GB2254391A - Collection box for geotextile fin drain - Google Patents

Description

2254,391 GEOTEXTILE FIN DRAINS This invention relates to geotextile fin

drains. These normally comprise a generally-planar core member which is covered by geotextile material. The core member typically has a corrugated or,egg-box" shape. The total thickness of the core and covering material is usually about 40 mm. The drains are buried underground with the geotextile-covered core normally extending in a generally-vertical plane. The core member is typically 300 to 600 mm high in this orientation and can be up to about 40 m long. The geotextile material of the buried drain acts as a filter medium through which water drains into the region of the core member.

It has so far been customary to join lengths of geotextile material in fin drains by means such as adhesive tape. These joints tend to restrict the flow of drainage water and are generally inconvenient and unreliable.

The present invention provides an element for use in a geotextile fin drain system, the element being tubular and having at least one longitudinallyextending slot which can receive and engage the core member and textile covering of a run of geotextile fin drain.

Such an element, when incorporated into a fin drain system, can function satisfactorily with very little restriction of water flow through the system.

In use, the tubular element will normally be positioned upright in the ground with an end of the run of fin drain held in its slot or slots. An element with a single slot will function as an end member of the drain system; with two or more slots, junctions can be formed, for example between two runs of fin drain meeting at right-angles or between three runs meeting at a T-junction.

The tubular element is conveniently of plastics material and is preferably formed from destressed plastics pipe, for example de-stressed uPVC pipe, the pipe being de-stressed prior to the slot or slots being formed in it. De-stressing may be effected by heating the pipe to a temperature of 55 to 65C for a period of 150 to 210 seconds, preferably around 180 seconds, and then allowing the pipe to cool. The invention accordingly also provides a method of making a tubular plastics element for use in a geotextile fin drain system, comprising heating a plastics tube to a predetermined temperature for a predetermined time, subsequently cooling the tube, whereby the tube is destressed, and cutting a longitudinal slot in the destressed tub.

Whilst the slot of the tubular element will normally maintain itself at or close to the width with which it is formed, the element preferably includes means which assist in maintaining the width of the slot or slots at or close to a predetermined value. These means may take the form of one or more end caps secured to the tubular element, for example by welding.

Advantageously, the end of the tubular element which is the lower end in use has means connection to a drainage pipe, for leading away water collected by the fin drain.

According to another aspect of the present invention, there is provided a collection box for use in a geotextile fin drain system, comprising wall means defining an interior space, the wall means having first and second slots extending substantially parallel to each other, a further slot extending in a plane which is substantially perpendicular to the direction in is which the first and second slots extend and an outlet means for discharge of liquid collec-.ed in the inteiior space from respective runs of geotextile fin drain received in the slots.

A collection box of this type can be used between an adjacent pair of a series of piles, for example the piles of contiguous bored pile system, the first and second slots receiving respective fin drain runs, which extend approximately vertically and have their major dimensions approximately horiLjntal, and the further slot receives a further fin drain run which extends approximately vertically with its major dimension approximately vertical and parallel to the axes of the piles.

Preferably, the further slot is arcuate.

More preferably, the first and second slots are adjacent opposite ends of a semi-cylindrical side wall of the box, the further slot being in a semi-circular top of the box and the outlet means being in a semi circular bottom.

Embodiments of the invention will now be described by way of example with reference to the drawings, in which:

Figure 1 is a side view of a tubular element for use in a geotextile fin drain system, Figure 2 is a sectional view of the tubular element of Figure 1, Figure 3 is a side view of the tubular element of Figure 1 and shows also an end cap and a connection elbow, Figure 4 is a side view similar to Figure 3 of another tubular element having a connection T-piece, Figure 5a is a side view similar to Figure 3 of a third tubular element, Figure 5b is a sectional view of the tubular is element of Figure 5a, Figure 6 is an end vi..ew of a run' of geotextile fin drain, Figure 7 is a plan view of a collecting box for use in a geotextile fin drain systpTq, Figure 8 is a side view of the collecting box of Figure 7, Figure 9 is an end view of the collecting box of figures 7 and 8, Figure 10 is a plan view, not to scale, of a contiguous bored pile system which incorporates the collecting box of figures 7 to 9, and Figure 11 is a view similar to Figure 7 of a further connection piece.

The tubular element of Figure 1 comprises a section of uPVC pipe 10 which has an outside diameter of say, 100 to 160 mm. The 1-ength of the pipe will vary according to the depths of fin drain with which it is to be used, lengths in the range 300 mm to 600 mm are typical. The uPVC pipe has already been destressed by being heated to a temperature of 65C for 3 min and then being allowed to cool. After cooling, a longitudinal slot 12 of 20 to 25mm in width was cut in the pipe, starting from one end and extending to a point about 100 mm from the other end. Figure 2 is a transverse section through the pipe 10.

Figure 3 shows the slotted pipe 10 and also an end cap 14 which can be welded over the end of the pipe to which the slot 12 extends. Also shown is a connection elbow 16 which fits over the other end of the pipe and is welded thereto. Since the pipe 10 has a single slot 12, the slotted tubular element with end cap and connection elbow can function as the terminal member of a geotextile fin drain system and can be connected to a drainage pipe by means of the elbow 16.

:1 is Figure 4 shows a pipe 20 and end cap 24 similar to those of Figure 3. " Instead of the connection elbow however there is a T-piece 26 which allows the tubular element to be connected to drain into a run of a drainage pipe into which the T-piece is connected.

Figures 5a and 5b show a pipe 30 having three slots 32, 321, 321, cut in it, the slots being arranged so that the pipe can form a T-junction between three runs of geotextile fin drain. The tube is shown having a welded end caps 34, 34, at each end but could instead be fitted with a connection elbow or T-piece, similarly to the elements described above.

Figure 6 of the drawings is an end view of a portion of a run of geotextile fin drain comprising a plastics core 40 and a geotextile covering 42 wrapped thereover. The core 40 has a dimpled "egg-box" shape with orthogonal rows of dimples which alternate to the left and the right in each row.

The tubular elements described above are used as follows in a fin drain system. The elements of Figures 1 to 3 and Figure 4 are used at the end of a run of fin drain where the core 40 and covering 42 of the run are inserted into the slot 12 or 22 and are there trapped by resiliency of the core material. The element is connected to a drainage pipe by its connector 16 or 26, the water collected by the fin drain following into the pipe 10 or 20 and thence into the drainage pipe. It has been found that the flow of such water is very little impeded by the tubular element.

The element of Figures 5a and 5b is used similarly but to join three runs of fin drain by reception of their cores and coverings in the slots 32, 321, 32". An element with two, four or more slots can be used similarly. The advantage of very little flow restriction is also attained wit.h these junct:ion elements.

The collection box shown in Figures 7 to 9 is particularly useful for joining runs of fin drain adjacent piles of a contiguous bored pipe system. Figure 10 shows such a situation, there is typically a contiguous line of vertically-extending contiguous piles 100 (see figure 10) which form, for example, the retaining wall of a tunnel. The piles 100 retain earth 102 at one side and are faced with a layer of concrete 104 which forms the tunnel wall. Between the piles 100 and the concrete layer 104, a geotextile fin drain system is arranged, this consisting of runs of fin drains joined at regular intervals to collection boxes 106 such as the one shown in Figures 7 to 9. The collection boxes 106 are positioned between, say, every five piles or every 30m or less and serve to join the ends of two runs 108 of fin drain material, each of which extends undulating in contact with the piles in an approximately vertical plane with its major dimension extending approximately horizontally, to one end of a further run of fin drain material which is arcuate in horizontal section and which has its major dimension extending approximately vertically adjacent two adjacent piles and in contact therewith, at least above the box 106.

The collection box has a semi-circular top 50, a semi-circular bottom 52, a rectangular end wall 54, and a semi-cylindrical side wall 56. These parts are made from uPVC or high density polythene or other suitable plastics or metal, welded into the shape shown. The material may be plain or corrugated.

The top 50 of the box has an arcuate slot 58. Further, straight slots 60a, 60b are formed in the side 1 wall 56 adjacent its ends. The bottom 52 has a central circular aperture, around which a sleeve is welded to form a discharge pipe 62. The end wall 54 has a circular opening around which a protective sleeve 64 is welded. The opening is closed by a transparent cover 66 which is secured by four bolts and wing nuts so as to be removable to allow access to the interior of the box.

In this embodiment, the end wall 54 of the box measures 642 x 461 mm, the radius of the semicircular top and bottom therefore being 321 mm. Other sizes are of course possible.

The collection box is installed as follows. The box is first positioned between an adjacent pair of piles. Respective ends of two different runs 108 or geotextile fin drain material, as shown in Figure 6, are then inserted into the slots 60a, 60b. the runs 106 being orientated as mentioned above. The edges of the slots 60a, 60b hold the geotextile covering 42 against the plastics core 40 whilst allowing drainage water to flow from within the fin drain material into the interior of the collection box. A further run 110 or the fin drain material is similarly introduced into the arcuate slot, the drain run being curved into an arc in the horizontal plane and extending vertically upwards from the box into contact with the piles 100. After installation, shuttering is erected and the wall 104 formed.

When installed in this way, the box serves to collect drainage water from within the three fin drain runs and to channel the water away through the discharge pipe 62, which is connected to a pipe 112 passing through the concrete lining 104. If necessary, access can be had to the interior of the collection box by removal of the cover 66 and insertion of a hand into is the box, the sleeve 64 extending through the lining 104 for this purpose. Use of this geotextile materiai in this way allows the wall 104 to be cast in a single piece, without any special drainage layer.

A modified collection box (not shown) has a fourth slot of the same dimensions as the slots 60a, 60b extending parallel thereto in the side wall 56 midway between the slots 60a, 60b. The fourth slot can receive a further run of fin drain, in a similar way to that described.

In a further modification. the fourth slot is replaced by a pipeconnection aperture or spigot, to which a pipe extending between adjacent piles can be connected.

Between piles where no collection box is positioned, the fin drain runs may be joined by the connection piece shown in Figure 11. This is made of similar materials to the collection box and has slots 58a, 60c and 60d for connection to the drain runs, the connection piece being arcuate in plan, and having part-cylindrical walls 541, 561.

Claims (9)

1. CLAIMS is 1. A collection box for use in a geotextile fin drain system,

   comprising wall means defining an interior space, the wall means having f irst and second slots extending substantially parallel to each other, a further slot extending in a plane which is substantially perpendicular to the direction in which the first and second slots extend and an outlet means for discharge of liquid collected in the interior space from respective runs of geotextile fin drain received in the slots.
2. 2. A collection box as claimed in claim 1, in which the further slot is arcuate.
3. 3. A collection box as claimed in claim 1 or 2, in which the first and second slots face in substantially opposite directions.
4. 4. A collection box as claimed in claim 3, in which the first and second slots are adjacent opposite ends of a part -cylindrical side wall of the box, the further slot being in a top of the box and the outlet means being in a bottom.
5. 5. A collection box as claimed in claim 4, having an access port in a further side wall of the box, the access port having a removable closure means.
6. 6. A collection box as claimed in claim 4 or 5, having in the partcircular side wall another slot which lies between the first and second slots and extends parallel thereto.
7. 7. A connection piece for use in a geotextile fin drain system, comprising wall means defining an interior space, the wall means having first and second slots extending substantially parallel to each other, and a further slot extending in a plane substantially perpendicular to the direction in which the first and second slots extend, the first and second slots facing in substantially opposite directions and the further slot being arcuate.
8. 8. A connection piece as claimed in claim 7, in which the first and second slots are adjacent opposite ends of a part-cylindrical side wall and the further slot is in an arcuate top wall of the connection piece.
9. 9. A collection box for use in a geotextile fin drain system, the box being substantially as hereinbefore described with reference to the drawings.

   is