The invention relates to a drill point having an outer surface with a helical shape and a device for carrying out well drilling provided with such a drill point.
Such a drill point and device are known from FR-A-781.314, wherein the known drill point has a conical outer surface.
The drawback of the known device and drill point is that it requires a comparatively great deal of energy to force the known drill point into the ground by strokes of driving means, and that a great deal of noise, as much as 120 - 130 dB, is produced as a result of the large amount of energy required, which, even when ear mufflers are used, constitutes a high auditive load for the operators, and that furthermore a lot of undesirable vibrations are produced.
The object of the invention is to provide a drill point and a device whereby the drill point is effectively driven into the ground, and whereby less noise and fewer vibrations are produced.
In order to accomplish that objective the drill point according to the invention has features as recited in claim 1 and the device according to the invention has features as recited in claim 2. The advantage is that as a result of the combination of the substantially continuous rotary motion, with a substantially constant angular velocity, and the specified helical profile of the outer surface of the drill point, said drill point is rotated into the ground, instead of being hammered, as a result of which considerably less noise and fewer vibrations are produced. When an equal amount of mechanical energy is communicated to the means for driving the drill point into the ground, it is surprisingly found that in comparable circumstances it is at the same time possible to drill substantially deeper than with conventional devices. For environmental reasons this constitutes a considerable advantage in circumstances where in particular the structure of the higher ground layers, also after detonation of an explosive charge to be provided near the drill point in the borehole, should remain intact as much as possible, in order that the soil examination affects the ground water regime is as little as possible.
The means for driving the pipe into the ground is preferably a silent and commonly used hydraulic motor.
In a preferred embodiment of the device according to the invention the pipe has two projections, and the drill point has two corresponding recesses.
In practice this has appeared to be the most satisfactory embodiment, which in addition can be produced at a minimal cost price.
The invention will be further explained hereafter, with reference to the drawing, in which like numerals indicate like elements. In the drawing:
Figure 1 shows the bottom end of a pipe 1, said pipe 1, together with the drill point 2 illustrated in the Figures 2, 3 and 4, and the means (not shown) for carrying out the rotary motion of the pipe 1 and the drill point 2, forming part of the device for carrying out well drilling. The device comprises a hydraulic motor provided at the other end (not shown) of the pipe 1.
The pipe 1 is detachably coupled to the drill point 2, via projections 3 provided on the subterranean end of the pipe 1 and recesses 4, provided in the drill point 2, which correspond with said projections 3. A cylindrical part 6, provided with O-rings 5, of the drill point 2 fits into the pipe 1, whereby the projections 3 and the corresponding recesses 4 engage one another. By activating the hydraulic motor the drill point 2 is driven into the ground, after which the drill point 2 remains behind in the ground as a lost drill point 2.
The drill point 2 has a substantially conical outer surface 7. In the right-hand side elevational view of the drill point of Figure 2, which is shown in Figure 4, the outer surface 7 is even exactly conical, when seen in elevational view. However, when studying the extension of the section of the outer surface 7, in the direction of the point 8 of the drill point 2, in the elevational view of Figure 2 and the bottom view of Figure 3, in particular in Figure 2, said outer surface 7 appears to be more strongly contracted than can be derived from Figure 4. This stronger contraction, when seen in the elevational view of Figure 2, results from the helical profile of the outer surface 7. Figure 3 shows a bottom view of the helical extension, which is difficult to illustrate in a drawing, of the outer surface 7 of the drill point 2 illustrated in Figure 2.
When the drill point 2 e.g. runs through two fingers, said drill point 2 will be displaced, as a result of the specific helical shape of the outer surface. This property, which is typical of the outer surface 7, is expressed in terms of pitch of the helical outer surface 7. Said pitch is such that when the drill point is moved along its axial length the displacement of the drill point will be in the range of 10 - 40°.
With an axial length which is generally determined by the required mechanical strength of the drill point 2, the pitch of the helical outer surface 7 is to be determined such that, with a certain rotary velocity of the drill point 2 and with certain expected local soil conditions, the rotating drill point 2 is optimally adapted to the local soil structure and soil density.