2013 Water System Plan, Volume II - Seattle City Clerk's Office - City ...

Chapter 5 Water Infrastructure
Every trenchless project is unique and requires custom evaluation and analysis. Items to
consider include topography, soil conditions, regulatory issues, and site constraints.
A. Bore and Jacking
Bore and jack installation (also called horizontal auger boring) consists of installing a
casing by jacking and concurrently auguring the soils out through the casing. Alignment
is fairly accurate with bore and jacking. However, there can be potential problems with
high ground water and excessive lengths. Once the casing pipe is installed, the carrier
pipe is installed with spacers to support the pipe. The gap can be filled, typically with
blown sand or a non-shrink grout.
B. Micro-tunneling
Micro-tunneling is typically a closed-face pipe jacking process. Micro-tunneling requires
both launching and receiving shafts, which are typically constructed out of slurry walls.
Micro-tunneling machines are laser controlled remotely from the surface. Microtunneling
installs a casing pipe, and then a carrier pipe is installed. Because this process
allows precise grade control, it is frequently used in water and sewer applications.
C. Horizontal Directional Drilling
Horizontal directional drilling (HDD) consists of drilling progressively larger diameters
from ground surface to ground surface in an arch under the obstruction. No shafts are
constructed with HDD construction. Typically, the first pass of a drilling operation
creates the route. The pipeline route is then increased in diameter by forward and back
reaming the drill path. The hole is kept open with drilling fluids, typically a bentonite
slurry. During drilling, various methods are used to track the drill bit and determine the
route. Recent history has shown HDD pipeline installation to be relatively accurate.
Once the desired diameter is achieved, the carrier pipe is pulled through the drilled
path. No casing pipe is used in HDD applications.
D. Pipe Ramming
Pipe ramming consists of using a hydraulic hammer to push the pipe through the soil.
Once the casing pipe is installed, the center channel is removed, typically by an auger
method or compressed air. With small diameters, the carrier pipe may be rammed with
a closed end. Frictional forces can limit the overall length of the pipe ramming, and
there is no line or grade control.
5.8.3.9 Restraint Systems
See DSG section 5.6.3.9.
5.8.3.10 Vaults
See DSG section 5.6.3.11.
5.8.3.11 Appurtenances
Pipeline appurtenances, such as line valves, access ports, blow-off/drains, or air release/air
vacuum valves should be provided along the pipeline as needed to support the transmission
main function and operation. Appurtenance locations should be determined to avoid conflicts
SPU Design Standards and Guidelines
5-43