Auger drill

Description

[0001] The present invention relates to an auger for construction purposes, in particular for drilling holes into the ground, and a method of constructing high-friction piles in the ground utilizing such an auger.

[0002] Conventionally, two methods are in use to build a pile foundation using precast piles such as concrete piles or steel posts, namely, a pile-driving method and and an embedding method. In the pile-driving method, precast piles are driven directly into the ground, and in the embedding method, precast piles are inserted into prebored holes in the ground.

[0003] An example of the embedding method is descrided in U.S. 5.722.498.

[0004] Among the two aforementioned methods, the embedding method does have many advantages, but the boring of the holes requires the excavation of soil in excess of the volume of the piles. The disposal of this soil adds to the construction cost.

[0005] This invention was undertaken to resolve the aforementioned problems arising from the conventional method, and to this end aims at an auger for construction purposes and a method of constructing high-friction piles in which the amount of excavated soil can be reduced, and by which the number of piles that must be set for a pile foundation can also be reduced.

[0006] According to the present invention, the object is solved in a satisfying and advantageous manner.

[0007] According to a first aspect of the present invention, an auger for constructing purposes is disclosed in independent claim 1.

[0008] According to a further development of the auger according to the invention, the second helical blade comprises a pair of helical windings inserted between each other in the axial direction and extending in parallel with each other around the shaft.

[0009] According to a further development of the auger according to the invention, adjacent helical windings of the second helical blade are connected with each other at their outer peripheries by means of an exterior barrier.

[0010] In a specific embodiment of the auger according to the invention, a transition portion without any helical winding is provided along the shaft between the first helical blade and the second helical blade.

[0011] According to a further development of the auger according to the invention, plates extending radially from the periphery of the shaft and being spaced apart in axial and circumferential direction are provided between the first helical blade and the second helical blade.

[0012] According to a specific embodiment of the auger according to the present invention, the axial distance between adjacent helical windings of the second helical blade is about half the axial distance of the helical windings of the first helical blade.

[0013] According to a second aspect of the present invention, a method of constructing high-friction piles in the ground is disclosed in independent claim 7.

[0014] The invention will be explained in more detail with reference to the accompanying drawings and with reference to examples of the auger and the method according to the present invention.

Fig. 1

illustrates a high-friction pile with a surrounding plastic zone obtained according to the method of the present invention;

Fig. 2

is a diagrammatic view showing a first embodiment of the configuration of the auger according to the present invention used in constructing friction piles; and

Fig. 3

is a diagrammatic view showing another embodiment of the configuration of the auger.

[0015] In the following description, the auger for construction purposes and methods using the same will be disclosed in more detail.

Auger

[0016] An auger of the type as shown in Fig. 2 of the drawings is used for the construction of piles according to the invention. In particular, a helical blade 2 is molded at an angle around the virtual length of a rotatable shaft or shank 1 in the positive direction of rotation, except for the upper tip or top portion of the shaft. Such a positive rotation helical blade 2 is of the same configuration as a blade used on conventional augers for boring.

Reverse Rotation Blade

[0017] On the other hand, a helical blade 3 is molded at an angle around the top portion or upper tip of the rotatable shank or shaft 1 in the reverse direction of rotation from that of the positive rotation helical blade. In other words, when rotating the shaft 1 according to Fig. 2 from the top side in a clockwise direction, the first, positive rotation helical blade 2 moves forward, whereas the second, reverse direction helical blade 3 moves backward.

[0018] When drilling such an auger into ground, it is the reverse direction helical blade 3 provided on the upper part of the rotating shaft 1 which prevents the soil agitated by the positive rotation helical blade 2 from being pushed upwards. This is due to the fact that the helical blade 3 causes a movement in the opposite direction.

[0019] In a specific embodiment of the auger according to the invention, at least one hollow pipe 31 is provided extending in parallel with the shaft 1 and communicating an upper surface of a first helical winding with a lower surface of a second helical winding of the second helical blade 3.

[0020] The hollow pipe 31 forms a vertical passage between the helical windings of the second helical blade 3. Such a hollow pipe 31 can be advantageous when drilling holes into the ground with the auger, since the quantity of excavated soil will at once increase, depending on the circumstances, when drilling the auger into the ground.

[0021] In one embodiment of the present invention, there is only one second helical blade 3 with a suitable number of helical windings around the circumference of the shaft 1. In another embodiment of the present invention, the second helical blade 3 comprises a pair of helical windings inserted between each other in the axial direction and extending in parallel with each other around the shaft 1. This situation is shown in Fig. 2 of the drawings.

[0022] In a specific embodiment of the present invention, the adjacent helical windings of the second helical blade 3 are connected with each other at their outer peripheries by means of an exterior barrier 32. This configuration is shown in Fig. 3 of the drawings. Again, a hollow pipe 31 may be provided with a vertical passage formed between respective windings of the second helical blade 3.

[0023] As can be seen in Fig. 2 and Fig. 3 of the drawings, there is a transition portion without any helical blades between the first positive rotation helical blade 2 and the second, reverse direction helical blade 3.

[0024] In this transition portion, plates (6) extending radially from the periphery of the shaft 1 and being spaced apart in axial and circumferential direction are provided between the first helical blade 2 and the second helical blade 3.

[0025] The transition portion is provided and adapted to agitate the soil when rotating the auger and to reduce the upward pressure which is caused by the positive rotation of the helical blade 2. Hence the transition portion contributes to preventing the soil from rising towards the top surface of the ground where drilling takes place.

Preventing Upward Thrust of Drilled Soil

[0026] In order to drill holes in the ground, the auger as shown in Fig. 2 or Fig. 3 of the drawings is used and positioned on the ground. Then, rotation of the shaft 1 causes the positive rotation helical blade 2, the principal segment of the auger, to bore into the ground. By doing so, all or at least a portion of the soil pushed up by the rotation of the positive rotation helical blade 2 is prevented from rising towards the surface by the reverse rotation helical blade 3 mounted above the positive rotation blade 2. As a result, soil being agitated will not be discharged externally, but will instead be pushed back downward and thrust sideways into the surrounding soil.

[0027] Depending on the situation, a bentonite or other slurry can be admixed into the soil simultaneously with the boring procedure.

Formation of a Plastic Zone

[0028] During the boring operation for boring a hole, soil of an amount equivalent to the total volume of the shaft 1 and the helical blades 2 should inherently be discharged, leaving a cavity. However, by preventing this discharge, the volume of soil is instead thrust into the area of the surrounding soil. This thrust compacts the surrounding earth causing it to lose pore space, in other words the sum of the interstitial water and air within the soil particles, so that a plastic zone A of a prescribed width is formed in the soil surrounding the hole.

Setting Size of Plastic Zone

[0029] The size of the plastic zone A is determined by the modulus of elasticity of the shear and the adhesion of the soil. For example, the width of the plastic zone A can be determined by the following Formula 1.

wherein

R =

Radius from the center of the hole to the outer boundary of plastic zone A

G =

Modulus of elasticity in shear of the soil

Cu =

Undrained shear strength (adhesion) of the soil

a0 =

Diameter of small-diameter shaft

δ =

Variation in surface of hole wall.

Introduction of Hardening Agent and Insertion of Support Material

[0030] When a hole has been formed by the auger described above, mortar or another hardening agent 4 is poured into the cavity being supported by the plastic zone A as explained above. Next, a support material 5 is inserted into the hole before the hardening material 4 is completely hardened. The support material 5 can be, for example, an H-steel profile.

[0031] In such a method, the hardening agent 4 should only be introduced in an amount so that, when the support material or reinforcement material 5 is inserted, the hardening agent 4 is only displaced up to the top of the hole, but should not spill out of the hole after the support material or reinforcement material 5 has been inserted.

[0032] Once the hardening agent 4 is completely hardened, a pile is built in which the support material 5 and the plastic zone A surrounding the bored hole, now filled by the hardening agent 4 and the support material 5, form a monolithic body.

Effectiveness of the Invention

[0033] As can be inferred from the above explanations, the method of this invention is highly effective for constructing high-friction piles wherein soil from the boring of the hole is virtually prevented from being pushed up and discharged above ground. Instead of this, it is thrust, up to a prescribed range, into the soil surrounding the hole to create a plastic zone A. A hardening agent 4 is then poured into the hole, whereupon a supporting or reinforcement material 5 is inserted. Hence, the method according to the invention provides the following advantages.

[0034] The ground surrounding the pile is compacted and becomes more dense, wherein the plastic zone A, established up to a prescribed range around the pile, can be utilized effectively as part of monolithic pile body. Consequently, the number of piles which must be set into the ground is greatly reduced from that required by a conventional method so that construction costs can be reduced.

[0035] Virtually all of the bored soil is thrust into the surrounding earth with only a minimum amount being discharged above ground. Soil disposal cost is therefore minimal and construction costs are reduced.

Claims

1. An auger for construction purposes for drilling holes into the ground, comprising

- an elongated shaft (1) with a top portion and an extended main portion, and

- a helical blade (2) extending around the shaft (1) and projecting radially from the periphery of the shaft (1),

wherein the shaft (1) comprises a first helical blade (2) along the length of the main portion thereof with an inclination angle in the positive direction of rotation and at least one second helical blade (3) only along the top portion of the shaft (1) with an inclination angle in the opposite or reverse direction as that of the first helical blade (2).
characterized in that at feast one hollow pipe (31) is provided extending in parallel with the shaft (1) and communicating an upper surface of a first helical winding with a lower surface of a second helical winding of the second helical blade (3).

2. The auger according to claim 1,
wherein the second helical blade (3) comprises a pair of helical windings inserted between each other in the axial direction and extending in parallel with each other around the shaft (1).

3. The auger accordi ng to claim 1 or 2,
wherein adjacent helical windings of the second helical blade (3) are connected with each other at their outer peripheries by means of an exterior barrier (32).

4. The auger according to any of claims 1 to 3,
wherein a transition portion without any helical winding is provided along the shaft (1) between the first helical blade (2) and the second helical blade (3).

5. The auger according to any of claims 1 to 4,
wherein plates extending radially from the periphery of the shaft (1) and being spaced apart in axial and circumferential direction are provided between the first helical blade (2) and the second helical blade (3).

6. The auger according to any of claims 1 to 5,
wherein the axial distance between adjacent helical windings of the second helical blade (3) is about half the axial distance of the helical windings of the first helical blade (2).

7. A method of constructing high-friction piles in the ground,
comprising the following steps:

(a) preboring a hole in the ground by rotatingly driving an auger into the ground;

(b) a hardening agent (4) is poured into the hole obtained in step (a);

(c) a support material (5) is inserted into the hardening agent (4) in the hole before the hardening agent (4) is completely hardened; and

(d) the hardening agent (4) is allowed to harden so that the support material (5) and a plastic zone (A) surrounding the hole form together a monolithic pile,

characterized in that a specific auger according to any of claims 1 to 6 is used for preboring,
wherein, as the hole is being bored, a portion of the soil agitated by the positive rotation first helical blade (2) is prevented from being pushed upward by the reverse rotation second helical blade (3) and is instead thrust into the area surrounding the hole, and wherein the plastic zone (A) is formed up to a prescribed width around the hole.

Ansprüche

1. Erdbohrer für Bauzwecke zum Bohren von Löchern in das Erdreich,
wobei der Erdbohrer folgendes aufweist:

- einen länglichen Schaft (1) mit einem oberen Bereich und einem verlängerten Hauptbereich, und

- ein wendelförmiges Blatt (2), das sich um den Schaft (1) herum erstreckt und von dem Umfang des Schafts (1) radial wegragt,

wobei der Schaft (1) ein erstes wendelförmiges Blatt (2) entlang der Länge seines Hauptbereichs mit einem Neigungswinkel in der positiven Rotationsrichtung sowie mindestens ein zweites wendelförmiges Blatt (3) nur entlang des oberen Bereich des Schafts (1) mit einem Neigungswinkel in der gegenläufigen oder umgekehrten Richtung wie der des ersten wendelförmigen Blatts (2) aufweist,
dadurch gekennzeichnet,
daß mindestes ein hohles Rohr (31) vorgesehen ist, das sich parallel zu dem Schaft (1) erstreckt und eine obere Oberfläche einer ersten wendelförmigen Windung mit einer unteren Oberfläche einer zweiten wendelförmigen Windung des zweiten wendelförmigen Blatts (3) verbindet.

2. Erdbohrer nach Anspruch 1,
wobei das zweite wendelförmige Blatt (3) ein Paar wendelförmiger Windungen aufweist, die in Axialrichtung zwischeneinander eingefügt sind und sich parallel zueinander um den Schaft (1) erstrecken.

3. Erdbohrer nach Anspruch 1 oder 2,
wobei einander benachbarte wendelförmige Windungen des zweiten wendelförmigen Blatts (3) an ihren äußeren Randbereichen mittels einer äußeren Barriere (32) miteinander verbunden sind.

4. Erdbohrer nach einem der Ansprüche 1 bis 3,
wobei ein Übergangsbereich ohne jegliche wendelförmige Windung entlang des Schafts (1) zwischen dem ersten wendelförmigen Blatt (2) und dem zweiten wendelförmigen Blatt (3) vorhanden ist.

5. Erdbohrer nach einem der Ansprüche 1 bis 4,
wobei zwischen dem ersten wendelförmigen Blatt (2) und dem zweiten wendelförmigen Blatt (3) Platten vorgesehen sind, die sich radial von dem Umfang des Schafts (1) weg erstrecken und in Axialrichtung sowie in Umfangsrichtung voneinander beabstandet sind.

6. Erdbohrer nach einem der Ansprüche 1 bis 5,
wobei die axiale Distanz zwischen einander benachbarten wendelförmigen Windungen des zweiten wendelförmigen Blatts (3) ungefähr die Hälfte der axialen Distanz der wendelförmigen Windungen des ersten wendelförmigen Blatts (2) beträgt.

7. Verfahren zum Bauen von Pfeilern mit hoher Reibung im Boden,
wobei das Verfahren folgende Schritte aufweist:

(a) Vorbohren eines Lochs im Boden durch rotationsmäßiges Antreiben eines Erdbohrers in den Boden hinein;

(b) Gießen eines Härtungsmittels (4) in das in dem Schritt (a) gebildete Loch;

(c) Einbringen eines Abstützmaterials (5) in das Härtungsmittel (4) in dem Loch, bevor das Härtungsmittel (4) vollständig ausgehärtet ist; und

(d) Aushärtenlassen des Härtungsmittels (4), so daß das Abstützmaterial (5) und eine das Loch umgebende Kunststoffzone (A) zusammen einen monolithischen Pfeiler bilden,

dadurch gekennzeichnet,
daß ein spezieller Erdbohrer nach einem der Ansprüche 1 bis 6 für das Vorbohren verwendet wird,
wobei beim Bohren des Lochs aufgrund der gegenläufigen Rotation des zweiten wendelförmigen Blatts (3) verhindert wird, daß ein Teil des durch die positive Rotation des ersten wendelförmigen Blattes (2) bewegten Erdreichs nach oben gedrückt wird und dieser stattdessen in den das Loch umgebenden Bereich hinein gedrückt wird, und wobei die Kunststoffzone (A) auf eine vorgeschriebene Breite um das Loch herum ausgebildet wird.

Revendications

1. Tarière prévue à des fins de construction, destinée à percer des trous dans le sol, comportant

- une tige allongée (1) ayant une partie supérieure et une partie principale étendue, et

- une lame hélicoïdale (2) s'étendant autour de la tige (1) et faisant saillie radialement à partir de la périphérie de la tige (1),

   dans laquelle la tige (1) comporte une première lame hélicoïdale (2) le long de la longueur de sa partie principale, ayant un angle d'inclinaison dans la direction de rotation positive et au moins une seconde lame hélicoïdale (3) située uniquement le long de la partie supérieure de la tige (1), ayant un angle d'inclinaison dans la direction opposée ou inverse de celle de la première lame hélicoïdale (2),
   caractérisée en ce qu'au moins un tube creux (31) est agencé en s'étendant parallèlement à la tige (1) et faisant communiquer une surface supérieure d'une première spire hélicoïdale avec une surface inférieure d'une seconde spire hélicoïdale de la seconde lame hélicoïdale (3).

2. Tarière selon la revendication 1,
   dans laquelle la seconde lame hélicoïdale (3) comporte une paire de spires hélicoïdales insérées entre chaque autre paire dans la direction axiale et s'étendant parallèlement à chaque autre paire autour de la tige (1).

3. Tarière selon la revendication 1 ou 2,
   dans laquelle des spires hélicoïdales adjacentes de la seconde lame hélicoïdale (3) sont reliées l'une à l'autre au niveau de leurs périphéries extérieures par l'intermédiaire d'une barrière extérieure (32).

4. Tarière selon l'une quelconque des revendications 1 à 3,
   dans laquelle une partie de transition sans aucune spire hélicoïdale est agencée le long de la tige (1) entre la première lame hélicoïdale (2) et la seconde lame hélicoïdale (3) .

5. Tarière selon l'une quelconque des revendications 1 à 4,
   dans laquelle des plaques s'étendant radialement à partir de la périphérie de la tige (1) et étant écartées dans les directions axiale et circonférentielle sont agencées entre la première lame hélicoïdale (2) et la seconde lame hélicoïdale (3).

6. Tarière selon l'une quelconque des revendications 1 à 5,
   dans laquelle la distance axiale entre des spires hélicoïdales adjacentes de la seconde lame hélicoïdale (3) est environ la moitié de la distance axiale des spires hélicoïdales de la première lame hélicoïdale (2).

7. Procédé de construction de pieux à haute friction dans le sol,
   comportant les étapes consistant à :

(a) préaléser un trou dans le sol en entraînant de manière rotative une tarière dans le sol,

(b) déverser un agent durcissant (4) dans le trou obtenu à l'étape (a),

(c) insérer un matériau de support (5) dans l'agent durcissant (4) situé dans le trou avant que l'agent durcissant (4) ne soit complètement durci, et

(d) laisser durcir l'agent durcissant (4) de sorte que le matériau de support (5) et une zone plastique (A) entourant le trou forment ensemble un pieu monolithe,

   caractérisé en ce qu'une tarière spécifique selon l'une quelconque des revendications 1 à 6 est utilisée pour préaléser,
   dans lequel, lorsque le trou est alésé, une partie du sol agitée par la rotation positive de la première lame hélicoïdale (2) est empêchée d'être poussée vers le haut par la rotation inverse de la seconde lame hélicoïdale (3) et à la place est poussée dans la zone entourant le trou, et dans lequel la zone plastique (A) est formée jusqu'à une largeur prescrite autour du trou.

Drawing