Attachment_5_-_SECTION_312317_TRENCHING_UTILITIES.docx

SECTION 312317

trenching, bedding and backfill for utilities PART 1 - GENERAl

SUMMARY

The work in this Section includes excavation, dewatering, preparation of the trench bottom, supply and installation of bedding and backfill materials; and disposal of waste material for the installation of utilities and related appurtenances.

quality assurance Monitor and inspect the trenching installation and assure the quality of the work.

Perform all trench excavation in accordance with minimum requirements of OSHA Regulations. Provide shoring, bracing and tight sheeting to prevent caving and to protect workers in accordance with OSHA requirements and to protect adjacent property and structures.

Direct dewatering operations to natural drainages or storm sewers as appropriate. Perform discharge from dewatering operations in accordance with rules and regulations established by the Utah Department of Public Health and Environment.

SUBMITTALS

As specified in Division 1 Section, “General Requirements” submittal procedures.

Submit the source of bedding and initial backfill materials and certified sieve analysis for both.

Product Data: Provide manufacturer’s literature for the following:

Warning tape.

Closeout Submittals: As specified in Division 1 Section, “General Requirements” closeout procedures.

Field quality test reports.

project conditions The type, size and location of known underground utilities have been shown on the drawings; however, no guarantee is made as to the true location of such utilities.

Verify the existence and location of all underground utilities at the project site. Notify ‘Blue Stakes of Utah’ at 811 at least three business days prior to any excavation work. Locate utility company and government owned utility lines.

definitions Bedding: Layer placed over the excavated subgrade in a trench before laying pipe.

Backfill: Soil materials used to fill an excavation.

Initial Backfill: Backfill placed beside and over pipe in a trench, including haunches to support sides of pipe.

Subsequent Backfill: Backfill placed over initial backfill to fill a trench.

Borrow: Satisfactory soil imported off-site for fill or backfill.

Unclassified excavation: Excavation and disposal of all material encountered in the work, including excavation obtained from borrow source.

Rock excavation: Removal and disposal of igneous, metamorphic, and sedimentary rock which cannot be excavated without blasting or using rippers, and all boulders or other detached stones each having a volume of one-half cubic yard or more.

Muck excavation: Removal and disposal of saturated organic mixtures of soils or organic matter which requires additional work or equipment which would not normally be required for unclassified excavation.

PART 2 - products

PART 2 – PRODUCTS

Bedding Mixture of natural or crushed gravel, crushed stone, and natural or crushed sand, ASTM D 2940, except with 100 percent passing a ½- inch sieve and not more than 8 percent passing a No. 200 sieve. On site materials may not be used.

backfill and fill Initial Backfill: Mixture of natural or crushed gravel, crushed stone, and natural or crushed sand, ASTM D 2940, except with 100 percent passing a ½- inch sieve and not more than 8 percent passing a No. 200 sieve. On site materials may not be used.

Subsequent Backfill: Excavated material or borrow material, free from rock larger than 6 inches in the greatest dimension, frozen material, clods, debris, or organic material.

warning tape Detectable Warning Tape: Acid- and alkali-resistant polyethylene film warning tape manufactured for marking and identifying underground utilities, minimum 3 inches wide and 4 mils (0.1 mm) thick, continuously inscribed with a description of utility, with metallic core encased in a protective jacket for corrosion protection, detectable by metal detector when tape is buried up to 30 inches deep, colored as follows:

Red: Electric.

PART 3 - execution alignment and grade Stake out and establish grades for the location of pipelines and utility structures. Obtain Contracting Officer approval before starting excavation.

preparation Protect structures, utilities, sidewalks, pavements, and other facilities from damage caused by settlement, lateral movement, undermining, washout and other hazards created by earthwork operations.

Protect subgrades and foundation soils against freezing temperatures or frost. Provide protective insulating materials as necessary.

Provide erosion-control measures to prevent erosion or displacement of soils and discharge of soil-bearing water runoff or airborne dust to adjacent properties and walkways.

dewatering Prevent surface water and ground water from entering excavations, from ponding on prepared subgrades, and from flooding Project site and surrounding area.

Protect subgrades from softening, undermining, washout, and damage by rain or water accumulation.

Reroute surface water runoff away from excavated areas. Do not allow water to accumulate in excavations. Do not use excavated trenches as temporary drainage ditches.

Install a dewatering system to keep subgrades dry and convey ground water away from excavations. Maintain until dewatering is no longer required.

explosives Do not use explosives.

excavation, general If excavated materials intended for fill and backfill include unsatisfactory soil materials and rock, replace with satisfactory soil materials.

Remove topsoil from the area to be excavated and from the area where excavated material will be piled prior to excavation. Store topsoil as specified below.

Maintain the excavations to guard against and prevent injury to employees and the public. Provide adequate shoring and bracing as required by OSHA and other local governing regulations.

Fence excavations left open at the end of the working day to protect the public.

Notify the Contracting Officer when excavation is completed. Do not place conduit, bedding or backfill until the excavation is inspected by the Contracting Officer.

Notify the Contracting officer when conduit placement is completed. Do not cover conduit until conduit placement has been inspected by the Contracting Officer.

excavation for utility trenches Excavate trenches to indicated gradients, lines, depths, and elevations.

Excavate trenches to uniform widths to provide a working clearance on each side of conduit. Excavate trench walls vertically from trench bottom to 12 inches higher than top of conduit, unless otherwise indicated.

Clearance (General): 6 inches on each side of pipe or conduit.

Clearance from other utilities: 12 inches on each side of pipe or conduit.

Trench Bottoms: Excavate and shape trench bottoms to provide uniform bearing and support of conduit. Shape subgrade to provide continuous support for joints, fittings, and bodies of conduits. Remove projecting stones and sharp objects along trench subgrade.

Conduit less than 6 inches in nominal diameter: Hand-excavate trench bottoms and support pipe and conduit on an undisturbed subgrade.

Excavate trenches 6 inches deeper than elevation required in rock or other unyielding bearing material to allow for bedding course.

storage of soil materials Stockpile borrow materials and satisfactory excavated soil materials. Stockpile soil materials without intermixing. Place, grade, and shape stockpiles to drain surface water. Cover to prevent windblown dust.

Keep topsoil separate from trench-excavated material by stockpiling. Reuse topsoil after backfilling.

utility trench backfill Place bedding material on trench bottoms by hand and tamp as specified. Install bedding to the full width of the trench bottom to a minimum depth of 6 inches. Shape bedding course to provide continuous support for joints, fittings, and bodies of conduits. Do not install conduit until installation is approved by the Contracting Officer.

After conduit is jointed, place initial backfill material by hand along each side of the conduit to offset conditions that might tend to move the conduit off line and grade. Install initial backfill to a height of 12 inches over the conduit. Compact as specified. Compact evenly up on both sides and along the full length of conduit to avoid damage or displacement of conduit. Do not install additional backfill until installation is approved by the Contracting Officer.

Place initial backfill and bedding in layers not to exceed 6 inches in loose depth. Compact each lift as specified.

Place and compact subsequent backfill to final subgrade in layers not to exceed twelve inches in loose depth. Do not place large rock in the backfill material.

Fill voids with backfill materials while shoring and bracing, and as sheeting is removed.

Install warning tape 4 to 8-inches below final grade and directly above utilities.

moisture control Uniformly moisten subgrade and each subsequent fill or backfill layer before compaction to within 2 percent of optimum moisture content.

Do not place backfill or fill material on surfaces that are muddy, frozen, or contain frost or ice.

compaction of backfills and fills Contracting Officer shall witness compaction.

Perform minimum 3 passes with vibratory equipment after installing each of the following:

Bedding.

Initial backfill: Each 6-inch lift.

Perform minimum 1 pass with vibratory equipment after installing each of the following:

Subsequent backfill: Each 12-inch lift.

field quality control Notify Contracting Officer at least 48 hours before inspection and testing. Perform inspections in the presence of the Contracting Officer.

Inspections: Obtain Contracting Officer’s approval after each inspection prior to proceeding with work.

Perform inspection of trench prior to installing bedding and after each pass of vibratory equipment.

Correct excessive settlement or other evidence of improper backfill by reopening the trench or excavation to the depth required for proper compaction. Refill, compact, and re-inspect.

Pay for the correction of unacceptable work at no expense to the Government.

storage of soil materials Stockpile borrow materials and satisfactory excavated soil materials. Stockpile soil materials without intermixing. Place, grade, and shape stockpiles to drain surface water. Cover to prevent windblown dust.

Keep topsoil separate from trench-excavated material by stockpiling. Reuse topsoil after backfilling.

disposal of surplus and waste materials Disposal: Dispose surplus soil, waste material, including unsatisfactory soil, trash, and debris, off Government property.

END OF SECTION 312317