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be expected. If the area has been subjected to large landslides, trees,
and other natural or manmade objects may have been buried and
could be encountered. If the area has been subjected to low-energy
streams and rivers, then fine-grained deposits may be expected. Con-
versely, high-energy, steeply sloped stream beds may be covered with
cobbles and boulders from nearby mountains. Reports on surface
contours and elevations are also important so that any possible
ground movements, settlements, and heaves can be monitored. Dur-
ing the design and bidding phase of the project, it may be necessary
for engineers and contractors to visit the project site and visualize the
degree of job difficulty that may be encountered during the project
execution.
9.2.2 Subsurface Investigations
Subsurface investigation is the next step to surface survey. Subsur-
face features, which will impact trenchless installations, include
presence of existing underground pipelines and utilities or other
manmade structures, and method of their placement. Geotechnical
conditions, such as existence of solid rock, heavy gravelly soil, and
boulders and cobbles along the alignment of proposed trenchless
installation must also be investigated.
Locating Existing Utilities
Trenchless installation projects require the contractor to install the
pipe without seeing the excavation area. Therefore, the design
engineers should give contractors a record of potential conflicts and
utility crossings.
In the United States, the local one-call service like MISS DIG in
the state of Michigan or the national number 811 should be contacted
as a first step prior to design and construction of a trenchless project.
In other countries, and in the absence of one-call service, municipali-
ties and utility companies should be contacted individually to obtain
the required information. Obtaining as-built and record drawings,
geographic information system (GIS) data, utility maps, and locating
pipeline markers are also important. Geophysical methods subsur-
face utility locating may include surface-applied pipe locators,
ground-penetrating radar (GPR), electrical resistivity imaging, and
seismic survey. In addition to the information provided by design
engineers (usually in terms of soil-boring logs and possibly soil
reports), and contacting utility companies and one-call centers, con-
tractors must positively locate and expose existing utilities running
parallel less than 10 ft (at specified intervals, such as every 50 ft,
dependent on proximity and type of existing utility and trenchless
method used) or where it proposed trenchless alignment crosses
an existing utility or pipeline. Exposing utilities can be done by
mechanical equipment (such as a backhoe), hand shoveling, and/or