Section 02316 - Excavation Trenching and Backfilling for Utility Systems.doc

SECTION 02316

EXCAVATION, TRENCHING, AND BACKFILLING FOR UTILITIES SYSTEMS

PART 1 - GENERAL

1.1 summary

A. Includes excavating, trenching, backfilling and compacting for the installation of utility lines to the depths and dimensions shown on the drawings.

1.2 RELATED SECTIONS

A. Section 16400: Underground Control Cable & Power Distribution

1.3 PROTECTION

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

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

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

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

NOTE: Minimum and maximum trench dimensions are shown in construction drawings, however for bidding purposes only Contractor shall estimate all trench widths at 2’-00” and trench depths at 4’-00” E. Protect existing underground utilities from damage.

1.4 DEGREE OF COMPACTION

A. Degree of compaction shall be expressed as a percentage of the maximum density obtained by the test procedure presented in ASTM D 1557

1.5 SUBMITTALS

A. The following shall be submitted in accordance with Section “Submittals.”

1. Reports.

a. Soil Proctors

b. Field Density Tests. Testing of Backfill Materials

c. Copies of all laboratory and field test reports within 24 hours of the completion of the test.

1.6 DEFINITIONS

SPEC WRITER: DELETE DEFINITIONS NOT REQUIRED. rEVISE TO SUIT OFFICE OR LOCAL EARTHWORK PRACTICES.

A. Backfill: Soil materials used to fill an excavation.

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

C. Borrow: Satisfactory soil imported from off-site for use as fill or backfill.

D. Drainage Course: Layer supporting slab-on-grade used to minimize capillary flow of pore water.

E. Excavation: Removal of material encountered above subgrade elevations.

1. Additional Excavation: Excavation below subgrade elevations as directed by Contracting Officer (CO). Additional excavation and replacement material will be paid for according to Contract provisions for changes in the Work.

2. Unauthorized Excavation: Excavation below subgrade elevations or beyond indicated dimensions without direction by CO. Unauthorized excavation, as well as remedial work directed by CO, shall be without additional compensation.

F. Fill: Soil materials used to raise existing grades.

G. Subgrade: Surface or elevation remaining after completing excavation, or top surface of a fill or backfill immediately below subbase, drainage fill, or topsoil materials.

H. Utilities include on-site underground pipes, conduits, ducts, and cables, as well as underground services within buildings.

PART 2 – PRODUCTS

1.7 MATERIALS

A. Satisfactory Soils: ASTM D 2487 Soil Classification Groups [GW, GP, GM, SW, SP, and SM], or a combination of these group symbols; free of rock or gravel larger than 2 inches in any dimension, debris, waste, frozen materials, vegetation, and other deleterious matter. Contents suitable for the intended use.

B. Unsatisfactory soils: ASTM D 2487 Soil Classification Groups [GC, SC, ML, MH, CL, CH, OL, OH, AND PT] or a combination of these group symbols. Unsatisfactory materials also include manmade fills, trash, refuse, or backfills from previous construction. Unsatisfactory material also includes material classification as satisfactory, which contains root and other organic matter, frozen material, and stones larger then 3 inches. The (CO) shall be notified of any contaminated materials.

C. Cohesionless and Cohesive materials: Cohesionless materials shall include materials classified in ASTM D 2487 as GW, GP, SW, AND SP. Cohesive materials shall include materials classified as GC, SC, ML, CL, MH, and CH. Materials classified as GM and SM shall be identified as cohesionless only when the fines are nonplastic.

D. Rock (NOT APPLICABLE).

E. Unyielding Material: Unyielding material shall consisting of gravelly soils with stones greater than 3 inches in any dimension or as defined by the pipe; manufacturer, whichever is smaller.

F. Unstable material: Unstable material shall consist of materials too wet to properly support the utility pipe, conduit, or appurtenant structure.

G. Backfill and Fill: Satisfactory soil materials.

H. Subbase: Naturally or artificially graded mixture of natural or crushed gravel, crushed stone, and natural or crushed sand; ASTM D 2940; with at least 90 percent passing a 1-1/2 inch (38 mm) sieve and not more than 12 percent passing a No. 200 (0.75 mm) sieve.

I. Base: Naturally or artificially graded mixture of natural or crushed gravel, crushed stone, and natural or crushed sand; ASTM D 2940; with at least 95 percent passing a 1-1/2 inch (38 mm) sieve and not more than 8 percent passing a No. 200 (0.75 mm) sieve.

J. Bedding: Naturally or artificially graded mixture of natural or crushed gravel, crushed stone, and natural or crushed sand; ASTM D 2940; with at least 100 percent passing a 1 inch (25 mm) sieve and not more than 8 percent passing a No. 200 (0.75 mm) sieve.

K. Drainage Fill: Washed, narrowly graded mixture of crushed stone, or crushed or uncrushed gravel; ASTM D 448; course-aggregate grading Size 57; with 100 percent passing a 1-1/2 inch (38 mm) sieve and 0 to 5 percent passing a No. 8 (2.36 mm) sieve.

L. Detectable Warning Tape: Polyethylene film warning tape encasing a metallic core, minimum 6 inches (150 mm) wide and 4 mils (0.1 mm) thick, continuously inscribed with a description of the utility.

1. Color: Comply with ASME A 13.1, unless otherwise indicated.

PART 3 – EXECUTION

1.8 EXCAVATION

A. Excavation shall be performed to the lines and grades indicated. Excavations shall be unclassified. During excavation, material satisfactory for backfilling shall be stockpiled in an orderly manner at a distance from the banks of the trench equal to ½ the depth of the excavation, but in no instance closer than 2 feet. Excavated material not required or not satisfactory for backfill shall be disposed of off site. The Contractor shall be responsible for disposal of materials. Grading shall be done as may be necessary to prevent surface water from flowing into the excavation, and any water accumulating shall be removed to maintain the stability of the bottom and sides of the excavation. Unauthorized over excavation shall be backfilled in accordance with paragraph BACKFILLING AND COMPACTION at no additional cost to the Government. NOT APPLICABLE SEE NOTE “a” BELOW:

a. Due to the remote location of this project, the contractor will not be held responsible for disposing of any material deemed non-suitable for backfill. However, bedding & backfill over any utilities shall be free of debri and aggregate/rock larger than 3” in diameter. Depth for placement of said material shall be: 18 inches minus outer pipe diameter immediately above utility for both Water and Electric Utilties. Any excess excavated materials shall be spread out on site at a location deemed appropriate per COR.

B. Trench Excavation requirements: The trench shall be excavated as recommended by the manufacturer of the pipe to be installed. Trench walls below the top of the pipe shall be sloped, or made vertical, and of such width as recommended in the manufacturer’s installation manual. Where no manufacturer’s installation manual is available, trench walls shall be made vertical, Trench walls more than 5 feet high shall be shored, cut back to a stable slope, or provided with equivalent means of protection for employees who may be exposed to moving ground or cave in or as recommended in OSHA Standards 29 CFR. Trench walls, which are cut back, shall be excavated to at least the angle of repose of the soil. Special attention shall be given to slopes, which may be adversely affected by weather or moisture content. The trench width blow the top of pipe shall not exceed 24 inches plus pipe outside diameter (O.D.) for pipes of less than 24 inches inside diameter and shall not exceed 36 inches plus pipe outside diameter for sizes larger than 24 inches inside diameter. Where recommended trench widths are exceeded, redesign, stronger pipe, or special installation procedures shall be utilized by the Contractor. The cost of redesign, stronger pipe, or special installation procedures shall be borne by the Contractor without any additional cost to the Government.

1. Bottom Preparation: The bottom of trenches shall be accurately graded to provide uniform bearing and supported for the bottom quadrant of each section of the pipe. Bell holes shall be excavated to the necessary size at each joint or coupling to eliminate point bearing. Stones of 3 inches or greater in any dimension, or as recommended by the pipe manufacturer, whichever is smaller, shall be removed to avoid point bearing.

2. Removal of Unyielding Material: Where unyielding material is encountered in the bottom of the trench, such material shall be removed 4 inches below the required grade and replaced with suitable materials as provided in paragraph BACKFILLING and COMPACTION.

3. Removal of Unstable Material: Where unstable material is encountered in the bottom of the trench, such material shall be removed to the depth directed and replaced to the proper grade with base material as provided in paragraph BACKFILLING AND COMPACTION. When removal of unstable material is required due to the Contractor’s fault or neglect in performing the work, the resulting material shall be excavated and replaced by the Contractor without additional cost to the Government.

4. Excavation for Appurtenances: Excavation for manholes, catch basins, inlets, or similar structures shall be of sufficient size to permit the placement and removal of forms for the full length and width of structure footings and foundations as shown. Removal of unstable material shall be as specified above. When concrete or masonry is to be placed in an excavated area, special care shall be taken not to disturb the bottom of the excavation. Excavation to the final grade level shall not be made until just before the concrete or masonry is to be placed.

5. Jacking, Boring, and Tunneling: Unless otherwise indicated, excavation shall be by open cut except that sections of a trench may be jacked, bored, or tunneled if, in the opinion of the Contracting Officer, the pipe, cable, or duct can be safely and properly installed and backfill can be properly compacted in such sections.

C. Stockpiles: Stockpiles of satisfactory materials shall be placed and graded as specified. Stockpiles shall be kept in a neat and well-drained condition, giving due consideration to drainage at all times. The ground surface at stockpile locations shall be cleared, grubbed, and sealed by rubber-tired equipment, excavated satisfactory and unsatisfactory materials shall be separately stockpiled. Stockpiles of satisfactory materials shall be protected from contamination, which may destroy the quality and fitness of the stockpiled material. If the Contractor fails to protect the stockpiles, and any material becomes unsatisfactory, such material shall be removed and replaced with satisfactory material from approved borrow sources at no additional cost to the Government. Locations of stockpiles of satisfactory materials shall be subject to prior approval of the Contracting Officer. The Contractor shall be responsible for obtaining approved borrows materials from sources off site, as required.

D. Over excavation of Clay Layers: No clay is anticipated to be encountered during trenching and excavation on this project. COR will be present throughout the project, if clay is encountered and its removal is deemed critical for contract work, contractor shall remove and replace with suitable backfill material per COR guidance. This situation would be treated as an unforeseen condition and quantified appropriately so that it can be mitigated.

E. Boulders or Plate Rock: The Forest Service does not anticipate this boulders or plate rock (Rock not in clusters that are under 6” in diameter). If this condition is encountered and its removal is deemed critical for contract work, contractor shall remove and replace with suitable backfill material per COR guidance. This situation would be treated as an unforeseen condition and quantified appropriately so that it can be mitigated

1.9 BACKFILL AND COMPACTION

A. Backfill material shall consist of satisfactory material, or base material as required.

1. Sastifactory Material – Material not containing rock (> 3” in diameter) or debri

2. Base Material – Base coarse with pertinent soil proctor from distributor/supplier

NOTE: Native material shall be permitted for pipe bedding, backfill and fill so long as it meets the definition for “sastifactory material” above. No soil analysis and/or compaction testing shall be required for native material. Compact native material to a firm and stable surface per COR guidance.

Backfill shall be placed in layers not exceeding 6 inches (loose thickness for compaction by hand operated machine compactors), and 8 inches (loose thickness for other than hand operated machines), unless otherwise specified. For imported/trucked in material, each layer shall be compacted to at least 95 percent maximum density for cohesionless soils and 90 percent maximum density for cohesive soils, unless otherwise specified. Contractor shall provide soil proctors for all imported/trucked in material.

B. Trench Backfill: Trenches shall be backfilled to the natural surrounding grade and giving a 3” mound on top. Contractor shall make all efforts to pressure test prior to any backfilling; however, the trench shall be permitted to be backfilled to 18 inches (plus pipe OD) above the top of pipe prior to performing the required pressure tests if permitted by COR The joints and couplings shall be left uncovered during the pressure test. The trench shall not be completely backfilled until all specified tests are performed. All open trenches shall be backfilled within 24 hours.

1. Replacement of Unyielding Material: Unyielding material removed from the bottom of the trench shall be replaced with base or backfill material.

2. Replacement of Unstable Material: Unstable material removed from the bottom of the trench or excavation shall be replaced with base material in layers not exceeding 6 inches loose thickness.

3. Bedding Backfill: Bedding for utilities shall be of the type “Satisfactory Material” as defined and a minimum thickness of 3”. Refer to Section 02510 Water Distribution, Subsection 4.5 Laying Pipe.

4. Backfill material immediately surrounding the utility/pipe shall be of the type” Satisfactory Material” as defined and shall extend up 18” plus pipe outer diameter of the pipe (from bottom of pipe). Said material shall be placed and compacted with approved tampers to a height of at least one foot above the utility pipe or conduit. The backfill shall be brought up evenly on both sides of the pipe for the fill length of the pipe. Care shall be taken to ensure through compaction of the fill under the haunches of the pipe.

5. Final Backfill: The remainder of the trench shall be filled with satisfactory material. Backfill material shall be placed and compacted as follows:

6. Turfed or Seeded areas and Miscellaneous areas: Backfill shall be deposited in layers of a maximum of 12 inch loose thickness, and compacted to 85 percent maximum density for cohesive soils and 90 percent maximum density for cohesionless soils. This requirement shall also apply to all other areas not specifically designated above.

C. Backfill for Appurtenances: After the manhole, catch basin, inlet, or similar structure has been constructed and the concrete has been allowed to cure for 3 days, backfill shall be placed in such a manner that the structure will not be damaged by the shock of falling earth. The backfill material shall be deposited and compacted as specified fore final backfill, and shall be brought up evenly on all sides of the structure to prevent eccentric loading and excessive stress.

1.10 SPECIAL REQUIREMENTS

Special requirements for both excavation and backfill relating to the specific utilities are as follows:

SPEC WRITER: DELETE IF NOT SUITED FOR PROJECT

A. Water Lines: trenches shall be of a depth to provide a minimum cover of 48 inches from the existing ground surface, to the top of the pipe.

B. Electrical Distribution System:

1. Primary underground electric lines (NORA ELECTRIC): trenches shall be of a depth to provide a minimum cover of 48 inches from the existing ground surface, to the top of the conduit. NOTE: Forest Service will facilitate coordination of the placement of line to ensure the trench is not open longer than 24 hours. Contractor shall contact the Forest Service when he/she is ready to trench for the placement of NORA Electric’s new underground power distribution line.

2. Secondary underground electric lines: direct burial cable and conduit or duct line shall have a minimum cover of 24 inches from the finished grade, unless otherwise indicated. Bedding material shall be used for all direct burial cable.

C. Plastic Marking Tape: Warning tapes shall be installed directly above the utility. See construction drawings for trench details.

1.11 TESTING

Testing shall be the responsibility of the Contractor and shall be performed at no additional cost to the Government.

A. Imported Materials: For any/all material not native to the site, contractor shall provide soil proctors with compaction curves specifying maximum compaction levels and associated water content. All imported materials shall be compacted to 95% of the soil’s maximum compaction level. Note that the contractor will be responsible for performing at minimum one test per type of work to verify the level of compaction is met at which point that compaction effort shall be matched anywhere else that material is used for similar type of work.

a. Example: If contractor trucks in base coarse and uses it for backfilling a trench over a waterline, contractor shall order a test to ensure that the material is properly compacted per soil proctor and note the compaction effort required. Should the contractor use the same material to backfill a buried electric line, contractor will not be obligated to order another test. Contractor will be expected to use the same compaction effort for electric line as for the waterline.

B. Test Facilities: an approved commercial testing laboratory shall perform Tests. Approval of testing facilities and personnel shall be based on compliance with ASTM D 3740 and in accordance with Division 1 Section “Quality Requirements”

C. Testing of Backfill Materials: Classification of backfill materials shall be determined in accordance with ASTM D 2487 and the moisture-density relations of soils shall be determined in accordance with ASTM D 1557. A minimum of one soil classification and one moisture-density relation test shall be performed on each different type of material used for bedding and backfill.

D. Field Density Tests: Tests shall be performed in sufficient numbers to ensure that the specified density is being obtained. A minimum of one field density test per lift of backfill for every 500 feet of installation shall be performed. Field in-place density shall be determined in accordance with ASTM D 1556, ASTM D 2167, or ASTM D 2922. When ASTM D 2922 is used, the calibration curves shall be checked and adjusted using the sand cone method (ASTM D 1556) as described in paragraph Calibration of the ASTM publication. ASTM D 2922 results in a wet unit weight of soil and when using this method, ASTM D 3017 shall be used to determine the moisture content of the soil. The calibration curves furnished with the moisture gauges shall be checked along with density calibration checks as described in ASTM D 3017. The calibration checks of both the density and moisture gauges shall be made at the beginning of a job, on each different type of material encountered, at intervals as directed by the Contracting Officer. Copies of calibration curves, results of calibration tests, and filed and laboratory density tests shall be furnished to the Contracting Officer. Trenches improperly compacted shall be reopened to the depth directed, then refilled and compacted to the density specified at no additional cost to the Government.

END OF SECTION 02316