Page 392 - Trenchless Technology Piping Installation and Inspection

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2. Determine geological conditions: The type of soil in the path of
the installation determines the type of equipments, cutter-
heads, and drilling fluids that are best suited for the project
and whether HDD is a suitable tool for installing the pipe.
Depending on the job size, a geological survey may or
may not be conducted by an experienced geotechnical
engineer. If no geotechnical survey has been preformed,
the contractor must look for existing records associated
with nearby construction sites, as well as other public
records. Visual inspection of site geology and soil charac-
teristics at the entry and exit pits also provide information
on soil conditions.
3. Hazards, obstructions, and utility location: The installation of
underground utilities using trenchless methods limits vis-
ual verification of conditions near and surrounding the
installation. As with any underground construction, every
means must be used to locate and verify existing conditions.
These means include contacting the local one-call service
and area utilities, reviewing records, having a locating serv-
ice locate utilities, use locating equipment such as ground-
penetrating radar (GPR). When operating near existing
utilities or potential hazardous conditions, potholing must
be used to verify the exact location of the existing utility and
bore path.
4. Drilling fluids: As said earlier, drilling fluids stabilize the bore-
hole, which mitigates hydro fracturing (inadvertent return of
fluids or frac outs) and allows the product pipe to be pulled
in. The proper mix of drilling fluids is determined by the soil
conditions and characteristics of the water mixed with the
drilling fluid. Geotechnical information must be gathered in
advance of the project and soils extracted from the borehole
must be tested from time-to-time during the installation to
verify that the proper drilling fluid mix and additives are
being used. Water must be checked and adjusted for pH and
the presence of calcium.
5. Downhole equipment: The type of downhole equipment to be
used in an HDD installation depends on the soil conditions,
depth of the installation, and size and type of the product
pipe being installed. Different bits and reamers work better in
different soil conditions. Downhole transmitters come with
different signal strengths, which must match the depth of the
installation. In addition, certain installations may require that
breakaway swivels be used to protect the product being
installed. Also, pressure sensors can be used to measure fluid
pressure at the swivel location as well as to measure pulling
loads on the product pipe.