Note: Descriptions are shown in the official language in which they were submitted.
CA 02556276 2006-08-14
GROUND FREEZING METHOD AND APPARATUS WITH
GEOTHERMAL GRADIENT COMPENSATION
Field of the Invention
This invention relates generally to artificial ground freezing and is directed
more
specifically to improved ground freezing techniques that compensate for
geothermal gradients.
Background of the Invention
Artificial ground freezing is used to freeze selected areas of the ground for
a variety of
different purposes, including temporary earth support for excavations, ground
water containment
and control, confmcment of hazardous materials in the ground, and the creation
of impermeable
zones for hydroca.rbon or mineral extraction or processing. Typically, spaced
apart bores are
drilled and equipped with metal freeze pipes installed along a barrier line or
around a perimeter
of a proposed excavation or other site. Feed pipes extend into the freeze
pipes and direct a
refrigerant to the base areas of the bores. The refrigerant then flows
upwardly in the freeze pipes
and freezes the earth around them. The refrigerant is collected and cooled
again, and then
circulated through other freeze pipes. Eventually, a frozen subterranean
barrier is formed
continuously between the adjacent freeze pipes.
In applications requiring the ground to be frozen to a substantial depth,
geothermal
gradients can lead to a lack of uniformity in the freezing of the ground from
top to bottom.
Because the deeper areas are warmer due to the presence of geothermal
gradients, they require a
longer time to freeze, a problem that increases with increasing bore depth. As
a result, the
shallower areas freeze more quickly, and the subterranean frozen barrier that
is formed is
uneven. In some applications, this can be a significant problem that detracts
from the ability of
the barrier to function as intended.
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Summary of the Invention
The present invention is directed to a method and apparatus involving ground
freezing
techniques that compensate for geothermal gradients. Consequently,
subten:anean barrier walls
are formed more evenly and uniformly from top to bottom even when the bores
are relatively
deep.
In accordance with the invention, a bore that is drilled in the ground can be
equipped with
one or more freeze pipes. In the case of a bore with a single freeze pipe, at
least two separate
feed pipes are provided extending to different depths. The longer feed pipe is
larger in diameter
so that more refrigerant is supplied to the bottom area of the well where the
earth is wanner due
to geothermal gradients. By properly sizing the pipes based on the bore size
and depth, the earth
around the freeze pipe can be frozen in a relatively uniform manner from
bottom to top. The
refrigerant from the freeze pipe can be collected and recirculated through
other bores. The freeze
pipes and feed pipes can be of uniform diameter, or they can be dual diameter
pipes with
transition areas at a depth near the end of the shorter feed pipe.
In the case of a bore having plural freeze pipes, the freeze pipes extend to
different depths
with each having a separate feed pipe. The deeper freeze pipe receives more
refrigerant than the
shorter freeze pipe, as can be achieved by proper sizing of the pipes based on
the bore depth and
diameter.
Using the techniques of the present invention, the frozen subterranean barrier
is formed
more uniformly than is achieved by a single feed pipe in a single freeze pipe,
and compensation
is made for geothermal gradients in a way that results in an economically
formed subterranean
barrier that exhibits improved functionality.
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51743-31
An aspect of the invention relates to an apparatus for freezing
ground adjacent to a bore, said apparatus comprising: a freeze pipe in said
bore
extending therein from the surface; a first feed conduit in said freeze pipe
extending therein to a preselected depth and having a first diameter, said
first feed
conduit having an upper inlet end and a lower discharge end; a second feed
conduit in said freeze pipe extending therein to a depth greater than said
preselected depth and having a second diameter greater than said first
diameter,
said second feed conduit having an upper inlet end and a lower discharge end;
a
supply for supplying refrigerated heat transfer fluid to the inlet ends of
said first
and second feed conduits for flow therein to the discharge ends of said first
and
second feed conduits and upwardly through said freeze pipe to freeze the
ground
adjacent to said bore; and a collection arrangement for collecting the fluid
from
said freeze pipe.
Another aspect of the invention relates to an apparatus for freezing
ground adjacent to a bore, comprising: a first freeze pipe in said bore
extending
therein from the surface; a first feed conduit extending in said first freeze
pipe to a
preselected depth and having a first diameter, said first feed conduit having
an
upper inlet end and a lower discharge end in said first freeze pipe; a second
freeze pipe in said bore extending therein from the surface; a second feed
conduit
extending in said second freeze pipe to a depth greater than said preselected
depth and having a second diameter greater than said first diameter, said
second
feed conduit having an upper inlet end and a lower discharge end in said
second
freeze pipe; a supply for applying refrigerated heat transfer fluid to the
inlet ends
of said first and second feed conduits for flow therein to the discharge ends
of said
first and second feed conduits and upwardly through the respective first and
second freeze pipes to freeze the ground adjacent to said bore; and a
collection
arrangement for collecting the fluid from said first and second freeze pipes.
A further aspect of the invention relates to a method of freezing
ground adjacent to a bore extending from the ground surface, comprising:
applying refrigerated heat transfer fluid in a first quantity to a first depth
in the bore
and then upwardly from said first depth to the ground surface for freezing the
ground adjacent to the bore from said first depth to the surface; and applying
2a
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51743-31
refrigerated heat transfer fluid in a second quantity greater than said first
quantity
to a second depth in said bore greater than said first depth and then upwardly
from said second depth to the ground surface for freezing the ground adjacent
to
the bore from said second depth to the surface.
Still another aspect of the invention relates to a method of freezing
ground comprising the steps of: forming a bore into the ground from the
surface
thereof; applying a first quantity of refrigerated heat transfer fluid to a
first depth in
the bore and upwardly in the bore to the surface for freezing the ground
adjacent
to the bore from said first depth to the surface; applying a second quantity
of
refrigerated heat transfer fluid to a second depth in the bore greater than
said first
depth and upwardly in the bore to the surface for freezing the ground adjacent
to
the bore from said second depth to the surface, said second quantity of fluid
being
greater than said first quantity to compensate for thermal gradients in the
ground
and enhance uniformity to ground freezing in the depth of the bore.
2b
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Other and further objects of the invention, together with the features of
novelty
appurtenant thereto, will appear in the course of the following description.
Description of the Drawings
In the accompanying drawings which form a part of the specification and are to
be read in
conjunction therewith and in which like reference numerals are used to
indicate like parts in the
various views:
Fig. 1 is a diagrammatic view of a ground freezing pipe arrangement
constructed
according to one embodiment of the present invention;
Fig. 2 is a diagrammatic view of a ground freezing pipe arrangement
constructed
according to a second embodiment of the invention; and
Fig. 3 is a diagrammatic view of a ground freezing pipe arrangement
constructed
according to a third embodiment of the invention.
Detailed Description of the Preferred Embodiments
Referring now to the drawings in more detail and initially to Fig. 1, the
present invention
is directed to a method and apparatus for ground freezing which involves
drilling of a bore 10
downwardly from the surface 12 into the ground or earth 14. A freeze pipe 16
which may be
constructed of steel or another metal is installed in the bore 10 generally in
contact with the
sidewall of the bore. The freeze pipe 16 may extend to the bottom or base 18
of the bore 10.
Extending side by side within the freeze pipe 16 are a pair of feed pipes 20
and 22. At
their upper ends, pipes 20 and 22 are connected by a Y fitting 24 with a
common supply pipe 26.
Pipe 20 is substantially longer than pipe 22 and extends downwardly from the Y
fitting 24 to an
open lower end 28 which is spaced slightly above the bottom of the freeze pipe
16 near the base
18 of the bore. Pipe 22 has an open lower end 30 which is located well above
end 28 of pipe 20
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at a mid-depth location within the freeze pipe 16. The diameter of pipe 20 is
greater than the
diameter of pipe 22. The feed pipes 20 and 22 may be constructed of any
suitable material such
as high density polyethylene (HDPE).
By way of example, pipe 22 may be a one inch diameter pipe extending to a
depth within
the bore of 1000 feet. The other pipe 20 may be a two inch diameter pipe
extending to a depth of
1750 feet.
A suitable refrigerant is supplied to the feed pipes 20 and 22 through a hose
32 extending
from a suitable refrigeration source (not shown). The hose 32 connects through
a valve 34 with
the supply pipe 26 at a location above the ground surface 12. The freeze pipe
16 is provided
with a discharge pipe 36 at an above ground location. The discharge pipe 36 is
equipped with a
valve 38 that connects with a discharge hose 40. The discharge hose 40 may
connect with a
refrigeration plant (not shown) which cools the refrigerant and then
recirculates it through
another ground freeaing bore equipped with a pipe atrangement similar to that
of Fig. 1 or some
other ground freezing pipe arrangement.
In use, refrigerant is pumped from the refrigeration source (not shown)
through hose 32,
valve 34 and supply pipe 26 to the feed pipes 20 and 22. The refrigerant that
is pumped
downwardly through feed pipe 20 is discharged in the bottom area of the bore
10 which is
considerably warmer than upper areas of the bore due to geothermal gradients.
The refrigerant
that discharges from feed pipe 20 through its open lower end 28 passes
upwardly within the
freeze pipe 16 as indicated by the directional arrows 42, thus freezing the
earth around the entire
depth of bore 10. Similarly, the refrigerant that discharges through the open
lower end 30 of
feed pipe 22 passes upwardly within freeze pipe 16 as indicated by the
directional arrows 44.
This provides a freezing effect to the earth 14 around the upper portion of
bore 10. The earth 14
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around bore 10 is frozen over time until a solid frozen barrier is formed from
the freeze pipe 16
to adjacent freeze pipes in a manner known in the art.
The provision of the two feed pipes 20 and 22, with pipe 20 extending to a
deeper
location within the bore and having a greater diameter than pipe 22, results
in more refrigerant
being provided to the lower portion of the bore where the earth is warmer due
to geothermal
gradients. As a result, the warmer lower portion of the bore freezes
approximately as quickly as
the cooler upper portion of the bore so that the earth 14 is frozen uniformly
from top to bottom
around the bore 10.
Fig. 2 depicts an alternative embodiment of the invention in which a bore 110
is drilled
downwardly from the surface 112 of the ground or earth 114. The bore 110 is
provided with a
pair of side by side freeze pipes 116 and 117 which are preferably constructed
of steel or another
metal. Freeze pipe 116 extends to the base 118 of the bore 110, while the
other freeze pipe 117
extends downwardly into the bore to a mid-depth level well above the base 118.
A feed pipe 120 extends centrally within freeze pipe 116 and has a lower open
end 128
located a short distance above the bottom of freeze pipe 116. Another feed
pipe 122 extends
centrally within the other freeze pipe 117 and terniinates in an open lower
end 130 located a
short distance above the bottom of freeze pipe 117. The feed pipes 120 and 122
may be
constructed of any suitable material such as 1=IDPE.
A supply of refrigerant is delivered through a hose 132 and valve 134 to the
top end of
feed pipe 120. The shorter feed pipe 122 similarly receives refrigerant
through a hose 133 and
valve 135. A discharge pipe 136 is connected with the side of freeze pipe 116
at an above
ground location. The discharge pipe 136 connects with a valve 138 which in
turn connects with
a discharge hose 140. A similar supply pipe 137 coimects with the top end
portion of freeze pipe
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117 at an above ground location. The discharge pipe 137 is equipped with a
valve 139 which in
tum connects with a discharge hose 141. The discharge hoses 140 and 141 may
direct the
refrigerant to be recooled and recirculated.
The longer feed pipe 120 is preferably greater in diameter than the shorter
feed pipe 122.
Consequently, pipe 120 delivers more refrigerant to the deeper areas of the
bore 110 than is
delivered by the shorter feed pipe 130.
In use, refrigerant is supplied to feed pipe 120 through hose 132 and valve
134. The
refrigerant that discharges from the lower end 128 of feed pipe 120 passes
upwardly within
freeze pipe 116, as indicated by the directional arrows 142. As the
refrigerant passes upwardly
withiii freeze pipe 116, it provides a freezing effect to the ground
surrounding the entire depth of
bore 110. When the refrigerant reaches the surface, it passes through the
discharge pipe 136 and
valve 138 to the hose 140 which may deliver the refrigerant to a refrigeration
plant (not shown)
for recooling and recirculation through another bore.
Similarly, refrigerant is pumped through hose 133 and valve 135 to the other
feed pipe
122. The re.frigerant discharges from the lower end 130 of pipe 122 into the
freeze pipe 117.
The refrigerant flows upwardly within freeze pipe 117 as indicated by the
directional arrows 144
and thereby provides a freezing effect to the upper portion of the bore 110
and the surrounding
earth 114. The refrigerant within freeze pipe 117 passes through the discharge
pipe 137 and
valve 139 to hose 141 which may deliver the refrigerant to a refrigeration
plant for recooling and
recirculation.
Because the earth 114 is warmer at deeper locations around bore 110, the
provision of a
larger feed pipe 120 to provide greater amounts of refrigerant to the lower
portions of the bore
results in uniform freezing of the soil around the bore from bottom to top, in
a manner similar to
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that achieved by the embodiment of Fig. 1. In the embodiment of Fig. 2, the
metal freeze pipes
116 and 117 are of smaller diameter than in the case of a freeze pipe that
occupies the entirety of
the bore, and economies can be obtained in this regard in many applications.
Also, coiled tubing
and other types of piping can be used in the embodiment shown in Fig. 2.
Fig. 3 depicts still another embodiment of the invention in which a bore 210
is formed to
extend downwardly from the surface 212 into the ground 214. The bore 210 may
be formed as a
dual diameter bore and may be equipped with a dual diameter freeze pipe 216
having an upper
section 216A that is smaller in di.ameter than a lower section 216B which
connects with the
upper section by a transition section 216C situation at a mid-depth location.
By way of example,
section 216A may have a six inch diameter with section 216B having an eight
inch diameter.
The lower end of the larger section 216B is adjacent to the base 218 of the
bore 210.
A pair of feed pipes 220 and 222 extend side by side in the freeze pipe 216.
The feed
pipes 220 and 222 may be constructed of any suitable material including HDPE.
Feed pipe 220
may be a dual diameter pipe having an upper section 220A which is smaller in
diameter than a
lower section 220B. A transition section 220 connects the upper and lower
sections 220A and
220B and may be located in the area of the freeze pipe transition section
216C. By way of
example, with the feed pipe 216 having the dimensions previously set forth,
section 220A may
have a two inch diameter and section 220B may have a three inch diameter.
Section 220B
terminates in an open lower end 228 located a short distance above the bottom
of the feed pipe
216.
Feed pipe 222 may be smaller in diamcter than section 220A of the other feed
pipe 220.
For example, feed pipe 222 may have a one inch diameter. Pipe 222 is shorter
than pipe 220 and
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terminates in an open lower end 230 which may be located in the area of the
transition section
216C of the feed pipe 216, well above the end 228 of pipe 220.
The feed pipes 220 and 222 connect at their upper ends with a Y fitting 224
installed in
the feed pipe 216 at a location near the ground surface 212. The upper end of
the Y fitting 224
connects with a supply pipe 226 which in turn connects with a hose 232 through
a valve 234.
The hose 232 is supplied with refrigerant from a suitable refrigeration plant
(not shown). The
feed pipe 216 is provided on its side with a discharge pipe 236 which may be
at an above ground
location. The discharge pipe 236 is equipped with a valve 238 which connects
with a discharge
hose 240. The hose 240 may extend to a refrigeration plant which is uscd to
recool the
refrigerant and recirculate it to another bore.
In use, refrigerant is pumped through hose 232 and passes through the valve
234 and
supply pipe 226 and fitting 224 to the feed pipes 220 and 222. The refrigerant
supplied to pipe
222 discharges near the bottom of the bore 210 through the open lower end 228
of pipe 220. The
refrigerant then flows upwardly within the feed pipe section 216B as indicated
by the directional
arrows 242. The refrigerant thus cools the lower feed pipe section 216B and
the earth around the
freeze pipe and bore. The refrigerant continues to flow upwardly through the
smaller diameter
section 216A of the feed pipe to provide cooling of the earth around the upper
part of the bore.
Similarly, the refrigerant that is pumped into feed pipe 222 passes through
its open lower end
230 and then flows upwardly within the upper freeze pipe section 216A, as
indicated by the
directional arrows 244. The refrigerant thus provides a freezing effect for
freezing of the earth
214 surrounding the upper part of the bore 210. The refrigerant from both of
the feed pipes is
collected in the upper part of the freeze pipe 216 and is discharged through
pipe 236, valve 238
and hose 240.
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Again, by providing feed pipe section 220B with a larger diameter than feed
pipe 222,
more refrigerant is supplied to the lower, wanner part of the bore so that
freezing is achieved in a
relatively uniform manner from top to bottom.
It is thus evident that the present invention provides a method and apparatus
making use
of techniques that compensate for thennal gradients and overcome the effects
of thermal
gradients in order to achieve relatively uniform and even freezing of the
earth from top to bottom
of the bores. It is contemplated that the bores will be provided at spaced
apart locations so that
the ground that freezes between them eventually forms a continuous barrier of
frozen earth.
From the foregoing it will be seen that this invention is one well adapted to
attain all ends
and objects hereinabove set forth together with the other advantages which are
obvious and
which are inherent to the structure.
It will be understood that certain features and subcombinations are of utility
and may be
employed without reference to other features and subcombinations. This is
contemplated by and
is within the scope of the claims.
Since many possible embodiments may be made of the invention without departing
from
the scope thereof, it is to be understood that all matter herein set forth or
shown in the
accompanying drawings is to be interpreted as illustrative, and not in a
limiting sense.
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