Method of Laying Subsoil Membranes

The invention relates to the separation of upper soil layers from the subsoil by laying a membrane of a preferably impervious material at a predetermined depth below the soil surface. This separation by underground films or membranes is done for various purposes: to produce impermeable ponds, dam levees or reservoirs for water or other liquids. Impermeable membranes are being used in the building of roads, runways, subgrades, sidewalks and road margins. More recently, impermeable membranes have been installed in agricultural fields at several decimeters below the surface with the purpose of reducing leakage of rain or irrigation water below the root zone and thus to increase the yield.

Several methods of preparing an impermeable underground layer are known. In one of these methods the soil is excavated to the necessary depth, the surface is smoothed and compacted and the impermeable layer is brought up on this surface by either laying prefabricated sheeting or by spraying a suitable plastic or liquid material. The excavated soil is then returned onto the top of the membrane. The drawbacks of this method are that the costs of smoothing and compacting after removal of the top layer are very high, that the thickness and strength of the membrane must be sufficient to sustain the stresses imposed on it by the heavy earth moving equipment used in replacing the previously removed soil, as otherwise there may be the danger of tearing, punctures and imperfect cover.

An improved method has been suggested wherein a subsoil blade is dragged through the soil parallel to the surface and simultaneously a suitable material is ejected and sprayed from the rear edge of this blade forming an impervious membrane after hardening. In this manner excavation and replacing of the soil, as well as manual or mechanical laying of a membrane are avoided and combined in one continuous operation. The main drawback of this method is the high cost of the material destined to form the membrane, since the requirement of producing a perfect continuous membrane demands the spraying of a relatively thick layer. As an example, the use of asphalt calls for a thickness of several millimeters. In addition, production of this type of membrane is limited to soils having no rough clods or aggregates and permit smooth penetration of the blade. It is also required that the soil is compatible with the sprayed material to allow perfect spraying and bonding.

It is therefore the object of the present invention to improve on the last-mentioned method by laying and inserting into the ground a prefabricated film or membrane of predetermined properties by means of special equipment suitable for laying this membrane without the need of a previous excavation. Furthermore, the use of this equipment should permit the laying of such membrane in other configurations than flat and in parallel to the soil surface.

Another object of the invention is to provide a method of laying a subsoil membrane which can utilize a membrane of a prefabricated material which can be produced to a wide range of properties thus allowing various applications. Still another object is to provide a method of laying a subsoil membrane which can utilize a membrane of a very thin and inexpensive plastic material in order to save costs.

The method consists of dragging a hollow cutting blade having a straight or otherwise formed cutting edge, an upwardly sloping front portion and a downwardly sloping rear portion ending at about the same height as the front edge, through the soil at a predetermined depth by means of a traction vehicle, providing for the supply of prefabricated thin, e.g. between 10 and 40 microns, sheeting of a pliable material to the interior of the blade and for the feeding of the said sheet material from the interior of the blade parallel to the rear edge thereof, at the velocity of the progress of the blade through the soil. The feeding is automatic in that the sheet material is held back by the soil falling onto its upper surface after having been raised by the passing blade.

In a preferred embodiment of the invention, the blade possesses a straight front edge and a straight hollow body of the said configuration, a flat bottom portion open at its rear, with a roll of the sheet material positioned rotatably in the blade interior in parallel to the front edge, the membrane being formed by the sheet material unrolling from the said roll through the said bottom opening into the cut made by the blade underneath the rear edge of the latter.

The method may also include the laying of pipes, cables or wires on top and adjacent to the sheet material forming the membrane by feeding these materials into the soil by any method known to the art.

FIG. 1 illustrates a vertical cross-section through a hollow blade serving to carry out the method according to the invention.

FIG. 2 is a perspective view of the blade illustrated in FIG. 1, showing attachment means to a traction vehicle.

FIG. 3 is a perspective view of the interior of the blade illustrated in FIGS. 1 and 2.

FIG. 4 is a cross-section through a blade together with equipment suitable for laying piping adjacent to the sheet membrane.

FIGS. 5A-5F illustrate respectively different ways of placing membranes by the method described.

Referring now to FIGS. 1, 2 and 3 of the drawings, the equipment for carrying out the operation includes a blade of the required width which is carried beneath a vehicle and is dragged through the soil 1 at a predetermined depth, with the front edge 2 cutting through the soil 1. Its bottom portion 5 form a release angle a with the cut soil so as to prevent friction between the bottom of the blade and the soil surface. The top portion 3 of the blade is sloped in an upward direction at an angle b for the purpose of pushing the soil above the blade, terminating in a substantially horizontal center portion 10. A rear portion 4 of the blade 3 is arranged at a rearward and downward slope with its rear edge 11 ending at a height slightly above the height of the front edge of the blade. Two side shields 12 close the hollow space formed between the top and the bottom of the blade. The blade is attached to a traction vehicle above ground by means of two substantially vertical arms or shanks 13 which are standard equipment with earthmoving equipment.

A hollow cylindrical support 7 carrying a roll 8 of a thin sheet material of a width commensurate with the width of the interior space is positioned within the space and carried at its ends on spaced rollers 16 attached to the end shields 12 permitting its free rotation about its axis. A free end 9 of the material is shown to have unrolled off the roll 8, and to be kept pressed between the stationary and the raised and replaced soil layers respectively.

All pivots of the above-mentioned rollers 16 are secured in the walls of a special chamber which includes a tray 14 which hinged to the end shields 12 by simple hinges that allow it to drop below the whole structure to facilitate unloading and reloading of the rolls 8 of thin sheet material. When the try 14 is lifted to a working position, as shown in FIGS. 3 and 4, it is automatically locked there by free-falling hooks 15.

This arrangement is not essential but exemplifies a specific design that has been built and field tried for reliance and simplicity of operation.

Wider or narrower blades and film strips may be used, depending on the type of soil, specific use, tractor available, etc. Other dimensions of the implement may also be changed due to the end uses and well-known laws of soil mechanics.

Various modifications and alterations may be carried out to the implement and to the method by a person skilled in the art, however within the limits of the invention and the scope of the appended claims.

The underground laying of prefabricated films may be combined with underground spraying by means of the same tool in the same pass. Thus any liquid may be injected by spraying for different purposes, such as softening the ground, introducing fertilizer, fumigation or any other end use.

The tool edge may be implemented with special teeth, chisels and vibrating parts to reduce the necessary forces in some heavier soils or in soils with some cohesive strength.

The tool edge may be straight, slightly curved or V-shaped so that the cross-section of the finished membrane is straight, curved or V-shaped. This is necessary to obtain special effects, such as illustrated in FIGS. 5A-5E.

The implement is equipped with standard aids as are common in earthwork machines and agricutural machinery, but are not part of this invention. They are, for example, edge markers to aid in exact performance; depth indicators, depth wheels and/or automatic depth controlling sensors to indicate the flow of the unrolled film and even to assay its length.

Of special importance is the possible combination of prefabricated membrane and underground pipes, wires and/or cables. The techniques of laying underground pipes, wires and cables are well known. An implement is dragged through the soil while a pipe, a wire or a cable is unrolled through a special conduit in the implement straight into a mole hole which has been formed in the soil. The combination of a prefabricated membrane and such an underground pipe, wire and cable is of a unique advantage.

There may be regular pipes, perforated pipes, heat conducting pipes, stripped or insulated wires, cables and the like. The pipes may be laid below the membrane or above it. In the first case, the pipe, wire or cable is laid before the membrane is laid. In the second case, the pipe, wire or cable laying implement is a part of the main blade and the pipe, wire or cable is laid after the membrane. FIG. 4 shows such a combination. In addition to the equipment shown in FIG. 1 it contains a pipe conduit 18 through which the pipe or wire or cable 20 is fed.

The pipes, wires or cable may be laid at the seams between neighboring membrane strips. The invention thus includes the combination in one implement of both installations of prefabricated membrane and piping or wiring.

The above-mentioned implement is usually dragged through the soil by an appropriate tractor or any other vehicle that has the necessary drawbar pull for the specific blade in the specific soil. However, it may also be dragged by a vehicle specially built for the purpose in which the knife is not dragged behind, but is anchored underneath the vehicle in a form that allows various degrees of freedom such as depth, tilt, angle, etc. This last arrangement may be similar to motograder.

It will be obvious to those skilled in the art that various changes may be made without departing from the scope of the invention and the invention is not to be considered limited to what is shown in the drawings and described in the specification.