Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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YIELDABLE BEARING BLOCK
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application claims priority to United States Provisional Patent
Application
No. 62/399,693 filed September 26, 2016, the disclosure of which is hereby
incorporated in
its entirety by reference.
BACKGROUND OF THE INVENTION
Field of the Invention
[0002] The present invention relates to a mine roof bolting system, and more
particularly, a
mine roof bolting system including a bearing member that yields or deforms
when subjected
to a load.
Description of Related Art
[0003] The roof of a mine is conventionally supported by tensioning the roof
with mine
bolts drilled in the mine roof that reinforce the unsupported rock formation
behind the roof.
Other structures may also be supported, such as walls or ribs of an
underground mine; thus
use of the term "roof' herein is also applicable to other such structures. The
end of the mine
bolt may be anchored mechanically to the rock formation by engagement of an
expansion
assembly on the end of the bolt with the rock formation. Alternatively, the
mine roof bolt
may be adhesively bonded to the rock formation with a resin bonding material
inserted into
the bore hole into which the mine roof bolt is inserted. A combination of
mechanical
anchoring and resin bonding can also be employed by using both an expansion
assembly and
resin bonding material.
[0004] Cable bolts are used in the mining industry, and particularly, hard
rock mining as
they provide several advantages over conventional mine roof bolts, for
example, ease of
handling and installation. Cable bolts are substantially easier to fit into a
borehole than the
elongated rods of conventional rod bolt systems. Regardless of the height
limitations in a
mine, cable bolts may be adapted to boreholes of any length due to their
flexibility.
Moreover, the strength capacity of cables typically exceed that of
conventional rod bolts.
[0005] With certain mining conditions, particularly those found in hard rock
mining, the
rock formation in the mine roof is susceptible to movement or rock burst as a
result of mine-
induced seismicity, the excavation of perimeter rock, minor seismicities, and
the like. Under
dynamic loading caused by rock bursts, the conventional mine roof bolts
described above are
vulnerable to failure.
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SUMMARY OF THE INVENTION
[0006] The present invention includes a simple, low cost, and easy to
manufacture mine
roof bolting system wherein at least a portion of the system deforms to absorb
some of the
dynamic loading caused by a rock burst or excessive load caused by squeezing
ground.
[0007] The present invention is directed to a mine roof bolting system
comprising a
bearing member having a first member, a second member spaced apart from the
first member,
and apertures defined through each of the first and second members; and a mine
roof bolt
extending through the apertures. When a load is applied to the mine roof
bolting system, the
bearing member yields.
[0008] The present invention is also directed to a mine roof bolting system
comprising a
bearing member comprising a first member defining a first aperture, a second
member spaced
apart from the first member and defining a second aperture, and a web
extending between the
first member and the second member and thereby defining a gap between the
first member
and the second member; and a mine roof bolt extending through the first and
second
apertures of the bearing member.
[0009] The present invention is also directed to a method for providing a roof
support in an
underground mine. The method includes providing a bearing member as described
above and
inserting a mine roof bolt through the apertures of the bearing member and
into a borehole in
a mine roof. The bearing member is adapted to yield upon application of a load
in excess of a
predetermined load. The mine roof bolt may be a cable bolt, a solid bolt, an
expandable
(inflatable) bolt, or a hollow bolt.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] The present invention will now be described in further detail with
reference to the
accompanying figures, in which:
[0011] FIG. 1 is a perspective view of a yieldable bearing member in
accordance with the
present invention;
[0012] FIG. 2 is a cross-section view of the yieldable bearing member of FIG.1
taken
along line 2-2;
[0013] FIG. 3 is a front elevation view of a mine roof bolting system
including a bearing
plate, the bearing member of FIG. 1, and a mine roof bolt;
[0014] FIG. 4 is a front elevation view of a mine roof bolting system
including the bearing
member of FIG. 1 and a mine roof bolt;
[0015] FIG. 5 is a perspective view of the bearing member of FIG. 1 after the
bearing
member has yielded; and
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[0016] FIG. 6 is a load deflection curve comparing yieldable bearing members
made in
accordance with the present invention.
DESCRIPTION OF THE INVENTION
[0017] The following description is provided to enable those skilled in the
art to make and
use the described embodiments contemplated for carrying out the invention. For
purposes of
the description hereinafter, the terms "upper", "lower", "vertical",
"horizontal", "top",
"bottom", "lateral", "longitudinal", and derivatives thereof relate to the
invention as it is
oriented in the drawing figures. It is to be understood that the specific
devices illustrated in
the attached drawings, and described in the following specification, are
simply exemplary
embodiments of the invention. Hence, specific dimension and other physical
characteristics
related to the embodiments disclosed herein are not to be understood as
limiting.
[0018] FIGS. 1 and 2 illustrate a yieldable bearing member made in accordance
with the
present invention. The yieldable bearing member 10, also referred to herein as
a yieldable
bearing block, generally includes a first member 14, also referred to as a top
member, a
second member 16, also referred to as a bottom member, and at least one web
18, 20
extending between the top member 14 and the bottom member 16.
[0019] The top member 14 may be spaced apart from the bottom member 16 and may
be
substantially parallel to the bottom member 16. The top member 14 and the
bottom member
may each be in the form of a plate which may take any suitable shape
including, but not
limited to a rectangle, a square, a trapezoid, a parallelogram, a polygon, and
a circle. The
web 18, 20 may extend from a first side 14a of the top member 14 to a first
side 16a of the
bottom member 16. A second web 18, 20 may extend from a second side 14b of the
top
member 14 to a second side 16b of the bottom member 16. First sides 14a, 16a
and second
sides 14b, 16b each may include curved portions connecting the top member 14
and the
bottom member 16. The top member 14, the bottom member 16, and the two webs
18, 20
may combine to define a central cavity 26 such that the yieldable bearing
block 10 has a
tubular configuration. The central cavity 26 extends along a central axis A
from a first end
22 to a second end 24 of the yieldable bearing block 10 such that a gap 30 is
formed between
an interior surface 32 of the top member 14 and an interior surface 34 of the
bottom member
16. The central cavity 26 may be open, or alternatively, may include a
compressible material
such as wood, plastic, hard rubber, aerated cement, or the like, to modify the
loading/deformation properties of the yieldable bearing block 10.
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[0020] In one embodiment, the webs 18, 20 may extend from respective sides
14a, 14b of
the top member 14 to respective sides 16a, 16b of the bottom member 16 such
that the webs
18, 20 are at right angles to the top member 14 and the bottom member 16. The
top member
14 and the bottom member may have the same size and shape and two webs 18, 20
may be
provided as shown in FIGS. 1 and 2. The top member 14, the bottom member 16,
and the
webs 18, 20 combine to define a central cavity 26 having a square or
rectangular cross-
section.
[0021] In another embodiment, the size and/or shape of top member 14 and the
bottom
member 16 may be different or the top member 14 may be offset from the bottom
member 16
such that the webs 18, 20 are angled with respect to the top member 14 and the
bottom
member 16. Two webs 18, 20 may be provided such that the top member 14, the
bottom
member 16, and the webs 18, 20 combine to define a central cavity 26 having a
cross-section
that is a trapezoid or a parallelogram.
[0022] In a further embodiment, at least one of the top member 14, the bottom
member 16,
and the webs may be curved. Two webs 18, 20 may be provided such that the top
member 14,
the bottom member 16, and the webs 18, 20 combine to define a central cavity
26 having a
cross-section that is a circle, an ellipse, or a truncated circle having two
flat sides and two
curved sides.
[0023] The yieldable bearing block 10 may have a length L measured along the
central
axis A from the first end 22 to the second end 24, a width W measured
perpendicular to the
central axis A between opposing webs 18, 20, and a height H measured
perpendicular to the
central axis A between the top member 14 and the bottom member 16. With
particular
reference to FIG. 2, an exterior surface 28 of the yieldable bearing block 10
and the central
cavity 26 define a wall thickness 14' of the top member 14, a wall thickness
16' of the
bottom member 16, and wall thicknesses 18' and 20' of the webs 18 and 20,
respectively.
The wall thickness 14', 16', 18', 20' of each wall 14, 16, 18, 20 may be equal
to each other
such that the yieldable bearing block 10 has a uniform wall thickness T or may
be different
from each other in order to provide different portions of the yieldable
bearing block 10 with
different mechanical properties. For example, the yieldable bearing block 10
may have a
uniform wall thickness T of 5/16 inch or 3/8 inch. As is further discussed
hereinafter, the
length L, width W, height H, and wall thickness T of the yieldable bearing
block 10 can be
manufactured to provide specific yield and tensile properties for various
underground mining
conditions, for example, hard rock mining.
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[0024] Apertures 36a, 36b for receiving a fastening mechanism, such as a mine
roof bolt
38, are defined in the top member 14 and the bottom member 16 of the yieldable
bearing
block 10. The apertures 36a, 36b may be positioned substantially at each of
the centers of the
top member 14 and the bottom member 16. The apertures 36a, 36b may be
dimensioned to
receive an elongated body 40 of a mine roof bolt 38 (FIGS. 3 and 4). For
example, the
apertures 36a, 36b may be dimensioned to receive a mine roof bolt 38 having a
diameter of
0.6 inch or 0.7 inch.
[0025] The yieldable bearing block 10 may be produced from any yieldable
material
having high strength, for example, steel or aluminum. The material may have a
minimum
yield strength of 46 ksi and a minimum tensile strength of 58 ksi. One such
material is
rectangular steel tube, for example, a rectangular tube made of ASTM A500-B
steel.
[0026] The yieldable bearing block 10 can be used as part of a mine roof
bolting system,
such as a mine roof bolting system 100, shown in FIG. 3, including the
yieldable bearing
block 10, a bearing plate 42, and a mine roof bolt 38, or a mine roof bolting
system 200,
shown in FIG. 4, including the yieldable bearing block 10 and a mine roof bolt
38.
[0027] Referring to FIG. 5, the yieldable bearing block 10 is designed to
yield, or deform,
such that the gap 30 of the yieldable bearing block 10 is reduced when a
predetermined load,
for example, 15 tons or more or 20 tons or more, is applied to the mine roof
bolting system
100 or the mine roof bolting system 200.
[0028] Referring to FIG. 3, the mine roof bolting system 100 includes the
yieldable bearing
block 10, the bearing plate 42, and the mine roof bolt 38. The bearing plate
42 may generally
include a planar body 44 having a bearing surface 46 for engaging the mine
roof R and a
contact surface 48 for engaging the top member 14 of the yieldable bearing
block 10. The
bearing plate 42 may be made of commercial grade steel. An aperture 50 may be
positioned
substantially at the center of the planar body 44. The bearing plate 42 may
optionally include
one or more rib members 52 surrounding the aperture 50 and positioned between
the aperture
50 and a peripheral edge 54 of the bearing plate 42. It should be appreciated
that other
bearing plates known in the art may be used in the system 100.
[0029] The mine roof bolting system 100 may be installed in a mine roof R to
provide
support to a rock formation. The mine roof bolt 38 is inserted through the
apertures 36 of the
yieldable bearing block 10 and the aperture 50 of the bearing plate 42 and
into a borehole B.
The mine roof bolt 38 may be a solid bolt, such as a solid rebar bolt or
smooth bar bolt, a
cable bolt, an expandable (inflatable) bolt, a hollow bolt, or any other mine
roof bolt designed
for supporting rock strata as is known in the art. A drive end 60 of the mine
roof bolt 38 may
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include a drive head that does not tension the bolt or may include a
tensioning system.
Suitable tensioning systems include an externally threaded bolt with a
tensioning nut
optionally having a shear pin or breakout portion or the like threaded
thereon, a barrel and
wedge assembly on a cable bolt or other drive heads as are known in the art
for installing
mine roof bolts.
[0030] By way of example, the mine roof bolt 38 may be a cable bolt formed of
a selected
length of a flexible multi-strand steel cable 56 having an anchor end portion
58 and a drive
end portion 60 including a barrel and wedge assembly 61a and a drive nut 61b.
Between the
anchor end portion 58 and the drive end portion 60, the cable 56 is flexible
and extends a
length as determined by the length of the borehole B in the rock formation. A
stiffening tube
57 may enclose the flexible multi-strand steel cable 56 at a proximal end
thereof, adjacent the
barrel and wedge assembly 61a. A washer 62 may optionally be placed between
the bottom
member 16 of the yieldable bearing block 10 and the barrel and wedge assembly
61a such
that the yieldable bearing block 10 does not directly contact the barrel and
wedge
assembly 61a.
[0031] When the mine roof bolting system 100 experiences loading due to a
shift in the
surrounding rock strata, the yieldable bearing block 10 yields, or deforms,
such that the
gap 30 of the yieldable bearing block 10 is reduced. As the yieldable bearing
block 10 yields,
the mine roof bolting system 100 absorbs some of the dynamic load such that
the mine roof
system 100 can support a greater load than a comparable system not including
the yieldable
bearing block 10.
[0032] Referring to FIG. 4, the mine roof bolting system 200 includes the
yieldable bearing
block 10 and a mine roof bolt 38. The mine roof bolting system 200 is
substantially the same
as the mine roof bolting system 100, but does not include the bearing plate
42. Instead, the
top member 14 of the yieldable bearing block 10 directly engages the mine roof
R such that
the yieldable bearing block 10 serves a dual function, acting as both the
yieldable bearing
block 10 and the bearing plate 42. For example, in the mine roof bolting
system 200, the
yieldable bearing block 10 may be at least 36 square inches.
[0033] When the mine roof system 200 experiences loading due to natural forces
of the
mine, the yieldable bearing block 10 yields, or deforms, such that the gap 30
of the yieldable
bearing block 10 is reduced. As the yieldable bearing block 10 yields, the
mine roof bolting
system 100 absorbs some of the dynamic load such that mine roof system 200 can
support a
greater load than a comparable system not including the yieldable bearing
block 10.
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[0034] The following tests were conducted to demonstrate the general
principles of the
present invention. The invention should not be considered to be limited to the
specific tests
presented herein.
EXAMPLES
[0035] Ten yieldable bearing blocks 10 having a rectangular cross-section and
various
lengths L, widths W, heights H, and wall thicknesses T, were tested to
determine a maximum
load and a maximum yield (i.e., maximum deflection) that each of the ten
yieldable bearing
blocks 10 could withstand prior to failure. A load was applied to the top
member 14 of the
yieldable bearing blocks 10 using a rod having a 1.75 inch diameter to
simulate the housing
of a mine roof bolt having a 0.6 inch diameter. The maximum load and
deflection achieved
before the gap between the top member 14 and the bottom member 16 is at least
partially
closed as the top member 14 and the bottom member 16 move toward one another
under the
load as shown in FIG. 5 was measured. The results of the tests are shown below
in Table 1.
Table 1 Test results showing maximum load and deflection
Tube size Sample
Max load Max deflection
Test # (W x H x T) length
(ton) (inch)
(inch) (inch)
1 4.5 24 1.95
2 4 x 3 x 3/8 4.0 22 1.88
3 3.5 20 1.76
4 4.5 21 1.21
4 x 2 x 5/16 4.0 20 1.16
6 3.5 18 1.11
7 4.5 34 1.22
8 4.0 33 1.20
3 x 2 x 5/16
9 3.5 31 1.12
3.0 24 1.06
[0036] Load deflection curves comparing the results of the yieldable bearing
blocks of
Tests 9 and 10 having a length of 3.5 inches and a length of 3 inches,
respectively, are shown
in FIG. 6. The results shown in FIG.6 demonstrate that a load up to a
predetermined load
(e.g., about 25 tons for Test 9 at a length of 3 inches and about 20 tons for
Test 10 at a length
of 3.5 inches) can be applied before maximum deflection is achieved. A mine
roof support
system incorporating the yieldable bearing block of the present invention can
withstand an
added load (e.g., 20-25 tons as shown in Tests 9 and 10), allowing the system
to yield upon
application of the load.
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[0037] The yieldable bearing block provided herein provides an easy to
manufacture and
low cost system for increasing the load for which a mine roof bolting system
can support.
The systems disclosed herein are particularly advantageous in hard rock mining
under which
dynamic loading is caused by squeezing and rock bursts.
[0038] While embodiments of the yieldable bearing block are shown in the
accompanying
figures and described hereinabove in detail, other embodiments will be
apparent to, and
readily made by, those skilled in the art without departing from the scope and
spirit of the
invention. Accordingly, the foregoing description is intended to be
illustrative rather than
restrictive. The disclosure described hereinabove is defined by the appended
claims and all
changes to the disclosure that fall within the meaning and the range of
equivalency of the
claims are to be embraced within its scope.
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