WO1996031661A1

WO1996031661A1 - Drainage system for draining water from a layer of the ground

Info

Publication number: WO1996031661A1
Application number: PCT/NL1996/000148
Authority: WO
Inventors: Marinus Antonie Viergever
Original assignee: STICHTING GRONDMECHANICA DELFT
Current assignee: STICHTING GRONDMECHANICA DELFT
Priority date: 1995-04-07
Filing date: 1996-04-09
Publication date: 1996-10-10
Anticipated expiration: 1997-10-07
Also published as: NL1000092C2; AU5126496A

Abstract

This invention relates to a drainage system (1) for draining water from a ground layer (2), which system comprises at least one draining means (5) to be inserted to a specific depth of insertion, which drainage system comprises a series of draining means running substantially parallel to each other at short intervals, which draining means (5) extend from the depth of insertion in substantially vertical direction.

Description

Title: Drainage system for draining water from a layer of the ground.

The present invention relates to a drainage system for draining water from a ground layer, which system comprises at least one draining means to be inserted to a specific depth of insertion. Such a drainage system is known from, e.g., the

International Patent Application WO 81/03354. This publication describes a process and means for inserting a drainage system consisting of a profiled 10-cm-wide plastic strip with a material wound around it which is permeable to water. The plastic strips are driven vertically and at intervals by means of a hoisting apparatus and an insertion tube into a compressible and water-saturated ground layer to a specific depth of insertion in order to drain the excess water contained therein. The time required for draining the excess water is the consolidation time. This excess water is the result of the settling of the compressible layer under the influence of gravity in, e.g., sludge deposits after depositing the sludge, or of the pressure on the compressible layer increased under the influence of an external load. The plastic strips are generally inserted from the surface. This surface must have a certain bearing capacity so that it can bear the drive-in mechanism. In a sludge deposit his bearing capacity is only obtained in course of time.

The consolidation time of the compressible layers mainly depends on the permeability of the drainage material and the intervals between the draining means. In the above discussed prior art these intervals are about 0.7 - 2.0 m and cannot be reduced in view of the width of the plastic strips and in view of the process to be applied to drive the draining means into the sludge deposit. This has the result that a clear shortening of the consolidation time is hardly possible with the known drainage means and the process for inserting them. The object of the invention is to solve the above- described problem by providing a drainage system of the above- mentioned type which is characterized in that it comprises a series of draining means running substantially parallel to each other at short intervals, which draining means extend from the depth of insertion in substantially vertical direction.

By taking the steps according to the invention, there is provided a drainage system which, on the one hand, clearly shortens the consolidation time and, on the other hand, can be easily inserted in the ground layer. A suitable spacing for draining means is, e.g., 50 mm to 100 mm. In any case, this spacing must be substantially less than the hitherto conventional spacing between drains, that is to say substantially less than ca. 1 m. With the drainage system according to the invention ca. 3 times as much sludge can be dewatered per time unit as with the known drainage systems. A sludge deposit will therefore be dewatered much more rapidly and have sufficient bearing capacity to start or otherwise apply building activities thereon.

A drainage system to be produced in a very easy and inexpensive manner is obtained when the draining means are made of threads and the water is drained through the space between the fibers in the thread. From a viewpoint of environmental engineering, it is particularly advantageous when the threads are made of a naturally degradable material, such as, e.g., coconut, hemp or jute.

In order to enable easy vertical insertion of the drainage system in the ground layer, the draining means are fastened with a first end to a grid element which, from a viewpoint of environmental engineering, is also preferably made of a naturally degradable material, such as, e.g., a naturally degradable plastic.

The invention also relates to a process which is preferably suitable for inserting a drainage system in a ground layer according to the invention, which process comprises fastening the draining means to the grid element and then driving the drainage system by means of a drive-in section into the ground layer to the depth of insertion, and cutting off the draining means of the drain after driving in on the side facing away from the first end. It is particularly advantageous when during insertion the draining means of the drainage system are kept at intervals by means of a guide element.

The excess water will mainly be drained to the top of the threads and will then be absorbed at the surface in the water present there, or will be drained laterally into a horizontal layer. In order to provide a horizontal draining surface in the ground layer, the drainage system is inserted in a first layer of the ground layer which may later be provided with further layers, on the surface of which first layer the draining means fall after cutting off so that, subsequently, they form a horizontal drainage surface.

The invention also relates to a drive-in section for carrying out the process according to the invention, which drive-in section comprises a cage or shaft element with a supporting frame, on the lower side of which supporting frame is arranged the grid element of the drainage system.

Further elaborations on the invention are described in the subclaims and will be explained in more detail on the basis of an example of embodiment, with reference to the accompanying drawings, in which:

Fig. 1 is a perspective view of an example of embodiment of the drainage system according to the invention during insertion in a sludge deposit;

Fig. 2 is a front view of the drainage system with a horizontal drainage surface being formed;

Fig. 3 is a perspective view of a two-part grid;

Fig. 4 is a side view of the two-part grid in a thread feeding position;

Fig. 5 is a side view of the two-part grid in a thread gripping position; and

Fig. 6 is a sectional view of a rib of the lower and the upper grid of the two-part grid. In the figures identical parts are indicated by the same reference numerals. Fig. 1 shows a drainage system 1 according to the invention during insertion in a ground layer 2, e.g., a sludge deposit. The insertion is effected from a pontoon 3, e.g. by means of a hoisting apparatus 4. The drainage system 1 is built up from a series of draining means 5 running substantially parallel to each other at short intervals, which draining means 5 preferably consist of water- permeable threads made of naturally degradable material, such as, e.g., coconut, hemp or jute. Virtually, all threads built up from a plurality of fibers are satisfactory for this purpose since the water is sucked up via the spaces between the fibers in the thread. The threads 5 are fastened with a first end to the crossings of a grid element 6 which is also made of a naturally degradable material, and which is driven into the ground layer at a specific depth of insertion. The depth of insertion often corresponds to the depth of the deposit, in other words, the grid element 6 is often placed on the bottom 7 of the deposit. It is also possible, however, that the deposit is first filled with a layer of sand or with a layer of sludge which has meanwhile been consolidated to the extent that the insertion of the grid is no longer possible. In that case the depth of insertion is determined by the upper surface of the sand layer or the consolidated first sludge layer.

In order to drive the drainage system 1 into the sludge deposit 2, a drive-in section 8 is used which comprises a cage or shaft element 9 and a supporting frame 10, the grid element 6 of the drainage system being disposed on the lower side of the supporting frame 10 in such a manner that the threads 5 of the drainage system 1 mainly extend in the vertical direction. The drive-in section 8 is inserted in the sludge deposit 2 in a known manner by means of the hoisting apparatus 4 located on the pontoon 3, the threads 5 of the drainage system 1 being unwound from a winding device 11. The front side of the winding device 11 or the pontoon 3 is provided with a guide element 12 which keeps the threads 5 of the drainage system 1 at the desired intervals during driving in.

As soon as the drainage system 1 has reached the bottom 7 of the sludge deposit, the threads 5 are cut off and the drive-in section 8 is drawn ouf of the sludge deposit 2. Subsequently, the hoisting apparatus 4 with the winding device 11 and the drive-in section 8 is moved, and a next drainage system 1 can be inserted in the sludge deposit 2.

Fig. 2 shows the drainage system 1 according to the invention after insertion in a sludge deposit 2 which has not yet been filled completely. When the threads 5 are cut off, they fall on the top side 13 of the sludge deposit 2 and form a horizontal drainage surface 14. A new layer of sludge can be deposited on the drainage surface thus formed, optionally after depositing a sand layer. The horizontal drainage surface forms a kind of drainage mattress which ensures lateral draining of the water from the deposit. Moreover, such a horizontal drainage surface forms a bearing surface, which drainage surface may serve instead of a bearing surface created by means of a geofabric.

In order to enable easy fastening of the draining means 5 to the grid element 6, the grid element 6 can be provided with an upper grid 15 and a lower grid 16 which are arranged for movement relative to each other. A part of such a grid 6 is shown in Fig. 3 in perspective. In a thread feeding position, shown in Fig. 4 in side view, the passage openings 15a of the upper grid 15 are in line with passage openings 16a of the lower grid 16. In a thread gripping position, shown in Fig. 5 in side view, the lower grid 15 has moved relative to the upper grid so that the passage openings 15a of the upper grid 15 are in line with passage openings 16a located beside the above-mentioned passage openings 16a. In this thread gripping position the lower grid 16 abuts with an upper side against the upper grid 15 so that the draining means 5 are gripped between the upper and the lower grid.

The movement of the lower grid 16 relative to the upper grid 15 may take place, e.g., along a guide 19 and may be energized by a hydraulic, electric or pneumatic drive unit, such as a motor or a piston/cylinder assembly.

In order to ensure that the draining means are gripped very firmly, it is particularly advantageous to provide the upper grid and the lower grid with a tongue 17 and groove 18 in the parts abutting against each other in the thread gripping position, as shown in Fig. 6.

When the draining means 5 are fastened to the grid element 6, the grid element 6 is set to the thread feeding position, after which the draining means 5 are passed through the passage openings of the grid 6 and the grid element 6 is then set to the thread gripping position while gripping the draining means 5. Subsequently, as described above, the grid 6 can be driven into the sludge deposit 2. Optionally, when the grid 6 is at the desired depth of insertion, the lower grid 16 may be moved relative to the upper grid 15 so that the grid 6 is in the thread feeding position again. In this thread feeding position the grid 6 can be moved up again while the threads remain behind. Thus the grid 6 is not lost and can be repeatedly used for the insertion of the threads 5. It is of course also possible, however, that the grid 6 is left behind at the desired depth of insertion and that a new grid is used each time.

It is self-evident that many further modi ications and variants are possible within the scope of the invention. Thus the threads may also be made of plastic. Besides, other forms may be conceived for the drive-in section. Under specific conditions the threads may also be at an angle to the vertical.

Claims

1. A drainage system for draining water from a ground layer, which system comprises at least one draining means to be inserted to a specific depth of insertion, characterized in that the drainage system (1) comprises a series of draining means (5) running substantially parallel to each other at short intervals, which draining means (5) extend from the depth of insertion in substantially vertical direction.

2. A drainage system according to claim 1, characterized in that the draining means (5) are made of threads permeable to water.

3. A drainage system according to claim 2, characterized in that the threads are made of a naturally degradable material, e.g., coconut, hemp or jute.

4. A drainage system according to at least one of the preceding claims, characterized in that the draining means (5) are fastened with a first end to a grid element (6).

5. A drainage system according to claim 4, characterized in that the grid element (6) is made of a naturally degradable material.

6. A drainage system according to claim 4 or 5, characterized in that the grid element comprises an upper grid (15) and a lower grid (16) arranged for movement relative to each other, in a thread feeding position of which the passage openings (15a) of the upper grid (15) are in line with passage openings (16a) of the lower grid (16), and in a thread gripping position of which the lower grid (16) is moved relative to the upper grid so that said passage openings (15a) of the upper grid are in line with passage openings (16a) located beside said passage openings (16a), in which thread gripping position the lower grid (16) abuts with an upper side against the upper grid (15).

7. A process for inserting a drainage system in a ground layer according to at least one of claims 1 - 6, characterized by fastening the draining means (5) to the grid element (6), driving the drainage system (1) by means of a drive-in section (8) into the ground layer (2) to the depth of insertion, and cutting off the draining means (5) of the drainage system (1) after driving in on the side facing away from the first end.

8. A process according to claim 7, characterized by spacing apart the draining means (5) of the drainage system (1) during insertion by means of a guide element (12).

9. A process according to claim 7 or 8, characterized by inserting the drainage system (1) in a first layer of the ground layer which may later be provided with further layers, on the surface (13) of which first layer the draining means

(5) fall after they cutting off, and by subsequently forming a horizontal drainage surface (14).

10. A process according to any of claims 7 - 9, using a grid element as described in claim 6, characterized by, for fastening the draining means (5) to the grid element (6), setting the grid element (6) to the thread feeding position, passing the draining means (5) through the passage openings of the grid (6) and subsequently setting the grid element (6) to the thread gripping position while gripping the draining means (5).

11. A drive-in section for carrying out the process according to at least one of claims 6 - 8, characterized in that the drive-in section (8) comprises a cage or shaft element (9) with a supporting frame (10), on the lower side of which supporting frame (10) is arranged the grid element (6) of the drainage system (1).