(a) General.
(1) Provide erosion control measures as required. Erosion control measures including seeding and mulching shall be designed, installed and maintained in accordance with the N.C. Department of Environment and Natural Resources, Land Quality Section's “Erosion and Sediment Control Planning and Design Manual”. The developer/engineer is responsible for securing all required permits.
(2) Pipe installation shall meet the following general guidelines:
a. Handle pipe and accessories in accordance with manufacturer's recommendations. Take particular care not to damage pipe coatings.
b. Carefully inspect pipe immediately prior to laying. Do not use defective pipe. Replace pipe damaged during construction.
c. Lay pipe to design grade and alignment.
d. Provide proper equipment for lowering pipe into trench.
e. Provide tight closure pipe ends when work is not in progress.
f. Keep pipe interior free of foreign materials.
g. Do not lay pipe in water or when the trench or weather conditions are unsuitable for the work.
h. Clean bell and spigots before joining. Make joints and lubricate gasket in accordance with pipe manufacturer recommendation.
i. Block fittings with concrete or restrained joints.
(b) Trenching for underground pipe installation.
(1) Definitions.
a. Backfill. A specified material used in filling the excavated trench and placed at a specified degree of compaction.
1. Materials. Materials listed herein include processed materials plus the soil classifications listed under the Unified Soil Classification System, (USCS) (Method D2487 and Practice D2488). The soil materials are grouped into five broad categories according to their suitability for this application.
i. Class I: Angular, 6 to 40-mm (1/4 to 1-1/2-in.), graded stone, including a number of fill materials that have regional significance such as coral, slag, cinders, crushed stone, and crushed shell.
ii. Class II: Coarse sands and gravels with maximum particle size of 40 mm (1-1/2 in.), including various graded sands and gravels containing small percentages of fines, generally granular and noncohesive, either wet or dry. Soil Types GW, GP, SW, and SP are included in this class.
iii. Class III. Fine sand and clayey gravels, including fine sands, sand-clay mixtures, and gravel-clay mixtures. Soil Types GM, GC, SM, and SC are included in this class.
iv. Class IV: Silt, silty clays, and clays, including inorganic clays and silts of medium to high plasticity and liquid limits. Soil Types MH, ML, CH and CL are included in this class. These materials shall not be used for bedding, haunching, or initial backfill.
v. Class V: This class includes the organic soils OL, OH, and PT as well as soils containing frozen earth, debris, rock larger than 40 mm (1 ½ in.) in diameter, and other foreign materials. These materials shall not be used for bedding, haunching, or initial backfill.
2. Backfill zones. Each backfill zone shall extend the full width of the trench bottom.
i. Foundation. Extending down from the bottom of bedding zone as defined below.
ii. Pipe embedment.
A. Bedding. Extending from four inches below the pipe bottom to the pipe bottom for 30-inch diameter and smaller and six inches below the pipe bottom for pipes larger than 30 inches in diameter.
B. Haunching. Extending from the bedding (bottom of the pipe) to the pipe spring line.
C. Initial backfill. Extending from the haunching (pipe spring line) to one foot above the top of the pipe.
iii. Final backfill. Extending from the initial backfill to the finish ground elevation.
b. Laying conditions.
1. Type 1. Flat bottom trench with loose backfill.
2. Type 2. Flat bottom trench with backfill lightly consolidated to centerline of pipe.
3. Type 3. Pipe bedded in four inches minimum of loose soil and backfill lightly consolidated to top of pipe.
4. Type 4. Pipe bedded on Class I material to 1/8 pipe diameter (four-inch minimum) backfill compacted to top of pipe a minimum of 80% of standard proctor.
5. Type 5. Pipe bedded in compacted Class I material to pipe centerline with four-inch minimum under pipe. Backfill to top of pipe with Class I, II, or III and compact to 90% of standard proctor.
c. Compaction. Process of mechanically stabilizing a material by increasing its density at a controlled moisture condition. “Degree of compaction” shall be expressed as a percentage of the maximum dry density obtained by the test procedure presented in ASTM D698 (Standard Proctor).
d. Excavation. The removal of soil or rock to obtain a specified depth or elevation.
e. Hard material. Solid, homogeneous material which is not included in the definition of “rock” but which may require the use of heavy excavation equipment with ripper teeth. Amount must exceed one cubic yard in volume. Material having a standard penetration resistance as determined by ASTM D1586 between 60 and 150 blows per foot is defined as “hard material.”
f. Lift. Layer of soil placed on top of a previously prepared or placed soil.
g. Rock. Solid, homogeneous material which cannot be removed without the systematic drilling and blasting exceeding one cubic yard in volume. Material having a standard penetration resistance as determined by ASTM D1586 greater than 150 blows per foot is defined as “rock.” Removal of “hard material” will not be considered rock excavation because of intermittent drilling and blasting that is performed merely to increase production.
h. Pipe springline. A line running horizontally through the center of the pipe.
i. Topsoil. Natural, friable soil, representative of productive soils in the vicinity of the site. Topsoil shall be free from roots, stones larger than one inch, objectionable weed seeds, toxic substances, and materials that hinder grading, planting, and maintenance operations.
(2) Products.
a. Stone.
1. Class I material shall be #67 or #78M stone in accordance with NCDOT specifications Section 1005, General Requirements for Aggregate.
b. Warning and identification tape.
1. Tape shall be a minimum three-inch wide polyethylene plastic tape manufactured specifically for identification of buried utilities with means of enabling detection by a metal detector to a minimum depth of three feet. Tape shall be color coded and continuously imprinted with warning and identification markings in bold black letters to read “CAUTION - BURIED (utility) LINE BELOW.” Color and printing shall be permanent, unaffected by moisture or soil and shall be as follows:
Utility | Color | Marking |
Utility | Color | Marking |
Water | Blue | Caution - Buried Water Line Below |
Gravity Sewer | Green | Caution - Buried Sewer Line Below |
Force Main | Green | Caution - Buried Force Main Below |
Electric | Red | Caution - Buried Electric Line Below |
Gas | Yellow | Caution - Buried Gas Line Below |
Telephone | Orange | Caution - Buried Telephone Line Below |
SCADA | Orange | Caution - Buried SCADA Line Below |
2. Tape shall be by Blackburn Manufacturing, Joseph G. Pollard Co., or Reef Industries Inc.
c. Tracer wire.
1. Tracer wire shall be #12 solid copper wire. All connections shall be by wire nuts and taped.
2. Splices in tracer wire are to be kept to a minimum and joined with copper split nuts of appropriate size.
(3) Project safety.
a. Contractor is responsible for project safety.
b. Perform work in conformance with applicable State and Federal safety regulations including, but not limited, to the following:
1. North Carolina Safety and Health Standards for the Construction Industry (29CFR 1926 Subpart P).
2. NC OSHA Industry Guide No. 14, Excavations.
3. NC OSHA Industry Guide No. 20, Crane Safety.
c. Provide barriers, warning lights, and other protective devices at excavations as necessary for safety of workers and the public.
d. Provide sloping of bank, shoring, sheeting, or other means of maintaining the stability of the trench in accordance with the requirements of the Associated Contractor's Manual of Accident Prevention OSHA, Part 1926.P.
(4) Protection of underground facilities.
a. Investigate underground facility location prior to start of construction.
b. Installer is required to contact North Carolina 811 prior to start of construction.
c. Repair damage to any existing facilities.
(5) Water control.
a. Prevent surface water from entering the trench.
b. When trench bottom is below the existing ground water table, install a dewatering system to maintain water table one foot below trench bottom. Provide a man experienced in dewatering work at the job site.
c. Maintain dewatering until backfilling has proceeded above the existing ground water level.
d. Dispose of water from dewatering operations in accordance with the North Carolina Sedimentation Pollution Control Act.
(6) Use of explosives.
a. Explosives may not be used on any excavation unless specifically approved by the city.
(7) Excavating.
a. Excavation shall be by open cut method. Short sections of trench may be tunneled or direct bored with the approval of the city.
b. Stockpile excavated material in such a manner that it will not obstruct the flow of runoff, streams, endanger work, impair the use or appearance of existing facilities, or be detrimental to the completed work.
c. Contractor shall segregate excavated material so as to maintain material suitable for backfill separate from material that is unsuitable.
d. Trench dimensions at the pipe embedment and foundation zone unless noted otherwise shall be as follows:
1. Minimum width. Pipe outside diameter plus 18 inches.
2. Maximum width. Pipe outside diameter plus 24 inches.
3. Sides shall be vertical to a minimum of one foot above the top of pipe.
e. Shape trench bedding to provide uniform bearing for the full pipe length. Bottom shall be free of protrusions that could cause point loading on pipe. Provide bell holes as required for properly making pipe joint.
f. Do not over excavate. Excavation below grade shall be backfilled with Class I material.
g. Undercut soils that become unsatisfactory by construction activity or by being left exposed to the weather and backfill with Class I material.
h. Remove shoring, bracing, and sheeting, unless otherwise noted, as the trench is backfilled.
i. Excavation of trench shall not advance more than 200 feet ahead of the installation. In no case should the excavation extend beyond that which can be backfilled by the end of the workday.
j. Correct unstable soil conditions encountered at trench foundation by one of the following methods:
1. Excavate below grade as approved by engineer and backfill with Class I material or approved substitute material.
k. Rock and hard material.
1. Excavate rock and hard material to a minimum depth of four inches below the pipe for pipes smaller than 30 inches and six inches for pipes 30 inches and larger.
l. Pressure lines.
1. Provide a minimum three feet of cover.
2. Excavate trenches to provide vertical curve chords that will not exceed the pipe manufacturer's recommended joint deflection.
3. Provide concrete thrust blocks having a compressive strength of 3,000 psi at 28 days at change in horizontal and vertical direction and reduction in the pipe size, unless other restraint systems are approved. Cut trench sides vertical and square to receive concrete. Provide bearing area against trench wall as indicated in the standard detail.
m. Gravity lines.
1. Excavate trench to the design alignment and grade.
n. Utility structures. Provide a minimum of 12 inches below subgrade and backfill with Class I material compacted to 95% maximum density. If the soil conditions are found to be unsuitable for structural stability of the manhole, city may require additional depth of Class I material.
(8) Backfilling.
a. General.
1. Temperature must be above freezing and rising.
2. In windy, hot, or arid conditions with a high rate of evaporation add moisture to the material to maintain the optimum moisture content.
3. Do not proceed in rain or on saturated subgrade.
4. Do not place material on surfaces that are muddy, frozen, or contain frost.
5. Maintain backfill operation within 200 feet from pipe laying operation.
6. Backfill trench to existing ground surface with select excavated material at the specified compaction.
7. If excavated material is unsuitable to obtain specified compaction, provide suitable off-site borrow material for backfill.
8. Re-excavate trenches improperly compacted. Backfill and compact as specified.
9. Provide appropriate tamping equipment, and water to obtain proper moisture content, to achieve specified compaction of backfill.
10. Conduct operation of heavy equipment above pipe installation as to prevent damage to pipe.
11. Install warning/identification tape over utilities. Bury tape one foot below finished grade above the utility.
12. Install tracer wire for non-metallic pressure pipe. Bury tracer wire with pipe. Wire shall be looped into valve boxes to allow access for direct contact location.
b. Backfill in pipe embedment zone (bedding, haunching, and initial backfill).
1. General.
i. Backfill with material as specified below. Material shall be free from objects larger than two inches.
ii. Where rock and hard material has been excavated below pipe bottom, backfill and compact bedding with Class I material. Class II or III material may be used for bedding with engineer's approval.
iii. Place backfill material to assure placement of material under pipe haunches.
iv. Take care during placement and compacting of material to avoid movement of pipe.
2. Place backfill in bedding and haunching zones in six-inch maximum lifts and compact to a minimum of 90%. Provide backfill material in pipe embedment zone as specified below.
i. Pressure lines (flexible and rigid pipe).
A. Excavation in Class I, Class II, and Class III soils suitable for bedding, the bedding surface shall provide a firm foundation of uniform density. Backfill with select excavated material.
B. Excavation in Class IV or Class V, running water, and other unstable soil conditions, excavate a minimum of four inches below pipe bottom and provide Class I material for bedding and haunch zone. Backfill with Class I, II, or III material in initial backfill.
C. Ductile iron over 16 inch.
1) Depth Zero to 12 feet: Type 2 laying conditions same as for pressure pipe.
2) Depth over 12 feet: Provide Class I material for bedding and four inches up from bottom of pipe.
ii. Gravity sewer lines, rigid pipe and ductile iron.
A. Excavation in Class I, Class II, Class III, and stable Class IV soils suitable for bedding, the bedding surface shall provide a firm foundation of uniform density. Backfill with select excavated material.
B. Excavation in Class V, unstable Class IV soils, running water, and other unstable soil conditions, excavate a minimum of four inches below pipe bottom and provide Class I material for bedding and haunch zone. Backfill with Class I, II, or III material in initial backfill.
iii. Gravity sewer lines, flexible (PVC SDR 35).
A. Depth Zero to 14 ft. Provide Class I material for bedding and haunching. Backfill with Class I, II, or III material in initial backfill.
B. Depth over 14 ft. Provide Class I material for bedding, haunching, and initial backfill.
c. Final backfill.
1. Backfill with materials free of stones and free of debris larger than six inches in dimension. Place backfill in lifts not exceeding the thickness and compacted to the minimum density specified below.
2. Trench backfilled with non-cohesive materials may be compacted with water flooding; except under roadways, shoulders of roadways, and other areas subject to vehicular movement, provided the method of compaction is approved by the city and provides the degree of compaction required.
3. Lifts and density.
i. Undeveloped areas (i.e., forests, fields, and, croplands). Trench may be filled with bulldozer blade provided material fall will not damage pipe. Mound soil over the trench area sufficiently to settle level over time. Degree of compaction shall be 85%.
ii. Lawns. Backfill in 12-inch lifts and compact to 90%. Top 12 inches shall be free of material with a dimension over two inches.
iii. Roads (including rights-of-way), drives, parking areas (including areas within 20 feet), and adjacent to existing utilities. Backfill in six-inch lifts compact to 95%.
iv. Within 20 feet of foundations. Backfill in six-inch lifts compacted to 95%.
d. Utility structures. Bring backfill to grade in even lifts on all sides. Lift depths and compaction densities shall be as specified according to area of installation for pipe above. Backfill against cast-in-place concrete structure only after concrete has attained the specified 28-day compressive strength.
(c) Relation of sewer to water main, wells and storm sewer.
(1) Lateral separation. Lay at least ten feet laterally from existing and proposed water main. Where existing conditions prevent a ten-foot lateral separation, the following shall be followed with approval of the city.
a. Lay sewer in a separate trench, with the elevation of the top of the sewer at least 18-inches below the bottom of the water line.
b. Lay sewer in the same trench as the water main with the sewer main located at one side on a bench of undisturbed earth, and with the elevation of the top of the sewer at least 18 inches below the bottom of the water line.
(2) Crossing separation. Lay top of sewer at least 18 inches below the bottom of the water. Where existing conditions prevent an 18-inch vertical separation, construct both the water main and sewer of ferrous materials and with joints that are equivalent to water main standards for a distance of ten feet on each side of the point of crossing. Both the water and sewer line must be pressure tested to 150 psi to insure water tightness.
(3) Crossing a sewer over a water main. When it is necessary for a sewer to cross over a water main, construct both the water main and the sewer of ferrous materials and with joints equivalent to water main standards for a distance of ten feet on each side of the point of crossing. A section of water main pipe shall be centered at the point of crossing.
(4) A 24-inch vertical separation shall be provided between sanitary sewers and storm sewers or ferrous pipe specified.
(5) Lay sewer pipe to true lines and grades by use of laser beam equipment or other acceptable means.
(6) Minimum separation distances.
a. 100-foot horizontal separation from wells or other water supplies.
b. Twenty-four-inch vertical separation from storm sewers or ferrous pipe shall be used.
(d) Ductile iron pipe.
(1) Install pipe in conformance with AWWA C600 and the following:
a. For laying pipe in a vertical or horizontal curve, each full length pipe may be deflected by the following offset distance:
1. Push-on joint.
i. Three to 12-inch pipe: 14-inch offset.
ii. Fourteen to 36-inch pipe: eight-inch offset.
2. Mechanical joint.
i. Three to six-inch pipe: 20-inch offset.
ii. Eight to 12-inch pipe: 15-inch offset.
iii. Fourteen to 20-inch pipe: eight-inch offset.
iv. Twenty-four to 36-inch pipe: six-inch offset.
b. For laying restrained joint pipe in a vertical or horizontal curve, except for horizontal directional drills (HDD), each full length pipe may be deflected by the following offset distance:
1. Six to 12-inch pipe: 11-inch offset.
2. Sixteen to 20-inch pipe: seven-inch offset
3. Twenty-four to 30-inch pipe: five-inch offset.
4. Thirty-six-inch pipe: four-inch offset.
5. Forty-two to 48-inch pipe: 1- 1/4-inch offset.
(e) PVC pressure pipe.
(1) Install PVC C900 pipe in conformance with AWW A C605.
(2) Bell and spigot joints. Clean bell and spigot ends prior to jointing. Ends of field cut pipe shall be beveled with file. Gasket shall be clean and lightly lubricated. Joint shall be made as recommended by the manufacturer.
(f) Encasement pipe.
(1) General.
a. Verify the subsurface conditions at each boring site.
b. Stabilize and maintain bore pit bottom to provide proper equipment support and maintain pipe alignment. Dewater as necessary for site. Excavate bore pit in accordance with OSHA regulations. Provide adequate barricades, railings, and warning lights throughout the boring operation. Conduct operation in such a manner so as not to create a hazard to, nor impede the flow of traffic.
c. Install encasement pipe by dry boring and jacking.
d. Boring auger diameter shall not be greater than the outside diameter of the encasement pipe and shall not extend more than six inches ahead of the cutting edge of the encasement pipe. Fill voids that are formed during the operation with a 1:3 portland cement grout pumped at 50 psi to ensure that there will be no settlement of the roadway.
e. As the boring operation progresses, butt weld each new section of the encasement pipe to the section previously jacked into place. Maintain proper alignment. Confirm the grade of the encasement pipe as the work progresses.
f. If an obstruction is encountered during the boring operation, efforts should be made to remove the obstruction. If obstruction cannot be removed, withdraw the encasement pipe and fill the void with 1:3 portland cement grout at 50 psi. If the encasement pipe cannot be withdrawn, seal ends before moving to another bore site. City shall approve location of new bore site.
g. Provide seals at each end of encasement pipe.
(2) Carrier pipe.
a. Install carrier pipe in the encasement pipe using manufactured pipe supports. Supports shall prevent movement of the carrier pipe within the encasement. Space supports as specified.
(g) Sewer cleanouts.
(1) General.
a. Sewer cleanouts connected to ductile iron pipe shall also be ductile iron sewer pipe conforming to these specifications.
b. Sewer cleanouts connected to PVC pipe shall also be PVC sewer pipe schedule 40 conforming to ASTM-D-3034 latest revision. Use elastomeric gaskets for pipe joints.
c. Service wyes shall be used on new PVC pipe. Service saddles shall be used on existing PVC, solvent welded to the main and fastened with double stainless steel bands.
d. Cleanouts shall be a minimum of four-inch diameter. Provide sewer cleanouts with screw-in watertight cap. Installation shall be in accordance with the standard detail.
(h) Service connections.
(1) General.
a. Make service connections in accordance with the standard detail.
b. Service connections to the main lines shall be perpendicular to the main line to the edge of the right-of-way or easement line.
c. Four-inch lines shall have a minimum slope of 1.0 % and have cleanouts every 75 feet at a minimum in addition to a cleanout at the right-of-way line or at the edge of the easement.
d. Six-inch lines shall have a minimum slope of 0.60 % and have cleanouts every 100 feet at a minimum in addition to a cleanout at the right-of-way line or at the edge of the easement.
e. Six-inch service lines shall tie directly into a manhole.
f. Service lines, which are connected into manholes, shall be installed less than 2.5 feet above the invert or shall be installed as a standard drop.
(i) Anti-seep collars.
(1) General.
a. Anti-seep collars. Provide anti-seep collars to prevent groundwater flow along pipe in wetlands. Collars shall extend past trench walls and bear against undisturbed soils. Dimension of collars shall be as indicated on the standard details. Do not place stone in area of anti-seep collars.
b. Concrete collar. Provide Class B concrete with minimum cement content of five sacks per cubic yard (five and one-half sacks for angular course aggregate); 6.8 gallons of water per sack water-cement ratio; two 4-inch slump range; and 28-day strength of 2,500 psi.
(j) Pavement patching.
(1) General.
a. Repair damaged pavement structure.
b. Cut existing pavement for utility installation in straight lines generally parallel to the utility. Properly dispose of removed pavement structure.
c. Extend pavement patch one foot beyond each side of trench on firm subgrade. Slope new surface to drain.
d. Asphalt pavements. Replace asphalt pavement with a pavement structure no less than as shown on the standard details. For roadways under NC Division of Highways jurisdiction, pavement shall be replaced in accordance with their requirements.
e. Concrete pavements. Replace concrete pavement with pavement structure equal to existing but no less than six inches. Concrete shall be minimum 3,000 psi. When existing concrete joint is within five feet of trench remove existing concrete to joint. Provide expansion joint at edge of existing concrete. Surface treatment shall match existing.
f. Curbs, gutters, and sidewalks. Replace curbs and gutters, and sidewalks removed or damaged with similar sections to match the existing. Remove to nearest existing joint.
g. Approval of other authorities. Pavements under the jurisdiction of the NC Division of Highways shall be subject to the approval of a representative of that Division.
(k) Grading and clean-up.
(1) General.
a. Provide for testing and clean-up as soon as practical, so these operations do not lag far behind the pipe installation. Perform preliminary clean-up and grading as soon as backfill is complete.
b. Provide positive drainage of finished grade and drain away from structures. Finished grade shall be reasonably smooth, compacted, free from irregular surface changes and comparable to the adjacent existing ground surface.
c. Seed disturbed areas.
d. Upon completion of backfilling, remove and properly dispose of excess material and waste.
(Ord. of 11-7-16, No. 10-16)