GROUND BARRIER

Abstract: For installing a screen of flexible material in the soil, a trench is dug in the soil and the screen is fed into the trench. To provide a method in which the sagging or dragging along of the screen by the collapsing soil is avoided in a simple manner without use having to be made of an additional machine or the like, facilities are added to the screen itself to prevent its sagging into the still unfilled trench. The facilities may consist of a wire strung through the top edge of the screen and held under a certain tension, a strip which is bonded along the top edge of the screen and which is held under a certain tension, or an inflatable sleeve fitted to the top edge of the screen. Further it is possible that the entire screen is constructed in a sleeve-like form and is filled with gas, liquid or substance.

Description: The invention relates to a ground barrier including a vertical longitudinally elongate trench and a barrier screen positioned vertically within and longitudinally along said trench, said trench including an open top and a bottom, said screen including a top edge generally at the open top of said trench, and a bottom edge generally adjacent the bottom of said trench. Such a ground barrier is disclosed in EP-A-0191533. It is used, inter alia, to prevent spreading of pollutants by a horizontal soil water flow, to achieve a difference in water level on either side of the screen, to restrain musk rats and to prevent disturbance of a dike as a result of water seepage to the dry land side. Usually the screen consists of a plastic film, but the possibilities also include other materials such as impregnated paper and sandwiches of paper and bitumen. Digging of the trench, temporarily keeping the trench open and introducing the screen into the trench is carried out with one and the same machine. It has been found that, in the case of the known ground barrier, there is a risk of the flexible screen sagging or being dragged downwards under the influence of gravity or collapsing soil. The sagging of the screen in an uncontrollable manner may result in a serious delay. This could be avoided by squeezing the top of the trench at intervals by means of an excavator travelling alongside the trench. This method requires an additional machine with a skilled driver. In addition, the width of the working strip is relatively large. Another method would be to cut off wedge-shaped pieces from the top edge of the trench and to secure the top edge of the screen therewith. This method is also labour-intensive and would not lead to reliable results. The most obvious method of avoiding sagging of the screen is ― as described in said EP-A-0191535 ― to secure the top edge of the screen with pegs or sticks to the top edge of the trench. However, if the trench collapses, the screen is found to drop a number of decimeters along with the pegs or sticks. The object of the invention is to provide a ground barrier of the type mentioned in the introduction in which the sagging or dragging along of the screen by the collapsing soil is avoided in a simple manner without use having to be made of an additional machine or the like. According to the invention, for this purpose the screen comprises an elongate inflatable sleeve formed longitudinally along at least said top edge of said screen and inflated to transversely span said trench and define a substantially continuous support for said screen within said trench. To stabilize the screen within the trench either a second inflatable sleeve is formed longitudinally along said bottom edge of said screen and transversely expandable across a trench, or the screen, for the full extent thereof within said trench, is an inflatable sleeve transversely expandable to span and clamp within said trench between the open top of said trench and the bottom of said trench. In both cases the detaching can be carried out with such sleeves. If the inflatable sleeve, being for the full extent thereof within the trench, is filled with gas, buoyancy can be prevented by widening both the trench and the sleeve at the bottom. To prevent the sleeve or sleeves deflating in the event of one single leak, the sleeve or sleeves could be divided into compartiments by approximately vertical seams. The inflation of the sleeve or sleeves may take place by filling it with gas or liquid. The invention will now be explained in more detail by reference to the figures in which a number of exemplary embodiments of the method according to the invention is shown. Figure 1 shows a side view of a machine for installing a flexible screen in the soil, the protective housing connected to the machine being sectioned in the longitudinal direction for clarity. Figures 2 to 4 inclusive show perspective views of a number of embodiments in which a screen installed in the soil is provided with means for preventing sagging into the dug trench. The trench excavating machine 1 which is shown in figure 1 and is known per se comprises an excavating beam 2 which is provided with an excavating chain 3 and has a pivot point at 4. The excavating beam can be tilted through a certain angle by means of two hydraulic cylinders 5. Two hydraulic cylinders 6 are present to make it possible to adjust the depth of the excavating beam. A protective housing 7 is attached to the machine and can be used to keep the dug trench open over a certain distance. Moreover, there are a number of rollers 8, 9, 10 in the protective housing and above the housing a supply roll 11 of film is provided. The doubly folded film 12 which is drawn off the roll 11 is unfolded by means of the rollers 8, 9, 10 and fed into the trench. Details are described in the EP-A-0191533. Of course, a screen which is not doubly folded beforehand can also be installed in the trench. According to the invention, facilities are added to the screen to prevent sagging thereof into the as yet unfilled trench. A practical solution to the problem of the film installed in the open trench failing to remain upright is shown in figure 2: the film is provided at its top edge with a sleeve 15 which, after the film has been installed in the trench, is inflated. The diameter of the cross section of said sleeve is such that the sleeve is securely clamped in the trench or rests on the surface level. For example, a valve debouching into the sleeve is provided at the beginning of a film sheet. There is the possibility of making use of a large number of sleeve sections, which are separated from each other by non-sleeve-like double-walled film sections instead of a sleeve running along a great length. Each sleeve section then has its own valve. Figure 3 shows a variant: the bottom edge of the film is also provided with a sleeve 16 into which preferably water or another liquid is fed after it has been installed in the trench. This lowermost sleeve prevents buoyancy. In figure 4 it can be seen that the entire film is constructed in the form of a sleeve 17 and after it has been installed in the trench, it is inflated so that it is securely clamped in the trench. The possibility is not excluded that the sleeve of film is filled with a medium other than air, for example with water. A compound which remains plastic or which sets is also possible. As a result of this buoyancy can be completely avoided. Inflating the sleeve or filling it with liquid or substance contributes to preventing the trench collapsing rapidly. To prevent the film completely deflating if there is a leaf in it, the sleeve of film can be divided into compartments by bonding two walls of the film locally to each other in the transverse direction. Each compartment has its own filling valve. If a compartment becomes leafy, the film of said compartment is held up by the adjacent compartments. The compartments may have the form of columns which may be in communication with each other as groups. The use of a setting compound in the sleeve of film results in a very reliably protective wall. The fact that the soil next to the wall of the trench does not collapse may benefit the stability of the environment (underpinning of building). If the sleeve according to figure 3 is inflated with air, there is a risk of buoyancy as a result of water or mud present in the trench. This may be prevented by ballast material, which is an expensive method. It is cheaper to widen the trench at the bottom in accordance with figure 4 and also to construct the sleeve 17 more widely at the bottom in the inflated state. To dig a trench with a widened lowermost section, use may be made, for example, of the machine according to figure 4 of the EP-A-0.191.533.

Claims: 1. Ground barrier including a vertical longitudinally elongate trench and a barrier screen (12, 17) positioned vertically within and longitudinally along said trench, said trench including an open top and a bottom, said screen (12, 17) including a top edge generally at the open top of said trench, and a bottom edge generally adjacent the bottom of said trench, characterized in that said screen (12, 17) comprises an elongate inflatable sleeve (15) formed longitudinally along at least said top edge of said screen (12, 17) and inflated to transversely span said trench and define a substantially continuous support for said screen (12, 17) within said trench. 2. Ground barrier according to claim 1, characterized in that a second inflatable sleeve (16) is formed longitudinally along the bottom edge of said screen (12, 17) and transversely expandable across said trench for stabilisation of said screen (12, 17) within said trench. 3. Ground barrier according to claim 1, characterized in that said screen (12, 17), for the full extent thereof within said trench, is an inflatable sleeve (17) transversely expandable to span and clamp within said trench between said open top of said trench and the bottom of said trench. 4. Ground barrier according to claim 3, characterized in that both the trench and the inflated sleeve (17) are widened at the bottom. 5. Ground barrier according to one of the preceding claims, characterized in that the inflated screen portion(s) is divided into compartiments by approximately vertical seams.

Inventors: DE WAARD, WILLEM, HOFMAN, ARIE ANTHONIE, STEENBERGEN, BASTIAAN GORIS
Applicants: DIGGING TRADING COMPANY, N.V.
Application year: 1988
Main classification: E02D19
IPC codes: E02D19