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.
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.
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.
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 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.
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.
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.
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 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.
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.
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.
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.
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 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.