Drainage material

Abstract

 The invention relates to a drainage material (1) comprising a core (2) provided with cavities or grooves (3) for transporting a liquid, and a filter material (4) which, at least after the drainage material has been installed in the ground, abuts against the core and is supported on the edges (S) of at least some of the cavities or grooves (3), forming channels (6) therewith. The spacing between at least some adjacent edges is less than 2.9mm. Thus the discharge capacity of the material is increased significantly.

Description

[0001] The invention relates to a drainage material comprising a core provided with cavities or grooves for transporting a liquid, and a filter material which, at least after the drainage material has been installed in the ground, abuts against the core and is supported on the edges of at least some of the cavities or grooves, forming channels therewith.

[0002] Such a material is known, for example from US 3,765,783. Said document shows (in figure 4) and describes a drain consisting of a thin, wave-shaped strip of a plastic material, which is provided with a sheet of paper on either side. When the drain is put into the soil, water will penetrate through the paper, into the channels and along these to the open earth surface.

[0003] Another example of such a drain is available under the name of Mebra Drain. This strip-shaped drain comprises a polypropylene core having a herringbone-like cross-section. Said core is enveloped by a filter material (Typar™) , which allows passage of water while stopping soil particles. Such drains, which serve to accelerate the process of settling of ground to be built on, are installed in the ground at regular intervals, for example by means of a device as disclosed in EP 226 251 and EP 672 795. Pore water that is present in the ground can then flow in a horizontal direction to the nearest drain and subsequently drain away practically without impediment.

[0004] Many of the usual drains have a herringbone core and a standard width of 100 mm. They comprise 27 to 33 channels in the longitudinal direction.

[0005] It is an object of the present invention to provide an improved drainage material.

[0006] To this end, the drainage material according to the invention is characterised in that the spacing between at least some, preferably most or even all adjacent edges (5) is less than 2.9 mm. Preferably, said spacing is less than 2.5 mm, more preferably less than 2.3 or even 2.0 mm. In practice, it is further preferred that the said spacing is in excess of 0.5 mm, or more preferably in excess of 0.8 mm.

[0007] It appeared that such a material has a significantly increased discharge capacity.

[0008] The channels may extend in various ways, for example in an undulating or zigzag manner, but it is preferred for the channels to extend linearly, parallel to the longitudinal direction of the core. Furthermore, it is preferable for the core to have a herringbone-like section.

[0009] It is also preferred that the drainage material has a discharge capacity, measured in accordance with ASTM D 4716 - 87 at a lateral pressure of 500 kPa, in excess of 20 10^-6 m³/s, preferably in excess of 40 10^-6 m³/s, after 10 days, preferably also after 20 days.

[0010] The invention further relates to a strip for vertical drainage, sometimes also referred to as a drainage wick, which comprises the material as described above or which, at least for the greater part, consists thereof.

[0011] The invention will now be explained in more detail with reference to the drawings, which schematically show an embodiment of the material according to the present invention.

[0012] Figures 1A and 1B are cross-sectional views of a drainage strip according to the prior art.

[0013] Figures 2A and 2B are cross-sectional views of a drainage strip according to the present invention.

[0014] Figure 3 is a diagram showing the results of a discharge test in accordance with ASTM D 4716 - 87.

[0015] Parts which are identical to each other or which perform at least substantially the same function are indicated by the same numerals.

[0016] Figures 1A and 1B are cross-sectional views of a strip-shaped drain 1 having a width and thickness of, in this case, 100 x 4.5 mm. The drain 1 comprises a polyolefine, e.g. propylene, core 2 having a fishbone-like cross-section defining a plurality of continuous and parallel grooves 3 on either side of the core 2. The grooves 3 further have a trapezoid cross-section and extend in the longitudinal direction of the core 2. The core 2 is enveloped, e.g. by means of (ultrasonic) welding, glueing or stitching, in a filter material 4, preferably consisting of a nonwoven material, such as Typar. The filter material 4 is supported on the edges 5 of the grooves 3, thus forming continuous open-ended channels 6 of substantially trapezoid cross-section with said grooves 3. In this specific example, the core 2 comprises 28 grooves 3 on either side, with the edges 5 of the grooves 3 having a spacing (at the location of the filter material 4) of 3.2 mm.

[0017] Figures 2A and 2B are cross-sectional views of a strip-shaped drain 1 according to the present invention, which drain 1 differs from the drain 1 as described above in that the core 2 comprises more than 35 grooves 3, in this example 39 grooves 3 on either side of the core 2, with the edges 5 of the grooves 3 having a spacing (at the location of the filter material 4) of 2.2 mm.

[0018] The two drains 1 were tested in accordance the Standard Test Method for Constant Head Hydraulic Transmissivity of Geotextiles and Geotextile related Products, ASTM D4716 - 87, (at i=0.5 and a lateral pressure of 500 kPa). Figure 4, containing the results of these tests, clearly show that the discharge capacity of the drain according to the invention is much greater than that of the prior art drain, especially after a few days have lapsed.

[0019] The drainage material according to the invention provides a better support for the filter material, as a result of which the filter material is pressed inwardly to a lesser degree and the channels are kept open more adequately (see Figures 1B and 2B). In addition to that, it is possible to use a thinner filter material and/or a core having a smaller wall thickness, so that material is saved and transport of the material is facilitated. Furthermore, it appeared that the discharge capacity of relatively lightweight drainage materials is less affected by buckling of the material whilst be installed in the ground.

[0020] As a matter of course, the invention is not limited to the embodiments as described above and can be varied in several ways without departing from the scope of the invention as defined in the claims.

Claims

1. A drainage material (1) comprising a core (2) provided with cavities or grooves (3) for transporting a liquid, and a filter material (4) which, at least after the drainage material has been installed in the ground, abuts against the core (2) and is supported on the edges (5) of at least some of the cavities or grooves (3), forming channels (6) therewith, characterised in that in that the spacing between at least some adjacent edges (5) is less than 2.9 mm.

2. A drainage material (1) according to claim 1, wherein said spacing is less than 2.5 mm, preferably less than 2.3 mm.

3. A drainage material (1) according to claim 1 or 2, wherein the core (2) comprises a number of parallel grooves (3) extending in the longitudinal direction of the core (2).

4. A drainage material (1) according to claim 3, wherein the core (2) has an at least substantially fishbone-like cross-section.

5. A drainage material (1) according to any one of the preceding claims, having a discharge capacity, measured in accordance with ASTM D 4716 - 87 at a lateral pressure of 500 kPa, in excess of 20 10^-6 m³/s, preferably in excess of 40 10^-6 m³/s, after 10 days, preferably also after 20 days.

6. A strip for vertical drainage which comprises the material according to any one of the preceding claims or which, at least for the greater part, consists thereof.

Drawing