A screw drilling device

Abstract: A screw drilling device has a rotatable unit (9) which forms a plate (10) having a first axial opening (12) and a cylindrical wall (11) having a first radial opening (19); the unit (9) is mounted on the lower portion (3a) of a central tubular element of the screw and can adopt a boring configuration in which the plate (10) is oriented so as to afford access for debris between the turns of the screw through the axial opening (12) whilst the cylindrical wall (11) is oriented so as to close a second radial opening (4b) formed in the tubular portion (3a) for discharging fluid from the duct (4), and a second, injection configuration in which the plate (10) closes the screw at the bottom and the cylindrical wall (11) is oriented so as to put the first and second radial openings (19, 4b) into communication.

Description: The present invention relates to a screw drilling device particularly for producing concrete foundation piles, of the type comprising a spiral screw integral with a central tubular element in which a duct is formed for the supply of a fluid to be injected into the borehole formed by the device. Screw boring devices of the aforementioned type, in which the lower end of the duct is closed by a plug, are known (see for instance EP-A-0 378 348). During drilling, the earth is broken up and caused to rise along the turns of the screw whereas, in the closed position, the plug prevents earth from blocking the concrete-supply duct. Upon completion of the drilling, concrete is pumped through the duct; the concrete under pressure expels the plug and fills the cavity of the hole bored whilst the screw full of debris is extracted therefrom. Extraction is effected with the screw kept stationary, that is, not rotating, or rotating slowly clockwise; anticlockwise rotation would cause the debris to fall from the screw, contaminating the concrete and compromising the quality of the product. Upon completion of the extraction and before the next drilling operation, the plug, which is connected to the screw by a chain, is usually replaced manually. This operation requires the presence of an operator at the bottom of the screw in a position which is dangerous because debris may fall from the screw. To improve the quality of the concrete injected into the borehole, a device has been proposed which, at the beginning of the pumping stage, provides for a second, coaxial tubular element, extending throughout the length of the screw and connected to suitable lifting and lowering members, to extend telescopically from the lower end of the central tubular element. The lower end of the second tubular element admits the fluid into the mass of fluid previously injected, beneath any debris and contaminants which, since they have a lower specific weight than concrete, tend to float and can therefore be removed upon completion of the pour. Problems inherent in this technique are the vertical dimensions of the members for moving the second tubular element which reduce the depth of boring which can be achieved by a given machine, as well as complications in the mounting of the screw and of the second tubular element which are formed by several connectible elements. The object of the present invention is to provide an improved screw drilling device which can prevent the problems mentioned above. This object is achieved, according to the present invention, by a device having the characteristics set out in Claim 1. A further object of the present invention is to provide a device which can produce a borehole with a diameter larger than that of a conventional tube used to line the first metres of the hole. This object is achieved, also according to the invention, by a device having the characteristics recited in Claim 6. Further important characteristics are recited in the other dependent claims. Further characteristics and advantages of the invention will become clearer from the detailed description of an embodiment thereof, given with reference to the appended drawings, provided by way of non-limiting example, in which: Figure 1 is a partially axially sectioned elevational view of a device according to the present invention in a first operative condition, Figure 2 is a partially axially sectioned elevational view of the device of Figure 1 in a second operative condition, Figure 3 is a transverse section taken on the line III-III of Figure 1, and Figure 4 is a transverse section taken on the line IV-IV of Figure 2. With reference first of all to Figures 1 and 2, a screw boring device according to the present invention is generally indicated 1. The device 1 comprises a spiral screw 2 welded around a tubular core 3 in which a central duct 4 is formed for the supply of concrete or other mixtures to be injected into the borehole 5 formed by the device 1. The boring device 1 is rotated and translated vertically about and along the central axis x in known manner and is preferably guided in the first metres of the drilling by a coaxial cylindrical outer tube 6 having the main function of lining the upper or initial portion of the borehole 5. The lower end of the screw, which terminates in a sharp radial cutting edge 2a, is firmly attached to a horizontal plate 7 in the form of a disk sector extending through an angle greater than 180°, that is, in the embodiment shown, an angle of about 240°. The plate 7 which is referred to herein as the fixed plate, defines a circular-sector-shaped opening 8 extending through the complement to 360° of the above- mentioned angle, that is, through about 120° in the embodiment shown. The terms "radial" and "axial" as used herein, should be interpreted as relating to the axis x of the borehole unless stated otherwise. The tubular core 3 extends below the level of the plate 7 forming a lower end portion 3a of predetermined length "L", preferably of between 50 and 100 cm and generally comparable to the diameter of the screw. As shown in Figure 1, the lower portion 3a has a cylindrical outer surface 3b which is preferably offset from the central axis x by an eccentricity "e". Inside the tube portion 3a, the central duct 4 bends outwardly forming an inclined end duct portion 4a which opens in the outer cylindrical wall 3b with a lateral opening 4b. A rotatable unit, preferably formed as a single body, generally indicated 9, is fitted on the lower tube portion 3a and forms a plate-like portion 10 in the shape of a disk sector the shape and size of which correspond to those of the fixed plate 7, and a cylindrical bush-like portion 11. As can be seen in Figures 1 and 3, the plate 10, which is referred to herein as the rotatable plate, defines a circular-sector-shaped axial opening 12 complementing the plate to 360°, and having a geometrical shape corresponding to that of the opening 8 in the fixed plate 7. The lower surface of the rotatable plate 10 bears a plurality of members 13 for breaking up the ground. On one of the radial sides which define the opening 12, the rotatable plate 10 forms an abutment 14 which projects axially in order to come into abutment alternatively with one of the two sides 8a, 8b of the opening 8 in the fixed plate 7, as will be explained further below. The bush-like portion 11 has an eccentric inner cylindrical surface 15 and an eccentric outer cylindrical surface 16; the internal surface 15 which houses the lower tube portion 3a has the same eccentricity "e" as that tube portion and the outer surface 16 has a diameter corresponding to that of a conical tip 17 situated at the lower end of the device and fixed to the bottom of the tube 3a at 18 so as to clamp the rotatable body 9 axially relative to the tube 3a and hence to the screw. The conical tip 17 bears a further set of breaking-up members 20. The bush-like portion 11 has a lateral or radial hole 19 situated at the same level as the opening 4b in the tube portion 3a and preferably inclined in the same manner as the final portion of the duct 4a in order to be joined thereto in one of the two working conditions of the device, as shown in Figures 2 and 4. The relative orientations of the radial hole 19 and of the axial opening 12 are such that, in the first working condition which the device adopts during the boring stage (Figures 1 and 3), the angular openings 8 and 12 of the respective plate-like portions 7 and 10 are aligned axially and the opening 4b of the duct 4, 4a is blocked by the bush-like portion 11 whereas, in the second working condition, which is adopted at the stage of the injection of concrete and simultaneous extraction of the device from the borehole (Figures 2 and 4), the angular opening 8 is closed by the rotatable plate 10 and the radial hole 19 meets the opening 4b. The device of the present invention operates as follows. As shown in Figure 1, during the boring stage, the screw device performs a combined clockwise rotational and vertical downward translational movement, as indicated by the arrow A. During rotation in this direction, the side 8a of the "fixed" plate 7 abuts the abutment 14 of the rotatable body 9 causing the body 9 to rotate (Figure 3). In this condition, as stated, the angular openings 8 and 12 coincide and allow ground debris broken up by the members 13 to enter and rise between the turns of the screw 2. The rotatable body 9 is oriented in a manner such that the cylindrical outer surface 16 of the bush-like portion 11 coincides with the circular profile of the base of the conical tip 17. The duct 4, 4a, is closed by the bush-like portion 11. When the desired depth of bore has been reached, a reverse rotation is imparted to the screw; the friction generated by the contact of the rotatable body 9, particularly its breaking-up members 13, with the ground, restrains the body 9 whilst the screw and the plate 7 rotate relative to the body 9 (anticlockwise, Figure 4) until the side 8b abuts the abutment 14. In this condition, the bottom of the screw is closed by the plate 10 which prevents the debris accumulated between turns of the screw from falling into the borehole (Figures 2 and 4). The holes 4b and 19 coincide, allowing concrete to be admitted to the borehole through the duct 4, 4a. In the preferred embodiment, as shown in Figure 2, the hole 19 is located in the vicinity of the lower end of the bush-like portion 11 at an axial distance L' slightly shorter than the above-mentioned length L. This facilitates the injection of the fluid beneath the free surface 21 of the cast fluid; any floating waste is therefore not covered and trapped in the cast fluid but will rise and remain on the surface and can be removed, thus improving the quality of the concrete constituting the product. The eccentric configuration of the rotatable body 9 relative to the axis of the screw is particularly advantageous since it enables a borehole of a diameter considerably larger than that of the screw and of the outer covering tube 6 to be produced. As can be seen in Figures 1 and 3, the plate-like portion 10 also carries breaking-up members 13 on its peripheral portion which, in the boring condition, extends radially beyond the screw and the tube 6. This enables the borehole produced to have a diameter larger than that of the lining tube which can easily be fitted in the hole without having to be rotated; simpler machinery can therefore be used for moving the tube. In the casting and extraction position (Figures 2 and 4), the plate-like portion 10 is included within the shape of the fixed plate 7 so that the entire device can be extracted from the tube to permit subsequent operations such as the positioning of reinforcement for strengthening the concrete. Naturally, the principle of the invention remaining the same, the forms of embodiment and details of construction may be varied widely with respect to those described and illustrated purely by way of non-limiting example, without departing from the scope of the invention as defined in the appended claims.

Claims: A screw drilling device, particularly for producing concrete foundation piles, of the type comprising a spiral screw (2) integral with a central tubular element (3) in which a duct (4) is formed for the supply of a fluid to be injected into the borehole (5) formed by the device, characterized in that it comprises a unit (9) forming a first wall (10) having a first axial opening (12) and a second wall (11) having a first radial opening (19), the unit (9) being mounted rotatably on a lower portion (3a) of the tubular element (3) and being able to adopt two alternative operative positions: a first position, in a boring configuration, in which the first wall (10) is oriented so as to afford access for debris between the turns of the screw through the first axial opening (12) and the second wall (11) is oriented so as to close a second radial opening (4b) formed in the lower tubular portion (3a) for discharging the fluid from the duct (4), and a second position, in a fluid-injection configuration, in which the first wall (10) is oriented so as to close the screw at the bottom and the second wall (11) is oriented so as to put the first and second radial openings (19, 4b) into communication. A device according to Claim 1, characterized in that the rotatable unit (9) comprises: a radial plate (10) constituting the first wall, parallel to and facing the underside of a radial plate (7) fixed to the screw, the plate (10) bearing breaking-up members (13) on its underside, and the plates (10, 7) forming respective axial openings (8, 12) which can be superimposed in the first position, and a cylindrical bush-like portion (11) forming the second wall in which the second radial opening (4b) is formed. A device according to Claim 2, characterized in that the plates (7, 10) are shaped as disk sectors extending through angles greater than 180° and the axial openings (8, 12) are circular-sector-shaped openings formed in the respective plates. A device according to Claim 3, characterized in that the plates (7, 10) are shaped as disk sectors extending through angles of about 240°. A device according to Claim 2, characterized in that the rotatable unit (9) forms an abutment means (14) for abutting alternatively, in the first and second positions, respective opposed end surfaces (8a, 8b) fixed for rotation with the screw. A device according to any one of the preceding claims, characterized in that the lower tubular portion (3a) is eccentric relative to the axis (x) of the screw and the rotatable unit (9) also bears breaking-up members (13) on the peripheral part of its plate-like portion (10) so that, in the first operative position, at least one of these members extends radially at least up to a distance from the central axis substantially corresponding to the radius of a tube (6) for lining the borehole (5). A device according to Claim 6, characterized in that the bush-like portion (11) has an eccentric, cylindrical surface (15) in which the lower tubular portion (3a) can be fitted. A device according to Claim 6, characterized in that the bush-like portion (11) has an outer cylindrical surface (16) having a diameter corresponding to that of a conical tip (17) which is fixed (18) to the lower end of the tubular portion (3a) so as to clamp the rotatable unit (9) axially to the screw. A device according to Claim 1, characterized in that the radial openings (4b, 19) are formed at an axial distance (L') no less than approximately 50 cm from the radial plate (10).

Inventors: PEDRELLI MARCO, PEDRELLI, MARCO
Applicants: SOILMEC SPA, SOILMEC S.P.A.
Application year: 1999
Main classification: E21B10
IPC codes: E21B34, E21B10, E02D5, E21B21