2004 Specifications
SPECIAL PROVISION
476---003
Jacking, Boring, or Tunneling Pipe or Box
For this project, Item 476, “Jacking, Boring, or Tunneling Pipe or Box,” of the Standard
Specifications, is hereby amended with respect to the clauses cited below, and no other clauses
or requirements of this Item are waived or changed hereby.
Article 476.3. Construction, Section A. Jacking. The third paragraph is voided and replaced by
the following:
Ensure that excavation for the underside of the pipe for at least 1/3 of the circumference of the
pipe conforms to the contour and grade of the pipe. Ensure that the excavation for the bottom
slab of the box conforms to the grade of the box. If desired, over excavate to provide not more
than 2 in. of clearance for the upper portion 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. When jacking of pipe has
begun, the operation shall be carried on without interruption, insofar as practicable, to prevent
the pipe from becoming firmly set in the embankment. Pressure-grout any over excavation of
more than 1 in. When shown on the plans, pressure-grout between the carrier pipe and casing.
Article 476.3. Construction, Section B. Boring. The fifth paragraph is voided and replaced by
the following:
1. Larger Diameter Boring Methods. For drainage and large utility borings, use the pilot hole
or auger method. Pressure-grout any over excavation of more than 1 in. When shown on the
plans, pressure-grout between the carrier pipe and casing.
a. Pilot Hole Method. Bore a 2 in. pilot hole the entire length of the crossing, and check it
for line and grade 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.
b. Auger Method. Use a steel encasement pipe of the appropriate diameter equipped with a
cutter head to mechanically perform the excavation. Use augers of sufficient diameter to
convey the excavated material to the work shaft.
2.
Electrical and Communication Conduit Boring. For electrical and communication
conduit borings, limit over excavation to the dimensions shown in Table 1. Increased boring
diameters will be allowed for outer diameters of casing and couplings. Pressure grouting
will not be required for electrical and communication conduit borings.
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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 4 conduits in one bore. Submit boring diameters for the Engineer’s approval when more than 4 conduits are to
be placed in a bore.
Article 476.3. Construction, Section C. Tunneling is supplemented by the following:
When shown on the plans, pressure-grout between the carrier pipe and liner plate.
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