Percussive core barrel

The present invention relates to an equipment for boring large diameter holes into rocks.

In the present specification, large diameter holes mean holes having a diameter within the range of 1 to 3 metres and a depth within the range of one to 10 metres into the rock. Such holes are to be bored in the rock for foundation piles or other similar purposes.

The surface of the rock may be at ground level or may be covered by up to 50 metres or more of soil. Where there is soil lying over the rock, a hole will be bored down to the rock by some other means, and held open by a steel casing or support fluid, or a combination of both. Then a specific equipment is used to drill the rock itself.

Four methods of boring large diameter holes into rock are in common use at the present time :

Boring with a rock roller bit with the rollers arranged in such a way as to bore out the rock over the entire diameter of the hole.

A rock roller bit requires considerable downward force to be applied to the rollers to penetrate into the rock. The bit is normally attached to a drill pipe which is rotated by a machine at the ground surface. Vertical force is applied to the bit either by hydraulic rams pressing down on the drill pipe or by heavy collars attached to the drill pipe on top of the bit. The rollers are equipped with teeth or hemispherical buttons which crush the rock as they pass over its surface. Discs are also used for this purpose in very strong rock.

Boring with a rock roller core barrel with the rollers arranged in such a way as to bore out a ring of rock, leaving a core of rock in the centre to be removed later by some other means.

A rock roller core barrel operates in a similar way to a rock roller bit, but much less vertical force is required because less rock is bored out by the rollers.

Boring with a percussive drill, having a single large bit or several smaller bits arranged in such a way as to bore out the rock over the entire diameter of the hole.

A percussive drill penetrates into the rock at a much faster rate than a rock roller bit or a rock roller core barrel. It is normally operated by compressed air which drives a single large hammer and bit or a number of smaller hammers and bits arranged together in a cluster. The drill is normally attached to a drill pipe which is rotated by a machine at the ground surface and is also used to convey the compressed air to the hammer or hammers. The energy required to operate a percussive drill is much higher than for a rock roller bit or rock roller core barrel, but is needed over a much shorter period.

Boring augers, toothed core barrels, digging buckets, cleaning buckets and chisels are used mainly for boring holes in weak rocks where acceptable progress can be made with this type of equipment. These tools, with the exception of the chisel, are normally attached to the Kelly bar of a piling rig. Chisels are raised and dropped in the hole either by a separate service crane or by the piling rig itself which may have hoisting facilities for this purpose.

The present invention relates to a drilling equipment which allows the cutting of an annular ring in the rock.

The object of the present invention is to provide a drilling equipment for boring large diameter holes into rock which combines the high speed of percussive drilling with the economy of boring out only a ring of rock around the perimeter of the hole instead of boring out the rock over its full diameter.

To achieve this object, according to the present invention, the equipment for boring large diameter holes into the rock comprises :

• a cylindrical core tube having a vertical axis, an upper end and a lower end.
• a plurality of hammer means provided with percussive bits for penetrating into the rock, each hammer means having a vertical axis and being secured to the outer face of the core tube close to the lower end thereof so that the bits project beneath the lower end of the tube,
• pressure fluid means for operating said hammer means,
• pressure fluid feed means for supplying pressure fluid in the vicinity of the bits of said hammer means,
• driving means connected to the upper end of said core tube for rotating said core tube about the vertical axis thereof; and
• exhaust means connected to said core tube for collecting the pressure fluid supplied in the vicinity of the bits and the rock cuttings transported by said pressure fluid from the bottom of the hole to the ground surface.

It will be understood that the drilling equipment which will be called a "percussive core barrel" in the following description, requires less energy than a percussive drill because it only bores out a ring of rock instead of rock over the entire diameter of the hole due to the fact that the hammers are rotated about the vertical axis of the core tube.

Moreover, the percussive core barrel will penetrate into the rock at a much faster rate than a rock roller bit or a rock roller core barrel.

Finally, little downward force has to be applied to the percussive core barrel compared to a rock roller bit or rock roller core barrel, enabling a lighter or less powerful machine to be used at the ground surface to supply the downward force.

According to a first embodiment, the hammer means are operated by compressed air and the pressure fluid supplied in the vicinity of the hammer bits is the compressed air for operating said hammer means.

According to a second embodiment, the hammer means are operated by a pressurised liquid and the pressure fluid supplied in the vicinity of the hammer bits is compressed air supplied by pipes extending down to the level of the hammer bits.

According to a third embodiment, the hammer means are operated by a pressurised liquid and the pressure fluid supplied in the vicinity of the hammer bits is also the pressurised liquid used to operate the hammer means.

Other features and advantages of the present invention appear better on reading the following description of several embodiments of the invention given by way of non limiting examples.

The description refers to the accompanying figures in which :

• - Figure 1 is a vertical section of the percussive core barrel on line I-I of figure 4 ;
• - Figure 2 is a vertical section view of the machine on line II-II of figure 4 ;
• - Figure 3 is a vertical section view of the machine on line III-III of figure 4 ;
• - Figure 4 is an horizontal section view of the machine on line IV-IV of figure 1 ;
• Figure 5 is an horizontal section view of the machine on line V-V of figure 1;
• Figure 6 is an horizontal section view of the machine on line VI-VI of figure 1;
• Figure 7 is an horizontal section view of the machine on line VII-VII of figure 1 ; and
• - Figure 8 is an horizontal section view of the machine on line VIII-VIII of figure 1.

Referring to the drawings, it will be seen that the percussive core barrel 10 comprises a cylindrical core barrel 12, a plurality of percussive hammers 14 and a drill pipe 16 which extends to the ground surface.

The core barrel 12 has a vertical axis XX', an upper end 12a, a lower end 12b and a free lower edge 12c. The diameter D of the barrel 12 is equal to 1 500 mm in the present example. More generally, this diameter is between 1 and 3 metres. The length L of the barrel is equal to 4 metres. More generally, this length is between 3 to 6 metres.

In the particular example, the machine comprises 8 hammers 14 having a vertical axis and including a body 14a secured to the outer face of the lower end 12b of the barrel and a percussive bit 14b, the bit 14b projecting below the lower edge 12c of the barrel. As better shown in figure 5, the hammers are regularly angularly disposed around the barrel 12.

In this example, the hammers have a diameter of about 20 cm. These hammers are operated by compressed air at a minimum air pressure of 14 bars. The total volume of air required for the 8 hammers is approximately 155 m³/min. As explained hereinafter, the hammers can also be operated by pressurised water or liquid. Additionally, the number of hammers might be different.

The hammers 14 are located in an annular volume 17 limited by the lower end of the barrel 12, an outer cylindrical shell 18 and an horizontal annular plate 20. The compressed air is supplied to the hammers by means of feed pipes 22 which connect the hammers to a compressed air source (not shown) disposed at the ground surface.

The machine 10 also comprises exhaust pipes 24 which connect the annular volume 17 wherein the hammers are located to a tubular member 26 secured to the upper end of the barrel 12. This tubular member 26 is connected to a frusto conical tubular piece 28 which is secured to the drill pipe 16.

As better shown in figure 2, the machine also comprises a cylindrical spacer ring 30 secured to the barrel 12 and surrounding the upper end 12a of the barrel to act as a guide for the core barrel in the bore. Of course, the diameter of the outer shell 18 and the spacer ring 30 is slightly less than the diameter of the hole to be bored.

Figures 2 and 5 show that the machine is equipped with depth control plates 32. These plates 32 secured to the core barrel extend below the lower edge 12c of the barrel and they are located between the hammer bits 14b. The purpose of these plates is to prevent the bits 14b from penetrating too far into the rock if the hammers 14 are operated without the core barrel being rotated by the drill pipe 16.

The operation of this first embodiment of the percussive core barrel 10 will be now described in detail.

The core barrel 12 is rotated by the drill pipe 16 and the compressed air is supplied to the hammers to operate the bits 14b.

As a result, the bits 14b travel along a circular path around the core tube 12 and the bits 14b bore out a ring of rock, the width thereof corresponds to the size of the bits, leaving a core of rock inside the core tube 12.

When the desired annular bore is obtained, the core of rock may be removed by means of a heavy steel chisel, weighing several tons, which is dropped on to the core of rock to break it into small pieces which can be removed from the hole by a mechanical grab or similar tools. If the depth of the hole required in the rock is more than the internal length L of the barrel 12, boring will be carried out in several stages, the core of rock from each stage being removed before the next stage has begun.

The compressed air is expelled through the bits 14b and most will return to the ground surface via the exhaust pipes and the drill pipe 16. This air will transport most of the rock cuttings produced by the bits. Some of the air will escape up the outside of the core barrel past the outer shell 18 because the outside diameter of the outer shell is slightly less than the outside diameter of the ring of rock bored out by the bits 14b. However, this will not have a significant detrimental effect on the performance of the percussive core barrel.

In the first embodiment above described, the hammers 14 are operated by compressed air.

According to a second embodiment, the hammers are operated by hydraulic power and the rock cuttings are still transported by compressed air from the bottom of the hole to the ground surface, therefore a smaller volume of air is required.

The compressed air feed pipes are detached from the hammers and extended down to the level of the bits, so that air to transport the rock cuttings can be fed down to the bottom of the hole. Most of the air and rock cuttings will return to the ground surface via the exhaust pipes but some will escape up the outside of the core barrel past the outer shell. Separate pipes (not shown in the figures) are attached to the hammers 14 to transport the hydraulic fluid used for their operation.

According to a third embodiment of the percussive core barrel, water is used as hydraulic fluid to operate the hammers and is fed down via the feed pipes to the hammers and expelled through the bits. The hole in which the percussive core barrel is being operated is kept full of water to the ground surface by means of a discharge pipe from a suitable water supply. Compressed air is fed into the lower part of the machine to cause water and rock cuttings to rise up the exhaust pipes 24 and drill pipe 16 to be discharged at the ground surface.