Note: Descriptions are shown in the official language in which they were submitted.
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HORIZONTAL BORING PIPE PENETRATION DETECTION
SYSTEM AND METHOD
BACKGROUND
Horizontal underground boring has become a popular and
cost effective method for installing gas piping and other
underground utilities. In such systems, a bore head or drill
bit on the end of a rotating pipe stem is pushed forward
through the soil by the boring machine. Typically, horizontal
boring machines use drill stems in lengths of ten or twenty
feet, which are added to the end of the stem as the bore head
penetration continues.
Prior to the initiation of horizontal boring, it is
necessary to locate electric lines, water lines, sewer lines,
and other pipes in the path of the boring machine, to avoid
penetrating or damaging such pipes. A first step in this
process is to obtain maps of the area in which the horizontal
boring is to be made, to ascertain the location of pre-
existing pipes. Frequently, however, such maps are incompleteor inaccurate. All metal pipes in the path of a boring
machine may be accurately located with standard
electromagnetic pipe locators. Similarly, plastic pipes with
tracer wires also can be accurately located. Plastic pipes
without tracer wires, however, or with broken tracer wires,
and other non-conductive pipes cannot easily be located.
Sewer lines typically are made of clay or orangeburg pipe, or
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of plastic pipe, which makes such lines difficult to locate.
Systems have been developed for detecting underground
sewer lines or water lines, where the pipe for such lines is
not made of metal or plastic pipe with tracer wires in it.
One such system for detecting the location of an underground
portion of a sewer line is disclosed in the U.S. patent to
Ziska No. 4,911,012. In this patent, a sound source is
provided to introduce sound of a predetermined frequency into
an accessible (above ground) portion of the sewer line. The
sound vibration then propagates into the underground portion
of the line. The location of the underground portion of the
sewer line is identified by sensing the vibration through a
detector located at the ground surface or inserted into the
ground above the underground portion of the sewer line. A
number of different locations of the detector are made in
order to "zero in" on the underground line. This system
requires considerable effort; and while it is capable of
tracing the path of the underground line, it is not capable of
determining the depth of that line.
The U.S. patent Heitman No. 5,036,497 is directed to a
method and apparatus for detecting the location of an
underground water line. In this system, a pulsing valve is
placed on the water line to cause the water intermittently to
flow and to be shut off. The result is a water hammer effect
in the water line to send shock waves outward from the pipe.
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Spaced seismic sensors are employed to provide a differential
indication of the signals; and movement of the sensors to a
point where the signals received by the two sensors is equal,
along a spaced path, is used to trace the path of the water
line. As with the system of the Ziska patent, this is a
tedious and time consuming process. It also requires the
insertion of the pulsing valve in order to produce the hammer
effect needed to produce the seismic signals.
The U.S. patent to Huebler No. 5,127,267 employs a system
similar to that of the Ziska patent mentioned above. In the
system of Huebler, an audio speaker is used to inject an audio
signal into an underground pipe from an accessible above
ground input. The location of the pipe then is detected by a
plurality of detectors positioned at varying distances from
the pipe. These detectors generate signals, which are
supplied to a signal processor. The time of arrival of the
acoustic signal to the various detectors then is processed to
determine the detector which is located nearest the concealed
pipe. This position is marked, the detectors are moved; and
the test is repeated to plot or map the direction of the pipe
underground. As with the systems of Heitman and Ziska above,
the depth of the pipe is not ascertained by the system of
Huebler.
The U.S. patent to Alspaugh No. 2,620,386 is directed to
an earth strata cutting indicator. The system of this patent
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is used in conjunction with a horizontal boring machine for
mining coal. For such a machine, it is important to keep the
machine in a layer of coal and out of adjacent strata of rock,
if possible, by remote control. To determine this, sensors
are provided on the bore head for transmitting signals back to
an oscilloscope. The vibrations of the bore head when it is
cutting through coal differ from vibrations caused when it is
cutting rock strata. These vibration differences are visibly
indicated on the oscilloscope; and a synchronizing system is
provided between the cutting head and the indicator to provide
indicia of the circular motion of the scanning tube as the
bore head cuts the strata face. Thus, the precise position of
the change in strata can be determined. This then permits the
operator of the machine to guide it by manipulation to cut
into the desired layer of coal, and to avoid rock formations.
The U.S. patent to Jackle No. 4,457,163 utilizes
acoustical (microphone) technology for detecting a broken
below-grade pipe. In this system, the emission noise
generated by a leak is picked up by a microphone and an
amplifier, which controls a peak noise indicator. Different
measuring points detected by the amplifier are supplied to a
digital memory for displaying a histogram showing noise
distribution along the pipe. This information then is
employed to locate the leak in the pipe.
The systems of the prior art noted above and known to
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applicant, however, do not provide an indication to the
operator of a horizontal boring machine of the penetration of
the bore head or drilling bit into a sewer pipe.
Consequently, it is desirable to provide a system and method
for providing such an indication to the operators of a
horizontal boring machine.
SUMMARY OF THE INVENTION
It is an object of this invention to provide an improved
horizontal boring system.
It is another object of this invention to provide an
improved method for operating a horizontal boring system.
It is an additional object of this invention to provide
a penetration detection system for a horizontal boring system.
It is a further object of this invention to provide
multiple sensors of different types for continuously
monitoring the operation of a horizontal boring machine to
provide an output indication of the penetration of the bore
head into sewer pipe or the like.
In accordance with a preferred embodiment of this
invention, a method and system for detecting pipe penetration
by the bore head of a boring machine includes placement of a
sensitive audio microphone in the nearest sewer manhole to the
location of the bore head to detect acoustic signals
transmitted through the ground by the bore head. This
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microphone produces a first output signal, which is
representative of these detected acoustic signals. A seismic
pick-up device or geophone is placed in a position in the
vicinity of the bore head to detect vibrations of ground
caused by the movement of the bore head through the ground.
This seismic pick-up device produces a second output signal,
which is representative of the detected vibrations caused by
the movement of the bore head. The signals from the
microphone and the seismic pick-up device are utilized to
determine pipe penetration by the bore head, as a result of
the changes in the signals detected by both the microphone and
the seismic pick-up device. The nature of a pipe penetration
differs from changes in signals caused by the bore head
glancing off a pipe, or striking a rock or tree root.
BRIEF DESCRIPTION OF THE DRAWING
Figure 1 is a combination diagrammatic representation and
electrical block diagram of a preferred embodiment of the
invention;
Figures 2A, 3A, 4A and 5A are diagrammatic
representations of different conditions encountered by the
system of Figure 1 during its operation; and
Figures 2B, 3B, 4B and 5B are waveform representations of
signals produced in a part of the system shown in Figure 1 for
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the conditions of Figures 2A, 3A, 4A and 5A.
DETAILED DESCRIPTION
Reference now should be made to the drawing, in which the
same reference numbers are used throughout the different
figures to designate the same or similar components. As
illustrated in Figure 1, a horizontal boring system is
diagrammatically depicted in conjunction with a below-grade
sewer pipe 12, located buried in the ground 10. The sewer
pipe 12 includes spaced manholes, one of which 14 is
illustrated in Figure 1, extending from the pipe 12 to the
surface or grade level in a known manner.
A standard boring machine is employed. For that reason,
no details of the machine are shown; but it is represented in
diagrammatic form as including a bore head 16 on the
penetrating end of a drill pipe 18, which is rotated by a
motor 20 through a pair of supports or pillow blocks 21 and
22. It is to be noted that hydraulic pressure (from a source
no shown) is applied to the end of the drill stem 18 to push
the bore head or drill bit 16 into the ground in the direction
of the elongated arrow paralleling the drill stem 18. The
motor 20 rotates the drill stem 18 in the direction of the
circular arrow shown in Figure 1 to cause a pushing and
rotational force to be constantly applied to the bore head 16
as it penetrates through the ground. As illustrated in
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Figure 1, the stem 18 is shown entering at an angle to the
horizontal surface of the ground. It is to be understood,
however, that the bore head 16 is guided to a horizontal
direction, once it has entered the ground, by means of
standard technology. A pressure gauge 24 is employed in
conjunction with the hydraulic mechanism pushing the drill
stem 18 and bore head 16 into the ground to provide a constant
indication of the amount of pressure required to move the bore
head 16 forward in the drilling operation. If the bore head
16 strikes a rock or rock strata after passing through soft
earth, or if it strikes a buried pipe of some type, there will
be an immediate indication of a pressure increase by the
pressure gauge 24.
In order to determine whether the bore head 16 penetrates
a sewer pipe 12 or water pipe 12, two different types of
sensors are employed. These are used in conjunction with one
another to provide an indication to the operator of the
horizontal boring machine of the possible penetration of the
pipe 12. The first one of these sensors comprises a seismic
sensor in the form of a geophone 26. In a preferred
embodiment of the invention, this sensor is a one Hz Geospace~
geophone. This geophone is placed on the ground 10 or
inserted into the ground at a position above the location of
the bore head 16.
Many variables affect the amplitude of the seismic signal
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produced by the rotating bore head 16. For ideal operation of
the geophone or seismic pick-up device 26, undisturbed soil is
the best transmission medium, as opposed to disturbed soil.
Through field tests, it has been determined that the geophone
26 should be located within twenty feet from the bore head in
undisturbed soil, and within ten feet in disturbed soil.
Since a typical horizontal boring machine drill stem 18
is ten feet long, the geophone 26 typically is moved ten feet
ahead of the bore head 16 each time a new section of stem 18
is added during the drilling operation. Signals from the
geophone 26 then are applied to one input of a two-channel
strip chart recorder 30 over a lead 28, illustrated in Figure
1. A filter capacitor 31 is connected across the geophone
lines at the strip chart recorder 30 to filter out local radio
station interference. In an actual embodiment of the
invention, the recorder 30 is set to a sensitivity of 1
Millivolt per division for the seismic channel, indicated in
Figure 1 as coupled to the "red pen" input of the strip chart
recorder. The output of the strip chart recorder 30 is a two-
channel paper strip 32, with the seismic signal recorded onthe strip 34, as indicated in Figure 1.
Since the object of the invention is to detect the
possible penetration of the sewer pipe 12 by the bore head 16,
additional monitoring of acoustic signals in the sewer line 12
by means of a sensitive audio microphone 40 also is employed.
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The microphone 40 is attached to the end of a long pole
(preferably an aluminum pole) 42, and is placed near the
bottom of the manhole 14 to pick up sounds transmitted through
the sewer line 12. The output from the microphone 40 is
applied over a lead 43 to a pre-amplifier 44 and an amplifier
46 connected to the second input (blue pen) of the two-channel
strip chart recorder 30. The audio signals also may be
applied through a microphone 48 to provide an audible sound
input to the operator of the boring machine, as well as
producing an output strip 50 on the recorded two-channel strip
32 obtained from the strip chart recorder 30. A strip chart
recorder which has been used in conjunction with the system
shown in Figure 1 is a two channel M-TEK~, model 222, AC/DC
portable pen recorder. The recorder is operated to provide a
sensitivity on the acoustic channel 50 of 200 Millivolts per
division; and the chart speed of the strip chart 32 typically
is set to twelve inches per hour. This chart speed, however,
may be varied in accordance with the operating speed and
characteristics of the horizontal boring machine.
As noted above, the seismic sensor or geophone 26
converts the vibration energy transmitted through the soil
into an electrical signal, the frequency of which is sub-audio
(typically, 1 Hz). Consequently, this signal must be
recorded. The strip chart recorder 30 has been found to be a
suitable device for making the seismic recordation on the
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channel 34, as described above. The seismic background signal
picked up by the geophone 26 is very small. People or animals
walking near the geophone 26 generate a momentary burst of
energy which coincides with their steps. The system operator,
however, easily can identify such steps of people or animals
because they are situated in the field of vision of the
operator, who can see the people or animals creating these
vibrations. In addition, the actual vibration of the pen on
the recorder 30 to produce the signal recorded on the strip 34
sounds very similar to the footsteps of a person walking
nearby. It is important, however, for the operator to be
aware of surrounding activities, which can produce signals to
be picked up by the geophone 26.
The boring head 16 produces distinct seismic signals when
it encounters any object that is harder than the surrounding
soil. The most notable signals are due to tree roots, rocks,
concrete and pipes. All of these objects cause a burst of
energy when they are struck by the bore head 16. A
significant distinction, however, exists when the bore head 16
penetrates both walls of a pipe 12, because this produces a
distinct double burst of energy. The energy signals, which
are produced by the bore head striking these different
objects, are illustrated in Figures 2A through 5A; and the
seismic signals produced by the geophone 26, for the objects
of each of these figures, are illustrated in the accompanying
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waveforms 2B through 5B. For example, Figure 2A illustrates
the signal produced when the bore head strikes a tree root 52
to produce the output signal 34A illustrated in Figure 2B.
This signal 34A is recorded on the channel 34 of the strip
chart recorder 30.
Figure 3A indicates a glancing blow by the bore head 16
on the surface of a sewer pipe 12 to produce the signal 34B,
shown in Figure 3B. Figure 4A indicates the situation which
occurs when the bore head 16 penetrates through a sewer pipe
12. The unique double burst seismic signal 34C is produced by
this occurrence. This is contrasted with the single burst
signals 34A and 34B for the situations described in
conjunction with Figures 2A and 3A. If the bore head
encounters a rock in otherwise soft soil (54), the signal 34D
shown in Figure 5B is produced.
It is readily apparent from an examination of the seismic
signals 34A, 34B, 34C and 34D, that only the penetration
through the two walls of a sewer pipe 12 (or other pipe)
produces the unique double burst signal 34C. The other
signals, 34A, 34B, and 34D, all are single burst signals of
varying lengths, depending upon the nature of the obstruction
encountered by the bore head 16.
If the bore head 16 is pushing forward but is not
rotating, the amplitude of the seismic signal recorded on the
channel 34 of the chart 32 iS greatly reduced. AS a
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consequence, it is difficult for the system operator to detect
the bore head 16 striking some object. Even if the bore head
16 is rotating, as noted above, the seismic signal may be
quite weak. Because of this, the system employs two other
factors to aid in detection of pipe penetration. One of these
is the pressure gauge 24, which provides a constant indication
of the pressure encountered by the bore head 16 against the
hydraulics pushing the drill stem 18 into the ground. The
machine operator can both feel and see, on the pressure gauge
24, sudden pressure increases caused by the bore head 16
striking hard objects. If the operator knows that a sewer
pipe 12 is in the general area, the operator either will back
up and go over the object or dig a hole to the bore head 16 to
guide it over the object. Consequently, the operator attempts
to feel or observe any pressure buildup as the bore head moves
forward. Most tree roots, such as the root 52 (Figure 2A) and
small rocks, are not felt. Clay or orangeburg sewer lines
which are in poor or deteriorated condition, however, will not
be felt or noticed by the pressure gauge 24 either. The
seismic sensor usually picks up these conditions, but
sometimes generates a very small signal.
To complement the seismic signal recorded on the channel
34 of the strip chart recorder 30, the sensitive microphone 40
is placed at the bottom of the nearest sewer manhole 14. As
is well known, the bore head 16 emits high pressure water,
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14
which serves as a lubricant during the boring process. This
water noise is detected by the microphone 40, and is heard by
the detection system operator over the loudspeaker 48. This
background noise also is recorded by the "blue pen" of the
two-channel strip recorder on the channel 50, as described
above. If the bore head 16 breaks through the wall of the
sewer line 12, the operator sometimes can hear the sewer
lateral walls break as the bore penetrates them by the change
in sound over the loudspeaker. The sound intensity
significantly increases in amplitude; and this is recorded on
the strip chart recorder. This low frequency amplitude
envelope of the acoustic signal is recorded on channel 50
adjacent the seismic signal on the channel 34 on the chart 32
of the recorder 30. Correlation of the two signals (seismic
and audio), plus possible simultaneous pressure buildup on the
pressure gauge 24, indicates that a sewer lateral 12 has been
penetrated if a seismic "double burst" signal 34C is recorded.
If correlation between both this "double burst" seismic signal
and the audio signal occurs, this generally is indicative of
the penetration of a sewer lateral. If, in addition to these
two signals, pressure buildup however, also is indicated on
the pressure gauge 24, boring immediately is terminated; and
the boring contractor digs down to the bore head to confirm
the event, and then to steer the bore head 16 around the pipe
12. Repairs to the pipe 12 then can be made in an expeditious
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manner. As noted above, however, in not all cases will there
be a pressure increase on the pressure gauge 24, even though
the pipe 12 may have been penetrated, particularly if the pipe
12 is in deteriorated condition.
After periods of heavy rain, there also typically is
substantial water noise in the sewer system 12/14. This can
make it difficult to obtain an audio pick up of the bore
penetration and water injection by the microphone 40. At
times, the sewer manhole 14 is too far from the bore head 16
to hear the penetration. As a consequence, it is important
for the boring contractor also to know whether sewer laterals
cross the boring machine path. By knowing sewer lines 12 are
in the path of the boring machine, the operator can remain
more sensitive to the seismic, acoustic and pressure signals;
so that any correlation of two or all three of these signals
will cause the operator to stop the boring operation to dig up
all suspicious contacts.
In the system shown in Figure 1, the geophone 26 and the
acoustic microphone 40 both are connected to the strip chart
recorder 30 by means of small gauge speaker wires 28 and 43,
which may be placed on long cable reels (such as 500 foot
reels). To eliminate the necessity for stringing the wires 28
and 43, however, the geophone housing 26 can also be expanded
to incorporate batteries to operate either an FM low power
radio or an infrared transmitter. A similar modification may
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16
be added to the microphone pre-amp 44, which would be
physically located at or near the position of the microphone
40. Complementary wireless receivers then may be installed at
the chart recorder 30. Thus, the two sensors 26 and 40 will
not require wires, and are easier to deploy. In addition,
microprocessor based signal analyzers can replace the strip
chart recorder 30 to provide an alarm or indication to the
operator when the signal analysis indicates the likelihood
that a pipe penetration has occurred. Similarly, a
transmitter may be added to the boring machine pressure gauge
24; so that this signal can be fed to the analyzer or to the
strip chart recorder (adding another channel) for inclusion in
the correlation process.
Various other changes and modifications will occur to
those skilled in the art to produce a system which performs
substantially the same function, in substantially the same
way, to achieve substantially the same result, without
departing from the true scope of the invention as defined in
the appended claims.
