Device for drilling in hard rock formation

Abstract

The invention concerns a drilling device having a plurality of rotary drilling members arranged to rotate about axes transverse to the drilling direction. Said drilling members are arranged in pairs mounted one on either side of and adjacent to a plate-like support.

Description

The present invention relates to devices for drilling, boring or excavating the ground.

At the present time, numerous methods exist for carrying out drilling, boring or otherwise excavating holes into the ground beneath the water table. Many of these are carried out in the presence of bentonite mud.

Some of these methods use inverse circulation with disintegrating devices which operate either by percussion or by rotation and which are furnished with single or multiple tools with vertical or horizontal axes. Other methods use discontinuous attacking devices which attack the bottom of the borehole with single or double ladle buckets.

These methods are in general adequate in alluvial formations such as gravels, sands, silts and clays, in soft rocks such as sandstone in process of formation or in volcanic tuff.

On the other hand, in harder rocks such as limestone, sandstone, volcanic rocks and so on, through which it is necessary to drill either for the purpose of achieving an anchorage or in order to descend to lower levels, these methods are either too slow or ineffective.

According to the present invention a drilling device has at least two rotary drilling members rotatable about axes transverse to the drilling direction, the rotary members being mounted in pairs, the drilling members of a pair being mounted one on either side of and adjacent to a plate-like support.

Such a device has the ability to cut through semihard and hard rocks more effectively and speeds up drilling in soft rocks and alluvia.

Preferably each support carries a motor unit having a single rotatable shaft extending towards and carrying both of a pair of drilling members.

This motor unit may be hydraulic or electrical, its supply and control being effected by means of flexible ducts or cables passing through the common support.

The presence of the support between the rotary members means that, when the device is in operation, there is a thin tongue of ground which is not attacked by the tools of the rotary drilling members and this tongue should be as thin as possible, so that it may be destroyed without difficulty as the drilling or excavating continues.

So that the thickness of the tongue can be reduced, whilst at the same time providing a support of suitable strength, each of the rotary drilling members possesses, at its edges adjacent to the support, at least one tool which projects laterally from that edge towards the support, the support having annular grooves coaxial to the rotary drilling member through which the ends of these tools pass when the rotary member is rotated.

The portion of the support situated beyond the grooves relative to the axis of rotation of the rotary members may advantageously be thicker than that situated on the inner side of these grooves.

For a given section or strength of the support it is therefore possible to arrange a smaller distance between the tools of the two rotary members which pass closest to one another and, therefore, to reduce the thickness of the tongue of earth which remains between the rotary members. This tongue, therefore being more fragile, will now break more easily and into smaller fragments, which can be more easily removed.

For sinking holes of rectangular cross-section, the device may with advantage comprise at least two plate-like supports disposed in a single plane symmetrically arranged about a central transverse plane of the device the rotary members being arranged to rotate in such a direction that the excavated material is brought towards this central plane, at which position is arranged means for removing the excavated material.

The removal of the material may be carried out by a conventional process involving inverse circulation of the mixture of excavated material with water or with a bentonite mud intended for supporting the walls of the excavation (such as immersed pump or surface pump, compressed air, hydro-ejection).

The device according to the invention is mechanically simple as a result of the elimination of any drive system involving gears, chains, or bevel gears, and the risk of wear, blockage or mechanical breakage is thus reduced to a minimum. The opportunity of being able to utilise the space available to the minimum (less than 60 cm in the case of trenches to be concrete) allows installation of a slow running, high power motor (100 horsepower at 150 r.p.m. for example).

The avoidance of having any ground faces not attacked directly by the tools and requiring destruction by an auxiliary action (such as preliminary drilling, action by lateral percussion etc), simplifies things greatly.

These parts therefore make it easier than was previously possible, to drill in harder ground such as in conglomerates, sandstones, limestone, etc.

Two examples of devices constructed in accordance with the present invention will now be described with reference to the accompanying drawings in which:

FIG. 1 is a diagrammatic side view, of a first example, half-sectioned through I--I of FIG. 2;

FIG. 2 is an elevation, half-sectioned along II--II of FIG. 1;

FIG. 3 is a partial section through a plane passing through the axis of rotation and parallel to the direction of drilling, of a second device furnished with a grooved support; and

FIG. 4 is a partial section along IV--IV of FIG. 3.

In the example shown in FIGS. 1 and 2, the drilling or excavating device has a frame 1, substantially in the form of a parallelepipedic box section furnished, at its upper part, with rings 2 which enable it to be suspended from flexible or rigid suspension members 3. The frame is also furnished at its sides with guide plates 4, having angled edges, which are intended to co-operate with the walls of the hole 5 which the device is excavating.

To the lower face of the frame 1 there are fixed, along the longer of its two centre lines, plate-like supports 6, having, for example a thickness of the order of 5 cms, which each carry an hydraulic or an electric motor 7, having a speed which is variable, for example from 0 to 150 revolutions per minute. Such low speed motors may possess a high torque and a relatively high power, and yet be reasonably small.

The two supports 6 lie along the central plane of the device, in such a way that the axes of the motors are perpendicular to this plane and are arranged symmetrically relative to the transverse central plane of the frame. On either side of the latter plane, the motors rotate in opposite directions, as indicated by the arrows in FIG. 1, in order to cancel out as far as possible the resulting force reactions. They are supplied and controlled through lines 8 which may provide hydraulic or electrical power. Preferably these are flexible and pass through the supports 6.

The shafts 9 of the motors 7 project outwards from both sides of the housing, and to each shaft end there is keyed a disc 10, carrying a drum 11 which extends from adjacent to the support 6 to the plane of the guide plate 4 above it. Each of the drums 11 is fitted around its periphery with one or more helical protuberances 12, carrying tools 13 such as teeth or small rollers enabling the ground to be broken up and excavated.

The helical threads are symmetrically arranged relative to the support 6, and are of opposing pitch and so selected that, when the drums revolve in the direction indicated in FIG. 1, the excavated materials are brought towards the centre of the device so that they can be removed through a central duct 14 mounted for this purpose on the frame 1 and connected to a flexible extract duct.

Such a device can be used in the following manner:

At the start, the device is placed in a preliminary trench having dimensions so calculated that the guide plates 4 are in contact with the ground.

The initial drilling operation is carried out at low speed to enable the furrows hollowed out by the tools 13 to be easily started. Simultaneously, mud, for example bentonite-based mud, is poured into the excavation, for the purpose of filling the excavation and preventing its walls from falling in. This mud is continuously removed by the duct 14 together with the excavated material, in accordance with the well known principle known as "inverse circulation;" it is then sieved and treated in an "ad hoc" installation and is re-introduced at ground level into the excavation.

By adjusting the rotational speed of the drums and the speed of descent of the device to achieve an optimum speed, corresponding to the type of ground being drilled and to the facilities for the removal of the mud and excavated waste, the drilling is carried on until the desired depth is reached.

In order to excavate a trench it is possible to form successive parallel drilled holes, separated by a web of ground having a length less than that of the device, and then to return later to drill out the intermediate web, the riding of the drums on the web ensuring the guiding of the device in the longitudinal direction. The device may later be used for smoothing out uneveness at the bottom of the trench.

It is possible to carry out either elementary excavations having a section corresponding to that of the device; or wall elements of greater or lesser complexity; or again continuous walls, even in hard ground.

In the second example shown in FIGS. 3 and 4, it is possible again to see the support 6, upon which the motor 7 is mounted, the shaft 9 of this motor carrying the discs 10 of the drums 11. The motor is supplied with power through lines 8, which pass through the support 6, and this is welded at its upper end to a saddle 15, enabling it to be mounted on the frame of the drilling device.

On each of the revolving members 11, there are tools 130 which are situated adjacent to the edge 110 of the drum which itself is closest to the support 6. These tools 130 are oriented obliquely towards the support and towards the outside of the member, so as to project beyond the plane of the edge 110.

In addition, opposite the external end of each of the tools 130, the support 6 is hollowed out to a circular groove 16, for example having a trapezium-shaped section, which permits the corresponding tool 130 to pass, with the desired clearance, when the device is in operation.

In this way, the distance d separating the extreme edges of the tools 130 of the two rotating members can be kept less than the thickness e of the support 6.

In order that the presence of the grooves 16 shall not weaken the support, the portion 17 of the support which is further than the grooves 16 from the axis of rotation of the members 11 is thicker than the portion of the support situated between the members 11.

If, for instance, the section of the support is considered which passes through a plane perpendicular to the support and to the direction of drilling and which intersects the grooves 16, such as the section plane IV--IV of FIG. 4, it can be seen that the loss of material resulting from the presence of the grooves is considerably compensated for by the extra thickness offered by the portion 17 (FIG. 4).

For example, a dimension of 50 mm may be selected for the thickness e, 40 mm for the distance d, and the portion 17 may be given a thickness of 60 mm.

Claims

I claim:

1. A drilling device comprising:

at least two pairs of rotary drilling members, each pair being arranged to rotate about an axis transverse to the drilling direction;

a plate-like support for each pair of said drilling members, said supports being disposed in a common plane symmetrically on either side of a central transverse plane of said device, each pair of said drilling members being mounted on either side of, and adjacent to a plate-like support;

a motor unit carried by each of said plate-like supports having a single rotatable shaft extending toward each drilling member of said pair, said drilling members being mounted for rotation on said shaft, the direction of rotation of said drilling members being such that excavated material is carried toward said central transverse plane;

means for providing power to each of said motor units passing through each of said plate-like supports; and

means for removing said excavated material from the vicinity of said device.

2. A device according to claim 1, wherein said support is mounted on a frame, said frame having guide elements arranged to cooperate with the side walls of the hole to be excavated and said frame including attachment means for supporting members.

3. A device according to claim 1 wherein each drilling member of said pair has a protruding helical configuration thereon to which are affixed drilling tools, said pair of drilling members defining opposed helical paths so that on rotation of said drilling members, excavated materials are carried by said configuration toward said plate-like support.

4. A device according to claim 3, wherein at least one of said tools on each of said rotary drilling members is mounted adjacent said support and projects laterally towards said support, said support having a corresponding annular groove, coaxial with said support, to receive said tool on rotation of said drilling member.

5. A device according to claim 4, wherein the portion of said support radially outside said groove is thicker than the portion of said support radially inside said groove.

6. A device according to claim 4, wherein said tools are oriented towards said support, inside said grooves and radially outwardly of the axis of rotation of said drilling members.