Note: Descriptions are shown in the official language in which they were submitted.
This invention lies in the field of linings for boreholes drilled
into the earth.
Drilled shafts or boreholes in the earth are used for a wide
variety of purposes, including entries into mines, points of entry for mine
storage facilities and for the storage of biological waste and for other
purposes.
The most common linings for drilled boreholes or shafts in the
earth are rigid steel casings, which are grouted into place by filling the
annulus between the borehole wall and the steel casing with a Portland
cement grout. The cost of rigid steel casing is high, especially in cases
where large dia~eters are involved and large hydrostatic pressures are antici-
pated. The steel casings have great weight, which necessitates the use of
specialized equipment, capable of handling ver~ large weights, to run the
casing into the shaft or borehole.
Another disadvantage of grouted-in-place rigid steel casing is that
of transporting the casing to the borehole, because of its size and weight.
Still another disadvantage of the rigid steel casing is the time
involved in placing it into the shaft prior to grouting, because of the
; requirement that many lengths must be welded together and the welds allowed
to cool, before the casing can be further lowered into the hole. This is a
stepwise operation, where one length of casing is welded to a preceding
length, the weld is allowed to cool and then the casing is lowered by the
new length prlor to welding still another length, etc.
A thin lightweight lining material offers many advantages in that
the lining can in some application be an essen~ially continuous membrane,
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which will have a relati~ely low weight and can be delivered to the site in
a collapsed condition. It may be delivered in one continuous length or in
a ~ew pieces of substantial length, requiring fewer joints to provide the
full depth of liner.
Though the concept appears ideal~ heretofore there has been no
means of maintaining the correct internal diameter of membrance linings of
low flexural rigidity while grouting in place or when subjected to external
pressure.
- This invention describes a new technique for using a combination
lo of a membrane liner of low flexural rigidity with Portland cement grout
to create a rigid waterproof lining which is impervious to the movement of
fluid, either into or out of the borehole, or shaft~ and in which the
membrane is rigidly joined to the grout and can withstand relatively high
differential pressures by virtue of the reinforcement created by the enclo~ing
cement grout.
Basically, the invention is a liner of low fle}cural rigidity adapted
to be grouted into a borehole drilled in the earth comprising: a thin-walled
cylinder of selected diameter, less than that of said borehole, so that
when said cylinder is inserted into said borehole an annular space will be
provided between said cylinder and the wall of said borehole for receiving
grout therein; and a plurality of circ~mferentially spaced keys, each key
having its inner end attached to said cylinder and its outer end spaced
radially outwardly from said cylinder.
In a preferred embodiment of the invention, support rings and rods
are keyed -to the cylinder to impart greater rigidity thereto~
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The invention also encompasses the method of installing a liner of
low flexural rigidity adapted to be grouted into a borehole in the earth, said
liner comprising a cylinder having a plurality of spaced outwardly extending
keys attached at their first ends to said cylinder and extending outwardly,
with their outer ends having suitable means to lock to the grout~ the
me-thod comprising the steps of: (a) inserting said liner, axially, into said
borehole, with its bottom end at a selected distance above the bottom of said
borehole; (b) inserting a plurality of grou~ipipes circumferentially spaced
into the annulus between said cylinder and the wall of said borehole to
a point near the bottom of said borehole; (c) pumping in Portland cement
grout through said pipes into said annulus, while (d) raising said pipes,
as the level of grout in said annulus rises, always keeping the bottom ends
of said pipes- below the surface of said grout.
A better understanding of the invention will be evident from the
following description taken in conjunction with the appended drawings, in
which:
Figure 1 illustrates schematically one embodiment of this invention
inserted into an open borehole in the earth;
Figures 2 and 3 illustrate in plan and elevation sections the
detailed construction of one embodiment of this invention;
Figures ~, 5, 6 and 7 illustrate~details of the various types
of keys which are imbedded at one end into the cylinder and serve to tie the
cyli.nder to the grout, to outer support rings and to support rods; and
Figure 8, on the same sheet as Figure 1, illustrates schematically
one method of installing the embodiment of FIGURES 2 and 3.
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Referring now to the drawings and in partic~ar to Figure 1J there
is shown schematically one embodiment of the invention. The mlmeral 10 in-
dicates generally the system comprising a cylinder 20 of low flexural
rigidity material of suitable wall thickness and diameter, positioned axially
inside of a borehole 18 in the earth 16 extending from the surface 14 down to
a depth 17. There is an annular space 12 between the cylinder 20 and the
wall 18 of the borehole. In this annular space are provided a plurality of
support rings 22, which are spaced axially and are maintained in their
positions by means of a plurality of circumferentially spaced support rods
24. The support rings and support rods are attached to the cylinder 20 by
means of a plurality of keys which will be fully described in connection
with Figures 4, 5, 6, and 7.
Referring now to Figures 2 and 3, there is shown in horizontal
and vertical cross-section one embodiment of the invention. There is a
thin-walled cylinder 20 of suitable low flexural rigidity material. There
are a plurality of support rings indicated generally by the numeral 22,
which may be of any selected cross-sectional shape, such as the H cross-
section illustrated, having outer walls 30, inner walls 32, and a hori~ontal
web 34~ These support rings are of suitable diameter so as to oe
spaced outwardly from the cylinder 20. They are held in this posltion by a
plurality of radial keys 36 which are locked at their inner end to the
cylinder and are attached to the support rings by any suitable means~ such
as the threaded ends interlocking with the support rings illustra~ed.
A plurality of circu~ferentially spaced support rods 24 are utilized
to connect adjacent support rings, and are attached to the support rings, so
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that the entire liner~ including the cylinder, support rings, and support
rods, forms a fairly rigid elongated structure, by means of which the liner
can be lifted and lowered into the borehole.
Another type of key 38 is provided which is locked at its irner
end into the wall of the cylinder and is attached to the support rods at its
outer end, such as by having an opening or eye through which the rods are~
passed so as to maintain the position of the rods at intermediate points
between the support rings, so as to mak0 the cylinder more rigid.
In Figure 6 the H cross-section of the ring is shown in greater
detail than in Figure 3 and it is attached to the cylinder by means of the
keys 36 which have inner ends 60, imbedded in the wall of the cylinder and
shanks 62 which are threaded at the end 64 and are locked to the ring by
means of nuts 66, for example.
The support rings can be of any desired cross-sectional shape and
si~e, and can be attached in any way to the wall of the cylinder 20. There
is no limitation on the details of such shape, si3e or manner of attachment.
Illustrated in ~igure 4 is a detail of the construction and assem-
bl~ of the support rods 24 to the webs 34 of the support rings, illustrated
in Figures 3 and 6. The rods 24 are threaded at top and bottom ends. ~t
the top end is a fixture 40 which has an internal thread 44 on the bottom,
which mates with the threaded end 42 of a rod 24. This fixture has a
shoulder 46 and a threaded end 47 which is locked to the web 34 by means of
a collar 50 which screws down on the threaded end 47 and locks the web. The
upper end of the collar 50 has a threaded opening which is adapted -to
receive the bottom threaded end of another support rod 24 etc. Of course,
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other means may be provided for attachment of the support rods to the
support rings.
In Figure 5 is illustrated one type of key indicated generally
by the numeral 38 which has an inner end 54 by means of which it can be
imbedded in, or attached to~ the cylinder 20. It has a spacing shank 56
and an eye 58 adapted to pass a support rod 24 and to hold it in proper
spaced relation to the cylinder 20.
Figure 7 illustrates another key 70 which can be attached at 72
to the cylinder 20 and which has a shank 74 of selected length, terminating
in a head 76 spaced a selected distance from the cylinder. If desired,
the shank 74 or head 76 ma~ have a weak section designed in so that the
head will shear or break off at a selected applied force.
When the cylinder is assembled with the support rods, support
rings and keys and is lowered in the borehole, the support rings, keys,
support rods, etc., are all imbedded in the Portland cement grout that fills
the annular space and serves to strongly and rigidly tie the cylinder to
the grout and!!make a watertight, rigid, thick-walled cylindrical liner for
the boreholeO
Three di~ferent types of keys have been illustrated, one which is
just to provide a bond between the cylinder and the grout, such as illustrated
in Figure 77 another type 36 which is utilized to tie the support ring to the
cylinder, as illustrated in Figure 6, and a third type 3~ in Figure 5,
which is used to tie the support rods to the cylinder at intermediate points
between the support rings. However, if the diameter of the borehole is small
and if the ratio of the thickness to the diameter is not too small, the
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cylinder will have sufficient rigidity that i-t may not be necessary to
provide the support rings and support rods. In that case, keys of the type
shown in Figure 7 would be utilized for the purpose of anchoring the cylinder
wall to the grout and that would be all that would be necessary. On the
other hand, if the diameter of the hole is large and it is impractical to
provide a great enough thickness to make the cylinder self supporting, then
the addition of the support rings and support rods would be advisable.
Various materials can be used for the cylinder~ For example,
if the material is castable, such as plastic, then the keys illustrated in
Figures 4, 5, 6 and 7 can be inserted into the wall and be cast integral
with it~ On the other hand, the cylinder may be made of a suitable material
that can be extruded and the keys can be then attached to the extruded cylin-
der, provided suitable means are utilized to make the bond strong enough
between the key and the cylinder.
Another way of constructing the cylinder and the key would be
to make the cylinder of suitable thermoplastic material and, similarly,
to mold or extrude the keys of the same type of material. The keys can be
attached to the cylinder by thermal fusion, as is used in the joining
of sections of large diameter pipes made of thermoplastic materials. Such
a process would involve means to heat a selected area of the outer wall of
the cylinder and to heat the surface of the key until they were both at a
suitable elevated temperature and then to press the two heated surfaces
together, so that they will bond and form a monolithic structure.
Another way of constructing the keys which are used to bond the
cylinder to the grout and illustrated in Figure 7 would be to use a short
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section of a thermoplastic thin-walled pipe to form a thin strap or loop,
which is attached to the outside wall of the thermoplastic laner by the heat
fusion method, etc.
Having constructed the assembly as indica-ted in Figures 1, 2 and 3,
in accordance with the details of ~igures 4, 5, 6, and 7, it becomes
necessary to install this assembled liner into a borehole and to grout it into
position This is indicated in Figure 8, which shows in cross-section, a
borehole having a wa11 18 of suitable diameter in the ear~h 16, drilled
from the surface 14 down to a bottom 84 at a depth 17. The liner is schema-
tically indicated by numeral 10 without all of the detail of Figure 1. This
is lowered into position in the borehole with the bottom end 82 at a selected
distance 83 above the bottom 84 of the borehole. The liner 10 is centered
in the hole, providing an annular space 86 of uniform radial width.
Assume that this hole has been drilled by the use of drilling mud
and is filled with drilling mud at the time the liner is to be inserted. The
liner is dropped into the mud-filled hole to the proper depth~ A plurality
of grout lines 90 of suitable diameter are positioned in the annulus in
circumferentially-spaced relation, with the bottom ends close to the bottom
84 of the hole. Portland cement grout is pumped in from the surface in
accordance with arrows g6 and the grout, because of its greater density, dis-
places the mud upwardly. The level of the grout is indicated 97 in Figure
8. As the grout rises and pushes upwardly the mud in the annulus 86, the
grout pipes 90 can be raised. Mowever, their bottom end must be maintained
below the interface 97 between the grout 85 in the space 88 and the mud 87
in the ann~lus on top of the grout. The interior space 92 inside the cylin-
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der 10 is also filled with mud. ~s grout is pumped in and the grout lines
are wi-thdrawn the annulus will be filled with grout. Because of the greater
density of the grout, than the mud inside the space 92, in the inside of
the cylinder, it may be advisable to close off the top of the cylinder by
means of a closure 91 and to apply pressure through the closure to the
surface of the mud inside the cylinder. The added pressure is required to
prevent the collapse of the cylinder inwardly because of the greater hydro-
static force of the cement grout.
In other cases the hole may be drilled by mining or other means
and is dr~. In that case the liner is positioned as before. The grout lines
90 are installed. Also, a mud line 9~ is provided so that mud can be
; inserted into the inside of the cylinder in accordance with arrows 98, then,
as the grout fills the bottom end 88 of the annular space 86 and rises with
a surface such as 97, the hydrostatic force in~ardly of the grout on the
cylinder can be compensated by mud in the space 92 having a longer column
; from the top 93 than the column of grout, such as to balance the hydro~static force inwardly of the cement. As the cement grout is applied and the
top swrface 97 moves upwardly, likewise, the level 93 of the mud is
increased as necessary. As in the previous description, when the cement
grout reaches the top surface, it may be necessary to fill the entire in-
ternal space of the liner with mud and to apply a suitable pressure to the
top in accordance with arrow 89.
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