UNDERGROUND BARRIER AND DRAIN

Abstract: High density polyethylene sheets (50, 51) are sealed at their lateral edges (54, 55; 56, 57) to form a sheath or envelope (S) for sandwiching a drain mesh (DN) therein. A plurality of spaced apart bore holes (H1...HN) is formed along the line of the cut-off and drain barrier and a coupling member (10, 11) is positioned, one in each bore hole, respectively, each coupling member having at least one locking keyway slot (12, 13) formed in a side thereof. These coupling members (10, 11) have stainless steel keyway protectors or cement stops (14) so that cementious material, cast in the bore holes so as to stabi­ lize the coupling members, do not fill the keyway through open­ ings (15). After the cementious material has set, the space be­ tween bore holes up to the keyway slots (14) is excavated in­ cluding the cementious material between the facing edges of the keyway material. Then a drain barrier panel (S) with rigidify­ ing perforated pipes (21, 22; 60, 61; 67, 68) secured in the ends thereof, is inserted into the excavated slot with the perfo­ rated pipes being telescopically received in and retained by the keyway slots. After insertion of the drain barrier panel (S), the trench is backfilled with a material such as cement betonite backfill (BF).

Description: The present invention relates to an underground barrier and drain. The formation of underground impermeable barriers and drains using slurry trench techniques have been widely developed in recent years and, in a number of instances, attempts to utilize impervious plastics or rubber sheets to form impermeable barriers in such cut-off walls has been suggested. Drainage nets sandwiched between two high density Polyethylene films or geomembranes have been used in landfill, pollution control and other drainage systems. Typical drainage nets are dimensionally stable grids consists of two sets of parallel strands with the intersecting strands forming overlayed sets of continuous drain channels to provide high flow capacity. It is known from WO 84/03315, BE-A- 761 499 and FR-A-1 438 464 to form underground barriers by excavating a slot or trench in the ground, arranging at least two and preferably a series of upright supports at spaced intervals along the slot or trench, and then securing panels or membranes between consecutive or adjacent supports to form a continuous impervious barrier to fluid flow throughout the slot or trench. Alternatively the upright supports may be inserted into the ground in bore holes prior to the excavation of the slot or trench between consecutive supports. The panels or membranes may be secured to the supports by adhesive or welding or may be slid telescopically into open grooves or recesses formed in opposing faces of the supports. In the latter case there is no provision to prevent earth, backfill or cementitious material from entering the open grooves or recesses during construction, thereby preventing or hindering subsequent telescopic introduction of the panels or membranes therein to form the barrier. According to the present invention, a method of constructing an impervious underground barrier wherein plastics panels are secured within a trench excavated in the ground and between rigid supports set vertically in the ground by cementitious material applied to each side of the panels, is characterised by the steps of excavating at least a pair of spaced apart bore holes positioning a rigid plastic coupling member in each bore hole, each coupling member having at least one locking keyway slot formed therein facing a similar slot in the other coupling member and with a removable stop member located in each keyway slot, casting an excavatable cementitious filling within each bore hole around the coupling member positioned therein, allowing the cementitious filling to set, excavating, in the presence of liquid excavating slurry, the earth between consecutive bore holes including the set cementitious filling between facing locking keyway slots, removing the stop members from the facing slots, and positioning an impervious flexible plastic sheet barrier, rigidifying plastic end members in the slurry so as to bridge the space between consecutive bore holes by telescopically sliding each rigidifying plastic end member into one of the facing keyway slots. Also according to the present invention, an underground barrier formed by the aforesaid method is characterised by comprising at least a pair of spaced apart vertical coupling members of rigid plastic material embedded in holes below ground in a cementitious material apart from their facing surfaces which exhibit vertically-extending keyway slots previously filled during casting of the cementitious material by keyway slot protectors or stops and subsequently revealed after the setting of the cementitious material by the removal of such protectors or stops, and a plastic sheet barrier panel section bridging the space between the coupling members and having rigid plastic end members engaged in the slots with the plastic panel extending therebetween through the open entrance-ways of the slots. The plastic panel draining section may be a drainage panel and comprise a pair of rectangular flexible plastic sheets sealed along at least three adjacent edges to form a sheath or envelope, a plastic drain mesh sandwiched between the plastic sheets, and at least one perforated drain pipe in the sheath. The drain mesh may be a drain net of the type manufactured and sold by the Tensar Corporation under the trademark Tensar. The vertical coupling members which, in a preferred embodiment, may be perforated hollow pipes, are secured or connected to the lateral ends of the sheath or envelope to rigidify the ends. The sealing of the lateral ends of the sheath can be by way of sealing to the perforated pipe. The drain net, like all the plastic structures referred to in this specification, is preferably high density polyethylene which is substantially resistant to attack by a wide variety of chemicals. In forming the excavation, a plurality of bore holes are spaced apart typically on 33 to 40 feet (10.06 to 12.19 metres) centred along the line of the pollution control barrier. A plastic coupling member, which for all intermediate bore holes has oppositely facing locking keyway slots formed therein, is inserted into the bore hole with a stainless steel blocking member, in the form of a protector or stop, filling each slot so that upon positioning the coupling member in the bore hole and verticalizing same, the space around the coupling member can be filled with an excavatable cementitious material. After the excavatable cementitious material has set, the earth in the space between bore holes is excavated as by a clam shell, backhoe excavator, or kelly rig excavator, or the like, so as to remove the soil and earth in the space therebetween, all the while maintaining the excavation full of bentonite or other slurry trenching liquid material. Bentonite is preferred because it forms a mud cake on the excavation wall which serves as a barrier to pollutant flow and hence is used in making the bore holes. After the intervening soil has been excavated between a given pair of coupling elements, the steel protectors or stops are withdrawn from the slots so as to open the keyway slots and then the plastic panel members described above are inserted with the end perforated drain pipe members fitting telescopically within the keyway slots of the coupling member. Then the space between the sidewalls and the plastic panel members is filled with a cement-bentonite mixture preferably by the tremie pipe method and the displaced bentonite is used in adjacent excavations or in forming the cement-bentonite mixtures. The present invention will now be further described by way of examples, with reference to the accompanying drawings, in which: Fig.1 is a top plan view of a pollution control barrier constructed according to the present invention; Fig.2 is a side elevation view thereof taken in section along the line 2-2 of Fig.1; Fig.3 is a partial cut-away view to a larger scale of a plastics panel section as used in the invention; Fig.4 is a perspective view of a modification of the plastics panel section of the invention, and Fig.5 is a top plan view of a further pollution control barrier constructed according to this invention. Referring to Figs. 1 and 2, a series of bore holes H1, H2, H3 ... HN is constructed along the line of the pollution control barrier PB, each bore hole, H1, H2, H3 ... HN having a diameter D which is substantially equal to the width of the wall and, in a typical installation, can be about 3 feet (0.91 metre). The distance between bore holes is, typically, about 33 feet (10 metres) but can vary according to the terrain and possible obstructions that need to be avoided. The depth of the barrier or wall is quite large, and can extend several hundreds of feet or metres into the earth, if desired. During the excavation of the holes H1, H2 ... HN, they are maintained full of a bentonite slurry BS. Each bore hole has a coupling member 10 of rigid plastic material inserted therein through the slurry, the opposing faces along the line of the barrier PB having vertical, plastic panel keyway slots 12 and 13 formed therein which, in Figs. 1 and 2, are of a circular cross section. The coupling member 10 at each end of the control barrier PB (see that in hole HN in Fig.1) has only one slot 12. As shown in Figs. 1 and 2, the keyway slots 12, 13 are provided with protector block-outs or cement stop members 14, which, preferably, are stainless steel inserts, and which effectively fill the slots 12,13 and block the entranceways 15 thereof, so that the cementitious material introduced into the holes will not flow into the keyway slots 12,13. After coupling members 10 have been inserted in the holes H into the slurry, excavatable backfill cementitious material is inserted into the holes so as to displace the slurry and retain the coupling members 10 vertical in their respective holes, no cement being able to enter the keyway slots 12,13 in members 10 because of the cement stops 14. After the cementitious material has set or has achieved sufficient rigidity to maintain verticality of the coupling elements 10 during excavation of the earth between two holes H2 and H3, for example, the earth between those holes is excavated, and the keyway slot protectors or cement stops 14 are telescopically removed to leave open entranceways 15. As noted above, when a pair of holes have been prepared, and coupling members 10 positioned therein, and the excavatable cementitious material 16 has been introduced therein, the soil between the pair of holes is excavated by a clam shell excavator (CSE), or excavating tools as is disclosed in United States Patent Specification No.3,139,729, but modified to excavate up to removing the segment of cement at least on the opening entranceways 15 of the keyway slots which face each other in the respective bore holes H2 and H3. Bentonite slurry is introduced during excavation to prevent collapse of the trench. The drainage barrier panel section 20 with rigidifying end members 21 and 22 is then introduced into the slurry and members 21,22 are telescopically inserted in the slots 13 and 12. Thereafter, a cement-bentonite mixture C-B is inserted ... into the trench to displace the bentonite slurry that has been used to maintain the trench or slot open during the excavation. Preferably, the bentonite is displaced by the cement-bentonite mixture using the tremie pipe method as diagrammatically illustrated by the tremie pipes 30 and 31 in Fig.2. This provides even loading on the drainage barrier 20 since the cement-bentonite mixture has a different density than the bentonite alone. It will be appreciated that the order of forming and inserting the pollutant barrier sections is not critical and alternate ones may be formed and then the intervening spaces excavated to form the intervening control barrier units with their respective plastic drainage barrier installed. Moreover, the particular configuration of the coupling members can vary as will be illustrated more fully hereafter. Each of the vertical coupling members has coupling keyways formed therein except for the end ones which, as illustrated for a hole in HN has only one keyway slot formed therein. As illustrated in Fig.5, the pollution control barrier can be an endless one closing on itself. In the embodiment of Figs. 1 and 2, each of the end rigidifying members 21 and 22 are preferably high density polyethylene pipes, and one or both may be perforated. A drainage barrier panel section 20 (Fig.3) is comprised of a pair of high density polyethylene pipes or tubular drain pipe members 60 and 61 having diameters of about 6 to 8 inches (15.25 to 20.3 cms) which are sealingly connected by high density polyethylene sheets 50,51 which, in this example, are about 60 mils thick, but which obviously can be of greater or lesser thickness and can be of any other plastics material having appropriate chemical resistance and mechanical strength properties. The lateral ends 54,55,56 and 57 of the high density polyethylene sheets 50,51 are sealingly bonded either to the external surfaces of high density polyethylene pipes 60 and 61 or to each other in a fluid-impervious type manner by electronic or chemical welding, fusion or joining and sealing, all of which are conventional techniques. Each high density polyethylene sheet may be composed of several layers which are fusingly joined or bonded at their edges to form the desired barrier, but in the preferred embodiment the single integrally formed sheet is used so as to assure that there are no leaks in the sheet. Plastics sheets 50,51 are joined to pipes 60 and 61 at their lateral edges prior to telescopic insertion of same into facing key slots 12 and 13 of coupling members 10. One or both of pipes 60,61 may be perforated. Once the drainage barrier panel section 20 is installed, the bentonite slurry on each side of sheet 50,51 is displaced by a backfill which can be a mixture of soil-bentonite, cement-bentonite or concrete, or the like. As shown in connection with the filling of the panel section between holes H2 and H3, 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 31,32 which are gradually raised so that their lower ends remain within the heaps BF of backfill material on both sides of sheets 50,51 so that there is no differential backfill loading applied to the sheet. The lower ends of the tubes remain within the backfill heap BF and the slowly rising heap of backfill material moves 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 operation 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. The pipes 60 and 61 have wall thicknesses of 3/4 to 1 inch (1.96 to 2.54 cms). They may be cast or extruded, with or without reinforcement fibres or the like. It will be appreciated that the trench or slot excavations can be made using any conventional slurry trench excavation technique such as a clam shell, kelly bar, rotary drill bits or even backhoed for shallower depth walls. While in Fig. 2, there is illustrated a funnel shaped device PF for receiving the backfill material, it will be appreciated that this is purely diagrammatic as illustrating a means for supplying backfill materials for filling the trench sections on each side of the polyethylene sheets 50, 51 at substantially equal rates so as to avoid undue loading and distortion and stretchings of the sheet. If there is any space between the pipes 60 and 61 and the keying slots of the coupling members, a non-shrinkage grout can then be pumped into the pipe connections or into the space between the outer surfaces of the pipes and the inner surfaces of the larger keyway slots so as to form a tight joint to maintain integrity of the joint. Instead of round pipe sections, rectangular or oval pipe sections can be utilized. As noted earlier, the walls can go to a depth of up to about 300 feet (91 metres). In the forming of the bonding of the polyethylene sheets to the rods, channel members or pipes, it is good practice to first sand or roughen the surfaces and preheat same to about 120 degrees F (49 degrees C). A bead of at least about 1/2 inch (1.27 cms) 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 necessary. The pipe can be reinforced by fibre material such as fibreglass and the like but this is not necessary. The joint can be formed by chemical fusion or the like. As shown in Fig.3, the plastic drainage barrier panel 20 is constituted by a pair of rectangular high density sheets 50 and 51 which, typically are 60 mils thick and have their lower edges 52,53 sealed together and their lateral edges 54,55 and 56,57, respectively sealed together to form a sheath or envelope S. A drainage net DN is contained within the sheath S and is comprised of a high profile high flow capacity mesh structure manufactured from chemically inert polyethylene and, in one embodiment, can be Tensar (TM) drainage net as manufactured by the Tensar Corporation. In a preferred embodiment, such a drainage net has a thickness of approximately 1/4 inch (0.64 cms) and consists of two sets of parallel strands DNH and DNV with the intersecting strands being welded or otherwise joined together to form two overlayed sets of continuous channels CC to provide the high flow capacity. Since the drainage net DN is composed of high density polyethylene, it may be readily spot welded as at SW to the plastics sheets 50 and 51 to maintain positional integrity. Moreover, the drainage net may be composed of several rolls of about 6 feet (1.83 metres) width which are unrolled to the full depth of the sheath S, and in the illustrated embodiment, where the spacing between the bore holes is about 33 feet (10 metres), there are about five sections of drainage net DN. Strict verticality of the channelling CC in the drainage net is not necessary and, in fact, the drainage net can have diagonally running strands instead of horizontal DNH and vertical DNV running strands as indicated in Fig.3. The end rigidifying members or pipes 60 and 61 are perforated plastic drain pipe and of high density polyethylene which, as indicated earlier, can be welded to the plastic sheets 50 and 51, respectively. In Fig.3, perforations 62,63 in drain pipes 60,61 face the inner portions of sheath S so as to receive any drain pollutant that may penetrate the barrier. These drain pipes 60 and 61 typically are six to eight inches (15.25 to 20.3 cms) in diameter and hollow throughout their length so that small diameter drain pumps 65 can be lowered into the lower ends or bottoms thereof so that any pollutant or other liquid which penetrates the drain barriers will be removed from the system via lines 66. The electrical power lines (not shown) to the pumps 65 can be formed as an integral part of the drain line 66. In Fig.4, the end rigidifying members are hollow or solid members 67 and 68 at the lateral ends of the sheath S'. In this case, a perforated drain pipe 71 is positioned in the lower end of the sheath S' and a centrally located perforated drain pipe 69 is joined at 70 to the lower horizontal drain pipe 71. In this case, the pump 65' is in the centre drain pipe 69. Referring now to Fig.5, the drain net can be eliminated and in this case, the feature of coupling of the plastics panel elements utilizing the technique disclosed in Fig.1 is utilized. In this case, the plastics panel elements 80-1, 80-2 --- 80-N form a closed loop. In this case, the coupling members 10 are positioned in the bore holes 90-1, 90-2 ... 90-N with their respective key slots KS containing the stainless steel blockout member to protect the slot until the earth section spanning the space between two bore holes is excavated. Then the stainless steel sections are telescopically removed so as to open the slots for the insertion of the plastics panel sections. In this case, the plastics panel sections comprise end rigidifying members which are telescopically received into the keyway slots. Moreover, these members may be given a slight rotational movement so as to introduce a slight taughtness in the plastic sheeting to eliminate wrinkles and the like. In this case, the coupling elements are retained in positon initially by the filling of the excavatable cementitious material about the coupling members themselves. As shown in Fig.5, in hole 90-2, the coupling elements need not be rectangular but can be circular or, as indicated in hole 90-3, the coupling members can have rectangular keyway slots and the end rigidifying members can be rigid rectangular members for telescopic reception into the rectangular keyway slots.

Claims: A method of constructing an impervious underground barrier wherein plastics panels are secured within a trench excavated in the ground and between rigid supports set vertically in the ground by cementitious material applied to each side of the panels, characterised by the steps of excavating at least a pair of spaced apart bore holes (H1, H2....HN), positioning a rigid plastic coupling member (10) in each bore hole (A), each coupling member (10) having at least one locking keyway slot (12, 13) formed therein facing a similar slot in the other coupling member (10) and with a removable stop member (14) located in each keyway slot (12, 13), casting an excavatable cementitious filling (16) within each bore hole (H) around the coupling member (10) positioned therein, allowing the cementitious filling (16) to set, excavating, in the presence of liquid excavating slurry, the earth between consecutive bore holes (H) including the set cementitious filling (16) between facing locking keyway slots (12, 13), removing the stop members (14) from the facing slots (12, 13), and positioning an impervious flexible plastic sheet barrier (20), having rigidifying plastic end members (22, 21; 60, 61; 67, 68) in the slurry so as to bridge the space between consecutive bore holes (H) by telescopically sliding each rigidifying plastic end member (22, 21; 60, 61; 67, 68) into one of the facing keyway slots (12, 13). A method as set forth in claim 1, characterised by backfilling the space on each side of the flexible plastic sheet barrier with a cementitious mixture (BF) to displace the excavating slurry, and allowing the mixture to set. A method as set forth in claim 1 or 2, characterised in that the liquid excavating slurry is bentonite. An underground barrier formed by the method of claim 1, 2 or 3 characterised by comprising at least a pair of spaced apart vertical coupling members (10) of rigid plastic material embedded in holes (H) below ground in a cementitious material (16) apart from their facing surfaces which exhibit vertically-extending keyway slots (12, 13; KS) previously filled during casting of the cementitious material (16) by keyway slot protectors or stops (14) and subsequently revealed after the setting of the cementitious material (16) by the removal of such protectors or stops (14), and a plastic sheet barrier panel section (20; S) bridging the space between the coupling members (10) and having rigid plastic end members (21, 22; 60, 61; 67, 68) engaged in the slots (13, 12) with the plastic panel (20; S) extending therebetween through the open entrance-ways (15) of the slots (13, 12). An underground barrier as claimed in claim 4 characterised in that the plastic panel drainage section (20) is a drainage panel and comprises a pair of rectangular flexible plastic sheets (50, 51) sealed along at least three adjacent edges (52,53; 54, 55; 56,57) to form a sheath or envelope (S), a plastic drain mesh (DN) sandwiched between the plastic sheets, and at least one perforated drain pipe (21,22; 60,61 or 69) in the sheath (S). A drainage barrier as set forth in claim 5, characterised in that the drainage net (DN) is spot welded at a plurality of points (SW) to both of the pair of flexible plastic sheets (50,51) An underground barrier as claimed in claim 4, 5 or 6 characterised in that one or both of the pair of rigidifying members (21,22; 60,61) is hollow and perforated, and forms the drain pipe or pipes. A drainage barrier as claimed in claim 7, characterised by pump means (65,65') in the or each hollow and perforated rigidifying members (60, 61) or in a separate drain pipe (69). An underground barrier as claimed in claim 4, characterised in that the pair of vertical, spaced apart rigid plastic coupling members (10) have mutually facing first surfaces and oppositely facing second surfaces, the plastic sheet (S) spanning the space between the first surfaces and having lateral edges (54,55; 56,57) which are sealingly coupled to mutually facing first surfaces on the plastic coupling members (10), and a slot (12,13) formed in each oppositely facing surfaces of the plastic coupling members (10). Apparatus as set forth in claim 9, including first and second spaced apart vertical rigid plastic end members (21,22; 60,61; 67, 68) having mutually facing third and fourth surfaces, respectively, the plastic panel section (S) spanning the space between said mutually facing third and fourth surfaces and having lateral edges (54,55; 56,57) which are sealingly joined to the facing third and fourth surfaces, respectively, each said spaced apart rigid plastic end member (21,22; 60,61; 67,68) being of a size as to be telescopically receivable in one of the first named pair of spaced apart coupling members (10) with the flexible plastic sheet (S) passing through the slots (12,13).

Inventors: CAVALLI, NICHOLAS J., MIOTTI, GIOSUE
Applicants: FINIC B.V.
Application year: 1986
Main classification: E02D19
IPC codes: E02D19