Note: Descriptions are shown in the official language in which they were submitted.
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PRESSURE BARRIER LINER
Field of the Invention
This application pertains to pressure barrier liners
for containment of valuabl~ and/or hazardous and/or polluting
fluid or solid waste materials. More particularly, the applica-
tion pertains to pressure barrier liners having membranes which
encapsulate regions of relatively high permeability such that the
regions may bP pressurized or depressurized to pressure levels
sufficient to create a barrier which substantially prevents fluid
escapement through the liner. Pressure barrier liners con-
structed in accordance with the invention may also be tested to
assess their integrity, to determine whether they are leaking,
and to assess their capability to retain fluids or prevent
leakage in the absence of such pressurization or depressuriza-
tion.
Back~round of the Invention
Membrane or sheet liners are commonly used to line
excavations or other containment facilities to prev~nt escapement
therefrom of hazardous and/or polluting fluid wastes, solid waste
leachates or valuable fluids. Such materials must be stored at
the lowest possible cost on either a short term or a long term
basis. Membrane liners consist of a number of membranes or
flexible sheets of liner material joined together at their edges
and ioined to bounding structures to yield a continuous liner
interposed between the fluid to be contained and the surroundings
into which flow of the contained fluid is to be prevented.
Conventional membrane liners have a finite permeability
and may suffer from a number of imperfections including holes in
the membrane or sheet material which are inadvertently produced
during manufacture of the material; holes which are inadvertently
caused during the process of construction of the liner from the
sheet or membrane material or during the process of installing
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the liner in the excavation or other containment region;
imperfections in the welds or seams used to join adjacent
segments of membrane or sheet material to form the liner; and,
holes which develop in the liner after it is installed, due to
punching, shearin~, settling, chemical attack and a variety of
other causes.
Liners are conventionally subjected to fluid pressures
from both sides of the liner. Ambient air pressure subjects both
sides of the liner to a first fluid pressure. Since this
pressure is normally equal on both sides of the liner it does not
produce a significant pressure gradient across the liner and
therefore does not induce significant flow through the liner.
Fluids contained in the region above the liner exert a second
fluid pressure on the upper surface of the liner. Ground water
in the reglon ~eneath the liner exerts a third fluid pressure on
the lower surface of the liner. Accordingly, liners are
conventionally subjected to fluid pressure gradients caused by
the differential betwe~n the second and third fluid pressures.
If the fluid pressure above the liner exceeds that beneath the
liner, fluid will flow from the fluid containment region above
the liner through any disruptions in the liner (i.e. holes,
imperfect seams, etc.~ and into the region beneath the liner,
thus defeating the objective of the liner, which is to prevent
such fluid escapement.
In practice, all liners have a finite permeability due
to the inherent porosity of the material used to construct the
liner. Accordingly, all liners leak at a small but finite rate.
If holes are inadvertently made in the liner, or i~ the seams
which join adjacent segments of liner material are imperfect,
then the rate of leakage may increase dramatically and it is such
increased leakage which is desirably prevented. In the prior
art, high security composite liners have been constructed with
double or even triple layers of liner material. Drainage layers
are typically established between layers of liner material.
Fluid which escapes through the uppermost liner passes into the
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drainage layer beneath the uppermost liner and flows towards
drainage collection points established in the drainage layer.
However, if holes occur in the liner located immediately beneath
the drainage layer then secondary leakage may occur through the
lower liner. If the leakage rate through the uppermost liner is
sufficiently rapid then a localized fluid pressure may develop
within the drainage layer and consequential high rates of leakage
can occur through the lower liner before the fluid escaping
through the uppermost liner can be collected and removed by the
drainage system.
In practice, it is difficult to det~rmine the rate of
leakage through a field installed liner, particularly if the
leakage rate is relatively low and particularly if a composite
liner, comprised of multiple layers of liner material is
involved. Large fluid losses may occur before the leakage is
detected. If the stored fluid is valuable, or hazardous, or
would produce a particularly undesirable impact on the surround-
ing environment, then such leakage should ideally be prevented.
It is also desirable that the liner system be testable to
determine whether the potential for leakage exists so that steps
can be taken to prevent leakage.
The present invention provides a pressure barrier liner
which significantly reduces the possibility of leakage through
the liner, while facilitating testing of the liner to determine
whether leakage could occur through the liner, even at relatively
low leakage rates.
Summary of_the Invention
The invention provides a liner comprising a plurality
of low permeability flexible membranes disposed one above the
other. Separate regions of relatively high permeability are
encapsulated between each adjacent pair of membranes. A
pressurizing means may be used to pressurize a selected group of
the encapsulated regions to a s01ected pressure or pressures.
~L3~31!5 ~i3
Means are provided for preventing separation of the regiQns while
they are pressurized. A depressurizing means may also or may
alternatively be used to depressurize a selected group of the
encapsulated regions to a selected pressure or pressures. A
separator means is provided for maintaining separation of
membrane which encapsulate depressurized regions.
A relatively high permeability flexible membrane may
be disposed outside the outermost of the low per~eability
membranes to encapsulate a further region of relatively high
permeability between the high permeability membrane and at least
one outer surface of the liner. A depressurizing means may be
provided for depressurizing the region between the high permea-
bility membrane and the liner outer surface. Means are provided
for maintaining separation of the high permeability and outermost
membranes while the further region is depressurized.
The encapsulated regions may contain a relatively high
permeability core material which may be connected between the
adjacent membranes which encapsulate the respective regions to
give the liner sufficient strength to resist tensile stresses
which could cause the membranes to separate. As an alternative
to core material, the membranes may be textured such that contact
between the membranes does not obstruct fluid flow within the
encapsulated regions. The textured membranes may also be
connected together to enable the liner to resist tensile
stresses.
A drainage means may extend within a selected group of
the encapsulated regions for withdrawing liquids from within
those regions. A layer of geotextile material may be disposed
cutside at least one of the outermost of the membranes to inhibit
passags of particulate materials into the liner.
A composite liner may be constructed by providing a
first plurality of low permeability flexible membranes disposed
one above the other with separate regions encapsulated between
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each adjacent pair of membranes. For each one of the first
plurality of membranes, a second plurality of low permeability
membranes is disposed beside said one membrane; and, separate
regions are encapsulated between each vertically adjacent pair
of the second plurality of membranes. The liner may be extended
to attain any desired siæe and shape by similarly providing
further pluralities of vertically layered mel~ranes beside the
existing multiple membrane liner
The invention also provides a connector means for
sealingly connecting edges of liner membranes clisposed beside one
another. The connector means further facilitates selective fluid
communication between encapsulated regions.
The pressurizing means may comprise a floating constant
head apparatus for floating in fluid contained by the liner and
for applying a constant low positive head pressure within a
selected group of encapsulated regions. The depressurizing means
may comprise a vacuum pump for applying a low negative head
pressure within a selected group of high permeability regions.
The invention also provides a method of testing for
leakage of a liner during construction of the liner. The method
comprises the steps of disposing first and second low permeabil-
ity membranes one above the other to encapsulate a regiontherebetween. The encapsulated region is then pressurized or
depressurized to a selected pressure (alternatively, a detectable
fluid is injected into the encapsulated region). The pressure
within the region is then monitored tor the region is monitored
for escape of detectable fluid thexefrom). If the region
maintains pressure (or contains the detectable fluid) then it may
be determined that the membranes are not leakin~. However, if
the region fails to maintain the selected pressure (or fails to
contain the detectable fluid) then the uppermost of the membranes
is inspected to locate leaks therein which are then repaired.
The pressurization and monitoring steps are then repeated. If
the region still fails to maintain the selected pressure (or to
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contain the detectable fluid) then the lowermost membrane is
inspected to locate leaks therein which are then repaired. A
further low permeability membrane is then disposed above the
uppermost membrane to encapsulate a further region between the
further and uppermost membranes. The pressurization, monitoring,
inspecting and repair steps are then rep~ated with respsct to the
further region so established. Additional low permeability
membranes are then added and tested as aforesaid until the liner
comprises a selected plurality of low permeability membranes
disposed one above the other with separate regions encapsulated
between each adjacent pair or membranes.
Brief Description of the Drawinqs
Figure 1 is a simplified cross-sectional side vie~ of
a typical prior art liner positioned within an excavation to
contain fluid in a containment pond.
Figure 2 is a simplified diagram which illustrates the
potential escapement of fluids through holes or imperfect seams
in the liner of Figure 1.
Figure 3 is a simplified cross-sectional side view of
a portion of a prior art liner having inner and outer membranes
and having a drainage layer between the membranes.
Figure 4 is a cross-sectional side view of a portion
of a dual membrane pressurized liner.
Figure 5 is a somewhat enlarged cross-sectional side
view of a portion of the liner of Figure 4.
Figure 6 is a cross-sectional side view of a portion
of a dual membrane depressurized liner.
Figures 7a through 7f illustrate alternative liner
panel joints.
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Figures 8a and 8c are, respectively, diagrammatic top
plan illustrations of a portion of a dual membrane liner
incorporating alternative embodiments of a connecting strip for
selective fluid communication between regions within adjacen~
liner panels and for sealingly engaging the edges of the first
and second membranes of adjacent liner panels,,
Figure 8b is a cross-sectional view with respect to
line A-A of Figure 8a.
Figure 8d is a cross-sectional view with respect ~o
line B-B of Figure 8c.
Figures 9a through 9d are, respectively, cross-
sectional end views of alternative connecting strips.
Figure lOa is a top plan view of a containment pond
having a multiple cell dual membrane liner which has been shaped
and sized to fit the containment pond excavation.
Figure lob is a cross-sectional view taken with respect
to line A-A of Figure lOa.
Figure 11 illustrates the manner in which the inner
surfaces of the membranes comprising a liner constructed in
accordance with the invention may be channelled or otherwise
textured such that contact between the membrane inner surfaces
does not obstruct fluid flow between the membrane inner surfaces.
Figure 12 illustrates a "shingling" technique for
constructing and progressively testing a liner in accordance with
the invention.
Figure 13 illustrates a connector strip which is
specially adapted to the construction of liners in accordanc~
with the "shingling" technique of Figure 12.
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Figure 14 is a cross-sectional side view of a portion
of a triple membrane liner.
Figure 15 is a cross-sectional side view of a portion
of a quadruple membrane liner.
Figure 16 is a cross-sectional side view of a connect-
ing strip adapted to the construction of multiple me~brane
liners.
Figure 17 is similar to Figure 11, but illustrates a
multiple membrane liner.
Figures 18a and 18b illustrate two stages in the
construction of a multiple membrane liner.
Figure 19 illustrates the operation of a leaking dual
membrane depressurized liner.
Figure 20 illustrates the operation of a leaking
quadruple membrane liner having depressurized outer segments and
a pressurized or non-pressurized inner segment.
Figure 21 illustrates operation of a leaking triple
membrane liner in which both liner segments are depressurized;
the degree of vacuum in the upper liner segment exceediny that
in the lower liner segment.
Figure 22 illustrates operatiGn of a leaking triple
membrane liner in which both liner segments are pressurized; the
pressure in the lower liner segment exceeding that in the upper
liner segment.
Figure 23 illustrates operation of a leaking triple
membrane liner in which the lower liner segment is pressurized
and the upper liner seyment is depressurized.
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Figure 24 illustrates the provision of a high permea-
bility flexible membrane beneath the lowermost low permeability
liner membrane to facilitate fluid dxainage ~rom beneath the
liner.
Detailed Description of the Preferred ~mbodiments
A background discussion will first be provided with
reference to the prior art. Dual membrane pressurized and
depressurized liners will then be described, together with
techniques for joining adjacent liner panels to construct liners
of desired sizes and shapesO Techniques for liner leakage
detection will then be described. A detailed description of
connecting strips will then be provided in the context of dual
membrane liners. A "shingling" technique for constructing dual
membrane liners is then described. This is followed by a
description of a dual membrane liner having multiple cells.
Multiple membrane liners are then described, together with
connectiny strips and leakage detection and liner construction
techniques specifically adapted to multiple membrane liners.
Background and Prior Art
Figure 1 illustrates a prior art fluid containment pond
comprising excavation 10 which is surrounded by embankment 12 and
lined with a liner 14 formed of material such as polyvinyl
chloride, high or low density polyethylene, butyl rubber,
chlorinated polyethylene, elasticized polyolefin, polyamide,
chlorosulphonated polyethylene, or other material suitable for
potential long term containment of valuable, hazardous or
pollutant ~luid 16. Conventionally, liner 14 is formed by
joining together several segments or sheets of liner material
using heat welding, extrusion welding, solvent welding or
bonding, adhesive bonding, ultrasonic welding, dielectric
welding, electro-magnetic welding, or other known techniques for
joining such materials to form a single composite liner.
13~386;3~
However, as illustrated in Figure 2, holes 18 may be inadvertent-
ly made in liner 14 during manufacture of the liner material,
during formation of the liner, during installation of the liner,
or after the liner has been installed; thereby allowing fluid 16
to leak through hole 18 into the region 20 benPath liner 14,
which is desirably avoided. Similarly, imperfections in the
seams or welds used to join adjacent sheets or segments of liner
material together may result in flow channels or paths as
illustrated by reference number 22 in Figure 2, enabling further
leakage of fluid 16 through liner 14 and into region 20. If
disruptions such as holes 18 or seam imperfections 22 exist in
liner 14 then leakage w.ill occur if the pressure component 'IP1"
exerted on the upper surface of liner 14 by fluid 16 exceeds the
pressure component "P2" exerted on the lower surface of liner 14
by fluid ~i.e. ground water) in region 20.
Figure 3 is a cross-sectional side view of a portion
of a prior art double liner having first and second liners 24,
26 between which a drainage layer 28 formed of material such as
sand is established. ~ere again, holes 30, 32 and/or seam/weld
imperfections 34, 36 can result in escapement of fluid 16 through
liner 24 into drainage layer 28 and thence through liner 26 into
region 20 if the pressure P1 exerted on liner 24 by fluid 16
exceeds the pressure P2 exerted on liner 26 by fluid in region
20. If a drainage system is installed in drainage layer 28 then
a reduced pressure IIP3~1 results in drainage layer 28. The value
of P3, while small, is always positive and may be increased where
the geometry or the permeability of drainage layer 28 is such
that increased pressure heads are required to achieve the flow
rates necessary to drain fluids which enter drainage layer 28
through holes/imperfections 30, 34 in first liner 24. If Pl is
greater than P3, and if P3 iS greater than P2, then fluid 16 will
flow through holes 30 and seam imperfections 34 into drainage
layer 28; part of which flow will be drained away by the drainage
system and part of which will escape through second liner 26
through holes 32 and seam imperfections 36 to region 20. In
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practice, P2 is seldom greater than P3 over the entire extent of
second liner 26.
Dual Membrane Pressurized Liner
Figure 4 illustrates a dual membrane pressure barrier
liner 38 comprising a plurality of liner panels 40a, 40b, 40c,
0tco Each liner panel in turn comprises dua:L (i.e. first and
second) low permeability flexible membranes 42, 44 disposed one
above the other. The term "above" is used in the relative sense.
Membranes 42, 44 may for example by oriented one beside the other
if liner 38 is placed against a vertical sidewall of a contain-
ment pond. As in the case of the prior art liners, membranes 42,
44 may be formed of any suitable material such as high or low
density polyethylene, polyvinyl chloride, chlorinated polyethy-
lene, elasticized polyolefin, polyamide, chlorosulphonated
polyethylene, rubbers, Hypalon , butyl rubber, asphalt, concrete,
soil cement or other suitable low permeability materials. In the
context of the present invention the term "low permeability"
means a material having an overall permeability of less than
1 X 10-7 cm/sec. relative to the flow of water and may ideally be
as low as 1 x 1015 cm/sec.
A relatively high permeability core material 46 such
~5 as sand, geonet, geotextile, textured sheet, or other open-pore
material having a permeability greater than approximately
1 X 10 3 cm/sec. relative to water is encapsulated between first
and second membranes 42, ~4. Opposed first and second surfaces
of permeable core material 46 are preferably (but not necessar-
ily) connected to the inner surfaces of first and secondmembranes 42, 44 respectively to resist the effective tensile and
compressive stresses between membranes 42, 44. If the effective
normal stress between membranes 42, 44 is negative, then the
membrane will tend to separate. To resist potential bursting,
the me~hanical connection establisbed by connecting core material
46 to membranes 42 and 44 must be capable of withstanding an
average tensile stress which is equal to the effective normal
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tensile stress between the membranes. Alternatively, if the
effective normal stress between membranes 42, 44 is compressive,
then permeable core material 46 is subjected to compressive
stress which it must be able to withstand without crushing to the
extent that the permeability of core material 46 is reduced to
tha point that fluid pressure cannot be distributed throughout
the region between membranes 42 and 44.
A pressurizing means such as a pump (not shown) is used
to introduce a pressurized fluid such as air, water, or other
environmentally acceptable fluid into the region encapsulated
between first and second membranes 42, 44. The highly permeable
core material 46 allows the pressurized fluid to distribute
throughout the region encapsulated between membranes 42, 44. To
further facilitate distribution of pressurized fluid throughout
the region between membranes 42, 44 fluid distribution conduits
58 may be placed within or adjacent to core material 46.
Conduits 58 may comprise slotted or perforated pipes, channels
or other conduit material suitable for fluid transmission. If
the pressure within the region between membranes 42, 44 is
maintained so that it exceeds both P1 and P2, then any leakage of
fluid through disruptions caused by holes or weld/seam imperfec-
tions in either of membranes 42, 44 will consist of escapement
of environmentally acceptable pressurizing fluid ~rom the region
between membranes 42, ~4 into the region which contains fluid 16,
or into region 20. More particularly, leakage of fluid 16 into
the region between membranes 42, 44 is prevented by maintaining
the pressure within that region in excess of Pl, thereby
preventing escapement of fluid 16 through liner 38.
The pressurizing means may alternatively be a floating
constant head apparatus (not shown) capable of applying a
constant low positive head fluid pressure within the region
between membranes 42, 44. Such apparatus could be allowed to
float on the surface of fluid 16 to maintain a small differential
overpressure (less than 2 psi.) within the region between
membranes 42, 44 independent of the level of fluid 16 above liner
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38. This slight overpressure would require only a small
coverload to be maintained on upper membrane 42 (for example, by
placing a shallow layer of soil or gravel on top of upper
membrane 42) sufficient to prevent membranes 42, 44 from
separating, in which case the cost and labour involved in
establishing a mechanical connection between core material 46 and
membranes 42, 44 may be avoided.
In many cases, the pressurized fluid introduced into
the region between membranes 42, 44 will preferably be a gas such
as air so as to ensure uniform pressurization throughout the
encapsulated region. Gas pressurization is particularly well
suited to situations where a drainage layer such as a leachate
collection system of the sort typically employed at land fill
sites is installed above the uppermost liner membrane. In such
situations, the contained fluid exerts only a low pressure head
Pl on the upper liner surface which can easily be offset by a
higher gas pressure within the liner. Gas pressurization is also
preferred in situations where ~ntroduction of additional fluids
of any sort into fluid 16 cannot be permitted: or where introduc-
tion of fluid of any sort into region 20 is undesirable.
Core material 46 is not essential. One need only
ensure that a region of relatively high permeability is encapsu-
lated between membranes 42, 4~. For example, as an alternativeto the provision of core material 46, the inner surfaces of
membranes 42, 44 may be channelled as shown in Figure 11. Ridges
90 which separate channels 92 in each of membranes 42, 44 contact
one another and hold the membranes away from channels 92, thereby
ensuring that contact between the membrane liner surfaces does
not obstruct fluid flow within channels 92~ It is expected that
channelled membrane material may be easily and inexpensively
fabricated in large quantities and that liners may be easily and
inexpensively constructed of such material due to the elimination
of the core material. It is also expected that the inner
surfaces of channelled membrane material may be more easily and
inexpensively connected together to resist bursting of the
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pressurized liner than would be the case if core material were
disposed between the membranes, since both sides of the core
matsrial must be connected to the inner membrane surfaces.
Instead of channelling the membrane material as shown in Figure
11, it may be striated, stippled, rippled, or otherwise manufac-
tured with a randomly textured surface such that the inner
surfaces of adjacent textured membranes are supported away from
one another to prevent obstruction of fluid flow within the
region encapsulated by the membranes.
A further alternative liner fabrication technique would
be to pass a sheet of relatively high permeability material
between a pair of heated rollers to seal the outer surfaces of
the material against fluid permeability and then seal the
material around its outer edges to encapsulate the high permea-
bility material. Surface sealants or other methods of developing
low permeability characteristics in the outer surfaces could be
used instead of passage between heated rollers. In the context
of this application the term "low permeability membrane" includes
a material surface in which low permeability characteristics have
been dsveloped as aforesaid. An advantage of this technigue is
that it eliminates entirely the difficult process of connecting
a discrete encapsulated high permeability core material to the
membrane inner surfaces, or connection of textured membrane inner
surfaces to each other.
Techniques for Joinin~ Liner Panels
Figure 5 provides a more detailed cross-sectional side
view of a portion of a dual membrane pressure barrier liner 38
employing encapsulated core material 46. Adjacent liner panels
48a, 48b, etc. each comprise first and second membranes 42, 44
as in the embodiment of Figure 4~ A relatively high permeability
core material 46 is encapsulated between first and second
membranes 42, 44 and has first and second surfaces which are
preferably (but not necessarily) connected to first and second
membranes 42, 44 to resist the effective tensile and compressive
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stresses aforesaid. Adjacent liner panels 48a and 48b are joined
together by overlapping and sealing together adjacent edges of
the first membranes 42 of each of panels 48a and 48b and by
overlapping and sealing together adjacent edges of the second
membranes 44 of each of panels 48a, 48b. This method af joining
panels 48a, 48b facilitates fluid communication between the
regions between first and second membranes 42, 44 of each of
panels 48a, 48b. Such fluid communication enables dis~ribution
of pressurized fluid between adjacent liner panels, thereby
reducing the need for separate conduits for distributing
pressurized fluid throughout the liner. Membranes 42, 44 of the
outermost liner panels are sealed together around their outer
edges 76 to prevent loss of pressurized fluid and to encapsulate
core material 46.
Figures 7a through 7f illustrate a variety of alterna-
tive techniques by means of which adjacent liner panels 48a, 48b
may be joined together. For example, Figure 7b shows a lap joint
in which the outer edges o~ membranes 42, A4 of each panel 48a,
48b are joined together along their inside surfaces before the
two panels are joined together by joining the lower surface of
the lower membrane 44 of panel 48b to the upper surface of the
upper membrane 42, of panel 48a. By injecting pressurized fluid
into the encapsulated region between membranes 42, 44 o~ each of
panels 48a, 48b the seal and potential leakage from each panel
can be checked and leakage through each panel can be prevented
as described above~ However, a flow path 22, could exist through
the joint between the two panels, through which leakage of fluid
16 into region 20 could occur which would not be prevented or
detected by injection of pressurized fluid into the region
encapsulated between membranes 42, 44. Accordingly, joints of
the type shown in Figure 7b should be avoided in preference to
joints o~ the type shown in ~igure 7a and 7c-7f.
Figures 7c and 7d illustrate the manner in which high
permeability material 46 within each of panels 48a, 48b may be
inwardly recessed to leave a gap 50 between the overlapped,
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sealed panel edges. The gap serves as a flow conduit for
distribution of pressurized fluid throughout the liner. As shown
in Figure 7d, gap 50 may be filled with an insert 52 formed of
the same high permeability material disposed between the
membranes comprising each of liner panels 48a, 48b to provide
continuity of core material 46. Alternatively, gap 50 may
receive a conduit insert which serves as 21 means for fluid
communication between the regions within adjacent liner panels,
as hereinafter explained with reference to Figure 8.
Figures 7e and 7f illustrate lap joints which may in
some situations be preferred to the butt joints illustrated in
Figures 7a and 7c through 7d. More particularly, Figure 7e shows
how the first membrane 42 of each of liner panels 48a, 48b may
comprise a single continuous membrane. The second membranes 44
of each of liner panels 48a, 48b may each then comprise discrete
membranes which are overlapped in the manner shown in Figure 7e.
The joint shown in Figure 7e isolates and facilitates separate
pressurization and testing of the region encapsulated within
liner panels 48a and 48b respectively. If pressure testing of
both encapsulated regions (conducted in the manner hereinafter
explained) indicates that there are no leaks from either
encapsulated region, then fluid 16 cannot leak through the liner
to region 20. The joint of Figure 7e is therefore advantageous
for the prevention and detection of leaks, as compared with the
lap joint in Figure 7b and may be used to establish isolated
sections (cells) in the liner.
Figure 7f illustrates a lap joint in which the outer
edges of membranes 42, 44 of each of panels 48a and 48b are
joined together along their inside surfaces before the two panels
are overlapped to produce a third high permeability material
filled space 56 between panels 48a and 48b. The edges of space
56 are sealed by joining the under surface of the lower membrane
44 of panel 48b to the upper surface of the upper membrane 42 of
panel 48a at the outer edges of panel 48b and by joining the
upper surface of the upper membrane 42 of panel 48a to the lower
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surface of the lower membrane 44 of panel 48b at the outPr edges
of panel 48a as shown at 64. The regions encapsulated within
each of panels 48a, 48b and region 56 may each be pressurized to
prevent leakage of fluid 16 into region 20 and to facilitate
detection (as hereinafter described) of such leakage.
Dual Membrane D~pressurized Liner
Figure 6 illustrates a dual membrane liner which is
generally similar to the liner described above with reference to
Figures 4 and 5, except that the pressurizing means is replaced
with a depressurizing means such as a vacuum pump (not shown) for
depressuriæing the region encapsulated between first and second
membranes 42, 44 to pressures below ambient air pressure, and
except that high permeability core material 46, if used, need not
be connected to membranes 42, 44 as it preferably ~though not
necessarily) is i~ the liner is pressurized. In the depressuri-
zed liner of Figure 6, ~luid distribution conduits 58 (which are
preferably, although not necessarily provided) function as a
liquid drainage means and extend throughout the region between
first and second membranes 42, 44. The depressurizing means is
coupled to liquid drainage conduit 58 and is operated to maintain
the region encapsulated between first and second membranes 42,
44 at a pressure which is less than both P1 and P2. Accordingly,
any liquids which pass through disruptions caused by holes or
seam/weld imperfections in membranes 42 or 44 are drawn toward
drainage conduit 58 and eventually pass into conduit 58, through
which they are ultimately removed and/or returned to the
containment pond.
In the absence of water or other liquid fluid pressures
on either side of the liner there will still be ambient air
pressure acting on the outer surfaces of membranes 42, 44.
Depressurization of the region encapsulated between membranes 42,
44 results in an inflow of air at holes 66 in the membranes, or
at seam/weld imperfections 68, thus preventing or reducing the
potential for outflow of liquids. ~ore particularly, fluid 16
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cannot escape through the liner into region 20 because the
pressure gradient established by the depressurizing means ensures
that any fluid flow through disruptions in the liner will be from
the region outside the liner to the region within the liner and
ultimately out of that region via drainage conduit 58. Drainage
conduit 58 may comprise geotextile, geonet, slotted pipe, "egg
crate wa~fle" molded conduits or channels, sand, gravel, or other
suitable known drainage ducts or materials.
The dual membrane depressurized liner of Figure 6 (and
possibly also the dual membrane pressurized liner of Figures 4
and 5) may incorporate first and second layers of geotextile
material (not shown) disposed above and below the liner to
inhibit passage of particulate matter toward the liner which
might clog the region encapsulated between the membranes,
drainage conduit 58, the vacuum pump, or otherwise interfere with
proper operation o~ the liner.
Liner Leakaqe Detection
Significantly, even very small leakage rates may be
detected with the aid of the dual membrane liners of Figures 4-
6. For example, in the pressurized liner of ~igures 4 and 5, the
rate at which pressurizing fluid must be injected into the region
encapsulated between first and second membranes 42, 44 to
maintain the pressure in that region constantly above Pl and P2
is a measure o~ the rate at which fluid -is escaping by leakage
through either of first or second membranes 42, 44. If this
leakage rate is sufficiently low then it may not be necessary to
operate the pressurizing means continuously (although it may in
some cases be desirable to couple a liquid drainage means to
conduits 58 in order to remove li~uids which may accumulate
within the liner during periods when the pressurizing means is
not operatedl. Similarly, with ragard to the depressurized liner
of Pigure 6, the rate at which the depressurizing means must be
operated to maintain the pressure in the region encapsulated
between first and second membranes 42, 44 at a constant level
- 18 -
~a
~3~38~3
which is below P1 and P2 is a measure of the rate at which fluid
is leaking through either of first or second membranes 42, 44.
Here again, if the measured leakage rate is sufficiently low then
it will not be necessary to continually operate the depressuriz-
ing means to maintain a reduced pressure (i.e. suction) betweenfirst and second membranes 42, 44. Suitable pressure sensing
means and/or fluid flow rate sensing means may be employed to
sense the fluid pressures in to or out of the region between
membranes 42, 44 or to sense the rate of fluid flow within that
region, thereby providing an indication of the leakage rate.
Moreover, fluid flow rate sensing means for sensing ~luid flow
rates within the encapsulated region may be employed to measure
the flow direction and/or velocity of fluid flow within the
encapsulated region and thereby pinpoint leaks. A plurality of
pressure sensing means may be employed to detect pressure
gradients within the encapsulated reyion as a further leak
location techni~ue. A still further leak detection technique
would be to pressurize the liner with a detectable gas or liquid,
and then inspect the liner, or the material above the liner,
either visually, or with apparatus specially adapted to detect
low concentrations oE that gas or liquid, thus assisting in
pinpointing leaks. This technique facilitates detection of
leakage in liners which are either uncovered or which are covered
by liquids or by permeable solids (i.e. the technique may be
employed to detect leakage in liners which have been placed in
service).
Dual membrane liners which are ultimately intended to
operate as either pressurized or depressurized liners may be
tested before they are placed in service by pressurizing the
encapsulated region (or regions in the case of liners having a
plurality of liner panels) and then monitoring the pressurized
liner as above to detect leakage therefrom. Upon detection o~
such leakage a sealant may be injected into the encapsulated
region. The leakage of pressurizing fluid through holes or
weld/seam imperfections will carry the sealant to the leakage
sites and into the holes or weld/seam imper~ectionsl thereby
-- 19 --
~3~3~
effectively plugging them. It may be necessary to provide
sealant injection points and vents at multiple locations on the
liner so that s~alant can be applied uniformly throughout the
liner.
Connecting Strip
Figures 8a and 8b illustrate a "conduit means" or
connecting strip 60 which may be formed of suitable rigid or
semi-rigid material and to which ~irst and second me~branes 42,
44 of adjacent liner panels 48a, 48b may be s~ealed with the aid
of suitable mechanical connectors, heat weldiny, solvent welding,
adhesivè bonding or other known joining techniques. Connecting
strip 60 may include a major aperture 70 which extends longitudi-
nally through conduit 60 and a plurality of branch apertures 72
which extend at an angle to aperture 70. When connecting strip
60 is sealed in place between adjacent liner panels 48a, 48b
apertures 70, 72 facilitate fluid communication between the
encapsulated regions within each o~ liner panels 48a, 48b. If
apertures 70 and 72 are omitted from connecting strip 60 then
connecting strip 60 serves as a barrier to flow between the
encapsulated regions within each of liner panels 48a, 48b. By
joining adjacent liner panels using connecting strips with or
without apertures 70, 72 the overall liner can be selectively
separated into cells in which the encapsulated regions within
particular liner panels are in fluid communication with or,
alternatively, are isolated from fluid communication with the
encapsulated regions within adjacent panels.
Connecting strip 60 facilitates rapid construction of
liners and also eases the ordinarily difficult task of joining
segments of liner material together, thus minimizing the
occurrence of liner disruptions due to imperfect welds and/or
seams. Connecting strip 60 may be utilized in either pressurized
or depressurized liners. That is, pressurizing fluid may be
injected through apertures 70, 72 to pressurize liner panels
sealed along either side of connecting strip 60. Alternatively,
- 20 -
,Ip,~.~
:a3~3E3~;3
a depressurizing means may be used to depressurize the liner
panels by withdrawing fluid from within the liner panels through
apertures 70, 72.
Apertures 72 may in some cases be omitted ~rom either
or both sides of connecting strip 60 to prev~nt ~luid communica-
tion from aperture 70 to either or both of the liner panels
sealed along each side of strip 60. This facilitates isolation
of selected liner panels as aforesaid for the establishment of
liner cells of different pressures, or, if desired, establishment
of separate pressurized and depressurized cells within the same
liner and even facilitates the use of different pressurizing
and/or depressurizing fluids within the same liner. Similarly,
as shown in Figure 9a, connecting strip 60 may be provided with
a second longitudinal aperture 82 parallel to aperture 70.
Aperture 70 may be connected to a series of apertures 72 along
one side of strip 60, while aperture 82 is connected to an
opposed series of apertures 72 along the opposite side of strip
60. This also facilitates isolation of liner panels sealed along
the opposed sides of strip 60 which may then be independently
pressurized or depressurized as above.
Although Figures 8a and 8b show sealing of liner panels
48a, 48b to connecting strip 60 by overlapping membranes 42, 44
on strip 60 it may in some cases be convenient to seal the edges
of liner panels 48a, 48b within grooves provided along opposed
sides of an alternative strip 60' as shown in Figures 8c and 8d.
For example, if permeable core material 46 extends to the
outermost edges of liner panels 48a, 48b then the liner panel
edges will be relatively rigid and easily insertable into the
grooves for subsequent sealing therein. To add mechanical
strength, strips 80 (Figures 9a and 9b) of plastic or other rigid
material may be laid over the edges of connecting strips 60 and
secured by bolting or riveting through strips 60 and 80. It will
also be understood that a plurality of connecting strips 60 may
be sealed together in end to end fashion or may be connected or
fabricated in "T" or other convenient shapes so as to facilitate
- 21 -
~3~38163
construction of liners of any desired size or shape. Figures lOa
and lOb illustrate a liner formed by sealing a plurality of liner
panels together with connecting strips so as to provide a
"custom" liner of a shape and size which will fit a particular
containment pond excavation.
A particular advantage Qf the invention, as compared
with prior art liners employing drainage layers, is that such
prior art liners necessitate the provision of a containment pond
excavation having a floor which slopes uniformly toward a sump
located at the low point of the floor. The cost of constructing
such ~acilities can be high and it is thus expected that
considerable time, labour and cost may be saved in terms of
construction and floor preparation through exploitation of the
invention, which does not require a uniformly sloped excavation
floor or sump.
Figure 9c illustrates a connecting strip 60 having
grooves along opposed sides thereof for receiving liner panels
48a, 48b in the manner explained above, and also having thin
metallic conductor strips 84 which extend along the opposed liner
surfaces of each groove to contact membranes 42, 44 o~ each liner
panel. In a process known as electro-magnetic welding, a short
duration pulse of high voltage current is applied to conductor
strips 84 to heat them and melt the adjacent portions of
membranes 42, 44 which, as they cool, are effectively welded
within the connector strip grooves, thereby simplifying the time,
cost and labour required to secure liner panels 48a, 48b to
connector strip 60.
Figure 9d illustrates a connector strip 60 having
staggered lips 61a, 61b, 63a, 63b along opposite sides of one
surface thereof. Lips 61a and 61b are for sealingly engaging
membranes 44 of adjacent liner panels and lips 63a, 63b are for
sealingly engaging membranes 42 of the panels. The advantage of
this configuration is that the operation of sealing each of
membranes 42, 44 to connector strip 60 may be carried out from
- 22 -
~3~313~3
above the strip - it is not necessary to turn the strip or the
partially compl~ted liner over to complete the sealing operation.
Strip 60 of Figure 9d is thus very convenient to use and assists
in minimization of leakage at the juncture of the liner panels
and connector strips.
Shinqling Construction Technique
Figure 12 illustrates a "shingling" technique for
1~ constructing and progressively testing a liner. This technique
is expected to be extremely e~fective for construction of liners
having minimal leakage characteristics. The technique uses
overlapping joints to seal sections of membrane material together
to form a continuous liner having a plurality of encapsulated
high permeability regions segregated from one another. Undesir-
able lap joints like that shown in Figure 7b are avoided. A
first low permeability membrane 150 is laid above a second low
permeability membrane 152 placed upon the floor of the contain-
ment pond excavation which is to be lined. Membrane 152 has a
larger surface area than membrane 150 (if need be, membrane 152
is constructed by overlappingly sealing, as at 153, two or more
sheets of low permeability membrane material). Membrane 150 is
joined around its edges to membrane 152 to encapsulate a region
of relatively high permeability between the two membranes. (If
desired, high permeability core material may be placed in the
encapsulated region, or the membranes may be textured as
hereinbefore described. Also, depending upon the pressure to be
maintained within the encapsulated region, the inner surfaces of
the membranes may be connected together, or connected to any
encapsulated core material, before the membranes are joined
around their edges). The encapsulated region is then pressurized
and monitored to detect leakage therefrom. Any leaks detected
ara repaired; if need be by separating the membranes or, if
desired, by injecting sealant material into the encapsulated
region to plug the leaks. Membrane 152 is then extended by
sealing an edge thereof to a further section of low permeability
membrane material as shown at 154. A further section of low
- 23 -
13~3~
permeability membrane material 156 is then sealed to membrane 150
with edge 158 of section 156 overlapping the joint of membranes
150, 152. The remaining edges of membrane 156 are then sealed
to the extended lower membrane to encapsulate another high
permeability region between membrane 156 and the extended lower
membrane. The newly encapsulated region is then pressurized,
monitored for leaks and repaired as xequired. The process is
repeated by further extending the lower membrane and overlapping
or '7shingling" low permeability membrane sections thereabove
until the liner attains its desired size and shape. A particular
advantage of this technique is that all membrane sealing
operations may be conducted from above the liner, thereby
simplifying construction. Moreover, if the rightmost edge (as
viewed in Figure 12) of each of the upper membrane sections are
only temporarily sealed to the lower membrane ~i.e. with tape)
then the membranes may easily be separated for repair if leaks
are detected and then permanently resealed. However, such
temporary sealing may entail problems which outweigh its
theoretical advantage aforesaid.
Figure 13 illustrates a connector strip 160 specially
adapted to the construction of liners in accordance with the
shingling technique of Figure 12. The base of connector strip
160 is sealed directly to the upper surface of lower membrane 152
along the site of the desired joint. The upper surface of
membrane 150 is then sealed to the undersurface of lip 162 which
projects to the lert of strip 160 as viewed in Figure 13.
Membrane 156 and any encapsulated core material 46 is t~en laid
over the top of strip 160 and joint 158 is made by ssaling the
undersurface of membrane 156 to the upper surface of membrane
150.
MultiE~Le Cell Dual Membrane Liner
Figures lOa and lOb show how the bottom of a contain-
ment pond may be lined with a low cost dual membrane liner 100
comprised of membranes which need not be mechanically connected
- 24 -
~3~3~363
to each other or to any high permeability core material which may
be encapsulated between the membranes. Bottom liner 100 is
joined, around its edges, to a plurality of liner panels or cells
102, 104, 106 and 108 laid against the sloping side walls of the
containment pond (liner panels 102, 104, 106 and 108 are each "I,"
shaped as viewed in Figure lOa). Side wall liner panels 102,
104, 106 and 108 pr~ferably comprise dual membranes which are
mechanically connected to each other or to any high permeability
core material which may be encapsulated betw~en the membranes.
A low pressure overload applied to pond bottom liner loO by a
thin co~ering layer of granular material 110 prevents the opposed
membranes comprising pond bottom liner 100 from separating.
Moreover, if the density of the pressurizing fluid within side
wall liner panels 102, 104, 106 and 108 is about the same as the
density o~ the fluid to be contained by the liner (assuming
pressurization of the side wall liner panels) then only a small
positive differential pressure head need be maintained within the
side wall liner panels and the mechanical connection between the
membranes comprising the side wall liner panels or between those
membranes and any hi.gh permeability core material within the side
wall liner panels need only be capable o~ resisting relatively
small tensile forces, which implies lower cost as well.
Note that the individual liner panels 100, 102, 104,
106 and 108 may be independently pressurized or depressurized.
For example, a low pressure device such as floating low positive
differential pressure head device 112 may be used to pressurize
pond bottom liner 100 via flexible hoses 114 coupled to conduits
within connecting strips 116 which join together liner panels
lOOa, lOOb, lOOc and lOOd which together comprise pond bottom
liner 100; while a vacuum pump ~not shown) is used to depres-
surize side wall liner panels 102, 104, 106 and 108 via line 118,
conduit 120 which encircles the outer periphery of the contain-
ment pond and conduits 122, 124, 126 and 128 coupled, respective-
ly, to conduits within connecting strips 130, 132, 134 and 136
which join together liner panels 102a, 102b; 104a, 104b; 106a,
106b: and, 108a, 108b which together comprise side wall liner
25 -
13~31~363
panels 102, 104, 106 and 108 respectively. Pond bottom liner 100
is joined around its outer periphery to each of side wall liner
panels 102, 104, 106 and 108 by connecting strip 138 which has
no conduit therewithin, thereby ensuring that the bottom and side
wall liners may be maintained at different pressures. Similarly,
there is no need for conduits within connecting strips 139 used
to join the outer edges of side wall liner panels 102, 104, 106
and 108 together~ since connecting strips 139 function primarily
to provide a substantial outer border for the liner. Note
however that connecting strips 140 used to join adjacent edges
of side wall liner panels 102, 104, 106 and 108 to one another
do contain conduits to facilitate pressurP equalization through-
out the side wall liner panels.
Water will be a preferred pressurizing fluid in many
applications, due to its neutral environmental impact and due to
the fact that its density will often approximate that of the
fluid which is to be contained. However, portions of a water
pressurized liner which are exposed above the surface of the
fluid contained by the liner may freeze. To circumvent this
problem a composite liner having a lower portion (i.e. that
portion which will remain beneath the surface of the fluid to
be contained by the liner) comprised of water pressurized liner
panels and having an upper portion comprised of depressurized
(i.e. non-liquid containing) or air pressurized liner panels may
be employed. For example, pond bottom liner 100 shown in Figures
lOa and lOb may be pressurized with water supplied via device
112, while side wall liner panels 102, 104, 106 and 108 are air
pressurized or depressurized. The capability to divide the liner
into discrete panels or cells which may be independently
pressurized or depressurized iS thus a significant advantage.
It is also expected that composite liners constructed
in accordance with the invention will be well suited to situ-
ations in which the fluid pressure upon the uppermost linermembrane is relatively small due to the incorporation of a fluid
drainage/removal system above the liner. In such circumstances
- 26 -
A
~3~3i3~3
a low head air overpressure could be applied to prevent leakage
through the liner. The advantage of using air as the liner
pressurizing fluid in this case is that its low density results
in an essentially uniform low pressure within the liner. If
water were for example used as the liner pressurizing fluid then
increased overpressure would result within the liner at lower
elevations.
Multiple Membrane Liners
Dual membrane liners of the type hereinbefore described
may be stacked one over the other to construct multiple membrane
liners such that only a single common membrane separates the high
permeability regions encapsulated by adjacent membranes. For
l~ example, Figure 14 illustrates a triple membrane liner 200 having
first, second and third low permeability flexible membranes 202,
204 and 206 disposed one above the other. Membranes 202, 204
encapsulate a first high permeability region 208 and membranes
204, 206 encapsulate a second high permeability region 210. The
shingling technique described above with reference to Figure 12
is used to extend the liner of Figure 14 by joining low permea-
bility membranes 212, 214 and 216 to membranes 202, 204 and 206
respectively, thereby encapsulating high permeability regions 218
and 220 between membranes 212, 214 and 214, 216 respectively.
Additional membranes are added as required until the liner
attains its desired size and shape. The triple membrane liner
of Figure 14 provides an added measure of security in comparison
to the dual membrane liners hereinbefore described and also
facilitates leakage detection as hereinafter described.
Figure 15 shows how the triple liner of Figure 14 may
be extended to yield a quadruple membrane liner 222 by employing
the shingling technigue hereinbefore described to join additional
low permeability membranes 224 and 2~6 atop membranes 202, 204,
206 and 212, 214, 216 respectively, thus providing a further
measure of security and further facilitating liner leakage
detection as hereinafter described.
- 27 -
1303BEi3
It will thus be understood that a multiple membrane
liner may be constructed by providing a ~irst plurality of low
permeability flexible membranes disposed one atop the other to
encapsulate regions of relatively high permeability between each
adjacent pair of membranes. Each one of the membranes in the
first plurality can be extended horizontally as required by
joining corresponding membranes of a second plurality of low
permeability membranes beside that one membrane. The extended
membranes lie atop one another to encapsulate further regions of
relatively high permeability between each vertically adjacent
pair of membranes. It will be understood that construction of
a multiple membrane liner having "N" high permeability regions
disposed one above the other requires "N~1" low permeability
membranes.
Figure 16 illustrates how the connecting strip
hereinbefore described may be adapted to the construckion o~
multiple membrane liners. More particularly, Figure 16 illus-
trates a connecting strip 228 having staggered lips 230, 232, 234
and 236 which may be affixed, respectively, to the upper surfaces
of low permeability membranes 202, 204, 206 and 224 of low
permeability membrane 222 shown in Figure 15. Such affixation
may be by means o~ welds as shown at 238 in Figure 16. Connect-
ing strip 228 is provided with a series of major apertures 240,
242 and 244 each having branch apertures 240a, 240b; 242a, 242b;
and, 244a, 244b. When connecting strip 228 is sealed in place
between adjacent panels of a quadruple membrane liner, apertures
240, 242 and 244 together with their respective branch apertures
facilitate fluid communication between the high permeability
regions encapsulated between each adjacent pair of low permeabil-
ity membranes. This in turn facilitates selective pressuriza-
tion, depressurization or non pressurization o~ the high
permeability reyions. Those skilled in the art will further
appreciate that connecting strips like that illustrated in Figure
16 may be adapted to the construction of composite multiple
membrane liners having groups o~ cells which may be selectively
- 28 -
.~'
~3~3~
pressurized, depressurized or left non-pressurized to accommodate
sp2cific operating and leak detection objectives by isolating
cell groups as aforesaid.
Figure 17 illustrates how the inner membrane surfaces
of the triple membrane liner 200 of Figure 14 may be channelled
or otherwise textured as described above with reference to Figure
11 to avoid obstruction of fluid flow between adjacenk low
lo permeability membranes.
Figures 18a and 18b show two stages in the construction
of a triple membrane liner. More particularly, Figure 18a shows
how a dual membrane liner 246 is first constructed in accordance
with the shingling technique described above with reference to
Figure 12. Before construction proceeds further, each of the
high permeability regions encapsulated within dual membrane liner
246 is pressurized to a selected pressure and the regions are
then monitored to ensure that they each sustain that pressure.
If any region fails to sustain the pressure then the two
membranes which encapsulate the leaking region are carefully
inspected for leaks which are repaired. The pressurization,
leakage monitoring, inspection and repair steps are then repeated
until all high permeability regions in the dual membrane liner
will sustain the selected pressure. It is also advantageous to
depressurize each of the high permeability regions encapsulated
within dual membrane liner 246 to a selected pressure, monitor
the regions to ensure that they maintain the selected pressure
and inspect or repair any leaks until all high permeability
regions can sustain the selected vacuum pressure. This over and
under pressure construction testing technique has the advantage
of applying a positive pressure differential to the liner
membranes in both inwards and outwards directions. This may
reveal leaks which may not be evident under a single pressure
differential. The testing verifies the integrity of both liner
membranes and all perimeter and intermediate seams of the dual
membrane liner. If any particular high permeability region does
J} ~
13~38K3
not maintain the selected test pressure then all of its perimeter
welds are easily accessible and can be thoroughly inspected and
all leaks therein identified and repaired
Once the dual ~embrane liner of Figure 18a has been
successfully constructed and tested as aforesaid a third low
permeability membrane 248 may be added atop dual membrane liner
246 as shown in Figure 18b. All seams used to weld membrane 248
to dual membrane liner 246 are readily accessible and may be
thoroughly inspected and tested by the over/under pressurization
technique described above. Further low pexmeability membranes
may then be added atop dual membrane liner 246 and adjacent
membrane 248 to extend the liner as required to yield a triple
membrane liner of desired size and shape having very secure
leakage prevention characteristic~.
Those skilled in the art will understand that the same
technique may be employed to add still further low permeability
membranes atop the triple membrane liner just described to yield
a high security multiple membrane liner having "N" high permea-
bility regions encapsulated one atop the other by "N+1" low
permeability membranes.
One limitation of a dual membrane liner is that once
leakage therefrom is detected (for example, by a need to
introduce increased quantities of pressurizing fluid in order to
maintain the pressure within the encapsulated high permeability
region at a selected level) there is no way of determining which
of the upper or lower membranes (or both) are leaking. However,
a multiple membrane liner may be operated in a manner which
facilitates detection of specific leaking membranes. For
example, a detectable fluid may be injected into an encapsulated
high permeability region which has failed to maintain a test
pressure; and a partial vacuum may be applied to the vertically
adjacsnt high permeability region(s). If the detectable fluid
is detected in the drainage from the region(s) to which partial
vacuum is applied, then it can be concluded that the membrane
- 30 -
~311~3B63
between the region into which the detectable fluid was injected
and the region from which the detectable fluid was drained is
leaking. If no detectable fluid is detected in the drainage from
a particular adjacent region then it can be concluded that the
membrane betwean that particular region and the region into which
the detectable fluid was injected is not leaking. A further
disadvantage of a dual membrane liner is illustrated with
reference to Figure 19 which shows a dual membrane liner
comprising upper and lower membranes 250, 252 which desirably
prevents contained fluid 254 from passing into the region 256
beneath the liner. If the high permeability region encapsulated
between membranes 250, 252 is depressurized and if leaks occur
in both membranes then fluids may be drawn into the encapsulated
high permeability region and mixed. Such mixing may be undesir-
able. If the high permeability region encapsulated between
membranes 250, 252 is pressurized, then the pressurizing fluid
(either liquid or gas) will be forced out of the high permeabil-
ity region through the membrane leaks and into the containment
pond 254 or into the underlying region 256, or both, thus
allowing pressurizing fluid to mix with fluid in pond 254 and to
mix with ground water in region 256. In either case, such mixing
may be undesirable.
Figure 20 shows how a quadruple membrane liner 258 may
replace the liner of Figure 19 to prevent such undesirable fluid
mixing. Quadruple membrane liner 258 encapsulates three separate
high permeability regions 260, 262 and 264 respectively. The
outer regions 260, 264 are depressurized. The inner region 262
is either pressurized or it may remain non-pressurized. Even if
leaks occur in all four of the membranes comprising quadruple
membrane liner 258 it is still possible to maintain complete
segregation of contained fluid 254 and fluid from the region 256
beneath the liner. Specifically, with a partial vacuum applied
to each of regions 260, 264 air is drawn from region 262 through
the leaking membranes which encapsulate it, thus preventing flow
of fluid 254 (which leaks through the uppermost membrane into
region 264) or flow of fluids from region 256 (which leak into
- 31 ~
~3~3~
reyion 260 through disruptions in the lowermost liner membrane3
into region 262. Moreover, fluid 254 which leaks into region 264
may be drained therefrom and returned to the containment pond (or
otherwise handled). Similarly, fluid which leaks into region 260
from region 256 may be drained from region 260, analyzed to
confirm that it is uncontaminated and then returned to region
256.
Figure 21 illustrates a triple membrane liner in which
high permeability regions 268 and 270 are both depressurized with
the degree of vacuum in re~ion 270 exceeding that in region 268.
Should leaks occur in all three low permeability membranes
comprising liner 266 then fluid from region 256 is drawn into
region 268 and some of that fluid may pass into region 270 as
illustrated at 272. However, fluid 254 can only pass into region
270 due to the pressure differential hetween regions 268 and 270.
Analysis of the fluids drained from regions 268 and 270 facili-
tate confirmation that fluid 254 has not passed into region 268
and that there is accordingly no potential for escapement of
fluid 254 into region 256.
Figure 22 illustrates a triple membrane liner 274
having encapsulated high permeability regions 276 and 278 which
are both pressurized; the pressure in region 276 exceeding that
in region 278. The contained fluid 254 and fluids in regions 256
are both prevented from flowing into regions 276 and 278 by the
pressure differential (i.e. the pressures in region 276 and 278
are established such that they exceed the fluid pressures exerted
on liner 274 by fluid 254 or fluids in region 256). Moreover,
fluid flow from region 278 into region 276 is prevented because
the pressure in region 276 exceeds that in region 278. Thus
there is a double measure of protection against leakage of fluid
254 into region 256. Fluid in region 278 may be sampled and
tested for contamination by fluid 254. If no contamination is
detected then it may be concluded that fluid 254 is unable to
escape through liner 274 into region 256. If contamination is
found in region 278 then the fluid in region 276 may be sampled
- 32 -
~3~3E~3
and tested. If it is found to be uncontaminated then there is
still no potential of escapement of fluid 254 into region 256.
Figure 23 shows a triple membrane liner 280 which
encapsulates high permeability regions 282 and 284 respectively.
A pressurizing means is used to pressurize region 282 and a
depressurizing means is used to depressurize region 284. Double
protection against leakage of fluid 254 into region 256 is thus
again provided by the dual pressure different:ial created across
the interior low permeability membrane 286. The fluid in region
282 may be sampled and tested to confirm that there is no leakage
of fluid 254 into region 282. All the advantages of a pressur-
ized liner may be obtained in region 282 without leakage of the
pressurizing fluid into the zone which contains fluid 254.
In certain situations it may be necessary or desirable
to facilitate fluid drainage from beneath or above a multiple
membrane liner, for example either to prevent uplift of the liner
in the event of a rapid draw down of the liquid level in the
containment zone, or to effect leachate collection from within
the containment zone. Figure 24 illustrates a portion of a
multiple membrane liner which provides a capability for under
drainage. To construct a multiple membrane liner with an
integral under drain, a high permeability membrane 288 is
disposed beneath the lowermost low permeability membrane 290 of
the multiple membrane liner. High permeability membrane 288 may
be formed of any membrane material which is structurally stable
such that it will not migrate into the high permeability region
292 created between membranes 288 and 290. Application of a
suction to region 292 will result in evacuation and drainage of
that region, preventing uplift pressures on membrane 290 and on
the multiple membrane liner in general. Similarly, a high
permeability membrane may be disposed above the uppermost
membrane of a multiple membrane liner to encapsulate a region of
relatively high permeability between the high permeability
membrane and the uppermost low permeability membrane of the
liner. The high permeability region so encapsulated may then
- 33 -
~3~31!~63
serve ~s a dewatering layer. In some situations it may be
desirable to provide high permeability membranes both above and
below a multiple membrane liner.
Multi~le Membrane Liner Leakaqe petection
A technique for detecting leaks during construction of
a multiple membrane liner is described above. A generalized
technique for detecting leaks in an operating multiple membrane
liner will now be described in the context of a quadruple
membrane liner which encapsulates high permeability regions "1",
2" and "3".
The test begins by pressurizing (or depressurizing)
high permeability region 1 to a selected pressure or by injecting
it with a detectable fluido High permeability region 1 is then
monitored to see if it will sustain the selected pressure or
contain the detectable fluid. If the test is successful (i.e.
if the pressure is sustained or the fluid contained) then it may
be concluded that both the membranes which encapsulate high
permeability region 1 and their interconnecting seams are sound.
If the test fails then it may be concluded that either or both
membranes, or one or more of their interconnecting seams are
leaking.
High permeability region 2 is then tested in similar
fashion. If the test is successful then it may ba concluded that
the low permeability membranes which encapsulate high permeabil~
ity region 2 are both sound. Moreover, if the test of high
permeability region 2 is successful but the test of high
permeability region 1 fails then it may be concluded that the
outermost membrane encapsulating high permeability region 1 (i.e.
the membrane which is not also rommon to encapsulation of high
permeability region 2) is leaking. If the test of high permea-
bility region 2 is unsuccessful and if the test of high permea-
bility region 1 succeeded then it may be concluded that the
outermost membrane encapsulating hîgh permeability region 2 (i.e.
- 34 -
~3~38~`3
the membrane which is not common to encapsulation of high
permeability region 1) is leaking. If the tests of both regions
1 and 2 fail then it may be concluded that the common membrane,
or two of the three membranes which together encapsulatQ regions
1 and 2 are leaking. The test then proceeds as follows.
High permeability regions 1 and 2 are tested together
by pressurizing them to a selected pressure or by injecting them
with a detectable fluid. If the test is successful ~i.e. the
regions together sustain the selected pressure or contain the
detectable fluid~ then it may be concluded that the outermost low
permeability membranes are sound and that the innermost membrane
(i.e. the membrane which is common to encapsulation of both
regions) i~ leaking. If regions 1 and 2 together fail the test
then testing proceeds on high permeability region 3.
High permeability region 3 is tested by pressurizing
it to a selected pressure or by injecting it with a detectable
fluid. If the test is passed (i.e. if high permeability region
3 sustains the selected pressure or contains the detectable
fluid) then it may be concluded that the two membranes which
encapsulate high permeability region 3, and their interconnecting
seams, are both sound. Moreover, if the test of region 1 was
passed and the test of region 2 failed then it may be concluded
that there is a leak in the perimeter seams of region 2.
Alternatively, if the test of region 3 fails and if the test of
region 2 passed then it may be concluded that the outermost low
permeability membrane ti.e. the membrane which is not common to
encapsulation of regions 2 and 3) is leaking. Furthermore, if
the test of region 3 fails and if the tests of regions 1 and 2
also failed then it may be concluded that the membrane common to
encapsulation of regions 2 and 3; or any three of the four low
permeability membranes are leaking. Testing then proceeds as
follows.
Regions 1, 2 and 3 are tested together by pressurizing
them to a selected pressure or by injecting them with a detect-
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~L3~3~363
able fluid. If the test passes then it may be concluded that
both of the interior membranes (i.e. the membranes common to
encapsulation of regions 1 and 2 and encapsulation of reyions 2
and 3 respectively) are leaking.
It will be noted that the foregoing procedure facili-
tates isolation of the leaking membrane(s) only if at least one
high permeability region successfully passes the test. If all
regions fail the test then it is not possible to determine
whether all or all but one of the low permeability membranes are
leaking. However, this condition is considered relatively
unusual and sufficiently catastrophic that a major overhaul of
the liner would be desirable in any event.
As an alternative testing procedure, one may inject a
detectable gas or fluid into a particular high permeability
region and then attempk to withdraw that gas or fluid from an
adjacent high pe~meability region by applying a partial vacuum
to the adjacent region. If no gas or fluid is withdrawn from the
adjacent region then it can be concluded that the membrane
separating the two regions i5 not leaking. Note that it is
possible that the membrane separating the two regions is not
leaking even though either one of the two regions, or the two
regions together, fail to maintain a test pressure; due to
leakage of other membranes encapsulating the regions in question.
As will be apparent to those skilled in the art, in
light of the foregoing disclosure, many alterations and modifica-
tions are possible in the practice of this invention without
departing from the spirit or scope thereof. Accordingly, the
scope of the invention is to be construed in accordance with the
substance defined by the following claims.
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