EP0893570A1 - Multiple head drilling unit for loose soil drill - Google Patents

Abstract

This invention concerns a multiple head drilling unit for loose soil drills characterised in that its drilling heads are mounted parallel and close to each other on a common sliding trolley on a single rail.

Description

This patent application concerns a multiple head drilling unit for loose soil drills.

When excavating tunnels in loose soils it is indispensable firstly to strengthen the vault by grouting; only when the vault has been strengthened in this way can the soil underneath be removed without the risk of collapse.

The process for strengthening the vault of a tunnel of this type involves a tried and tested technique whereby numerous holes of considerable length are executed along a trajectory conforming to the cross-section of the tunnel. These holes are later filled with a cement mixture; once the mixture has hardened, a series of supporting cement ribs buried and anchored firmly to the ground, are formed all around the tunnel.

To date these holes have been made individually by means of a pressing rotating head which operates a drilling rod; in particular this head is mounted on a trolley sliding along a rail having a sub-horizontal inclination which in turn is generally mounted on a tracked vehicle.

It should be noted moreover that the above drilling rod is provided with a series of holes at the tip; when the rod penetrates the ground, strong jets of water are discharged through these holes in order to "wash" the hole, in other words to help carry the soil loosened by the drilling rod out of the hole.

Once the hole has been realised, the rod starts its backward run; during this backwards run a mixture of water-cement is injected through the same holes of the drilling rod which, in view of the very high injection pressure (approx. 500 bar), not only fills the hole but also filters by capillarity into the surrounding terrain in order to form a cement pole having a larger cross-section than that of the initial hole. Once all the hole-poles have been formed around a section of the tunnel and the ground is removed, the next section of the tunnel can be built using the same technique, drilling the ground on the bottom of the tunnel already built.

Considering therefore that a tunnel of this kind is built in separate and successive sections, it is evident that the cement support poles must always be inclined sub-horizontally in order to delimit a larger cross-section with respect to that of the mouth on the bottom of each section of the tunnel.

In this way the front ends of the pole delimiting the mouth of the next section of tunnel are encircled by the rear ends of the poles delimiting the bottom of the previous section of the same tunnel.

In order to accelerate the realisation times of this technique a special drilling machine has been developed which supports two separate and independent drilling heads, supported by two specific rails.

It should be noted however that the drilling machine in question is rather complex and bulky in that it requires double all the mechanical components used on the single-head drilling machines, with exception of the motor which drives both heads.

In addition, because of the fact that said drilling heads are independent, they can not work in synchrony and thus require two operators, each following the operation of each head during a specific working stage.

The reason for which said bits can not work in synchrony is due to the fact that the same are supported on their respective rails at a considerable distance from each other; in this way it is very probable - if not certain - that the two heads will drill two sections of terrain with different geological and structural characteristics.

For this reason it is evident that if one head is drilling more compact terrain, the drilling operating will require more time than that of the other head.

Moreover, this difference in the operating times is also increased by the fact that drilling generally takes more time than that required for injecting the cement mixture; this means that the two heads complete laying of the respective poles in different times.

The purpose of this invention is to realise a multiple head drilling machine which is simpler and more economical than these conventional drilling machines; the same is also more efficient and versatile and above all requires just one operator.

The new drilling machine in question in fact features a single rail on which a trolley supporting two or three heads operating respective drilling rods, slides; this alone makes it evident that the machine in question has a simpler structure with respect to conventional drilling machines with two heads and double rail.

Moreover, the heads fitted on the machine according to the invention are positioned close to each other and it is possible to change the centre to centre distance on board the trolley by means of a jack system; this feature is important from a practical point of view in that it permits setting the centre to centre distance of the cement poles which support the vault of the tunnel, as required.

Very important too is the fact that several heads can be mounted on a single trolley; this means that the same move forwards and backwards together.

The fact that the heads are positioned close to each other increases the possibility that the drilling rods will work on sections of terrain with the same characteristics; this should ensure that all the rods work the ground at the same speed.

Even if one of the rods meets more compact and harder terrain, involving longer drilling times, the forward synchronism of the rods is not lost in that the common supporting trolley does not move forward until this rod has completed drilling the more compact section of ground.

This ensures, as mentioned previously, perfect working synchronism of all the heads mounted on the trolley: they in fact move together step by step, during both the forward moving and backward moving stages.

In other words, all the heads of the machine according to the invention perform the same operating stage at the same time; the lack of operating differences between said heads means that they can easily be controlled by just one operator.

For major clarity the description according to the invention continues with reference to the enclosed drawings which are intended for purposes of illustration and not in a limiting sense where figure 1 is a top view of the rail-head supporting trolley mounted on the device according to the invention.

With reference to this figure, the drilling unit in question features a single rail (1) on which a trolley (2) slides; it being provided that said trolley (2) supports two operating heads (3), mounted parallel and close to each other and whose centre to centre distance may be varied by means of a jack (4) mounted orthogonally between the two heads (3).

The operating heads (3) operate respective drilling rods (5) generally provided at the tip with a series of holes, some of which are used to discharge the wash water and others to discharge the cement mixture.

The cement mixture is introduced into the unit in question through a special pipe (6) having two branches (6a), each of which supplies a specific head (3); a standard rotating joint (7) being provided along each of said branches (6a) and immediately upstream the respective head (3).

Standard jaw devices (8) to guide and hold the drilling rods (5) are also used. Figure 1 also illustrates that the above drilling rods (5) are of different lengths in order to prevent any interference between the cement jets discharged from the same rods (5).

Interference of this kind would in fact mean that the cement injected from a rod could easily prevent proper diffusion into the ground of the cement injected at the same time from another rod, thereby compromising the correct execution of the cement poles.

Claims (4)

1. A multiple head drilling unit for loose soil drilling machines of the type having several operating heads (3), each fed with a cement mixture through a specific pipe (6a) and operating a respective drilling rod (5), characterised in that its operating heads (3) are mounted parallel and close to each other on a common trolley (2) sliding on a rail (1).
2. A multiple head drilling unit for loose soil drilling machines according to claim 1, characterised in that one or more jacks (4) designed to change the centre to centre distance of the heads (4), are mounted orthogonally between the above operating heads (3).
3. A multiple head drilling unit for loose soil drilling machines according to claim 1, characterised by drilling rods (5) of the same length.
4. A multiple head drilling unit for loose soil drilling machines according to claim 1, characterised by drilling rods (5) of different lengths.

Images