EP0210682B1

EP0210682B1 - Method of manufacturing a screen in the soil

Info

Publication number: EP0210682B1
Application number: EP86201139A
Authority: EP
Inventors: Wolter Reinold De Sitter
Original assignee: Hollandsche Beton Groep NV
Current assignee: Hollandsche Beton Groep NV
Priority date: 1985-07-30
Filing date: 1986-06-27
Publication date: 1990-04-04
Anticipated expiration: 2006-06-27
Also published as: NL8502160A; EP0210682A1; DE3670111D1

Description

The invention relates to a method of manufacturing a screen in the soil by making use of a digging device to manufacture a vertical trench in the soil with spaced apart parallel vertical walls, guiding a foil having a width corresponding to the depth of the trench from a supply roll into the trench through a vertical slot of a casing which moves through the trench with the digging device, behind the latter, and which foil leaves the slot, seen in the direction of movement of the digging device, at the rearside of said casing, and filling the foil containing trench behind the casing with filling material.
A method of this kind is known from e.g. NL-A 6 900 976. According to said known method the space between the digging chain and a cylindrical casing surrounding a foil roll which casing has a rearwardly facing slot through which the foil can move into the open trench is kept filled with bentonite. Said foil surrounding casing has lateral skirts which engage the vertical side walls of the trench and have to prevent that bentonite or the like suspension penetrates passed the casing into the open trench space which is not yet or not yet completely filled with a suitable filling material. This filling material has to be a dry material since a liquid, such as cement mortar, would penetrate through the slot of the casing into the interior of the casing and spoil the interior by hardening deposits.
Although the skirts of the casing by engaging the earth walls of the trench serve to prevent that bentonite passes into the rearward open space this sealing cannot be perfect due to irregularities existing or formed in the walls of the trench. Under certain soil conditions a trench wall can partly collapse.
If filling material of a dry nature would enter the slot through which the foil leaves the casing then the foil would have to overcome large frictional resistances.
Purpose of the invention is to provide a method according to which the foil can more easily move outwardly through the slot of the casing and by means of which a filling material can be supplied which supports the walls of the trench and prevents them from collapsing and simultaneously forms the final screen in combination with the foil.
This purpose is achieved according to the invention in that the casing through which the foil is supplied towards the slot is kept filled with water to which has been added a viscosity increasing agent such as bentonite and that the filling material of the trench is a cement mortar liquid and that the bentonite pressure in the casing is kept higher than the cement mortar pressure on the other side of the slot. The casing, which can follow immediately behind the digging device, is now according to the invention filled with the bentonite and the foil is guided through said bentonite and to this end the foil supply roll is preferably placed above the casing.
In leaving the casing through the slot the foil is lubricated by the bentonite whereas the cement mortar cannot penetrate into the casing due to the fact that the bentonite pressure is kept higher.
When the foil is inside the trench having left the casing it is surrounded by the cement mortar so that no relative movements between cement mortar and foil occur and there are no frictional forces to be overcome. The cement mortar keeps the walls of the trench upright and prevents them from collapsing and after hardening forms the screen in combination with the foil.
It is observed that it is known in itself, e.g. from FR-A 2 038 719 to manufacture a screen from foil sections and concrete mortar. According to said known method, however, the foil sections are placed vertically next to each other and in overlapping arrangement which foil sections are placed into a previously manufactured trench. The foil sections are inserted into the trench from above which trench later on is filled.
It is observed moreover that in the non-prepublished Dutch patent application 8 500 421 a method and device have been proposed for inserting a foil section for a screen into the soil, in which said foil section is guided over a rod or roller extending at an angle with the horizontal such that the foil section entering from above into the trench from a supply roll after passing said inclined rod or roller, extend with its longitudinal axis in the direction of the trench and therewith also has a width which corresponds to the depth of the trench. Experiments did teach that if in that caser one applies as filling material concrete mortar problems are formed in that the filling material enters the area of the reversing rod or roller. The method according to the present invention can be applied by making use of such a reversing rod or roller inside the bentonite filled space of the casing. Cement mortar can according to the invention not penetrate into said casing and accordingly not disturb the guidance of the foil over the reversing rod or roller.
The invention now will be further elucidated with reference to the drawings.

Fig. 1 is a side view schematically showing a device for performing the method according to the invention.
Fig. 2 is a plan view belonging to it.

The drawings show a tractor 1 with tracks 2 which is movable over the soil 3. Said tractor carries a digging chain 5 from an arm 4 which by means of the cylinder 6 can be lowered or raised respectively. A foil supply device or casing 7 has been suspended pivotably from the arm 4 which device can swing about the pivot 8 by means of the cylinder 9. This device carries a foil supply roll 10. Inside the casing 7 there is a guide rod 11 placed at 45° about which the foil section moving from above downwardly is guided into a horizontal direction and accordingly extends in the direction of the vertical plane of the trench as indicated at 12.
The trench walls are indicated with 13 and 14. The casing 7 has a slot 15 through which the foil section 12 may move outwardly. According to the invention now water is supplied with a viscosity increasing agent, such as bentonite, into the space of the casing 7 containing the guiding rod 11, whereas in the space 16 behind the slot 15 cement mortar is supplied by means of which the foil section 12 can be pressed against the wall 13 of the trench.
Instead of bentonite the viscosity of the water can be increased as well by adding glucose, starch preparations, carboxyl methyl cellulose and other means.
In this way a hydraulic lock is formed at the location of the slot 15. The pressure increase inside the space 7 can be obtained by applying a higher liquid level than outside.
In this way a lock has been obtained through which the foil section can move without friction and without the cement mortar reaching the environment of the guide rod 11.

Claims

Method of manufacturing a screen (12) in the soil (3) by making use of a digging device (5) to manufao- ture a vertical trench (16) in the soil with spaced apart parallel vertical walls (13, 14), guiding a foil (12) having a width corresponding to the depth of the trench from a supply roll (10) into the trench (16) through a vertical slot (15) of a casing (7) which moves through the trench (16) with the digging device (5), behind the latter, and which foil leaves the slot (15), seen in the direction of movement of the digging device (5), at the rearside of said casing (7), keeping the casing (7) through which the foil (10, 12) is supplied towards the slot (15) filled with water to which has been added a viscosity increasing agent such as bentonite, filling the trench behind the casing with a cement mortar liquid, and maintaining the pressure of the liquid in the casing (7) higher than the cement mortar pressure on the other side of the slot (15).