Page 370 - Trenchless Technology Piping Installation and Inspection

320 Cha pte r Ei g h t

Protective Coatings
Pipeline coatings and linings that are specified for corrosion protec-
tion need to be protected against damage during all construction
operations. Damaged coatings must be repaired in accordance with
the pipe and/or coating manufacturer’s guidelines and pipe sections
with coating damage must be replaced. When necessary, cathodic pro-
tection systems must be supplied and installed in accordance with the
project plans and specifications. A corrosion engineer must be retained
to monitor the installation of all cathodic protection systems.

8.2.3 Construction

Minimum Allowable Depths
The recommended minimum depth of cover for microtunneling must be
6 ft or 3 times outside diameter of installed pipe, whichever is greater. In
locations where the road surface is elevated, the minimum depth of the
bore must be measured from the lowest side of the pavement surface.
Overcut Allowance
Overcut is the annular space between the excavated bore and the outside
diameter of the pipe. When using microtunneling method, the allowable
overcut must not exceed the outside pipe radius by more than 1 in. for
soft ground, but overcut for large machines in rock will require 1.5 in.

Watertight Joints
1. Watertight pipe joints are required to ensure the integrity of
the soil-pipe structure and street/roadbed. Pipe must be con-
structed to prevent water leakage or earth infiltration
throughout its entire length.
2. Pipe manufacturers provide proprietary joints for microtun-
neling and other trenchless technology methods. More infor-
mation on watertight specification for each type of pipe
material can be obtained through specific pipe material asso-
ciation and/or specific pipe manufacturer.

Lubrication
Appropriate lubrication must be used to reduce jacking forces in dif-
ferent types of soil. The most common lubrication is bentonite.

Slurry Spoil Removal Syayem
The pumping rate, pressures, viscosity, and density of the slurry
must be monitored to ensure adequate removal of spoil. The excess
slurry must be contained until it is recycled or removed from the
site. All slurry fluids must be disposed of or recycled in a manner
acceptable to the appropriate local, state, and federal regulatory
agencies.