Article 1 — Description
Furnish and install pipe or box by jacking, boring, or tunneling.
Article 2 — Materials
Use the following types of pipe or box: reinforced concrete pipe (except circular bell -and-spigot, arch, or horizontal elliptical pipe) meeting the special requirements for jacking, boring, or tunneling in accordanc e with Item 464, “Reinforced Concrete Pipe,” of the size, strength, and dimension shown on the plans; reinforced concrete box meeting Item 462, “Concrete Box Culverts and Drains,” of the size and type shown on the plans; or other types shown on the plans.
Article 3 — Construction
Excavate suitable shafts or trenches for conducting the jacking, boring, or tunneling operations and for placing end joints of the pipe or box if the grade at the jacking, boring, or tunneling end is below the ground surface. Maintain a 3:1 slope from edge of pavement on the shaft side of the road unless otherwise shown or directed. Provide a positive barrier when the shaft location is within the clear zone of the roadway. Protect excavations deeper than 5 ft. in accordance with Item 402, “Trench Excavation Protection, ” or Item 403, “Temporary Special Shoring.” Install pipe or box so there is no interference with the operation of street, highway, railroad, or other facility and no embankment or structure is weakened or damaged. Repair any pipe or box damaged in jacking, boring, or tunneling. Remove and replace any pipe or box damaged beyond repair at the Contractor’s expense. Backfill shafts or trenches excavated to facilitate jacking, boring, or tunneling immediately after installation of pipe or box.
3.1 Jacking . Provide jacks suitable for forcing the pipe or box through the embankment. Use even pressure to
all jacks during operation. Provide a suitable jacking head and suitable bracing between the jacks and the jacking head to apply uniform pressure around the ring of the pipe or circumference of the box. Use joint cushioning of plywood or other approved material. For plywood cushioning material, use 1/2- in. minimum thickness for pipe diameter 30 in. or less, and use 3/4- in. minimum thickness for pipe diameter greater than 30 in. Use 3/4- in. minimum thickness for all boxes. Use cushioning rings of single or multiple pieces. Provide a suitable jacking frame or backstop. Set the pipe or box to be jacked on guides that support the section of the pipe or box, and direct it on the proper line and grade. Place the entire jacking assembly in line with the direction and grade of the pipe or box. In general, excavate the embankment material just ahead of the pipe or box, remove the material through the pipe or box, and force the pipe or box through the embankment with jacks into the space bored or tunneled. Furnish a plan showing the proposed method of jacking for approval. Include the design for the jacking head, jacking support or backstop (thrust block), arrangement and position of jacks, and guides in the plan. 747 Ensure excavation for the underside of the pipe so at least 1/3 of the circumference of the pipe conforms to the contour and grade of the pipe. Ensure the excavation for the bottom slab of the box conforms to the grade of the box. Over -excavate, if desired, to provide no more than 2 in. of clearance for the upper portion and sides of the pipe or box. Taper this clearance to zero at the point where the excavation conforms to the contour of the pipe or box. Carry out jacking without interruption to prevent the pipe from becoming firmly set in the embankment. Monitor volume of soil excavated to avoid any appreciable over -excavation. Pressure -grout any over -excavation of more than 1 in. Pressure- grout betw een the carrier pipe and casing when shown on the plans. The distance the excavation extends beyond the end of the pipe or box must not exceed 2 ft. Decrease this distance as necessary to maintain stability of the material being excavated. Jack the pipe or box from the low or downstream end. The final position of the pipe or box must not vary from the line and grade shown on the plans by more than 1 in. in 10 ft. Variation must be regular and in one direction, and the final flow line must be in the direction shown on the plans. Use a shield or cutting edge of steel plate around the head end of the pipe or box extending a short distance beyond the end if desired. The minimum clear distance for parallel pipe or box jacking or tunneling is 3 ft., unless otherwi se shown on the plans.
3.2 Boring or Tunneling. Bore from a shaft in an approved location provided for the boring equipment and
work ers. Dispose of excavated material using an approved method. Use water or other appropriate drilling fluids in connection with t he boring operation only as necessary to lubricate cuttings and pipe or box; do not use jetting. Use a gel -forming colloidal drilling fluid consisting of high- grade, carefully processed bentonite to consolidate cuttings of the bit in unconsolidated soil formations. Seal the walls of the borehole and furnish lubrication for subsequent removal of cuttings and immediate installation of the pipe. Allowable variations from line and grade are specified in Section 476.3.1., “Jacking.” Pressure- grout any over-excavation of more than 1 in.
3.2.1 Larger Diameter Boring Methods . Use the pilot hole or auger method for drainage and large utility borings.
Pressure -grout any over -excavation of more than 1 in. Pressure- grout between the carrier pipe and casing when shown on the plans. 3.2.1.1. Pilot Hole Method. Bore a 2- in. pilot hole the entire length of the crossing and check it for line and grade during the boring or tunneling operation on the opposite end of the bore from the work shaft. This pilot hole will serve as centerline for the larger diameter hole to be bored. 3.2.1.2. Auger Method. Use a steel encasement pipe of the appropriate diameter equipped with a cutter head to mechanically perform the excavation. Use augers of large enough diameter to convey the excavated material to the work shaft.
3.2.2 Electrical and Communication Conduit Boring. Limit over -excavation to the dimensions shown in Table 1
for electrical and communication conduit borings. Increased boring diameters will be allowed for outer diameters of casing and couplings. Pres sure-grouting will not be required for electrical and communication conduit borings. 748 Table 1 Allowable Bore Diameter for Electrical or Communication Conduit or Casing Single Conduit Bores Multiple Conduit Bores Conduit Size (in.) Maximum Allowable Bore ( in.) Conduit Size (in.)1 Maximum Allowable Bore (in.) 2 4 4 6 3 6 5 8 4 6 6 10 6 10 7 12 – – 8 12 1. The diameter of multiple conduits is the sum of the outside diameter of the two largest conduits for placement of up to four conduits in one bore. Submit boring diameters for the Engineer’s approval when more than four conduits are to be placed in a bore.
3.3 Tunneling. Use an approved tunneling method where the characteristics of the soil, the size of the proposed
pipe, or the use of monolithic pipe would make the use of tunneling more satisfactory than jacking or boring, or when shown on the plans. Ensure the lining of the tunnel is strong enough to support the overburden when tunneling is permitted. Submit the proposed liner method for approval. Approval does not relieve the Contractor of the responsibility for the adequacy of the liner method. Pressure- grout the space between the liner plate and the limits of excavation. Pressure- grout between the carrier pipe and liner plate when shown on the plans.
3.4 Joints . Make the joints in accordance with Item 464 if reinforced concrete pipe is used. Make the joints in
accordance with Item 462 if reinforced concrete box is used.
Article 4 — Measurement
This Item will be measured by the foot between the ends of the pipe or box along the flow line. This is a plans quantity measurement Item. The quantity to be paid is the quantity shown in the proposal, unless modified by Article 9.2., “Plans Quantity Measurement.” Additional measurements or calculations will be made if adjustments of quantities are required.
Article 5 — Payment
The work performed and materials furnished in accordance with this Item and measured as provided under “Measurement” will be paid for at the unit price bid for “Jacking, Boring, or Tunneling Pipe” of the type, size, and class or design specified, or “Jacking or Tunneling Box Culvert” of the size specified. This price is full compensation for excavation, grouting, backfilling, and disposal of surplus material; furnishing pipe, box, and pipe liner materials required for tunnel operations; preparation, hauling, and installing of pipe, box, and pipe liner materials; and materials, tools, equipment, labor, and incidentals. Protection methods for open excavations deeper than 5 ft. will be measured and paid for as required under Item 402 or Item 403.