Field Location of Excavation Boundaries

DOE-HDBK-1092-2004

11.4.1 FIELD LOCATION OF EXCAVATION BOUNDARIES

Accurate identification of excavation boundaries is absolutely necessary. It accurately

communicates those boundaries to all workers and supervisors. It also sets the excavation

limits, based on the research and locator testing provided for that particular excavation.

a. Excavation maps can be used to identify exact excavation boundaries (Field markings

can easily be transferred from these maps)

b. Excavation maps can be attached to the excavation permits for additional

communication assurance.

c. Field excavation boundaries should be appropriately marked.

11.4.2 LOCATOR EQUIPMENT SELECTION AND LIMITATIONS

It is important to note that no locator technology should be relied upon as the sole source for

identifying buried or embedded utilities. Configuration management is the most effective

identification method.

The majority of underground utility locators being used today apply a signal to the underground

system being located. This signal may either be of an audio or radio frequency. An active

signal is applied to the underground utility by various methods with the signal being generated

from the transmitter unit of the location system. Proper setup of the transmitter increases the

accuracy of the receiver unit. Proper use of the receiver unit requires that the antennas be

moved in a straight path and not in a swinging motion. Accurate depth readings are gained

from experience.

The latest electromagnetic pipe and cable locators feature microprocessor-controlled

transmitters and receivers capable of detecting power lines, telephone cables, and metal piping

at depths up to 15 or 20 feet. These detection devices operate with multiple discrete broadband

frequencies, antenna configurations, and grounding capabilities.

DIRECT OR CONDUCTIVE METHOD

The most desired and accurate method of applying a signal to the underground system is the

direct or conductive mode, where there is access to a contact point on the utility to be located.

The direct connection is always the preferred and most accurate method of applying the signal

to the utility, as the operator has the most control of the signal. When using the direct mode, it

must be understood that the utility line to be located becomes part of the detection circuit. The

detection signal is applied to the utility using attachment leads. The signal is applied using one

lead, and returns on the other lead. An accurate location begins with the proper set up of the

transmitter and the key to setting up the transmitter is the grounding method used. A significant

percentage of all incorrect locates result from the failure to properly control the signal applied to

the target utility. Personal that is not properly trained, cannot notice the difference in most

cases.

INDUCTIVE CLAMP OR COUPLER

A second method of applying a signal to a known utility is the inductive clamp or coupler, where

the signal is induced to the utility by means of a jawed clamp placed around the utility access

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