Note: Descriptions are shown in the official language in which they were submitted.
~ :IB6%~;
This invention is dlrected to a method and apparatus
for cons~ructing a novel underground impervious ~luid
barrier which is useful for pollution control, lmpounding
water, oil and other flowable material, especially in
5 populated areas, where government and industries are
faced with the problem of arresting ~mderground seepages
and situations where there is little or no gradient
between the outside water table and the polluted area in-
side.
10 BACKGROUND AND BRIEF DESCRIPTION
Lining underground slurry trenches with impervious
films such as rubber liners, plastic sheets, foils and
the like has been attempted prior to this invention but
they have not been particularly successful. (See page
15 130 of R.G.~. Boyersl text entitled "Structural and Cut- off
Diaphragrn Walls", published by John ~laley & Sons). In Ranney U.S. Patent
2,048,710, an apparatus is disclosed for constructing an
underground wall in which two rolls of lining material
are carried inside wings of an excavating shield for
20 unrolling the lining material to line the walls o the
trench preparatory to filling of the trench with the
desired wall materi.al. There is no te~clill~ in Ranney
~r .,~ L~ .".illin~ .ntcr~ w1lictl 1~ folll~cl ~r otl~cr-
wise joined) at the bottom and of sufficient height to
25 comfortably drape over the sides of the trenc~. A fea-
ture of the process of the present invention is the use of
the fill material to weight the lining material and dis-
place the bentonite (using tne lining material to trans-
mit the displacino force to the bentonite). In Zaklewicz u.S.
30 Patent 3,603,099 and Caron et al u.s. Patent 3,759r044/ a
plastic sheet is immersed in a bentonic mud filled trench.
In the Zaklewicz patent the filling material is added to
each side of the plastic membrane to displace the exca-
~ating slurry and in the Caron et al patentl the plastic
.~
I ~668,56
sheeting is immersed in a cementious bentonite filled
trench and remains there until the wall material has
set. Neither of these prior art references disclose
the concept of applicant's double or folded plastic
membrane nor is there disclosed a membrane of sufficienk
vertical height to drape over the sides of the trench.
In the present invention, the double layer end fold
results in a basic wall structure not disclosed in these
prior art references.
The use of the lining for protecting underground
pipes and conduits has been known in the art as is disclosed
in Grodsk~v U.S. Patent 2,007,969 and in Keene U.S. Patent
3,675,432. However, these are non-analogous to the
present invention and neither of these is disclosed in
the context of a slurry trench excavating process and
obviously, do not in any sense teach the depth of the
wall and process as disclosed herein and do not teach
or suggest a membrane of 30 to ~0 feet in depth contain-
ing industrial pollutants or impounding water or other
flowable materials. In Grether et al U.S. Patents
3,298,183; 3,218,810 and 3,182,459, a fluid barrier is
disclosed for water impoundment and/or channelization but
there is no underground structure contemplated, and the
double folded material is simply folded at the top above
the ground and buried to anchor same against the force
of the upstream water.
The basic object of the present invention is to
provide an improved impervious underground wall struc-
ture and an improved method and apparatus for constructing
same, particularly for pollution control.
A basic feature of the invention is that the liner
is a folded plastic liner (forming a sheath or envelope
for the backfill material) of sufficient height so that
both sides thereof can extend and drape over the sides
of the slurry filled trench so that the backfill material,
~ 16B8.~;
..
which, pre~er-ral~ly, is hydraulicall~ placed and o~
; greater density than the slurry in the trench, carrles
the fold line ~o the bottom of the trench and disp1aces
the bentonite slurry towards the end of the excavation
5 where the excavation is taking place thereby reducing
the amount of slurry needed. '~he double layer plastic
is unrolled along the trench~ until e~tendi~g up above
the surface is opened up and ~he backfill material is
hydraulically placed between the sheets. Typ~.cally
lO the backfill material may be a mixture of sand and water
;which will have two efXects. It will sink the plastic
to the very bottom of the trench and make it adhere to
the sides o:E the trench and will dlsplace forward the
bentonite, reducing the need for a lot o bentonite for
15 excavation. The wall structure resulting rom this tech-
nique is novel in that the impervious barrier that is
constructed in the earth will consist o~ an area of soil
adjacent the excavation which has been permeated by
bentonite (e.g. the side walls of the trench), a benton-
:20 ite cake, the plastic membrane, the backfill material in-
side the plastic membrane (typically sand or coarse
grannular material~ and the same system repeated again on
the opposite trench wall side.
The advantages o the system are that it assures an
25 absolute water tightness by two identical pollutant
barrier systems in series, - the soil permea~ed bentonite
the bentonite cake and the plastic membrane~ Moreover,
the backfill material is used to slnk the plastic sheath
or envelope to the bottom of the trench, hence, once the
30 ini~ial insertion in the trench o the roll and a pre1im-
inary backfilling is accomplished, the plastlc material
is unrolled or unfolded from an accordion fold and
floats in the trench or slot until it is opened up at
the top and the backill material is inserted and the
bentonite slurry is displaced to ~he opposite end of the
--4--
. _. _ ._ ~_._ _ ___, _ . _ __.. __. , .. _ ._ ... ,. , . .. .... ~ . , .
I 16B8~g~
~` , . .
trencll or slot,
. ; .
`~ BRIEF DESCRIPTLON OF THE DRA~.LNGS
~'. The above and other objects, advantages and eatur~
`~ of the invention will become more apparent rom ~he
5 followlng specification taken in conjunction with the
.. accompanying drawings wherein: ~
:: Figure 1 is a sectional elevational view of an
excavation illus~rating one embodiment of the invention,
Figure 2 is a top plan view of the trench illustrated
10 in Figure 1,
~; Figure 3 is a sectional view taken on the lines 3-~
of Figure 1 illustrating the folded plastic sheet, sheath
' or envelope liner prior to being filled with a backfill
material,
:; 15 Figure 4 is a sectlonal view taken on lines ~-4 of
;: Figure 1 illustrating the plastic sheet, sheath or envelope
; liner after it has been filled with backfill material,
Figure 5 is a sectionaI elevational view of a further
~; embodiment of the invention illustrating the plastic liner
~; 20 being fed into the trench from a rack with an accordion
. folded liner, and
Figure 6 is a sectional view taken on lines 6-6 of
, Figure 5.
. The basic method of this invention ~or constructing
25 an under~round pol].ution control barrler cotnprlses excavat-
--- ing a narrow trench or slot along the desired line of the
. pollution control barrier in the presence of a bentonite
slurry. .It will be appreciated that while bentonite is :
. the preferred slurry, o-ther materials which perform the
. 30 same function as the bentonite slurry may be used but.. ~ bentonite slurry is preferred since it can be closely
. tailored to have the property of permeating the soil
! adjacent and contiguous to the excavation to form a
-~} . first barrier to the polluting substance. In addition, a
,` bentonite cake forms on the wall during the e~csvsting
1 ~6~.5~
process to serve as a second barrier to the Elow of any
polluting substances. After forming the initial trench
excavation or slot and while the trench is full of the
slurry maintaining lt open in the way disclosed in Veder U.S.
5 Patent 3,310,952, a sheath or envelope constituted by a
double layered plastic membrane which is folded at the
bottom of the trench and open at the top and of suffi
cient vertical extent to exten~ above tlle ground surace
on both sides of the trench, is inserted into the trench
lO or slot. The trencn or slot T in Figure 1 has been eY~ca-
vated by clam shell, backhoe, trenching apparatus and
the like, to the desired depth of the barrier. Typically,
this inven~ion will apply to depths of 30 to 40 feet and,
in the usual case about 20 feet or down to the water
15 table level. In the i.llustrated embodimentl the trench T
is filled with a bentonite slurry B to the top of the
trench slot all in accordance with the
teachings of Veder U.S. Patent 3,310,952. A
portion of the loading by the lifting and placing devices
?0 10 may bP transferred to the slurry by the use of the
slurry float teGhnique as disclosed in my Canadian patent application
serial No. 382,745. Li~ting and placing device lO has a
boom 11 carryin~ control cables 12 to a plastic fllm pay
out roll 13. A frame 14 havi.ng bearings 15 and 16 for
25 roll 13 is maintained in vertical relation by stabilizing
members 17 and 18 extendin~ ~rom lifting and placing
device 10. The plastic film F (forming the baclcfill
sheath or envelope) which, under certain circumstances
can be reinforced or complemented by a woven fabric WF
30 to give it additional strength, is capable of withstand-
ing the stress and avoidance of possible tears.
After the formation of the initial trench portion,
- the end of the sheath or envelope constituted by the
plastic film F is opened up and each of the ends is
draped o~er the sides of the trench so that the fold
.
~ ~6685~;
line lies in approximately the center of the trench.
In this sense, the end then will be floating on the
bentonite layer and at this time, the backfill material
has begun to be hydraulically placed between the sheets
of plastic. Typically, a mixture of sand and water can
be used which will have two effects. It will sink the
plastic to the bottom of the trench or slot and make it
adhere to the sides of the trench and will also displace
the bentonite slurry forward in the trench by the force
exited through the plastic layers thereby reducing the
need for a lot of bentonite for the excavation. On the
other hand, the end of the trench can be sealed and with
a rigid bar member forcing the end of the envelope down
to the bottom of the trench and then the envelope or
sheath is filled with the backfill material as described.
Of course, the end of the sheath can be heat sealed along
a vertical line joining the two sides, if desired~
By using a course granular material as a fill within
the plastic, a very pervious layer enclosed in plastic
can act as a filter. Draining the filter material is an
excellent method of maintaining the effectiveness of the
barrier and, with a minimum amount of pumping at long
intervals, guaranteeing that any pollutant which crosses
the initial barrier is collected and eliminated.
In Figure 3, the plastic film is shown as it is
being unrolled from roll 13. As shown in the top plan
view of Figure 2, the ends 20, 21 of the plastic film
are draped over the surface above the side walls of the
trench. The bentonite slurry B in trench T exerts a
hydraulic head on the sides of the plastic film which is
immersed thereby forcing any air out of the construction.
Thus, the hydraulic placement of the backfill material
applies a pressure against the inside surfaces of the
plastic film thereby forcing and displacing the bentonite
slurry towards the excavating end of the trench thereby
I 1 6 B? 8 ~ ~
recl~lcing the amount of bentonite required to perform the .
excavation.
It will be appreciated that the excavati~g slurry
can in fact by a cementious bentonite mixture and the
back~ill material 30 can itself be a sel:E-hardening
substance such as a cement-bentoni-te mixture.
When the end of the roll 13 is approached~ -the
backfilling is withheld ~or a distance of approximately
50 feet. The roll 13 i5 then lifted out of the excava-
tion and the remaining portions completely unrolled and
washed of bentonite material and laid flat. A second
roll is then placed on the carrier and lts end unrolled
and two ends are -then welded together using conventional
plastic sheet welding. For example, R.F. Welding or
other heat seam welding can be utilized to join the end
of the new roll to the end of the old roll. The new
roll is then lowered back into the trench or slot T
and the backfilling operation resumes along with the
excavating of the forward end oE the trench.
: 20 In this regard, instead of the -roll being ver~ical
and instead of a fold at the bottom of the trench, the
roll is not folded but is simply rolled along the top of
the trench so that it floats on the bentonite slurry.
The ends o~ the roll extend qu~te some ~ls~ance L?eyond
the edges of the excavation and the end o the roll is
then pushed to tlle bo~tom O;r t~e trench ~ither by the
back~ill material or by a rigid rod and the backfilllng
operation commenced. In this case, the roll per se never
goes below the surface but -the ends thereof is open and
clear for performing the welding operation to add -the
next roll on.
Larger rolls can be accomodated by varying the
thickness of the trench along the line of the barrier.
Thus, as the~roll is payed out ? the trench can be made
narrower, this approach having the advantage of permitting
longer -rolls and minimizing the number of join~s.
.
~ 6
Referring now to Figure S, a backhoe excavator 40
is shown excavating the trench or slot T' which is
maintained full of bentonite slurry B, A rack 41 with
a accordion folded liner F' is coupled by pulling
5 cables or a draw bar to backhoe 40. In this method, the
laying of the plastic comprises in folding it up accor-
dion style in a large roll above ground with the back-
fill material opening up the folds and pushing the plas-
tic down into the trench as illus trated in Fig~re S. The
lO joining of the ends of the film F' of a new roll to the
~ old roll does not thereby require the removing o~ the
; expended roll as in the embodiment of Figure 1. As
shown in Figure 6, there is as in the case of Figure 4,
a bentonite jell of a zone of bentonite intrusion 5, a
15 bentonite cake 6 and plastic layer or sheet 7 on each
side of the trench and the backfill material of'sand,
' gravel etc. It will be appreciated that the plastic
; film can be payed out from a pair of parallel rolls
and prior to entry to the trench heat sealed or other-
20 wise bonded at the lower edges o;E the two rolls to form
t the joint that will eventually be at the bottom of ~he
trench.
Thus, there has be~n disclosed an improved process
an~ apparatus ~or con.s~ructlng a novel ~mpe~me.~ble mem-
25 ~rLInc o~ 30 ~o ~0 eet in dcpth which i3 pnrticularl~
useful or containing areas of industrial pollutants and
arresting underground seepage where there is little or
i no gradient between the outside water table and the
polluted area inside. Moreover, the invention has
30 applicability to forming water and petroleum impound-
ments, cut-off walls and water channelization at rela-
tively high rate of installation and at relatively low
; cost.
~! '
~; While I have disclosed severaI embodiments of the
invention and sugg~sted other modifications, it will be
apparent that many modifications which will be obvious
3~e~ 6
to those skilled in the art and i~ is inten(led ~hat
such modifications be encompassecl within the spirit
and scope oE the claims appended hereto.
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