U.S. patent application number 10/195708 was filed with the patent office on 2004-01-15 for system and method for guided boring obstacle detection.
Invention is credited to Cribbs, Robert W., Niessen, Douglas G., Wu, Ching-Chen.
Application Number | 20040007070 10/195708 |
Document ID | / |
Family ID | 30000053 |
Filed Date | 2004-01-15 |
United States Patent
Application |
20040007070 |
Kind Code |
A1 |
Cribbs, Robert W. ; et
al. |
January 15, 2004 |
SYSTEM AND METHOD FOR GUIDED BORING OBSTACLE DETECTION
Abstract
A method and system for detecting an underground obstacle in
which a plurality of acoustic signal sensors are deployed in a
predetermined pattern on an area of ground defined by a guided
drill path. A drill head of a drill is inserted into the ground and
a borehole is drilled in the ground along the guided drill path.
The noise signal generated by the drill head is detected at at
least two of the acoustic signal sensors and the difference in
arrival time of the noise signal at the two acoustic signal sensors
is determined. This difference in arrival time of noise signal is
analyzed, whereby the presence or absence of an underground
obstacle is determined.
Inventors: |
Cribbs, Robert W.;
(Placerville, CA) ; Wu, Ching-Chen; (Folsom,
CA) ; Niessen, Douglas G.; (Folsom, CA) |
Correspondence
Address: |
Mark E. Fejer
Gas Technology Institute
1700 South Mount Prospect Road
Des Plaines
IL
60018
US
|
Family ID: |
30000053 |
Appl. No.: |
10/195708 |
Filed: |
July 15, 2002 |
Current U.S.
Class: |
73/598 |
Current CPC
Class: |
G01N 29/045 20130101;
G01N 29/07 20130101; G01V 1/001 20130101; G01S 15/04 20130101; G01N
2291/011 20130101; G01S 15/46 20130101; G01N 29/14 20130101; G01N
2291/106 20130101 |
Class at
Publication: |
73/598 |
International
Class: |
G01N 029/04 |
Claims
We claim:
1. A method for detecting an underground obstacle comprising the
steps of: deploying a plurality of acoustic signal sensors in a
predetermined pattern on an area of ground defined by a guided
drill path having a drill head insertion point; inserting a drill
head of a drill into said ground at said drill head insertion
point; drilling a borehole in said ground along said guided drill
path; detecting a noise signal generated by said drill head at at
least two of said plurality of acoustic signal sensors; determining
a difference in arrival time of said noise signal at said at least
two of said plurality of acoustic signal sensors; and analyzing
said difference in arrival time of said noise signal, whereby one
of a presence and an absence of said underground obstacle is
determined.
2. A method in accordance with claim 1, wherein a location of said
underground obstacle relative to said drill head is determined.
3. A method in accordance with claim 1, wherein said plurality of
acoustic signal sensors are deployed in a single row along said
guided drill path.
4. A method in accordance with claim 1, wherein said plurality of
acoustic signal sensors are deployed in at least two rows along
said guided drill path.
5. A method in accordance with claim 1, wherein said noise signal
received by each of said acoustic signal sensors is amplified, put
through a high pass filter, and digitized in an analog-to-digital
converter and conveyed to a processor for analysis.
6. A method in accordance with claim 1, wherein a cross-correlation
of said noise signal received at said at least two of said
plurality of acoustic signal sensors is performed.
7. A system for detecting an underground obstacle comprising: at
least one noise signal generator adapted for drilling boreholes in
said ground along a guided drill path, said at least one noise
signal generator being an only source of noise signal generated by
said system; a plurality of acoustic signal sensors disposed in a
predetermined pattern on an area of ground defined by said guided
drill path; means for measuring an arrival time of said noise
signal at each of said plurality of acoustic signal sensors; and
obstacle means for determining one of a presence and an absence of
said underground obstacle in said guided drill path using a
difference in said arrival time of said noise signal between at
least two of said plurality of acoustic signal sensors.
8. A system in accordance with claim 7, wherein said plurality of
acoustic signal sensors are disposed in a single row along said
guided drill path.
9. A system in accordance with claim 7, wherein said plurality of
acoustic signal sensors are disposed in at least two rows along
said guided drill path.
10. A system in accordance with claim 7, wherein said obstacle
means comprises an amplifier having a sensor signal input operably
connected to a sensor signal output of said plurality of acoustic
signal sensors and an amplified signal output, a high-pass filter
having an amplified signal input operably connected to said
amplified signal output of said amplifier and a filtered signal
output, an analog-to-digital converter having a filtered signal
input operably connected to said filtered signal output of said
high-pass filter and a digitized signal output, and a digitized
signal processor suitable for analysis of said a digitized signal
produced by said analog-to-digital converter operably connected to
said digitized signal output of said analog-to-digital
converter.
11. A system in accordance with claim 7, wherein said obstacle
means comprises means for performing a cross-correlation of said
noise signal received at said at least two of said plurality of
acoustic signal sensors.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] This invention relates to a method and apparatus for
detecting underground obstacles, in particular, plastic pipe
encountered in the path of guided drilling operations. More
particularly, this invention relates to a method and apparatus for
detecting underground obstacles by using the sound generated by the
guided drill head that is reflected off the obstacle. This sound is
then detected by sensors and analyzed.
[0003] 2. Description of Related Art
[0004] Many underground utilities are installed by drilling a hole
and pulling the utility through (guided directional drilling). In
some cases, it is possible for the drill to penetrate existing
utilities, thereby causing, for example, a gas leak that might
cause damage, injury or even death. In other cases, gas lines could
inadvertently be installed through sewer or other utility pipes. In
the process of clearing the sewer pipe, the gas lines could be
broken. This would fill the sewer pipe with gas that could be
carried to several buildings, leading to explosions that could
cause damage, injury, or death.
[0005] Using the current state of the art technology, underground
objects are detected using acoustics or ultrasound by transmitting
a pulse into the ground and sensing the return echo from the
underground object. The time of the echo return in conjunction with
the propagation velocity of the pulse provides the distance to the
object, and the beam shape or triangulation or image reconstruction
determines the lateral position of the object. However, such
methods are not suitable for use in connection with simultaneous
drilling operations as the amount of noise generated by the
drilling operation is likely to interfere with the detection
process. Accordingly, it is clear that there is need for a
technology capable of detecting underground obstacles, in
particular, utility pipes in the path of underground drilling
simultaneously with the drilling operation.
SUMMARY OF THE INVENTION
[0006] Accordingly, it is one object of this invention to provide a
method for detecting the presence of an underground object in the
path of an underground drilling operation.
[0007] It is another object of this invention to provide a method
for avoiding contact with underground obstacles during drilling
operations.
[0008] It is yet a further object of this invention to provide a
system for detecting the presence of an underground object in the
path of an underground drilling operation.
[0009] These and other objects of this invention are addressed by a
method for detecting an underground obstacle in which a plurality
of acoustic signal sensors are deployed in a predetermined pattern
on an area of ground defined by a guided drill path having a drill
head insertion point. The drill head of a drill is inserted into
the ground at the drill head insertion point after which drilling
of a borehole in the ground along the guided drill path is
commenced. A noise signal generated by the drill head is detected
at at least two of the acoustic signal sensors and a difference in
arrival time of the noise signal at the at least two acoustic
signal sensors is determined. The difference in arrival times of
the noise signal is then analyzed, whereby the presence or absence
of the underground obstacle is determined. Obstacles that are not
normal to the direction of the drilling operation, such as pipes
that are oriented in a skew direction, are detected by using two or
more rows of acoustic signal sensors and processing the signals to
detect and locate off-axis pipes. The obstacles to be detected may
be under roads or sidewalks of concrete or other materials. In
these instances, the acoustic signal sensors can be placed on the
surface of these materials to detect the obstacles.
[0010] The system for detecting the presence of an underground
object in the path of an underground drilling operation in
accordance with this invention comprises at least one noise signal
generator adapted for drilling boreholes in the ground along a
guided drill path, that is, a drill head of a drill, a plurality of
acoustic signal sensors disposed in a predetermined pattern on an
area of ground defined by the guided drill path, means for
measuring an arrival time of the noise signal generated by said
noise signal generator at each of the plurality of acoustic signal
sensors, and obstacle means for determining the presence or absence
of the underground obstacle in the guided drill path using a
difference in the arrival time of the noise signal between at least
two of the plurality of acoustic signal sensors. The key to the
system of this invention is that no other type of noise signal
generator is required to carry out the method of this
invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] These and other objects and features of this invention will
be better understood from the following detailed description taken
in conjunction with the drawings wherein:
[0012] FIG. 1 is a conceptual diagram of the method for detecting
underground obstacles in accordance with one embodiment of this
invention;
[0013] FIG. 2 is a diagram showing the principle of operation of
the method of this invention when no underground obstacles are
present;
[0014] FIG. 3 is a diagram showing the principle of operation of
the method of this invention when an underground obstacle is
present;
[0015] FIG. 4 is a diagram showing an exemplary 3 by 6 array of
acoustic signal sensors and drill head suitable for use in the
method of this invention;
[0016] FIG. 5 is a diagram showing the path of data from the point
of collection at the acoustic signal sensor to the data
processor;
[0017] FIG. 6 is a diagram showing a sound spectrum of a signal
received at an acoustic signal sensor;
[0018] FIG. 7 is a diagram showing a signal spectrum after
normalization;
[0019] FIGS. 8A-8D are diagrams showing various analysis patterns
suitable for use in the method of this invention;
[0020] FIG. 9 is a diagram showing the results of cross-correlation
in accordance with the method of this invention where no obstacle
is present; and
[0021] FIG. 10 is a diagram showing the results of
cross-correlation in accordance with the method of this invention
where an obstacle is present.
DETAILED DESCRIPTION OF THE PRESENTLY PREFERRED EMBODIMENTS
[0022] A key feature of the method of this invention is the
utilization of the noise created by the drill head as the acoustic
signal to detect obstacles in the path of the drill head. As shown
in FIG. 1, the method of this invention includes placement of a
plurality of acoustic signal sensors or receivers 10 on the surface
11 of the earth ahead of the drill head 12. These sensors detect
the direct acoustic wave 13 generated by the drill head 12. If
there is an obstacle 14, such as a utility pipe, in the path of the
drill head 12, the acoustic signal sensors 10 also detect the
acoustic reflection 15 from the obstacle 14. The acoustic signals
are then analyzed, as discussed hereinbelow, to determine the
presence and location of the obstacle.
[0023] In accordance with the method of this invention, a plurality
of acoustic signal sensors 10 are deployed in a predetermined
pattern on an area of ground defined by an anticipated guided drill
path. A drill head 12 of a drill is inserted into the ground at a
location on the anticipated guided drill path upstream of the array
of acoustic signal sensors 10. As used herein, the location of
"upstream" is determined based upon the direction of drilling.
Thus, because drilling is occurring in the direction of the array
of acoustic signal sensors 10, the point at which the drilling
operation is initiated would be considered to be upstream of the
sensor array. Drilling to produce a borehole is then commenced
along the guided drill path 16. The noise signal generated by the
drill head 12 is detected by the acoustic signal sensors 10 and the
difference in arrival time of the noise signal at at least two of
the acoustic signal sensors 10 (for example, sensor A and sensor B
in FIG. 1) is determined. Based upon analysis of the difference in
arrival time of the noise signal the presence or absence of an
underground obstacle can be determined.
[0024] The signal that is generated by the drill head is a wide
band, noise-like signal. The exact characteristics cannot be
controlled in detail, and the time of travel from the drill head to
the sensors cannot be determined. However, the difference in
arrival time at two or more sensors can be determined. If there are
multiple paths, for example, a direct path 13 and a reflected path
15, 17 from an obstacle, the difference in travel time between
these two paths can also be detected and measured. FIG. 2 is a
diagram showing the situation in which no obstacle is present and
FIG. 3 is a diagram showing the situation in which an obstacle is
present. In the case shown in FIG. 2, the signal 20 arriving at the
second sensor (sensor A) is a replica of the first signal 21
delayed in time arriving at the first sensor (sensor B). A
cross-correlation of these two signals provides a peak at this
time. In particular, if the two signals are s.sub.1(t) and
s.sub.2(t), the cross-correlation is 1 c ( ) = T s 1 ( t ) s 2 ( t
- ) t
[0025] where c=cross-correlation between s.sub.1 and s.sub.2
[0026] .tau.=difference in arrival time
[0027] T=a time interval with the drill head operating
[0028] s.sub.1=signal from sensor 1
[0029] s.sub.2=signal from sensor 2
[0030] t=time
[0031] The integral may be over a time interval of seconds
providing very high signal-to-noise ratio compared with pulse-echo
signals. The duty cycle of pulse-echo signals is typically 1%,
whereas the cross-correlation is continuous (100% duty cycle).
[0032] In the case shown in FIG. 3, there are four signal paths: 1)
drill head to sensor B 30; 2) drill head to sensor A 31; 3) drill
head to obstacle to sensor B 32; and 4) drill head to obstacle to
sensor A 33. The cross-correlation has peaks corresponding to the
difference in propagation time for all of these signals. Those with
the largest amplitudes are 1 and 2, 1 and 4, and 2 and 3. The peak
corresponding to the difference between 3 and 4 is weaker. It can
be detected by directional receivers that reject the direct wave
from the drill head, but the preferred embodiment uses paths 1 and
4.
[0033] In accordance with one preferred embodiment of this
invention, a pattern of sensors is deployed along the guided drill
path ahead of the drill as shown in FIG. 4. Although one row of
sensors can be used, two or more rows provides sensitivity to pipes
and other obstacles at skew angles to the drilling direction and,
thus, are preferred. As the drill progresses through the soil, data
is collected by amplifying and digitizing the acoustic signal in
each acoustic signal sensor. The pass band is filtered to pass
frequencies that reflect from the obstacle and reject frequencies
that diffract past the obstacle. In the case of a pipe having a
maximum diameter of d, any wavelength greater than .pi.d
(approximately 3d) will not reflect. The relationship between
wavelength and frequency in soil is:
f.lambda.=.nu.
[0034] where f=sonic frequency (Hz)
[0035] .lambda.=wavelength (cm)
[0036] .nu.=sonic propagation velocity (cm/sec)
[0037] For example, if the pipe had a diameter of 30 cm, then
wavelengths longer than 90 cm should be rejected. With a
propagation velocity of 30,000 cm/sec, this corresponds to
30000/90=333 Hz. Thus, only frequencies higher than about 300 Hz
should be processed.
[0038] The signal from each acoustic signal sensor 40 is processed
in hardware according to the diagram showing FIG. 5. The signal is
amplified by amplifier 41, then put through a high-pass filter 42
(300 Hz in this example) to eliminate parts of the spectrum that
contain no useful echo information (FIG. 6). The output is
digitized in an analog-to-digital converter 43 and sent to a
computer for further analysis.
[0039] The spectrum of the sound is normally high at low
frequencies and tapers to a low value at 3-5 kHz as shown in FIG.
6. A second normalization process is accomplished in software by
applying a filter that provides a constant amplitude across the
useful band of about 300 Hz to about 3 kHz in a typical case (FIG.
7). Then cross-correlations are taken between all acoustic signal
sensor pairs. For example, FIG. 8A shows an array of 18 sensors,
with 6 sensors disposed along the drill axis and 3 sensors disposed
lateral to the axis. These sensors can be labeled T.sub.ij where
i=1, 2, . . . 6 and j=1, 2, 3. For each j, all combinations of sets
of T.sub.ij are analyzed to determine if an obstacle is detected.
There are 15 pairs for each j as follows--1-2; 2-3; 3-4; 4-5; 5-6;
1-3; 2-4; 3-5; 4-6; 1-4; 2-5; 3-6; 1-5; 2-6; and 1-6.
[0040] FIG. 9 shows the cross-correlation when no obstacle exists.
In this case, the direct wave time difference is 155 milliseconds.
FIG. 10 shows the response with an obstacle in the beam. The time
difference is 260 milliseconds between the direct wave and the
obstacle. The times from different sensor pairs can be used to
triangulate the position of the obstacle. A least squares
triangulation of all data sets is used for the estimate.
[0041] If a detected signal occurs in some subset (for example, 4
in 15), a detection is declared. The difference in times for the
direct signal is used to estimate to velocity (.nu.) of
propagation. This is: 2 v = d T
[0042] where .nu.=velocity estimate (cm/sec)
[0043] d=distance between transducers (cm); and
[0044] T=difference in arrival time (sec)
[0045] The differences in times for the reflection are used to
estimate the position of the pipe. If the estimates from all j's
are the same, then the pipe is normal to the drill direction.
[0046] Then, for each i, the j's are similarly analyzed. This
process provides maximum sensitivity to pipes nearly parallel to
the drill direction. Then, each diagonal is analyzed. These include
patterns shown in FIGS. 8C and 8D. This provides sensitivity to
pipes at skew angles.
[0047] While in the foregoing specification this invention has been
described in relation to certain preferred embodiments, and many
details are set forth for purpose of illustration, it will be
apparent to those skilled in the art that this invention is
susceptible to additional embodiments and that certain of the
details described in this specification and in the claims can be
varied considerably without departing from the basic principles of
this invention.
* * * * *