douglas (Red) fir may be used as tree ties, unless otherwise approved by the Forest Service. Line jacks will be constructed as shown in R-6-16-RM 121.44. Steel posts shall be driven into the ground, past the top of the flange. It is acceptable to pre-drill post holes in rocky ground to permit the use of posts in these conditions. If this method is used, the flange may be knocked off prior to pounding, however the post must be secure in the hole with no wobbling. Posts will be driven with the wire spacers to the outside, so the wire loops will catch between the wire spacers when the fence is standing. Steel posts shall be relieved of upward pull of wires by use of deadman rock anchors and tiedowns as shown in R-6-16-RM 122.11. Tie downs can be secured using a large rock or a T-post driven at a 45 degree angle parallel to the fence (no more than 18 inches of post can remain out of the ground.) There can be no more than ten steel posts in a line (max 200 feet) without having a scabbed live tree ( 8" dbh or larger ) or a line jack to support the fenceline.

4.4 Tension Devices

These will be constructed at all stretch points prior to stretching wire. Sections shall be dead-ended on a 4"x4" split larch stay to tie-trees, rock crib or rock jack as shown in Exhibit 1. The rigging will be placed 6-8 feet from the base of the anchor point. The rigging must be assembled so that the fence can be “let down” flat on the ground and not hang up on the upright steel post.

An 8” ½ inch lag bolt will be used as the anchor/pivot point at tree or rock jack anchors. Where the pivot point attaches to the anchor, a short span of chain (3-4 links) inserted between the anchor and the 3/16 galvanized tension cables, will help the fence let down smoothly. Double 3/16 inch cable clamps will be used at each attachment point. Care must be taken when stretching the line wires to ensure that the wire loops that attach the dead ended stay to the upright steel post can be flipped over to allow the fence to be let down.

4.5 Stays

48” Split larch stays shall be used. One stay will be attached at each steel post, rock jack, tree tie or figure four. Stays will be attached to the line wire using 1 ¾ inch galvanized staples. The stays will be attached to the wires in a fashion which will allow the wire to remain on top of the stays as the fence is let down. This will prevent the staples from being pulled out while standing the fence up each spring.

The wood stay shall have a wire loop (see 4.1) of No. 9 wire stapled at the top and loose enough to hold or release from the post. This top loop shall be stapled to the outside of the stay. The bottom loop shall be looped around the post and stapled on the outside of the wood stay.

4.6 Gates (R6-16-RM 182.1)

The locations of the gates will be flagged by the Forest Service in red and white stripe flagging.

Gates 16 feet in width shall be placed at road crossings. All other gates shall be 14 feet wide.

Only four wires will be used for gates with three lighter weight larch stays for support between the heavier end pieces. Ends of the gate shall be attached to trees, rock jacks, rock cribs or H-braces.

4.7 Water Gaps

Water gaps will be constructed to allow the fence to be let down or may be constructed using the specifications shown in R6-16-RM 182.1.

4.8 Wire Stretching

Wire will be tightened adequately to set the wire twists and remove factory kinks. It is, however, important to refrain from stretching the wire excessively. Excessive tension will weaken the barbed wire by removing the capacity for it to stretch and makes it difficult to let the fence down.

Location of stretch points will be determined by topography and the availability of tie-trees.

4.9 Splicing (R6-16-RM 121.41)

Splices in the wire shall be made by wrapping the ends of the wire back around the wire three times, thereby forming an eye at the end of the wire; the other wire end is then placed through the eye and wrapped back around itself at least three times. All wraps shall lie directly adjacent to each other, thus forming neat, tight wraps.

4.10 Rock Jacks/Line Jacks (R6-16-RM 122.43-44)

Rock Jacks/Line Jacks/Post Jacks (cumulatively referred to as “rock jacks”) should not be spaced farther than 200 feet apart unless there is a tree-tie, rock crib, or H-brace within this interval.

Tree-ties or H-braces may be substituted for rock jacks. Rock jacks will be placed at the top and bottom of all abrupt breaks in the slope.

A shallow hole (6-10 inches deep) shall be dug to keep the jack from sliding if the jack is used as an end or in a pivot point in the fence. Set the upright post in place, pack soil around the post and nail the two braces to the other corners of the triangle and to the upright post. Use two 6" helix nails placed at binding angles in the end of each piece. The lower end of the post must be double nailed to extended ends of floor joists.

The two floor joists are nailed about 6 inches above the ground. Floor material can be trimmed to fit the triangular space it covers but is not nailed to the joist.

Use two nails placed at a binding angle at each nailed junction in all jacks. One-half the length of each nail should be in the piece being nailed to. Notch outside piece if necessary to allow full contact of each face. Rock jacks not constructed using this method will not be acceptable. Nails will be driven at right angles to the annual ring. Nails should not be closer than 6 inches to the end of any piece to minimize splitting. Nailed junctions should have sound wood against sound wood, no bark between.

All corners of the jack shall be wired with one tight wrap of either No. 9 or 12 ga. two strand barbless wire. Each of the three bottom corners shall have a rock set under the corner to allow settling of the jack, but to keep the jack floor from settling to the ground.

100 -150 pounds of rock shall be placed on the floor of each line jack. On rock jacks used as corners or tie points, the rock load shall be 300-500 pounds. No log chunks or other weight will be acceptable.

4.11 Rock Cribs

Rock cribs may be used in lieu of rock jacks or H-braces where it is impossible to set posts to the desired depth. Rock cribs must be able to resist either the inline or upward pull of the wire.

Minimum dimensions shall be four feet square and 48” deep. Cribs may be constructed using spit larch posts, 5-6” treated round posts for uprights and split material for the side pieces. 60d helix nails should be used securing split material. All sides must be reinforced using a diagonal brace placed against the pull of the wire. The braces must extend from the bottom corner to the opposite top corner on each side. The bottoms of the cribs should have brace in the center to support the rock load and prevent breakage. The cribs must be completely filled with rock to provide adequate weight to counter the pull of the wire. If the cribs are used as stretch points, the wire will be connected to the crib as shown in Exhibit 1.

4.12 Figure-Fours (R6-16-RM 122.41

Figure-fours will be required in locations where steel posts cannot be driven into the soil to specifications. Figure fours shall be constructed using heavy 4 foot split larch pieces for the stay portion of the figure four. 60” pieces will be used for the legs of the figure four as indicated in Figure 36. 6" helix nails shall be used for securing the figure four. See R-6 Plan No. 4 for spacing specifications.

4.13 Trees

Solid live trees over 8 inches dbh may be used in place of posts, provided they are located not over 3 feet out of line. Only Western larch, Ponderosa pine or Douglas (Red) fir may be used, unless otherwise approved by the COR. Tree branches shall be removed completely around the fence, to a height of 8 feet. Do not nick inner tree bark when limbing. A scab shall be securely nailed, with 6" helix nails to the tree at three points: top, center, and bottom. See R-6 Plan No. 2

4.14 H-Braces (R6-16-RM 121-51)

H-Braces may be used as end points if no tree-ties or rock is available for rock jacks. Posts will be buried a minimum of 3 feet and spaced 8 feet apart. A pressure treated 5-6” round post will be used as the cross-piece brace between the posts. This brace will be placed approximately 40" from the ground. Two diagonally placed tension wires of double wrapped 12 1/2 ga smooth two strand wire will be secured at ground level and 48" with pig-tailed ends. This is then tightened with a twitch stick made from a stay until the wire is very tight. The loose end of the twitch stick can be rested against the cross-piece.

4.15 Stapling (R6-16-RM 121.4)

1 3/4 galvanized barbed staples shall be driven at a slant to the grain of the wood to prevent the wood from splitting and will not be driven so deep as to nick the barbed wire. Staples should be driven to contact the barbed wire, but allow slippage of the barbed wire between the barbs. See R-6 Plan No. 2.

5. Materials

5.1 List of Materials

5 1/2 ft. 133 heavy duty "T" type steel fence posts

12 1/2 gauge galvanized barbed wire, 4” barb spacing, Class 1

12 1/2 gauge galvanized barbless wire, Class 1 for tie downs and wrapping rock jacks

1 3/4 hot dipped galvanized barbed staples

3/16 galvanized cable for tension devices

3/16 galvanized cable clamps for tension devices

6" helix nails

2.0 link chain for tension devices split larch wood material (for rock jacks and figure fours)

Stays—9 square inch cross section, 48” long split larch, use heavier stays as figure four uprights.

Rock Jack—approximately 3x6 cross section, 60” long split larch

Figure Four legs—approximately 9-12 inch cross section, 60” long split larch

No. 9 annealed wire for let-down loops

6"-7" round CCA treated posts for h-brace posts

5"-6" round CCA treated posts for h-brace horizontal brace