02221 trenching.doc

SECTION 02221 - TRENCHING, BACKFILLING AND COMPACTING FOR UTILITIES

GENERAL

1.01 Scope: This section specifies excavation and backfill for utilities, including excavation; locating and abandoning existing connections; furnishing, hauling and placing of backfill material; disposal of excess or unsuitable backfill material; grading; and sign placement.

1.02 Class of Material: Material to be excavated for installation of utilities is unclassified.

1.03 Disposal Site: The disposal site will be chosen by the COR after consultation with the Contractor. The site, or sites, will be located within 1000 feet of the trenching work.

1.04 Damage to Existing Underground Utilities: Stop all work associated with damage to existing utilities and notify the COR. Repair utility as directed by the COR.

Repair at Contractor's expense any operating waterline, underground power, telephone, sewer or propane gas utility lines damaged by the Contractor's operations.

PRODUCTS

2.01 Bedding Material: Fine soil or sand —100 % passing the #8 sieve.

2.02 Select Excavated Material: Excavated material containing no rocks larger than 6 (3?) inches in largest dimension.

2.03 Topsoil: Soil or loam containing no rock larger than 2 inches.

2.04 Underground Detection and Marking Tape: Metallic core, plastic marking tape, printed with the words "Warning - Buried Waterline" or "Warning - Buried Electrical Cable" or similar wording depending on the utility buried underneath.

2.05 Crushed Aggregate: Crushed aggregate meeting the requirements of AASHTO M-147, Grading D.

EXECUTION

3.01 General: Trench excavations shall be the shortest route possible (line of sight from source to treatment building). Contractor may request alternate trench routes for his/her convenience. All such alternate route changes shall be approved in writing by the COR prior to starting work.

Maintain trench excavations to guard against and prevent injury to employees and the public. Provide adequate shoring and bracing as required.

Minimum depth of soil cover for utility lines (measured from the top of the pipe, conduit, or cable to final construction ground elevation required):

1.

Power Lines

- 24 inches

2. Waterlines (Potable)

- 30 inch (Exception for replacing existing waterline in the roadside ditch where the minimum depth of soil cover shall be 12 inches all of Select excavated material)

4. Gas Lines – 18 inches

3.

Detectable Metallic Underground Tape

- 6 to 8 inches

3.02 Excavation: All excavation shall be by open-cut from ground surface.

The sides of trenches shall be kept as nearly vertical as practicable. In no instance shall the trench from 6 inches above the top of the pipe to the bottom of the trench be more than 16 inches wider than the outside diameter of the pipe. Minimum trench width shall be 12 inches.

Trenches more than 5 feet deep shall be sheeted, shored, braced, or sloped before any worker is allowed in the trench. When soil conditions are unstable (vertical wall will not remain in place), trenches shallower than 5 feet shall also be sheeted, shored, braced, or sloped.

Excavate trenches for waterlines and direct burial cable three (3) inches below required minimum depth.

Protect the excavation from frost action. Compact ground that has frozen and subsequently thawed as specified herein.

Prevent water accumulation in excavations. If clay soil becomes saturated, compact after it has dried as specified herein.

Depressions in the trench bottom shall be excavated with hand tools to accommodate valves, fittings, etc.

The use of trench digging machines shall be permitted except in places where they may cause damage to existing structures, utilities, or trees designated to remain; in which, hand methods shall be employed.

3.03 Backfilling and Compacting: Place 3 to 4 inches of bedding material in the trenches, as SHOWN ON THE DRAWINGS, prior to installation of waterline or control cable. Ensure bedding material is at a moisture content suitable for compaction. Compact the bedding material with mechanical compactor with a minimum of 3 passes. After installation, place bedding material in trench to a height of 12 inches above the pipe.

Backfill shall not be completed for waterlines until pressure and/or leakage tests have been performed and the pipeline is approved by the COR. Sufficient backfill shall be placed to prevent pipe movement under pressure tests. All joints, valves, etc., shall remain uncovered for inspection purposes during testing. After leak testing has been successfully completed, finish placing bedding material and complete compaction.

Place select excavated material in 12 inch lifts or less to within 8 inches of final grade. Compact each lift with 3 passes of mechanical compactor.

Install plastic warning tape over the full length of trenches as SHOWN ON THE DRAWINGS.

Finish backfill will normally consist of select excavated material. Mound and compact backfill as SHOWN ON THE DRAWINGS. In roadways and parking areas, decomposed granite or crushed aggregate base shall be used for finish backfill material.

3.04 Disposal of Excess Excavation and Unsuitable Material: Surplus excavated material and unsuitable material remaining on the site upon completion of the backfilling shall be disposed of by the Contractor at local sites approved by the COR.

3.05 Final Finish: After the utility installation and backfill has been completed, finish all disturbed areas, except trench area required to be mounded, to a smooth, uniform grade and texture, well blended to the original contours, showing minimum evidence of construction activity.

MEASUREMENT AND PAYMENT

4.01 Method of Measurement Measurement will be of the linear feet of actual length of trench excavated and backfilled according to the utility or combination of utilities listed in the Basis of Payment. Measurement will include trench length for in-line appurtenances including valves and fittings. Measurement will not include additional trench length added for alternative routing at the Contractor's convenience. However, measurement will include additional trench length ordered by the COR to avoid rock excavation or other obstacle. Measurement will stop at connections with existing utilities, building and structure limits, and at the vertical center lines of hydrants and other points of service.

4.02 Basis of Payment Payment will be at the contract unit prices for each item, measured as provided above, completed and accepted. Payment will be made under:

PAY ITEM

DESCRIPTION

PAY UNIT

02221-1 Trenching & Backfill for Waterline

LF

02221-2 Locate and abandon water service connections

LS

END OF SECTION

Salmon Creek Campground Paving