BACKGROUND AND BRIEF DESCRIPTION OF THE INVENTION

The formation of underground impermeable barriers using slurry trench techniques has been widely developed in recent years and in a number of instances, attempts to utilize impervious plastic or rubber sheets to form imper¬ meable barriers in such cut-off walls has been attempted. In Ranney patent 2,048,710, a pair of lining materials such as fabric or paper or other lining material which has been treated so that the lining material acts as a separator or divider between the earth material and the wall material after the wall material has been placed in the trench. In Zakiewicz patent 3,603,099, an intraground water proof baffle is disclosed in which the roll of flexible water proof plastic foil is displaced along the line of the exca¬ vation so that as the trench is cut, the foil is layed in a vertical plane behind the excavator and then the space between the foil and the sides thereof is filled with a wall forming material. In Piccagli patent 4,193,716 and Carron et al patent 3,759,044, plastic sheets are embedded in dia- phra walls. These .processes and structures are not amenabl to the placement of such synthetic plastic materials in deep excavation using the slurry wall construction technique. In Ressi application Serial No. 252,676, filed April 9, 1981 and assigned to the assignee hereof, a plastic sheath or envelope is provided in which the wall forming material is in the sheath or envelope.

A pollution control barrier according to a preferred embodiment of the present invention comprises a narrow slot excavated in the earth using the bentonite slurry technique as disclosed in Veder patent 3,310,952, such that the earthe walls are impregnated with bentonite and a bentonite cake is formed on the surfaces thereof. A plastic sheet is inserted

in the slot and, preferrably, is aligned with the center of the slot and a wall forming material fills the slot on both sides of the plastic sheet. An important feature in the present invention is in that the plastic sheeting is in panel sections as follows: a first series of the panel sec¬ tions having vertical plastic primary tubes or channels bonded to the lateral ends, respectively, of the plastic sheet, each said plastic tube or channel having a diameter at least equal to the diameter of the width of the slot in the earth with the ends of the plastic sheet f singly bonded to one side, respectively, of each said tube in a fluid impervious manner. Each of the vertical plastic tubes or channels has a slit or elongated opening in the opposite side to which the plastic sheeting is bonded. A second series of panel sections, alternating with the first series of primary panel sections along the line of the wall are constituted by a further plastic sheeting with secondary pipe or channel members secured to the ends of the sheet, the secondary pipe or channel members having a diameter or size small enough to telescope within the first tubes with the plastic panel sheeting passing through the slits or elongated openings, .respectively, in the primary tube or channel members and finally, a grouting means fills all of the voids in the tubes or channels displacing any bentonite that may have seeped therein. The grout is a non-shrink typ and is pumped into the joint connection to form a tight join The resulting wall has chemical resistivity and lower perme¬ ability. In addition, it allows the synthetic material to be placed in deep excavations using slurry wall construction methods and the joints will allow for a continuous imperviou wall system. It is simpler and easier to install in short panel sections. Different sections of the impervious wall can be tailored to have different properties. The cut-off

made according to the present invention can be used for deep excavations (at least over 70 feet deep) and still be continuous.

BRIEF DESCRIPTION OF THE DRAWINGS The above and other objects, advantages and features of the invention will become more readily apparent from the accompanying drawings in which:

Figure 1 is a top plan view illustrating in some¬ what diagrammatical manner construction of a deep environ- mental wall according -to the invention,

Figure 2 is an elevational view of the construction shown in Figure 1,

Figure 3 is an enlarged view of a joint according to the invention, Figure 4 is a top plan view of a modification of the invention and,

Figure 5 is a top plan view of a further modification of the invention.

Referring now to Figs. 1, 2 and 3, the primary panel sections P-,, P«... _N are formed in excavations which are carried out under a bentonite slurry to a depth D which is at least down to the level below which any expected pollu¬ tant may be found or expected to flow and typically is down to the water table and in panel lengths typically of 15 to 30 feet. A pair of high density polyethylene pipes or tubular channel members 10 and 11 having diameters equal to the width W of the trench section is connected by a high density polyethylene sheet 12 which, in this example, is about 100 mills thick, but which obviously can be of greater or lesser thicknesses and of any other plastic material having appropriate chamical and mechanical properties. The lateral ends 13 and 14 of high density polyethylene sheet 12 are bonded to the external surfaces of high density polyethy lene.pipes 10 and 11 in an impervious fluid type manner by

electronic or chemical welding, fusion or joining and sealing all of which are conventional. Single high den¬ sity polyethylene sheet 12 may be composed of several sheets which are fusingly joined or bonded at their edges to form the desired barrier but in the preferred embodi¬ ment, it is a single intregrally formed sheet so as to assure that there are no leaks in the sheet. Plastic sheet 12 is joined to pipes 10 and 11 at lateral edges 13 and 14 prior to insertion of same into the excavated trench.

Once the panel section is set, the bentonite slurry on each side of sheet 12 is displaced by a backfill which can be a mixture of soil-bentonite, cement-bentonite or concrete, etc. As shown in connection with the filling of secondary panel section SI, the backfill is accomplished by the tremie pipe technique whereby the backfill material is hydraulically introduced into the excavation on both sides of the sheet by hollow steel tubes 16-17 which are gradually raised so that their lower ends remains within the heaps 18 of backfill material on both sides of sheet 12 so that there is no differential backfill loading applied to the sheet. The lower ends of the tubes remain within the backfill heap 20 and the slowing rising heap of backfill material rises upwardly and the amount of bentonite which is in the excavation thereabove is displaced and removed for storage for use in other excavating operations. The opera¬ tion is terminated when the backfill material reaches the surface of the ground. A clay or concrete cap or cover may be applied at the surface of the wall. In accordance with the technique disclosed in this preferred embodiment, the length of the secondary panel SI is omitted and another primary panel P2 is installed fol¬ lowing the procedure described above.

The pipes .10 and 11 have wall thicknesses of 3/4 to 1. inch. They may be cast or extruded, with or without re¬ inforcement fibers, etc.

It will be appreciated that the primary excavations can be made using any conventional slurry trench excavation technique such as a clam shell, rotary drill bits and even backhoed in the shallower depth walls. Moreover, the trench excavations can be made in panel sections or as a continuous length trench in which the excavation is formed and main- tained in a bentonite slurry and first at least two primary panel sections PI and P2 are installed and backfilled to form stable structures and then the intervening secondary panel SI is installed between two primary panel elements PI, P2. In installing the secondary panel element SI, a secon dary panel of high density polyethylene sheet 22 has its lateral ends 23 and 24 secured to smaller diameter high den¬ sity polyethylene rods, pipes, tubes 26 and 27, respectively the facing surfaces of the larger diameter polyethylene pipe 10 and 11 have full length slits or slots in the surf ces, thereof facing the excavation for the secondary panel ele¬ ment SI. These slits or slots 30, 31 are made at least large enough so that they can easily accomodate the thicknes of the high density polyethylene sheets 22, the edges of the slits or slots being smooth and rounded without sharp edges so as to avoid damaging the plastic sheet. This panel section is then lifted and the two smaller diameter pipes 26, 27 are lowered or telescoped into the larger diameter pipes 10 and 11 as is illustrated in secondary panel section S2. The panel is lowered into the trench section and the bentonite slurry contained therein to its final depth and then the backfill material is inserted as described above and is illustrated in connection with tremie pipes 16 and 17

While in Figure 2 there is illustrated a funnel shaped device BF for receiving the backfill material, it will be appreciated that this is purely diagrammatic as illustrat¬ ing a means for supplying backfill materials for filling the trench sections on each side of the polyethylene sheets at substantially equal rates so as to avoid undue loading and distortion and stretchings of the sheet.

As shown in Figure 3, the thicknesses of the two pipes need not be the same nor need they even be of the same material. In order to remove any slack or lack of any tautness in the sheet 12, the smaller diameter pipe may be given a rotary twist or turn as indicated by the arrow 50 and the pipe 26 need not be hollow but can be a solid rod or pipe. Moreover, as will appear more fully hereafter, it need not be circular or round.

A non-shrinking grout 60 is then pumped into the pipe connections or space between the outer surfaces of the smaller diameter pipe 26 and the inner surfaces of the large diameter pipe 11 so as to form a tight joint. In Figure 4, instead of round pipe sections, rectangu lar pipe sections are utilized. In the primary panel sec¬ tion P10 a pair of generally square pipe or channel sections 110 of impermeable high density polyethylene or other plas¬ tic material having high chemical resistivity can be utilize In this case, the high density polyethylene sheet 112 is sealingly bonded or joined to the facing flat surfaces 110F and 111F throughout the entire length of the pipe or channel sections 110 and 111. Backfilling is carried out with the dual tremie pipe system as shown in connection with Figs. 1 and 2 to form the primary panel' elements P10, Pll. In secondary panel section S10, a pair of oppositely facing channel members 126 and 127 has the flat facing sections 126F and 127F bridging the gap between the legs 130 and 131

OMPI

of channel section 111 and 132 and 133 of Channel section 110. In this case, the legs 134, 135 of the smaller chan¬ nel member 126 are sprung outwardly slightly so that when section 126 is telescoped within the confines of pipe or channel member 111, legs 134, 135 make a good solid contact with the internal surfaces of channel 111 to thereby pro¬ vide a better seal and long paths to any pollutant. Again, the internal space 140 is filled with a non-shrink grout which is pumped into the connection to form a tight joint. The high density polyethylene sheet 122- is made taut and spans the full length of the panel section to form the impervious barrier. As shown, the ends of legs 136 and 137 of channel member 127 are turned inwardly so that the lengt of channel legs 136 and 137 is just slightly greater than the internal dimension of this space so that the legs 132 and 133 are sprung slightly outwardly so as to maintain a good tight joint. In this case, a slightly greater area of contact between the plastic pipes is utilized to form a tighter seal. To the left of element 4, the end of sheet 110' is sealed at two places 150 and 151 to a V-shaped channel member 160. Channel member 160 has a pair of legs 161, 162 which press against the inside surface 163 of channel member 110 and against the inside back surfaces of short legs 132, 133 of channel member 110. Again, any open space is filled with a non-shrink grout. It will be appreciated that various instrumentations may be installed in the joints to detect any imperfections in the joint. Instead of a grout, any bentonite in the joints may be removed after the wall forming material has been inserted and then the open spaces are filled with a chemical setting agent such as various resins and the like to bond with the surfaces of the two pipe or sections forming the joint.

In Figure 5, the left most joint incorporates a Z-shaped channel member which has a pair of legs 170, 180 which are transverse or normal to the line of the wall and a connecting leg 185 which urges the legs 170 and 180 into contact with their opposing surface legs 130, 131 and the inside surface 111 of channel member 111. As in the structure shown at the joint to the left of Figure 4, there are three elongated contact points forming three separate and distinct barriers A, B, C to the flow of pollutant through the joint.

As shown in Figs. 4 and 5, while it is preferrable to utilize the same type joint throughout the line of the wall, this is not necessary and the different type of joints may be intermixed as to take advantage of the different type constructions. While the walls have been shown as being straight walls, it will be appreciated that they may be curved and closed on itself to make an endless wall such as for an impoundment pond enclosure of the like. In other words, with reference to Figure 4, when the panel element 126, 136, 122 is inserted and the backfilling material placed, elements 110 and 111 may be the facing ends of one wall structure. It will be appreciated that instead of a single sheet being secured to the channel or pipe members, double sheets folded and/or secured at the bottom may be utilized in the manner disclosed in Ressi application Serial No. 252,676, filed April 9, 1981, entitled "Method and Apparatus for Constructing a Novel ^* Underground Impervious Barrier". As noted earlier, the walls can go to a depth of up to 300 feet. In the forming of the bonding of the polyethylene sheet to the rods, channel members, etc. it is good practice to first sand or roughen the surfaces and pre-heat same to about 120°F. A bead of at least about 1/2" or more of material provides

a good impervious joint. As noted above, while it is desirable to use the same materials in forming the sheet as well as the pipe and channel members, this is not nec¬ essary. The pipe can be reinforced by fiber material such as fiber glass and the like but this is not necessary. The joint can be formed by chemical fusion or the like.

With respect to the pipes themselves, the ratio of diameter of the larger pipe to the smaller pipe such as to make it easier to grout the larger space between the two. For example, for a 3 foot wall, the large pipe will be about 3 foot in diameter while the smaller pipe would be about 12 inches or 1 foot in diameter.

While there has been shown and described the pre¬ ferred embodiment of the invention, it will be understood that this disclosure is for the purpose of illustration and various omissions and changes in shape, proportion and arrangement of parts as well as the substitution of equi¬ valent elements for the arrangement shown and described may be made without departing from the spirit and scope of the invention as set forth in the appended claims.