Electricity: measuring and testing – Of geophysical surface or subsurface in situ – For small object detection or location
Reexamination Certificate
2000-02-14
2001-10-02
Metjahic, Safet (Department: 2862)
Electricity: measuring and testing
Of geophysical surface or subsurface in situ
For small object detection or location
C324S067000
Reexamination Certificate
active
06297638
ABSTRACT:
TECHNICAL FIELD
This invention relates to a technique for controlling a cable boring operation to avoid interference with an existing underground utility conveyance.
BACKGROUND ART
Utilities, such as those providing electric, gas, water, and telephone service, often bury their conveyances (i.e., pipes and/or cables) underground for reasons of safety and aesthetics. Usually, the environment and terrain dictate the method employed for burying such conveyances. In rural areas, utilities prefer direct burial, which they accomplish by plowing or trenching the earth. In urban environments, and when crossing waterways, boring is preferred. To complete a boring operation, the utility, or a contractor under its employ, first excavates a pit at each of the opposite ends of the intended path for the conveyance. From one pit, a boring machine (auger) forces a boring head horizontally through the earth into the other pit to create a tunnel through which a utility conveyance can pass.
Underground utility conveyance burial by boring does create a certain risk. An operator must carefully control the path of the boring head to avoid contact with one or more existing underground utility conveyances buried in proximity to the path established by the boring head. For this reason, many utilities, such as AT&T, have regulations governing the minimum allowable distance permitted between the boring head and an existing underground utility conveyance. To facilitate control of the boring head, most boring head manufacturers include a transmitter (hereinafter referred to as a “sonde”) in the boring head for transmitting a signal in the range of 8 kHz. to 33 kHz. The signal transmitted by the sonde radiates through the ground for detection by one or more detectors located above ground. By continuously monitoring the signal radiated by the sonde in the boring head, the operator of the boring machine can monitor the relative position of the boring head as it bores a path through the earth to avoid contact with an existing underground utility conveyance.
Unfortunately, the signal radiated by the sonde in the bore head tends to induce electromagnetic signals in other facilities, such as other underground utility conveyances, causing one or more of them to radiate signals in the vicinity of the conveyance of interest. The detectors (s) tuned to receive the signal radiated by the sonde also receive the signals induced in, and radiated by, such other facilities, especially when the sonde comes into close proximity with such other facilities, thus causing confusion regarding the actual position of the boring head. Hence, attempting to control the boring operation by continuously monitoring sonde signal can lead to errors especially when boring operations occur in close proximity to existing underground utility conveyances. Indeed, all too often, boring operations have damaged existing underground conveyances, leading to service outages and lost revenues, not to mention the cost associated with repairs.
Thus, a need exits for a technique for controlling a boring operation to reduce the risk of interference.
BRIEF SUMMARY OF THE INVENTION
Briefly, in accordance with a preferred embodiment of the invention, there is provided a method for controlling a boring operation carried out by a boring head to avoid possible interference between the boring head as it is pushed through the earth and an adjacent conveyance of interest. In accordance with the method, the location of the conveyance of interest is first established, typically by electronically locating the conveyance in a conventional manner. Thereafter, a safety zone is established about the conveyance such that the safety zone has a longitudinal boundary along the intended bore path generally parallel to, but spaced at least a prescribed distance from the conveyance. As a boring operation commences, a transmitter (referred to as a “sonde”) within the boring head radiates a signal at a known frequency. Along the boundary of the safety zone, a check is made for the presence of the sonde signal with a signal detecting device or series of signal detecting devices. The signal-detecting device(s) would be calibrated to the same frequency as the signal radiating sonde used by the bore operation. The bore sonde unit radiates a signal in the frequency band of 8 kHz to 33 kHz and the signal detecting device(s) would automatically scan the immediately area surrounding the bore for the radiating sonde frequency. Once positioned along the bore path, the signal detecting unit(s) would monitor for this boring sonde frequency. If the sonde signal is detected as a result of the boring head coming too close to the safety zone boundary, an alert is issued. In response to the alert, the boring operation either ceases, or the boring head path is shifted to avoid interference with the conveyance.
REFERENCES:
patent: 5337002 (1994-08-01), Mercer
patent: 5644237 (1997-07-01), Eslambolchi et al.
patent: 5757190 (1998-05-01), Mercer
Eslambolchi Hossein
Huffman John Sinclair
AT&T Corp.
Garg Rohini K.
Levy Robert B.
Metjahic Safet
Zaveri S A
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