U.S. patent application number 11/500096 was filed with the patent office on 2006-11-30 for apparatus for on-grade boring.
Invention is credited to Robert F. Crane, Mark D. Randa, Steven W. Wentworth.
Application Number | 20060269361 11/500096 |
Document ID | / |
Family ID | 27668832 |
Filed Date | 2006-11-30 |
United States Patent
Application |
20060269361 |
Kind Code |
A1 |
Wentworth; Steven W. ; et
al. |
November 30, 2006 |
Apparatus for on-grade boring
Abstract
A method for installation of an underground pipe includes an
initial step of boring a pilot hole through the ground at a
predetermined grade angle by extending a drill string having a
steerable boring bit mounted thereon through the ground. Upon
reaching an end location for the pilot hole, the bit is removed
from the drill string, and an expander having a diameter greater
than the pilot hole is attached to the drill string, which expander
is backed by an impact device such as a pneumatic impactor
including a striker that delivers repeated impacts to a rearwardly
facing surface of the expander, and by a pipe drawn along behind
the expander. The expander is pulled back through the pilot hole at
the grade angle while the impactor is operated to aid progress of
the expander through the ground and pull the pipe into place behind
the expander. Typically in this method the replacement pipe is
coupled to a rear end of the expander and the boring bit has a
sonde housing containing a sonde attached thereto to indicate to an
operator the orientation of a steering face on the boring bit.
Inventors: |
Wentworth; Steven W.;
(Brookfield, WI) ; Crane; Robert F.; (Oconomowoc,
WI) ; Randa; Mark D.; (Summit, WI) |
Correspondence
Address: |
PHILIP G. MEYERS LAW OFFICE
1009 LONG PRAIRIE ROAD, SUITE 300
FLOWER MOUND
TX
75022
US
|
Family ID: |
27668832 |
Appl. No.: |
11/500096 |
Filed: |
August 7, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10327601 |
Dec 20, 2002 |
7086808 |
|
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11500096 |
Aug 7, 2006 |
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60343148 |
Dec 20, 2001 |
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Current U.S.
Class: |
405/184 |
Current CPC
Class: |
E02F 5/10 20130101; E21B
10/40 20130101; E21B 7/30 20130101; E21B 7/064 20130101; F16L
55/1658 20130101; H02G 1/06 20130101 |
Class at
Publication: |
405/184 |
International
Class: |
E03F 3/06 20060101
E03F003/06 |
Claims
1. An apparatus for installation of an underground pipe,
comprising: a forwardly tapering cutting back reamer having front
and rear connecting portions, wherein the front connecting portion
is configured for attaching the cutting back reamer to a drill
string for rotation therewith, and the rear connection portion
includes a bearing joint; an expander connected to the cutting back
reamer by the bearing joint so that the expander does not
substantially rotate as the drill string and cutting reamer rotate,
which expander has a larger outer diameter than the cutting back
reamer and is configured to form a hole by compaction of
surrounding soil; and an impact device including a striker that
delivers repeated impacts to a rearwardly facing surface of the
expander.
2. The apparatus of claim 1, further comprising means for pulling a
pipe along behind the expander and impact device.
3. The apparatus of claim 1, further comprising a tubular body
having substantially the same outer diameter as a maximum outer
diameter of the expander, which tubular body extends rearwardly
from the expander, wherein a ratio of effective length of the
expander and body to the diameter of the body is at least 3.5 to
1.
4. The apparatus of claim 1, wherein the cutting back reamer has a
maximum outer diameter no more than 90% of the maximum outer
diameter of the expander.
5. An apparatus for installation of an underground pipe,
comprising: a forwardly tapering cutting back reamer having front
and rear connecting portions, wherein the front connecting portion
is configured for attaching the cutting back reamer to a drill
string for rotation therewith, and the rear connection portion
includes a bearing joint, wherein the cutting back reamer is
configured to permit steering of the cutting reamer by rotation
through less than 360 degrees and return to its starting position
for one or more cycles; means connected to the bearing joint for
pulling a pipe along behind the cutting back reamer without
substantial rotation of the pipe.
6. The apparatus of claim 5, further comprising a sonde housing
mounted in alignment with a steering portion of the cutting back
reamer for rotation therewith to indicate to an operator the
orientation of the steering portion of the back reamer.
7. The apparatus of claim 6, wherein the cutting back reamer has a
generally conical shape, and the steering portion comprises a cut
away steering face on one side thereof.
8. The apparatus of claim 6, wherein the cutting reamer has a
forwardly tapering, generally conical shape and is mounted
non-concentrically relative to the drill string, such that the
steering portion comprises an eccentrically extending portion of
the cutting reamer.
Description
[0001] This is a divisional of of U.S. patent application Ser. No.
10/327,601, filed Dec. 20, 2002.
FIELD OF THE INVENTION
[0002] This invention relates to methods and systems for the
installation of an underground pipelines such as sewer lines using
a directional boring machine.
BACKGROUND OF THE INVENTION
[0003] It is well known that installing `on grade` services such as
gravity sewer can be very challenging if HDD (Horizontal
Directional Drilling) is used as the method of drilling the bore
for the pipeline. Typically when these types of pipelines are
installed using the open cut method, the pipe is placed, checked
for grade, and if necessary, lifted up enough to adjust the grade
manually by adding or removing small amounts of bedding material
(usually sand or gravel). HDD does not permit fine adjustment after
the placement of pipe or any time after the pilot bore is created,
therefore the bore path needs to be not only accurate for elevation
on each end, but also very straight throughout its length. No
opportunity for fine intermediate adjustments is available using
currently known HDD methods once the pipe has entered the bore.
[0004] Methods and devices disclosed within the scope of this
invention will show that if proper care and attention are used with
the novel devices described, it is possible to place on grade
pipelines using a combination of HDD equipment and optional impact
back-reaming technology. In the discussion that follows, "back
reaming" is used to refer to the second stage of the process
wherein an expander or hole-opener is pulled backward through the
pilot hole to widen the pilot hole and optionally pull the new
pipeline into place. However, except as discussed below, according
to the invention widening the hole to its final size is done by
compaction and not by cutting or reaming per se, and thus is not a
reaming operation in the strict sense.
SUMMARY OF THE INVENTION
[0005] A method for installation of an underground pipe according
to the invention includes an initial step of boring a pilot hole
through the ground at a predetermined grade angle by extending a
drill string having a steerable boring bit mounted thereon through
the ground. Upon reaching an end location for the pilot hole, the
bit is removed from the drill string, and an expander having a
diameter greater than the pilot hole is attached to the drill
string, which expander is backed by an impact device such as a
pneumatic impactor including a striker that delivers repeated
impacts to a rearwardly facing surface of the expander, and by a
pipe drawn along behind the expander. The expander is pulled back
through the pilot hole at the grade angle while the impactor is
operated to aid progress of the expander through the ground and
pull the pipe into place behind the expander. Typically in this
method the replacement pipe is coupled to a rear end of the
expander and the boring bit has a sonde housing containing a sonde
attached thereto to indicate to an operator the orientation of a
steering face on the boring bit. Preferably the boring bit has an
outer diameter that does not substantially exceed the outer
diameter of the sonde housing.
[0006] According to a preferred form of this method, a cutting back
reamer is secured to the drill string ahead of the expander, which
cutting back reamer has a maximum outer diameter no more than 90%
of the maximum outer diameter of the expander. The drill string and
cutting back reamer are rotated during the pulling step
independently of the expander and impact device, which do not
substantially rotate due to a rotatable connection between the
cutting reamer and the expander. The cutting back reamer may be
configured to permit steering of the cutting reamer, further
comprising correcting deviations from grade by steering using the
cutting reamer.
[0007] According to another aspect of the invention, a method for
installation of an underground pipe includes the steps of boring a
pilot hole through the ground at a predetermined grade angle by
extending a drill string having a steerable boring bit mounted
thereon through the ground, upon reaching an end location for the
pilot hole, removing the bit from the drill string and attaching a
drill head including a cutting reamer having a diameter greater
than the pilot hole to the drill string, which cutting reamer is
configured to permit steering when rotated over less than 360
degrees and is backed by a device for pulling a pipe along behind
the expander, the device including a rotatable connection whereby
the cutting reamer can rotate in unison with the drill string
without substantial rotation of the pulling device and pipe,
pulling the pipe back through the pilot hole at the grade angle,
detecting deviations of the pipe from the grade angle, and steering
using the cutting reamer to correct deviations from the grade
angle. The cutting reamer preferably has a forwardly tapering,
generally conical shape with a cut away steering face on one side
thereof, and is mounted non-concentrically relative to the drill
string.
[0008] The invention further provides an apparatus for installation
of an underground pipe. Such as apparatus includes a forwardly
tapering cutting back reamer having front and rear connecting
portions, wherein the front connecting portion is configured for
attaching the cutting back reamer to a drill string for rotation
therewith, and the rear connection portion includes a bearing
joint, an expander connected to the cutting back reamer by the
bearing joint so that the expander does not substantially rotate as
the drill string and cutting reamer rotate, which expander has a
larger outer diameter than the cutting back reamer and is
configured to form a hole by compaction of surrounding soil, and an
impact device including a striker that delivers repeated impacts to
a rearwardly facing surface of the expander. Suitable means may be
provided for pulling a pipe along behind the expander and impact
device. These and other aspects of the invention are discussed in
the detailed description that follows.
BRIEF DESCRIPTION OF THE DRAWING
[0009] In the accompanying drawing, wherein like numeral denote
like elements:
[0010] FIG. 1 is a schematic diagram of a back reaming operation
according to the invention;
[0011] FIG. 2 is a side view of a first apparatus according to the
invention;
[0012] FIG. 3 is a cross section taken along the line 2-2 in FIG.
2;
[0013] FIG. 4 is a front view of the embodiment of FIG. 2;
[0014] FIG. 5 is a side view of a second apparatus according to the
invention;
[0015] FIG. 6 is a front view of the embodiment of FIG. 5;
[0016] FIG. 7 is a cutaway section view of the bearing referenced
in FIG. 5;
[0017] FIG. 8 is a side view of a third apparatus according to the
invention;
[0018] FIG. 9 is a front view of the embodiment of FIG. 8;
[0019] FIG. 10 is a lengthwise section along the line A-A in FIG.
9;
[0020] FIG. 11 is a side view of a fourth apparatus according to
the invention;
[0021] FIG. 12 is the apparatus of FIG. 11, in partial lengthwise
section;
[0022] FIG. 13 is a side view of a fifth apparatus according to the
invention;
[0023] FIG. 14 is a lengthwise sectional view of the apparatus of
FIG. 13;
[0024] FIG. 15 is a side view of a sixth apparatus according to the
invention;
[0025] FIG. 16 is a cross-sectional view along the line 16-16 in
FIG. 15.
DESCRIPTION OF PREFERRED EMBODIMENTS
[0026] According to the method of the invention, since directional
errors created in the pilot bore are often compounded and
exaggerated during any currently known back-reaming operation, any
operator attempting an on-grade boring method should remember and
emphasize these key factors:
[0027] 1. Steering corrections to maintain the desired bore path
must be made to hold grade as a first priority, not depth below the
immediate ground surface, also called depth of cover. Most HDD
transmitters are located in transmitter housings that have bits
with non-symmetrical projections that create a bore larger than the
sonde housing diameter. When drilling is stopped to read the grade
of the transmitter, it is not necessarily at rest with its axis
collinear to the axis of the bore. Non-symmetrical bit geometry
coupled with the oversize bore induce a grade error that can be
considered unimportant for conventional HDD boring, but must be
accounted for or eliminated in on-grade boring.
[0028] 2. Steering during pilot hole boring should be done with a
bit that is not substantially oversize to the sonde (transmitter)
housing behind it. Generally the transmitter housing is larger
diameter than the drill string and the bit is larger than the
transmitter housing. This geometry enhances the ability to bend the
rod within the bore and steer quickly and aggressively, a quality
appreciated during conventional HDD operation. As it is never the
desire of on grade boring to steer aggressively or radically, it
becomes reasonable to reduce the bit size to a diameter approaching
that of the sonde housing. This will tend to enhance the goals of
the first point outlined above. The primary reason to keep the bore
small is to provide a bore that will guide the rod during the
back-reaming operation. No steering corrections are normally
possible during the back-ream, therefore the pilot hole must be
accurate and function to closely guide the back-ream. To accomplish
the guiding process, a straight and accurate pilot hole only
slightly larger than the drill string rods will assist in keeping
the back-reamer on the intended course.
[0029] 3. The back-reaming process must be controlled so as to
minimize wander during the pullback. Wander is exacerbated by
changing ground conditions, by short reamers and by reamers that
are cone shaped and tend to be forced off their path by cobble
stones or other randomly placed obstructions. Even if the reamer
used (whether impact assisted or of conventional style) is
configured to be long in its body length and not of conical shape,
care must be taken during its launch into the bore. The designs
that will be discussed tend to go straight and do not respond to
applied forces quickly, such as the undesirable forces of cobble
stones or ground condition variation, or the desirable force
provided by the rod. Therefore the reamer should be launched into
the pilot bore with the reamer axis and the pilot bore coaxial to
each other. This may require a starter or launch pit that has
preparation qualities similar to that which would be used to lay on
grade pipe. One notable difference is the length of this bedded
pit, it need only be as long as the reamer, rather than the length
of the entire pipe installation.
[0030] Conventional pneumatic impact moles are generally designed
to traverse a straight path along the length of their bore. Three
design considerations help achieve this:
[0031] 1. Making the ratio of body length to bore diameter greater
tends to stabilize the mole. As an example, a 2.5 inch diameter
pneumatic mole will have an overall length (not including hose) of
approximately 48 inches, the bore diameter is 2.6 inches, giving a
ratio of (48.0/2.6) or 18.5 to 1. This is recognized as an accurate
and stable design even without the advantage of an accurate pilot
hole to follow. Typically reamers used in HDD have an aspect or
length to diameter ratio of 2 or 3 to 1. Use of an 18.5 to one
ratio may not be reasonable for typical on grade bore for 8.62''
diameter pipe, however ratios of 3.5 to 1 or even 7 to 1 can yield
a usable and effective reamer and are preferred for use in the
invention.
[0032] 2. Use of an active (axially movable) head, such as
described in U.S. Pat. No. 6,273,201, the entire contents of which
are incorporated by reference herein, reduces the tendency of a
pneumatic impact mole to wander off course during a free, or
unguided bore. It allows the body to stay stationary and not break
static friction with the ground while the head accurately punches a
bore in a direction exactly along the axis of the elongated body.
Static friction between the body and surrounding soil is less
likely to result in deflection of the body within the ground. A
moving body would more likely deflect as particles are displaced by
dynamic friction.
[0033] 3. Use of a stepped profile head as shown in U.S. Pat. No.
6,273,201 tends to result in a lower reaction force vectors not
aligned with the bore axis. These radial reaction components,
produced by randomly placed cobble stones or changing ground
conditions will have a significant effect on deviating the path of
the mole. By limiting their magnitude, the mole will tend to
maintain its straight course. This same physics applies to an
impact device when attached to an HDD drill string.
[0034] According to the invention, one, two or preferably all three
of these features are incorporated into the back reamer to be used
for on-grade boring.
[0035] Devices currently used to back ream generally function to
cut the soil about the pilot bore, mix it with a drilling fluid
such as bentonite, and flow the mixed cuttings from the bore. This
method is very functional for non-precision bores and has been used
to install hundreds of thousands of miles of buried pipe within the
last fifteen years. However, only a small percentage of these pipes
were specified to have a specific and tightly toleranced grade;
usually a specification only calls for a range of depth of cover.
The pipe in such a loosely specified installation will typically
have both positive and negative slopes over a short distance. While
pressurized product flows well through these pipes, gravity induced
flow (sewer) needs a constant and narrowly defined negative slope
in the direction of intended flow. Water flows downhill, any loss
in velocity due to a flat or positive slope will result in loss of
velocity. Excessive slope will result in a high water velocity.
Both are equally deleterious to the ability to carry solid matter
and will ultimately result in flow obstruction and system failure.
As a result, the typical grade for an on-grade sewer line
installation according to the invention is in the range of about
0.1 to 5 degrees, preferably 0.1 to 3 degrees, and remains constant
over the entire run of the pipeline. Storm sewers are similarly
graded.
[0036] HDD has many benefits, most notably minimal disruption of
the surface over which the pipes or utilities are placed. Its
weakness has been its inability to install pipes for
gravity-induced flow, or on grade bores. The device and method of
the invention outlined below eliminates that weakness.
[0037] Referring to FIG. 1, after completing an on grade pilot bore
11, preferably using the bit-transmitter housing arrangement
described above wherein the bit is the same diameter or only very
slightly larger diameter than the sonde housing at the front end of
a drill string 12, an accurate reamer launch pit 13 must be
prepared. This pit 13 will be coaxial with the pilot bore 11 and
have a slope at the nominal value of the specified slope. The
bottom is preferably filled with a compactable material such as
gravel, and be compressed and tamped to provide a stable base 14.
The pit 13 will be long enough so that the product pipe 16
(preferable high density polyethylene or HDPE) bend radius is loose
enough to not lift the tail of a reamer 17 from the launch pit base
14. If desired, an angled approach bore 18 can be used to bring the
product pipe 16 to the pit 13 at the desired angle.
[0038] The reamer 17 will be an impact device, preferably actuated
by compressed air, though a hydraulic or a shaft-powered impactor
(driven by rotation of the drill string, such as described in U.S.
Pat. No. 5,782,311, issued Jul. 21, 1998, the entire contents of
which are incorporated by reference herein) may also be used to
power the impactor. The reamer body will be long, and if the length
engaged by the ground is designated the effective length, the ratio
of effective length to bore diameter should be at least about 3.5
to 1, with a ratio of in the range of 3.5:1 to 7:1 being
preferred.
[0039] As shown in FIGS. 2-4, an expander or head 21 of the impact
reamer 17 is preferably made to impact the soil in a manner that is
decoupled from the drill rod axially, and only in the direction of
intended travel. "Decoupled" in this instance means the head moves
forwardly relative to the drill string in response to the impact
from the impact tool without transmitting more than a small
fraction of the impact to the drill string. The head 21 preferably
has an annular stair-stepped front profile 22. The elongated body,
being included in the effective length, may be merely a sleeve 23
comprised of HDPE trailing the head 21. It can be part of the pipe
24 or fused thereto, and serves as the member that functions to
maintain alignment of the impact hole opener. Sleeve 23 is secured
to head 21 by shear bolts set through holes 26 at the rear end of
head 21.
[0040] The impact mechanism 27 operates in substantially the same
manner as described in commonly-owned U.S. Ser. No. 09/946,081,
filed Sep. 4, 2001, the entire contents of which are incorporated
by reference herein. As described therein, mechanism 27 preferably
includes a control spool 28 that opens in response to pulling on
the drill string ending in starter rod 29, permitting compressed
air from an air passage 31 to enter the mechanism 27 and cause a
striker 32 to reciprocate. A pinned joint 33 permits uncoupling of
the head 21 from starter rod 29. Pinned joints and adapters used
herein are described in more detail in Wentworth et al. United
States Patent Application 20010017222, published Aug. 30, 2001, the
content of which is hereby incorporated herein by reference.
[0041] A further option according to the invention, as shown in
FIGS. 5-6, is to perform a nominal amount of material removal using
a cutting reamer 41 that is not unlike those used in conventional
methods. This cutting reamer 41, smaller in diameter than the
impact reamer 17, would be situated slightly in front of impact
reamer 17 and be turned (rotated) by the drill string. A swivel
connection such as a tapered roller bearing joint 42 is disposed
between the rear of the cutting reamer 41 and the front of the
impact reamer 17, preferably ahead of the pinned joint 33 and
connected thereto by a bearing adapter 35. The cutting reamer 41
may represent an enlargement of the starter rod and may replace the
starter rod in the end-to-end series of components forming the back
reamer or hole opener. A starter rod 50 connects cutting reamer 41
to the leading end of the drill string through a further pinned
joint 53, and these parts cooperate to supply compressed air for
the impact mechanism back through lengthwise passage 31. As an
optional component, a sonde 56 may be mounted on the inside of
plastic sleeve 31 for measuring the grade angle of the product
pipe, and the pipe depth and horizontal position. In this
embodiment, exhaust from the impact mechanism passes back through
the product pipe 24, typically a water or sewer line.
[0042] Referring now to FIGS. 8-10, use of cutting or disruption of
the soil to one side of the instantaneous path of the impact reamer
17 may be used to correct or deviate the path slightly. While the
path may not be severely altered, by using a method similar to that
used to steer in rock, a void can be created using a non-concentric
or asymmetrical cutting reamer. By using a reamer 51 that has a
forwardly angled cutaway face 52 on one side, or is generally off
center (as by being non-coaxially mounted relative to the drill
string), it is possible to create a void just to one side of the
rod axis that will serve to change the path of the impact reamer 17
very slightly. The shape of face 52 can vary substantially; it need
not be forwardly tapered. The motion of the rod used to steer would
include partial rotation of the cutting reamer 51 (say 270
degrees), then returning to the start position by either rotating
backwards or pushing the rod back (thereby shutting off the impact
reamer 17), and then rotating through the rest of the circle or in
the reverse direction. As the impact back reamer 17 always seeks to
have a balance of forces acting on it, the partially cut circle,
placed off center to the impact reamer, will cause the device to
deviate towards the void. This serves to accomplish a minor
steering correction.
[0043] Such a system would require a conventional HDD sonde to be
placed in or around the cutting back-reamer so that its orientation
is known to the operator. A sonde housing 61 is mounted ahead of
cutting reamer 51 for holding a second sonde 62 that enables the
operator to determine the orientation of the cutting reamer 51 for
steering purposes. The first sonde 56, in addition to performing
the functions described above, can be used in combination with
second sonde 61 to measure bending of the apparatus in the ground
by comparing grade angle at each location.
[0044] The cutting reamer of the invention can also be used by
itself, without the aid of an impact reamer, to accomplish on-grade
boring. As shown in FIGS. 11 and 12, a rearwardly extending flange
65 on reamer 51 is connected by a U-shaped shackle 66 to a
conventional pipe puller, such as an expanded taper pipe puller 67.
Shackle 66 is inserted through an eye 68 in flange 65 and secured
by means of a bolt 69 through an eye 71 in a frontwardly extending
flange 72 of pipe puller 67. Shackle 66 could be replaced by a
cable or any similar pulling connector used in the industry.
Additionally, it may be desirable to supply the cutting reamer 51
with drilling fluid (such as bentonite) through the hollow drill
string. The drilling fluid is ejected from a series of holes 74 on
the outer surface of the reamer 51 in a manner well known in the
art, which holes communicate with the central passage 31 through
the drill head. Cutting reamer 51 may also have teeth and/or spiral
grooves (76, FIG. 11) which are effective to enhance cutting
action.
[0045] If it is desired to use drilling fluid and a pneumatic
impact mechanism as well, the apparatus of FIGS. 13 and 14 can be
used. In such a case, since the drill string cannot then be used to
conduct compressed air, air is conveyed to a modified impact
mechanism 27A from the rear using a hose 77 extending through the
product pipe 24, such as described in connection with the
embodiment of FIGS. 20-26 in the foregoing U.S. Ser. No.
09/946,081, filed Sep. 4, 2001. Should a cutting reamer be used
with the impact reamer, the impact reamer 17A of this embodiment
can make use of an integral, self regulating on-off switch or
device 78 that would prevent the impact reamer from overtaking or
impacting the cutting reamer. In some cases, the resistance of the
ground itself will act to prevent the impact reamer from traveling
too far forward. The connection between the cutting reamer 51 and
impact reamer 17A may be designed to permit a certain amount of
relative movement, for example, by interposing a shackle, cable or
elastomeric link therebetween so that limited forward movement of
the impact reamer can occur relative to the cutting reamer.
[0046] It is also advantageous for purposes of the invention to use
an active head that is axially decoupled from both the rod and the
elongated body of the impact reamer. Since the head moves in small
increments per impact and the stroke of the head with respect to
the elongated body is limited, eventually the impact is applied to
the body, moving it forward to meet the head. This has the
advantage of keeping the body static during most of the applied
impact, thereby enhancing straight reaming. This is accomplished,
for example, by using a tool such as the one described in the
foregoing U.S. Pat. No. 6,273,201 as the impact reamer, or one
having a similar movable chisel or head.
[0047] A further variant of the invention is shown in FIGS. 15 and
16, wherein the cutting reamer is replaced by a can or tubular
steerable expander 81 that protects the device from dirt. The front
end of expander 81 can have a conical profile 82 with a cutaway
steering face 83, so that expander 81 can be used to steer in much
the same manner as reamer 51, but without a cutting action. A
rotary bearing 84 similar to bearing 42 is disposed inside a shaft
or mounting adapter 86 connected to the front end of the impact
reamer, which in this embodiment has a larger diameter than the
steerable reamer. An external hex surface of adapter 86 rotates
expander 81 in unison with the sonde housing and drill string.
[0048] In all but one of the concepts described herein, the hole is
sized using compaction rather than cutting. Cutting as illustrated
above is preferably employed as a means of reducing the amount of
work needed to be done by compaction, but ultimately the most
stable, straight and accurate bore is made by using impact
compaction. The head preferably creates a hole slightly oversize to
the product pipe to limit pipe friction. The amount of oversize,
derived from experience in pipe bursting activity using impact
compaction methods, should produce a hole diameter 12% to 20%
greater than the outer diameter of the pipe. An excessively
oversize hole will result in loss of grade tolerance, whereas
insufficient oversize will limit the length of pipe installed per
bore.
[0049] Approximately 80% of the pipe and conduit being placed
currently in the U.S. is not grade sensitive. The other 20% is
currently normally installed with open digging methods, resulting
in disruption, danger and significant surface restoration efforts.
The ability to do that 20% within the required tolerances is now
possible in accordance with the invention using impact compaction
methods coupled with HDD equipment and processes. In particular,
the present invention achieves several unique advantages,
including:
[0050] (1) hole upsizing while maintaining pilot bore grade and
line using impact compaction coupled to a directional drill;
[0051] (2) hole upsizing while maintaining pilot bore grade and
line using impact compaction coupled to a directional drill having
the impactor decoupled from the drill string in an axial direction
and along the direction of intended travel;
[0052] (b 3) hole upsizing while maintaining pilot bore grade and
line using an air impact compaction reamer coupled to a directional
drill having a self-regulating valve system.
[0053] (4) hole upsizing while maintaining pilot bore grade and
line using impact compaction directly behind a smaller cutting
reamer coupled to a directional drill and having a self-regulating
valve system;
[0054] (5) hole upsizing while maintaining pilot bore grade and
line using impact compaction coupled to a directional drill where
the elongated body has a length to diameter ratio of 3.5 to one or
more;
[0055] (6) Use of a drill bit that bores a hole diameter 20% or
less oversize to the transmitter housing and or rod or rod upset
diameters for the purpose of maintaining a straight bore path
during creation of the pilot bore without giving up all ability to
steer; and
[0056] (7) A method of using a non axi-symmetric shaped reamer
rotated through less than 360 degrees and returned to its starting
position for one or more cycles, thereby creating a cavity off set
to the axis of the drill string, the purpose being to deviate the
path of any sort of hole opening device, preferably an impact
reamer.
[0057] The invention as such includes the foregoing, as well as
those defined more specifically in the claims that follow.
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