15-19 (E) Casing Pipe Fill
Pump or place flowable fill; grout; or Class III, Class IV or Class V select materials into the annular void between the carrier pipe and casing pipes if required in the plans . 1540 -4 MEASUREMENT AND PAYMENT __" Encasement Pipe will be measured from end to end and paid at the contract unit price per linear foot for each size. Material used to fill the annular void is incidental to the work being performed. Payment will be made under: Pay Item Pay Unit __" Encasement Pipe Linear Foot 1550 -1 DESCRIPTION Install pipe using a trenchless method. Pipe refers to the specified pipe, which may be the primary carrier pipe or an encasement pi pe. Shoring means the earth support system used for installing the pipe. The terms for encasement, casing, encasement pipe and casing pipe are interchangeable. An engineer licensed by the State of North Carolina shall design the method for installation of the pipe in the native soil and certify the work will not damage the roadway above or endanger the roadway user. 1550 -2 MATERIAL Refer to Division 10. Item Section Portland Cement Concrete 1000 Encasement Pipe 1540 Flowable Fill 1000 -7 Structural Timber 1082 Structural Steel 1072 Treated Timber 1082 -3 Use pipe joints that are modified to suit the installation method. Provide engineering calculations for piping and shoring. Submit material certifications and obtain approval from the Engineer before installation. Use steel or concrete liner plates. Steel tunnel liner plates shall meet Section s 16 and 25 in AASHTO LRFD Bridge Construction Specifications . Concrete liner plates shall meet AASHTO specifications. Drilling fluids consist of water, bentonite and polymer additives. Other materials will be considered with adequate design and quality control. 1550 -3 CONSTRUCTION METHODS
A.General Apply Section 1505 for excavation, trenching, pipe laying and backfill. Install the pipe to the lines and grades shown in the plan s. Use workers that are skilled in the method of construction. Construct with good workmanship by skilled workers along with proper safety precautions.
15-20 Locate ends of trenchless construction and pits bey ond the vehicle recovery area of the
roadway. The vehicle recovery area may be reduced using accep table traffic control methods.
B.Design Contract plans will show a trenchless method including but not limited to length, profile and bore pit locations based on available information. The Contractor’s design shall confirm this method is appropriate for the field conditions , for the specified pipe and for the Contractor’s equipment . Subsurface information in the vicinity of the trenchless installation may be available in accordance with Section 102 -7. Assess soil conditions expected during trenchless operations. Design the method to minimize the vertical movement of the pipe or the completed roadway section. Use methods of construction and installation that will not disturb the soils outside of the immediate vic inity of the pipeline or pits. Before construction, provide detailed plans for the method of installation certified by an engineer licensed by the State of North Carolina . Provide certified calculations demonstrating the method of installation as safe and of minimal risk. Provide certified calculations of the structural adequacy of all materials. The design shall meet AASHTO LRFD Bridge Design Specifications . An engineer licensed by the State of North Carolina shall certify changes or modifications to the designed method as needed for actual field conditions.
C.Water Control Provide groundwater control and removal as appropriate for the method of excavation and installation. Remove the groundwater using an engineered dewatering system provided in the design submittal . Keep surface waters out of the excavation and pits.
D.Shoring Provide temporary or permanent shoring, as needed. Provide temporary shoring to maintain the hole or pit excavation for the duration of the work. Fill all voids around the excavation and shoring with structural fill material as work progresses. Either work continuously (24 hours/day and 7 days/week) on the operations from the time the excavation begins th rough the filling of voids or use an engineered system for shoring the excavation during work stoppage.
E.Pre-Construction Meeting The Contractor shall conduct a pre -construction meeting with the Engineer to review the proposed method for installation of the pipe. Conduct the meeting at least 48 hours before beginning installation. The meeting shall consist of, but is not limited to :
1.Presentation of the construction methods for understanding by all involved,
2.Presentation of methods for filling any potential voids around the pipe ,
3.Demonstrating that appropriate equipment and materials are on site ,
4.Providing a progress schedule , and
5.Demonstrating ability to react to failures or roadway settlement or heave . 1550 -4 TRENCHLESS METHODS
A.Bore and Jack For bore holes up to 6 inches in diameter in stable ground, the hole may be augured and the pipe pushed or jacked through the cleaned out hole. For bore holes greater than 6
15-21 inches , provide continuous support of the hole by simultaneously jacking the pipe or
casing into the hole. Use eq uipment suitably sized and designed to simultaneously bore or drill the soil or rock while pushing or jacking pipe on a controlled grade. Position the cutter head within one diameter of the leading edge of the pipe . In cohesive, dense and dry soils and r ock, position the cutter head in front of the leading edge. In non- cohesive or loose soils, position the cutter head inside the pipe . Dry bore only, do not use jetting or wet boring methods. Use drilling fluids only on the outside of pipe for lubr ication or hole stabilization. Minimize over bore, match cutter diameter to the outside diameter of the encasement pipe. Limit overbore to the O.D. + 2 inches . Provide steering controls as necessary to maintain line and grade. If conditions allow and with the ap proval of the Engineer , the Contractor may elect to use the pipe ramming method in lieu of bore and jack. Payment for the pipe ramming method will be paid as bore and jack.
B.Directional Drilling For drilled holes up to 6 inches in diameter in stable ground, the hole may be drilled and reamed followed by pulling the pipe into the hole within 8 hours. For drilled holes greater than 6 inches , simultaneously pull the pipe or casing into the hole as reaming occurs . When under pavement or within a one horizontal to one vertical distance from pavement, maintain the depth of cover shown in Table 1550- 1. TABLE 1550 -1 DEPTH OF COVER FOR DIRECTIONAL DRILLIN G Drilled Hole Diameter Minimum Depth of Cover 2" to 6" 6 ft > 6" to 15" 12 times the hole diameter > 15" to 36" 15 ft Begin bores at locations that allow transitioning the bore to meet the above depths. Use drilling fluids as appropriate for the type soils. Pump drilling fluids only while drilling or reaming. Monitor flow rates to match the amount leaving the bore hole. Do not increase pressure or flow to free stuck drillheads, reamers or piping. Limit drilled or reamed holes to 1.5 x O.D. for pipe 12 inches or less and O.D. + 6 inches for pipes larger than 12 inches.
C.Tunneling Tunnel using hand mining, mechanical excavation , tunnel boring machine (TBM), microtunneling , or other accepted tunneling method . Use tunnel shields or fore poling along with benched excavation and breast boarding as appropriate for the field conditions. Alternatively, the Contractor’s engineer may certify that the soils are self-supporting of the dead and live loads and design tun neling methods as appropriate. Provide active support to the tunnel walls. Shore tunnel walls using liner plates, steel ribs with lagging or other engineered method or by jacking piping into place. Limit over excavation to 2 inches larger than the line r or shield. Grout the external voids as work progresses and as specified by the Contractor’s engineer .
15-22 (D) Pipe Ramming
Use pipe ramming only where soils are homogeneous and free of rock, boulders, stumps and debris. Do not use in the vicinity of quick or liquefiable soils. Steel bands 1/2 inch thick are allowed on the outside of the leading edge of the pipe or casing to oversize the hole to reduce friction. S teel bands 1/2 inch thick may be used on the inside to compact the spoil and to prevent plugging. Install at the following minimum depth of cover shown in Table 1550- 2. TABLE 1550 -2 DEPTH OF COVER FOR PIPE RAMMING Pipe or Casing Diameter Minimum Depth of Cover 2" to 6" 4 ft > 6" to 14" 6 pipe diameters >14" to 72" 8 ft Contain spoil within the casing during ramming. After completion, use compressed air or augers to remove the spoil. Clean the interior using a pig. Provide appropriate safety devises. Limit air press ure to less than the rating of the pipe or casing. Use lubricants and surfactants as needed and ensure vibration induced consolidation of soils does not result in settlement greater than 0.02 feet .
E.Other Methods Other methods will be considered on a case by case basis when thoroughly engineered.
F.Lubrication and Drilling Fluids Use drilling fluids for lubrication. Do not use water alone. 1550 -5 QUALITY CONTROL The Contra ctor, at no cost to the Department , shall replace or repair damaged or defective installations. The method to be used shall be designed by the Contractor’s engineer and approved by the Engineer.
A.Ground Movement Before excavation, establish control points for measuring vertical movement of the road at 10 f eet intervals along the centerline and 10 f eet each side of the pipeline. A land surveyor licensed in the State of North Carolina shall monitor these points dai ly until construction is complete. Cease trenchless operations when measured movement exceeds 0.02 f eet. Determine cause of settlement and repair as necessary. Modify trenchless methods as needed.
B.Leakage Limit leakage through tunnel walls to minor seepa ge. A ll leaks in pipes, casing or other permanent shoring shall be sealed .
C.Roundness Provide permanent shoring maintaining at least 95% of nominal diameter in all directions.
D.External Voids Fill all external voids greater than 2 inches high or 2 feet wide . Fill with flowable fill, grout or Class II or III select material.
15-23 1550 -6 Measurement and Payment
Bore and Jack of ___" will be measured and paid in linear feet. Measurement will be made along the bore to the nearest linear foot. Directional Drilling of ___ " will be measured and paid in linear feet. Measurement will be made along the directional drill to the nearest line ar foot. Tunneling of ___" will be measured and paid in linear feet. Measurement will be made along the tunnel to the nearest linear foot. Measurement will be made along utility pipes with required trenchless installation. Payment for trenchless installation will be made as additional compensation for utility piping with contract pay items of the various sizes. No additional payment will be made for access pits or shoring required for the installation . No additional payment will be made for changes or modifications to the designed method. Shoring required for the maintenance of traffic or the protection of building or other structures, on or off the right of way, will be paid under Temporary Shoring. Material used to fill external voids is incidental to the work being performed. No payment will be made for abandoning defective installations. Payment will be made under: Pay Item Pay Unit Bore and Jack of ___" Linear Foot Directional Drilling of ___ " Linear Foot Tunneling of ___ " Linear Foot
Source: North Carolina Standard Specifications for Roads and Structures, 2024 Edition. Pages 745–750 of 857.