CONSTRUCTION SPECIFICATION

**[271. TIMBER RETAINING WALLS]{.underline}**

**1. [SCOPE]{.underline}**

> The work shall consist of furnishing the materials, and constructing
> timber retaining walls, to the lines and grades shown on the drawings,
> including the concrete backfill for the footings.

**2. [MATERIALS]{.underline}**

> [Structural timber and lumber]{.underline} shall be graded in
> accordance with the grading rules, applicable to the specified
> species, adopted by a lumber grading or inspection bureau or agency
> recognized as being competent and that conform to the basic principles
> of ASTM Standards D 245. The material supplied according to the
> commercial grading rules shall be of equal or greater stress value
> than the specified stress-grade.
>
> [Treated lumber, timber, piles, poles, or posts]{.underline} shall be
> free from heat checks, water bursts, excessive checking, results of
> chafing or from any other damage or defects that would impair their
> usefulness or durability for the purpose intended. The use of \"S\"
> irons will not be permitted. Holes bored for tests shall be filled
> with tight fitting treated plugs.
>
> [Treated timber and lumber]{.underline} shall be impregnated with the
> specified type and quantity of preservative and in the manner
> specified in Federal Specification TT-W-571.
>
> All material shall be sound wood, free from decay, and shall be
> adequately seasoned and dried before impregnation with preservative.
> The moisture content before treatment shall not exceed 25 percent.
>
> The column post shall be undressed No. 1 Post, coast region Douglas
> fir. The timber plank shall be undressed No. 2 Plank, coast region
> Douglas Fir. The size of column post and timber plank shall be as
> shown on the drawings. The posts and planks shall be treated with
> ammoniacal copper arsenate at the rate specified in Federal
> Specification TT-W-571. Posts shall have a 1-inch chamfer around the
> top.
>
> [Steel bolts]{.underline} shall conform to the requirements of ASTM
> Specification A 307, and shall be galvanized or zinc-coated. The zinc
> coating shall conform to the requirements of ASTM Specification A 153.
>
> [Washers]{.underline} shall be ogee gray iron castings or malleable
> iron castings unless washers cut from medium steel or wrought iron
> plate are specified on the drawings. Washers shall have a minimum
> thickness equal to 1/2 the diameter of the bolt and have a diameter
> equal to four times the thickness of the bolt. Holes in washers shall
> be not more than one-eighth inch greater in diameter than the bolt.

**3. [HANDLING AND STORING MATERIALS]{.underline}**

> All timber and lumber stored at the site of the work shall be neatly
> stacked on supports at least six inches above the ground surface and
> protected from the weather by suitable covering. Treated timber shall
> be close-stacked. The ground underneath and in the
>
> vicinity of all stacks shall be cleared of weeds and rubbish. The use
> of cant hooks, peavies, or other pointed tools, except end hooks will
> not be permitted in the handling of structural timber or lumber.
> Treated timber shall be handled with rope slings or other methods that
> will prevent the breaking or bruising of outer fibers, or penetration
> of the surface in any manner.

**4. [SITE PREPARATION]{.underline}**

> Site preparation shall consist of cleaning the area of undesirable
> material, excavation of the base material to the required grade, and
> includes filling any areas with compacted fill to the required grade.
> Fill material will be subject to the approval of the Engineer. Fill
> will be compacted to the same density as adjacent undisturbed
> material. All site preparation shall be completed prior to the
> placement of any posts.

**5. [CONCRETE FOOTINGS]{.underline}**

> Holes shall be bored or dug to the diameter and to the depths shown on
> the drawings. Any over excavation shall be backfilled with concrete at
> the contractor\'s expense. After the posts have been positioned,
> concrete backfill shall be placed and consolidated by rodding,
> vibrating, spading, or other acceptable methods. Posts shall be
> properly braced to provided for plumb and alignment while the concrete
> backfill is being placed and cured.
>
> The concrete shall be of a design mix to yield a compressive strength
> the of 3,000 psi at 28 days. Type II cement shall be used and the
> cement content shall contain not less than 5 bags per cubic yard and
> not more than 6 gallons of water per sack of cement unless otherwise
> specified. Air entrainment shall be used and shall be not less than 5
> or more than 8 percent. Concrete shall be delivered to the site and
> discharged into the holes within 1 1/2 hours after the introduction of
> the cement to the aggregates. At the time of placement, the concrete
> shall have a slump of not less than 4, nor more than 6 inches.
>
> When ready mixed concrete is furnished, the Contractor shall furnish
> the Engineer a statement-of-delivery ticket showing the time of
> loading, the revolution counter reading at time of loading and
> quantities of materials used for each load of concrete.

**6. [FABRICATION]{.underline}**

> All framing shall be true and exact, with alignment being true and
> straight. Timber and lumber shall be accurately cut and assembled to a
> close fit and shall have even bearing over the entire contact
> surfaces.
>
> No cut joints will be accepted which are due to misalignment of
> adjacent posts. Cut joints will be allowed only to accommodate curves
> in alignment as shown on the drawings, or as staked in the field by
> the Engineer. No open or shimmed joints will be accepted. Deep hammer
> marks in wood surfaces shall be considered evidence of poor
> workmanship and sufficient cause for rejection of the work.
>
> Washers shall be used in contact with all bolt heads and nuts that
> would otherwise be in contact with wood. Cast iron washers shall be
> used when the bolt will be in contact with earth. All nuts shall be
> checked or burred effectively with a pointed tool after being finally
> tightened. Cuts on of treated timber shall be carefully trimmed and
> coated with not less than three brush coats of the same preservative
> used in the original treatment.
>
> All holes bored in treated timber and lumber shall be swabbed with not
> less than three coats of the same preservative used in the original
> treatment. After field treatment any unfilled holes shall be plugged
> with tightly fitting wooden plugs treated with the same preservative
> used in the original treatment.

**7. [MEASUREMENT AND PAYMENT]{.underline}**

> For items of work, for which specific unit prices are established in
> the contract, the measurement of timber retaining walls will be to the
> nearest lineal foot measured at the site. The measurement will be made
> along the ground surface for the length specified on the drawings or
> as staked by the Engineer.
>
> Payment for timber retaining walls per lineal foot will be made at the
> contract unit price. Such payment will be considered full compensation
> for all labor, equipment, transportation, materials and all other
> items necessary and incidental to the completion of the structure in
> place including hardware and accessories, wood preservatives, and
> concrete backfill.

Compensation for any item of work described in the contract but not
listed in the bid schedule will be included in the payment for the item
or work to which it is made subsidiary. Such items and the items to
which they are made subsidiary are identified in Section 8.