Utility Locating
Using geophysics
to identify buried utilities
Safety and economy
are why geophysics is used to identify utilities and other objects buried
beneath the ground. A large variety of buried utilities can be encountered at a
site. Simple sites have water, gas, sewer and storm lines. Congested sites have
telecommunications, control and relay, electrical, compressed gas, and many
other buried lines. The potential for hitting one of these utilities exists at
every site. Finding a utility where one is not expected can be dangerous and
expensive.
J R Associates
performs utility investigations to reduce the risk of encountering an
unexpected pipe. Digging or drilling at a site without having accurate utility
locations is like driving blindfolded. Eventually something will be hit.
Hitting a utility is dangerous, disruptive and expensive. It puts people at
risk and delays projects. Yet few sites have accurate plans showing the
locations of buried pipes. Some sites may have mechanical drawings showing
where pipes should be, but many sites have no plans at all. Contractors and
drillers need to have utilities accurately located. J R Associates provides
this information. The next few pages will describe the techniques we use and
the services we provide.
Techniques-
Conventional Locators
J R Associates
uses high performance Radiodetection Incorporated
pipe and cable locators for all routine locating. These high performance
locators each have a receiver and a transmitter. The receiver detects electromagnetic
signals emitted from pipes. These signals can be naturally occurring 60-Hz
electrical noise and low frequency radio waves or these signals can be placed
on the pipes by the transmitter. There are several different ways we can place
a signal onto a pipe. The best way is to connect the transmitter directly to
the pipe. If a direct connection is not available, a signal can be induced onto
a pipe using a clamp that encircles the pipe or a coil lying above the pipe.
These locators detect metal pipes and cables that are either
welded, soldered or threaded together.
Nonconventional Locators
There are many
pipes made of materials that cannot be detected with conventional methods.
These include pipelines made of plastic, clay, concrete, and insulated cast
iron. Locating pipes made of these materials requires special locating methods
and skill. J R Associates uses many different techniques to identify these hard
to locate pipes.
Acoustic Locator
An acoustic
locator is used to identify and trace nonmetal water lines. The locator
consists of a transonde and a receiver. The transonde is attached to the water line either at a fire
hydrant, faucet or tap. The transonde sends a sound
wave through the water in the pipe. We use the receiver to listen for the sound
emitted from the pipe. Once located, the pipe's position can be marked on the
ground surface.
Sondes
Sondes are used to locate
nonmetal sewer pipes, storm drains and conduits. Sondes
also are used to locate cast iron drain pipe. A sonde
is a small radio transmitter inserted into a pipe. Once inside, a conventional
pipe locator is used to locate the sonde. The pipe's
position is then marked on the ground. The sonde is
pushed farther into the pipe, the receiver relocates the sonde
and the pipe's position is again marked. This process is repeated until the
desired section of pipe is traced. Another option is to have a plumber snake
the pipe. We can attach a transmitter to the snake and trace the line from the
signal the snake emits.
Radar
The ground penetrating
radar is used to augment our other locating techniques. The radar is used to
detect pipes buried near the ground surface. A unique feature of the radar is
that under some conditions, it can locate nonmetal lines, trenches where lines
were buried and many other buried objects. For example, we have used radar to
map large boulders lying in the paths of proposed duct banks. Another special
feature of the radar is its ability to provide a picture of what is buried in
the ground. This is particularly useful when pipes are clustered together and a
high degree of precision is needed.
Utility Depths
Often, the depth
of a utility can be obtained from one of the following three devices: the high
performance locators, the sondes and the radar. To
determine the depth of a metal pipe, we attach a transmitter directly to the
pipe and apply a signal. Using a high performance locator, we can measure the
depth to the center of the pipe. The pipe must emit a clean signal, run for
several tens of feet in a straight line and there must not be pipes or rebar
nearby. Also the pipe must be constructed of metal welded, soldered or threaded
together. The depth of a plastic or concrete pipe and be determined with a sonde. The pipe locator can determine the depth of a sonde lying inside a pipe. Sondes
usually lie near the bottom of a pipe and the depth measured is from the ground
surface to the sonde. Our last method uses the radar.
If a pipe creates a clean reflection in a radar profile, its depth can be
determined. Here, the depth is measured to the top of the pipe. These three
methods measure the depth to different parts of a pipe. For small diameter
pipes this is usually not important. On large diameter pipes the differences
need to be allowed for. Locators measure to the center of a pipe, sondes measure to the bottom of a pipe and the radar
measures to the top of a pipe.
Other Services-
Metal Detection
Metal detectors
and magnetometers are used to locate buried metal objects other then pipes.
Most commonly they are used to search for abandoned buried fuel storage tanks
and buried waste. The unique feature of a magnetometer is that it produces a
hard copy map of all the metal buried at a site. These maps are useful at sites
where hazardous materials may be buried that could disrupt construction
projects.
Seismic
Refraction
Seismic refraction is a
common service provided to utility districts proposing new pipelines. Seismic
refraction provides a two-dimensional profile of the earth's structure. Seismic
profiles show the important geological features such as shallow bedrock and
shallow water tables, both of which can delay a construction project. Seismic
refraction also indicates the ease with which a trench can be excavated. The
Caterpillar Tractor Company has performed extensive tests to determine the
relation between seismic refraction data and rock rippability.
Soil Borings
Some clients ask
for geotechnical soil borings as part of a utility investigation. In such
cases, we hire an outside geotechnical firm with a licensed geotechnical
engineer to perform the soil borings and report on the results. These reports
are added as an appendix to our utility investigation reports.
Reporting Results
J R Associates
provides different ways of reporting the location of buried utilities. We paint
the location of all utilities located during an investigation on the ground.
This is done at every site. Where possible, we identify the type of pipe by the
color of paint used. We follow the American Public Works Standard for
identifying pipes. Pipes that cannot be identified are marked in white. For
most jobs, no other reporting is performed. The paint on the ground marking the
location of pipes is the result of our investigation.
Some clients
require simple diagrams illustrating the location of utilities near a proposed
boring or trench. If requested, we will provide a field sketch showing the
utilities found during the investigation besides painting the utility locations
on the ground. The sketches are generated in the field and show the location of
utilities found during the investigation relative to the proposed trench or
boring. These drawings are not to scale. They are intended to alert operators
of utilities in their vicinity, not the utilities' exact locations. Always, the
location painted on the ground is the location of the utility found during the
investigation and takes precedence over the location shown on sketched field
maps.
CAD Services
J R Associates can provide
detailed CAD drawings of utilities located during an investigation. Typically
we start with CAD drawings provided by our client. These are usually design
drawings for new pipelines. They show the location of the proposed pipeline and
the locations of utilities known to be in the area of the new construction. We
field check the location of the utilities shown on the drawings and look for
utilities that may have been missed. The locations of all utilities found
during the investigation are painted on the ground surface. Any utility found
during the investigation that was not shown on the original drawings is added
to the drawings. The results are CAD plans showing the utilities originally on
the plans plus any additional utilities located during the investigation. The results
of magnetic and seismic investigations can be added to the CAD drawings as
well.
Limitations
Present technology
cannot detect every pipe buried in the ground. A pipe must emit a signal, ether
a naturally occurring signal or a signal transmitted by us, to be detected. The
most common type of utility not detected are nonmetal
service laterals and utilities under reinforced concrete slabs. At any site,
there will probably be a few buried utilities that will not be detected. Our
personnel are always available to explain the methods and their limitations as
they pertain to your site.
Clients can help a
utility investigation by providing mechanical drawings of what was buried at
the site. Although the drawings may not be accurate, they help us know what to
look for. These drawings often provide information on where pipes daylight and
locations where we can connect transmitters or insert sondes.
Clients should try to provide mechanical drawings when possible. The
information these drawings provide is worth the effort of obtaining them.
J R Associates
J R Associates is
a geophysical company specializing in providing information on what is
underground. Locating buried utilities has become a large part of our service.
We have an experienced staff that uses the latest technology to identify
underground pipes. All project members are highly trained and hold university
degrees in geophysics. A geophysicist tested and licensed by the California
Department of Consumer Affairs oversees each project. Quality equipment and
highly trained personnel set J R Associates apart from the rest. When you want
the very best locating, call J R Associates.
J
R Associates,
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