The subject of the invention is screw equipment for digging to construct diaphragms.

Diaphragms are underground vertical walls created for the purpose of impermeabilizing an underground void (e.g., the basement of a building, an underground station, a tank, the area downstream of a dam, etc.) from any lateral infiltration of water or other fluid and for supporting the soil of the walls.

Said diaphragms are made by digging and filling in individually adjacent panels with reinforced concrete.

Each panel has a vertical development that can extend for more than fifty metres and can have a cross section having the shape of a rectangle or a rectangle with semicircular shorter sides or ends.

The equipment for digging to construct said diaphragms is referred to as clamshell bucket or grab.

Traditionally, clamshell buckets are made up of two opposite leaves provided with teeth, which, with a rotation of less than 90 degrees each, remove and gather soil from the bottom of the digging (see Figure 1). Set above the leaves is a body with side walls that rest upon the walls of the digging so as to limit any deviation of the digging itself from the vertical direction.

In hard soils, clamshell buckets can work by percussion in order to penetrate better.

Said operation, however, is not allowed in urban areas on account of the vibrations that are produced, with possible harmful consequences for nearby buildings and disturbance of public peace.

The soil gathered by the clamshell bucket is then hauled up to the surface by hoisting the entire loaded bucket, using a rope system, and then emptying the bucket by opening the leaves.

However, the soil compressed between the leaves of the clamshell bucket is difficult to detach, and systems of expulsion are necessary to facilitate the manoeuvre, which otherwise would require percussion of the open bucket against the surface of the worksite.

This operating cycle hence comprises long unproductive steps of lowering, hoisting and unloading. In order to exploit the working cycle better, it is of fundamental importance to increase the amount of debris transported during each cycle.

The geometry of the leaves of the clamshell bucket, however, does not enable an unlimited increase in the internal volume.

As an alternative to buckets, continuously operating systems have been studied, in which breaking down of the soil is carried out by milling wheels and conveyance of the soil to the surface is carried out by pumping a jet of water with the debris suspended therein. The water is, then, poured back into the digging after separating off the solid part in order to resume the cycle of extraction of debris.

Milling wheels may be drums with horizontal axes (see Figure 2) or front disks with vertical axes (see Figure 3).

An example of tools with vertical axes is also the one described in the patent No. US 5,007,770; this embodiment, however, aims principally at supporting the walls using a formwork and is consequently limited in depth by the height and weight of the device.

It can be readily understood that continuous systems are much more costly, since they comprise systems for pumping and separation, which must be powerful and sophisticated in order to convey and separate all the soil that is dug out at the same rate at which it is broken down.

A purpose of the present invention is to propose a device for digging to construct diaphragms with a digging cycle of the first type, i.e., intermittent, with low costs and without sophisticated systems, characterized by a high loading capacity and absence of vibrations.

Another purpose of the invention is to preserve the possibility of making very deep diggings, typical of rope-suspended systems.

For the above and further purposes that will emerge more clearly understandable from what follows, the invention envisages providing screw equipment for digging to construct diaphragms as described in claim 1.

The device according to the invention will now be described with reference to the attached plates of drawings, in which:

• Figure 1 illustrates a traditional clamshell bucket;
• Figure 2 illustrates a traditional mill for digging with milling wheels made up of drums with horizontal axes;
• Figure 3 illustrates a traditional mill for digging with milling wheels made up of front disks with vertical axes;
• Figure 4 illustrates the digging device according to the present invention; and
• Figure 5, 6 and 7 illustrate three shapes of diggings which can be obtained using the device according to the present invention.

Continuous-screw digging equipment is known and its use is very widespread. Said equipment breaks down the soil ahead of it and conveys it to the surface with a screw-conveyor system, which is able to contain a large amount of soil. Such systems, which were initially used for soft soils, have undergone a development that renders them suitable and highly productive even in soils that contain stones and soft rocks. The system is substantially quiet and without any vibrations.

It is, however, digging equipment that is used for carrying out in soil cylindrical diggings with diameters that are substantially the same as the diameter of the screw itself.

The device according to the present invention (see Figure 4) is made up of a plurality of substantially vertical tubes 1 set alongside one another, each containing a screw 2. The top end of the screw is set in rotation by a motor assembly 3, whilst the bottom end 5 is provided with appropriate tools for breaking down the soil 4.

The bottom end 5 of each screw projects from the bottom mouth of the corresponding containment tube 1 and has a diameter larger than that of the tube itself so as to dig a cavity into which the tube 1 can conveniently sink, following the screw 2.

In order to limit the tendency of the equipment to deviate from the vertical direction or to descend screwing into the soil, the individual screws 2 must rotate in pairs in opposite directions.

The motor drive 3 of the screws can be a single one, with drive systems for the individual screws, or else multiple, with separate motors for each screw.

The length of the tubes 1 and of the screws 2 is such as to guarantee a large accumulation volume, which is limited only by the hoisting capacity of the crane which manoeuvres the equipment and by practical limits of encumbrance and transportation. Also the unloading stage is facilitated since it is sufficient to turn the screws in the direction opposite to the loading direction, which is obtained preventing any impact and any environmental disturbance.

The cross section of the digging would thus appear as a series of circles 8 set alongside one another or slightly interfering with one another (see top side of Figure 5). Said section can readily be transformed into a rectangle with semicircular shorter sides using radiusing blades or additional mills 6 (see bottom side 9 of Figure 5). It can also be transformed into a true rectangle, using the aforesaid radiusing blades 6 and other end blades 10 with a sharp edge as additional mills.

The action of percussion of the cutting blades 6, 10 against the fringes of soil is not necessary, since the front section of said fringes is modest and since windows 7 are made in the tubes for collecting the soil in front of the area of action of the aforesaid cutting blades. In this way, the debris that has detached from the blades finds a way of expansion in the windows.

Alternatively, the equipment according to the invention can be built in two parts of which one, namely the outer one, which has a rectangular layout, can slide on the internal one and is designed for a limited action of percussion around the digging. The internal part comprises the screws and containment tubes. Its function is that of digging, gathering and conveying the debris.

In addition, the equipment may also be configured as illustrated in Figure 7, i.e., made up of two separate bodies, the outer one 11 of which can slide, by means of guides 12, on the inner one, which is made up of the aforesaid tubes 1.

The internal body, which, as has been seen, is made up of screws and tubes, has the task of collecting and accumulating the soil, whilst the external one 11, which can be actuated as a bit in so far as it is provided at the bottom with appropriate tools, can be connected to the rope-hoisting system and has the function of cutting the soil along the boundary of the cross section of digging.

When the outer body 11 is lifted to be pulled out, the inner one slides on the guides 12 until a mechanical end-of-travel element is encountered and is then, in turn, hoisted out.

In this way, there is no longer any need to apply to the tubes the radiusing blades 6 and 10 illustrated with reference to Figure 4, 5 and 6, in so far as it is the outer body 11 that delimits the rectangle of digging.

It is evident that what has been described herein is a rectangular digging in so far as this is the most traditional shape employed, but it is understood that by suitably arranging the tubes set alongside one another, the radiusing blades 6 and 10, or else the outer body 11, it is possible to obtain an infinite number of configurations of the equipment as regards its cross section.

The advantages of the solution proposed by the invention as compared to the known art are evident:

• Higher digging efficiency in a wide range of soils
• High capacity for loading debris
• Absence of any vibration
• Ease of unloading
• Large digging depth

In addition, as compared to the solution referred to above in the patent No. US 5,007,770, the present invention consists of a device having a limited height and is lowered using ropes to greater depths, the only limit being the amount of rope that can be accumulated on the winch.