Liner joining system and method

A cutoff wall liner joining method includes the steps of: (1) excavating a slurry trench; (2) positioning a first layer of liner material within the excavated trench; (3) positioning two pipes adjacent to the liner material in such a manner as to form a substantially S-shaped configuration of the liner material around the pipes; (4) back filling a portion of the trench adjacent a first one of the pipes; (5) removing the other, second one of the pipes; (6) excavating an additional portion of trench extending away from the back filled portion; (7) positioning a second layer of liner material within the newly excavated portion to form a overlapping portion of liner material; (8) positioning a pipe adjacent to the remaining pipe in the trench such that it overlays the overlapping portion of liner material, then positioning a third pipe in the excavated additional trench portion; (9) back filling a portion of the trench adjacent the third pipe; (10) removing the third pipe; (11) back filling the space left by the third pipe; and then (12 ) removing the two remaining pipes, back filling the space left by each pipe as it is removed.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to methods for constructing cutoff walls 
having improved impermeability. In particular, the present invention 
relates to a method for joining liners installed in a slurry cutoff wall. 
2. Description of Related Art 
Cutoff walls typically are used to impede the lateral flow of ground water. 
Controlling the flow of ground water is essential to preventing 
contamination of the water supply. Cutoff walls are often used to isolate 
contaminated landfills and to prevent the ground water from being 
contaminated through contact with buried waste. Because of their low 
permeability, cutoff walls have also been used to seal darns, canal 
systems, and dikes for flood control purposes. Other applications for 
cutoff walls include: de-watering and protecting deep excavation projects, 
hydraulically isolating lagoons and holding ponds, and enclosing oil and 
chemical tank farms. 
As illustrated in FIG. 1, slurry cutoff walls are generally constructed by 
excavating a narrow trench (2-4 feet slide) with a back hoe or similar 
device. During the excavation process, the trench is filled with slurry 
and maintained at a level near the top of the trench. The use of slurry, 
conventionally of bentonite and water, allows excavation without the need 
for other lateral support. The narrow trench is then back filled with 
excavated soil and selected impervious materials to create a cutoff wall. 
The selected materials are typically commercially available clays and 
cement. One advantage of the slurry technique is that it is relatively 
inexpensive to construct such a cutoff wall. 
However, one problem with the cutoff walls of the prior art is their 
permeability. Slurry cutoff walls generally have a permeability that 
reaches at best 1.times.10.sup.-6 to 5.times.10.sup.-7 cm/sec. This 
becomes a problem when very low permeability is required such as when 
isolating hazardous wastes as shown in FIG. 2. When the waste site is near 
an aquifer or other ground water source, the permeability must be at least 
1.times.10.sup.-8 cm/sec. Very low permeability cutoff walls are also 
needed for flood control purposes to prevent seepage through dikes and to 
prevent influence on the areas surrounding the cutoff wall, as well as to 
prevent the collapse of dikes. 
One system for improving the impermeability of the area surrounding such 
cutoff walls is described in U.S. Pat. No. 5,246,312. In that system, a 
liner manufactured from impermeable material is inserted into a slurry 
trench as the trench is excavated. That system discloses positioning a 
single sheet of liner material adjacent to the cutoff wall. 
To further improve the impermeability of the cutoff walls, the liners are 
sometimes overlapped. However, if the overlapping portions of the liner 
are not joined, leakage and seepage between the overlapping portions of 
liner are detrimental to impermeability. Therefore, there continues to be 
a need for a method for efficiently joining overlapping liner material to 
improve cutoff wall impermeability. 
SUMMARY OF THE INVENTION 
The present invention overcomes the deficiencies of the prior art by 
providing a system and method for installing, overlapping, and connecting 
impermeable liner material to improve the impermeability of a slurry 
cutoff wall. The inventive method generally involves the steps of: (1) 
excavating a slurry trench; (2) positioning a first layer of liner 
material in the excavated trench; (3) positioning a first and second pipe 
on the opposite sides of the liner material to form a substantially 
S-shaped configuration of the liner material around the pipes; (4) back 
filling a portion of the trench adjacent the first pipe using a hardening 
filler material; (5) removing the second pipe; (6) excavating a portion of 
trench extending away from the back filled portion; (7) positioning a 
second layer of liner material in the newly excavated, additional trench 
portion, and then positioning a portion of the first layer of material 
parallel with a portion of the second layer of material to form an 
overlapping portion of liner material; (8) repositioning the second pipe 
adjacent to the first pipe in the trench such that the first and second 
pipes are on opposite sides of overlapping portions of liner material, (9) 
positioning a third pipe in the excavated additional trench portion; (10) 
back filling a portion of the trench adjacent the third pipe; (11) 
removing the third pipe from the trench; (12) back filling the space left 
by the third pipe with a hardening material; and (13) removing the two 
first and second pipes back filling the space left by each pipe with 
hardening material as it is removed. 
In a preferred embodiment of the liner joining system of the present 
invention, the pipes are spacing pipes that have a central rigid pipe 
structure surrounded by a housing fillable with air or water via an 
attached or integral nozzle. Once the spacing pipes are properly 
positioned in the trench with respect to the trench walls and the liner 
material, a liquid or gaseous material, such as water, is introduced 
through the nozzle to expand the housing around the central pipe, and 
thus, secures the pipe in position between the walls of the trench. To 
remove the pipes, the material is released using the nozzle, thus, 
diminishing the volume enclosed by the housing to allow removal of the 
pipe. 
In another embodiment of the method, an injection tube is installed between 
the first and second layer of liner material. Using the injection tube, a 
clearing material is first passed through the tube and between the first 
and second layer to clear away debris from between the layers of liner 
material. Next, an adhesive material is injected between the layers of 
liner to attach the layers of liner together. The injection tube may be 
either left in place, or removed after introduction of the adhesive 
material. 
In other embodiments of the method, the liner material is positioned in a 
substantially U-shaped configuration about the first and second pipes. In 
such an embodiment, the liner material forms a substantially M-shape 
around the first and second pipes. The ends of the first and second layers 
of liner material proximate the central portion of the "M" can be joined 
by installing a joint pipe (a C shaped tube with a slit). The joint pipe 
receives an end of each liner material, and is then filled with a 
hardening material to secure the liner material ends in the pipe. The end 
result, after the trench is back filled, is a substantially M-shaped liner 
material in the filled trench. 
Other features and advantages of the present invention will become apparent 
from the following description taken in conjunction with the accompanying 
drawings in which the like references designate the same elements and 
parts.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The inventive method and system first involves excavation of a trench 22, 
substantially as shown in FIGS. 1 and 2. The trench 22 may be excavated 
using standard excavation methods, preferably a slurry trench excavation 
method. In using a slurry trench excavation method, the slurry preferably 
is maintained at a level close to ground level during the excavation step 
by pumping additional slurry into the trench 22 as required. 
Liner material 12 is next positioned within the trench 22, as shown in FIG. 
4B. One preferred system for delivering liner material 12 into a slurry 
trench is shown in FIG. 3. Briefly, that system includes a sheet of liner 
12, an anchor 14, a support line 16, a positioning rod 18 and a guide 20. 
The liner 12 further includes weights 24 and fasteners 26. The liner 12 
preferably is stored in a rolled form before insertion into the trench 22. 
The liner 12 preferably is unrolled at a rate that is about the same as 
the rate at which the roll of liner 12 is moved along the trench. The 
liner 12 is unrolled by forcing it downward in a vertical orientation with 
the aid of the weights 24 and gravity. As the rod 18 carries the rolled 
portion of the liner 12 along the trench 22, the liner 12 is unrolled and 
forced about the guide 20 to a vertical orientation in the trench 22. The 
anchor 14 is secured in the ground near the beginning of the trench 22. 
The support line 16 is attached to the anchor 14, and pulled tight 
parallel above the trench 22. The fasteners 26 are attached to the support 
line 16 to ensure that the liner 12 extends between the top and the bottom 
of the trench 22. 
Although such a liner dispensing system 10 is herein disclosed as one 
embodiment for inserting a liner in a trench, other available methods and 
systems presently used by those skilled in the art may be used in 
practicing the present invention. 
Turning now to FIG. 4A, the trench 22 begins at beginning point A, and 
excavation is performed in the direction indicated by the arrow in FIG. 4A 
away from rear wall 33. As shown in FIG. 4B, the liner 12 initially is 
placed in the trench along a second wall 32b, with a first end proximate 
the rear wall 33. Before a significant amount of liner 12 has been placed 
in the trench 22, the liner 12 is repositioned in the trench 22, so that 
the first end of 12a of the liner 12 is adjacent to the rear wall 33 and 
the first wall 32a, as best shown in FIG. 4C. The first end is then 
secured in that position. The first pipe 30a is then inserted into the 
trench 22 between the liner 12 and the first wall 32a. The pipe 30a is 
then forced toward the rear wall 33 while it is being inflated, thereby, 
forcing the liner 12 into a L-shape against the rear wall 33 and the first 
wall 32b. Next, as shown in FIG. 4E, the second pipe 30 b is inserted into 
the trench 22 between the liner 12 and the second wall 32b. The second 
pipe 30b is then inflated while also being forced toward the first pipe 
30a. Once inflated, the liner 12 now forms a substantially backward 
S-shape configuration as in the top view of the trench 22 shown in FIG. 
4F. The trench can then be back filled between the liner 12 and the first 
wall as shown in FIG. 4G as excavation of the trench 22 continues. 
As shown, the trench 22 may continue to be excavated, and back filled with 
selected materials, such as commercially available clays, bentonite, or 
cement. The excavation and liner insertion process continues until a 
cutoff wall is constructed to isolate an area. Excavation of the trench 22 
is continued in the direction indicated by the arrow in FIGS. 4A-4G, until 
the beginning point A is reached by the leading trench edge 35 at position 
B, forming a closed loop trench 22, shown in FIG. 4H, and as also shown in 
FIG. 2. Once the two ends A, B meet and the trench forms a substantially 
closed loop, the second end of the liner 12b can be overlapped with the 
first end of the liner 12a, forming an overlapping portion 38. Once the 
liner 12, with its overlapping portion 38, is securely in position, the 
trench 22 may be back filled with a pre-selected hardening material, 
described in further detail below. 
Turning now to FIG. 5A, prior to continued excavation and once the two 
initial pipes 30a, 30b are in position, the first pipe 30a may be removed 
and the liner material 12 may be moved away from the trench wall 32b. The 
trench 22 may then be further excavated until it reaches the beginning 
point A. The leading end 12b of the liner material 12 may then be placed 
adjacent to the trench wall 32b, traversing the space left by the first 
pipe 30a and at least partially extending along the wall 32b of the newly 
excavated portion of the trench 22. The first end 12a of liner material 
then may be placed over the second end 12b to form an overlapping portion 
38 of liner ends 12a, 12b, as shown in FIG. 5B. 
The liner may be formed from the same sheet of material as the first liner 
12, or may be formed from a separate sheet of material. In a preferred 
form of the invention, the overlapping portion 38 is formed from opposite 
ends 12a, 12b of the same sheet of liner 12. 
As shown in FIG. 5C, the first pipe 30a is re-installed against the 
overlapping portion 38 of the liner 12. This first pipe 30a may be the 
same or different from the pipe initially installed. A third pipe 30c then 
may be installed next to the first pipe 30a, to secure the liner 12 
against the trench wall 32a, forming a serpentine configuration of the 
liner material 12 as shown in FIG. 5D. Once the third pipe 30c is in 
place, the trench 22 adjacent to the third pipe 30c may be back filled to 
secure further the liner 12 against the trench wall 32a as shown in FIG. 
5E. The same or different back fill material may be used for each of the 
back filling steps of the invention. 
The third pipe 30c then may be removed, followed by back filling the space 
left by the third pipe 30c between the liner and the second wall 32b, as 
shown in FIG. 5F. This step secures the liner material 12 in its position 
across the trench 22 and against wall 32a, and completes the back fill in 
the trench 33. Pipes 30a and 30b may each be removed, followed by back 
filling after removal of each pipe 30a, 30b. The exact order of removing 
pipes 30a, 30b may depend upon the specific circumstances of the 
excavation. However, it is important that a back fill step follow the 
removal of each pipe 30a, 30b to ensure that the liner material 12 remains 
in its desired position. 
In a preferred form of the inventive method, and as shown in FIGS. 5F-5H, 
the method may include installation of an injection pipe 34 in the 
overlapping portion 38. The injection pipe 34 may be constructed of any 
rigid material of sufficient length and diameter to fit within the trench 
22 and deliver solutions and adhesives. Preferably, the injection pipe 34 
has a diameter 1/10th that of the trench 22. The pipe 34 may be installed 
by any means available to those skilled in the art, and may include simple 
insertion of the pipe 34 into the overlapping portion 38 without any 
mechanical assistance. 
Preferably, a clearing solution, such as water, initially is forced through 
the injection pipe 34 and into the overlapping portion 38 to clear that 
portion 38 of debris between the liner 12. The injection pipe 34 then may 
be used to introduce an adhesive material between the liner 12. Although 
many commercially available adhesives may be used in practicing the 
present invention, preferred adhesive materials include cement, bentonite, 
or other commercially available chemical binding agents that would secure 
the liner 12 together. The injection pipe 34 may either be removed from 
the overlapping portion 38 after introduction of the adhesive material, or 
the trench 22 may be completely back filled leaving the injection tube in 
place. 
In a preferred form of the invention, the rigid pipes 30a, 30b, 30c are 
spacing pipes. FIG. 6 shows a cross-sectional side view of an exemplary 
spacing pipe 40. As illustrated, a typical spacing pipe 40 includes a 
central pipe 42 of steel, PVC, or other rigid material. Surrounding the 
central pipe 42 is a flexible housing 44, preferably of a rubber or other 
elastic form material that forms an expandable membrane. Attached to the 
housing element 44 is a nozzle 46 for introducing air or water into the 
housing element 44. The injection pipe 34 may be constructed of any rigid 
material of sufficient length and width to fit within the trench in a 
secure manner. Preferably, the pipe 34 has a diameter slightly less than 
the diameter of the trench 22, such that it presses against the interior 
walls of the trench. 
In practicing the present inventive method using a spacing pipe 40, the 
housing 44 initially is in a deflated state during installation of the 
pipe 40 into the trench 22. Once in position, air or water may be 
introduced into the housing 44 via the nozzle 46 to inflate the housing 44 
and expand the circumference of the pipe 40. In this manner, the pipe 40 
is secured in the trench 22 against both trench walls 32a, 32b. Removal of 
the pipe 40 is accomplished by opening the nozzle 46 to expel the air or 
water out of the housing 44 to reduce the circumference of the pipe 40. 
In an alternative embodiment, shown in FIGS. 7A-7C, the liner material 12 
is positioned around the first pipe 30a in a substantially inverted 
U-shaped configuration. The steps described above with respect to FIGS. 
4A-4G and 5A-5H apply generally in the alternative embodiment of FIGS. 
7A-7C. However, instead of the liner material 12 overlapping along a 
trench wall, the liner material 12 of the alternative embodiment of FIGS. 
7A-7C is positioned around each of the pipes 30a, 30b such that one end of 
each liner layer 12a, 12b overlaps between the two pipes 30a, 30b. Thus, 
the overlapping portion 38 may be held securely in place in the trench 22 
between the two pipes 30a, 30b. 
In practicing the illustrated embodiment of FIGS. 7A-7C, the liner end 
portion 12a is positioned in the excavated trench 22 and pipe 30a is 
positioned against the liner 12a to secure the liner 12a against trench 
wall 32a. This is achieved in a manner substantially similar to that 
described above. Following further excavation of the trench 22, a third 
pipe 30c may be positioned proximate the first pipe 30a, with liner layer 
12b secured between pipes 30c and the second wall. The other liner end 12b 
is then positioned against trench wall 32a and overlapping liner end 12a 
adjacent to pipe 30a. A second pipe 30b may be positioned against the 
liner layer 12b, to secure liner layers 12a, 12b between pipes 30a, 30b 
and 30c. Once the liner layers 12a, 12b are secured, the third pipe 30c 
may be removed and the space left by that pipe 30c may be back filled in a 
manner substantially similar to that described in further detail above. 
As shown in FIG. 7B, after pipe 30c is withdrawn, and the back fill is in 
place, the next two pipes 30a, 30b may be withdrawn and a joint pipe 50 
may be installed to retain the overlapping ends of liner layers 12a, 12b 
together. Once the joint pipe 50 is secured into position, the remainder 
of the trench 22 may be back filled with standard back fill material, as 
shown in FIG. 7C. 
A side view of an exemplary joint pipe 50 is shown in FIG. 8. Housing 52 
may be manufactured from steel, PVC, or another substantially rigid 
material. The pipe 50 preferably has a cross-sectional "C" shape, 
including a slit 54 running along the longitudinal axis of the housing 52. 
Typically, the slit 54 includes a fluted opening 56 at one end of the 
housing 52 to accept materials, such as liner material 12, to be joined. 
In practicing the present invention using the exemplary joint pipe 50, once 
the first pipe 30a and second pipe 30b are removed from the trench, the 
overlapping ends of the liner layers 12a, 12b are inserted into pipe ridge 
54 via the fluted opening 56. In a preferred form of the invention, an 
injection pipe 34, similar to that described above, is included in the 
joint pipe 50. Air or water may be first forced through the injection pipe 
34 into the joint pipe 50 to clear out any debris that may have been 
introduced during installation. Next, an adhesive material may be 
introduced into the joint pipe 50 via the injection pipe 34 to secure the 
ends of liner material 12 within the joint pipe 50. Preferably, both the 
joint pipe 50 and the injection pipe 34 are left in place when the 
remainder of the trench 22 is back filled. 
In another embodiment, as shown in FIG. 7B, a second injection pipe 34' may 
be positioned in the space 37 above the overlapping portion. The space 37 
may then be cleared using the injection pipe 34'. Once the space is 
cleared, it may be filled with grouting or other filler material. 
In yet another embodiment, shown in FIGS. 9A-9B, the trench 22 is 
excavated, and the liner material 12 is overlapped in a manner similar to 
that described above. However, in the present embodiment, the liner 
material 12 is positioned between one trench wall 32a and the two pipes 
30a, 30b with the liner material 12 forming a substantially U-shape about 
the two pipes 30a, 30b. An injection pipe 34 may be positioned between the 
liner layers 12a, 12b and introduce adhesive between the layers 12a, 12b. 
The trench 22 may then be back filled using the method described above, 
resulting in placement of overlapping liner layers 12a, 12b in a 
substantially U-shaped configuration, as shown in FIG. 9B. 
Having described the present invention with reference to specific 
embodiments, the above description is intended to illustrate the operation 
of the preferred embodiments and is not meant to limit the scope of the 
invention. The scope of the invention is to be limited only by the 
following claims. From the above discussion, many variations will be 
apparent to one skilled in the art that would yet be encompassed by the 
true spirit and scope of the present invention.