The present invention relates to a multi-shaft drilling apparatus
having three rotatable auger shafts, for use in forming a continuous wall under
A soil mixing process has been widely used for forming such a wall.
In a known soil mixing process, subsoil is drilled in a wall shape and a mixed
liquid containing cement or the like is supplied from an end of an auger shaft
to mix with the in-situ soil to develop a continuous wall, which can be a cut-off
wall or a retaining wall or shoring in underground works of civil engineering.
A known multi-shaft auger machine for forming such a continuous wall
will first be described with reference to Figs. 5 and 6 of the accompanying drawings.
In this machine a drive unit 3 is mounted to move vertically on a
guide post 2 mounted on a crawler truck 1, a multi-shaft drilling apparatus 4 is
connected to the lower part of said drive unit 3, and a plurality of auger shafts
(three in this embodiment) 5A, 5B and 5C are provided in said multi-shaft apparatus
A drilling cutter 6 is mounted at the lower end of each auger shaft
nothing 5. Screw type blades 7, whose diameter is the same as the drilling cutters
6, and bar-shaped auger blades 8 are alternately located above each drilling cutter
6. The auger blades cooperate reciprocally to form a continuous wall unit by mixing
the in-situ soil with mixed liquid as aforesaid. If necessary, water retention
and sealing ability may be improved by molding H-type steels or sheet piles to
the said continuous wall.
In this multi-shaft auger machine of the prior art, triangular irregularities
are generated between the overlapping paths of rotation of the drilling cutters,
longitudinally on both sides of the continuous wall unit formed by the auger shafts,
which are not desirable as regards the strength of the wall. Therefore, the present
applicant proposed a new apparatus for forming a straight-sided continuous wall
unit, in Japanese Patent Application Publication No. 2-115406. In such apparatus,
chain driven drilling cutters are provided close to the lower ends of the auger
shafts. This is quite effective, but there is a problem of reliability because
the machine is chain driven and the chains are apt to loosen or be damaged.
JP-U-5-054637 and JP-A-5-179649 disclose other examples of multi-shaft
drilling units for forming a continuous wall under the ground.
Thus an object of the present invention is to provide an improved
multi-shaft drilling apparatus for forming a continuous wall in a straight line.
According to the invention there is provided a multi-shaft drilling
apparatus having three auger shafts, for forming a continuous wall under the ground,
said apparatus including a housing arranged to maintain the pitch between said
auger shafts, said housing incorporating:
- first drive transfer means rotatable around the central one of said auger shafts;
- a pair of second drive transfer means engaging with said first transfer means;
- third drive transfer means integral with said second drive transfer means;
- fourth drive transfer means engaging with said third drive transfer means and
being fixed to a rotary shaft which crosses at right angles a straight line connecting
the center of said auger shafts; and
- cone-shaped cutters fixed on both end of said rotary shaft, the cutter diameters
increasing in the direction away from the said straight line.
In a preferred form of the invention, gears are used as the said
first and second drive transfer means, and bevel gears are used as the third and
fourth drive transfer means.
The said cone-shaped cutters are formed as circular cones and as
A guide shaft is preferably provided at one end of the drilling unit,
the said drilling shafts being arranged in a line. Such a guide shaft can be provided
at both ends of the unit. A jet nozzle is preferably provided on the or each said
guide shaft, said nozzle preferably being on a tangent line to the outside of the
The or each guide shaft is preferably provided with a tubular guide
bit formed with a concavity which partially embraces a bit of the adjacent drilling
A multi-shaft drilling apparatus constructed as above enables a triangular
region of soil, which has conventionally remained, to be completely cut off by
the said cutters, whereby a continuous wall unit with semicircular ends and straight
sides can be formed.
Since the said cutters are cone-shaped, i.e. truncated cone-shaped,
soil of an almost triangular section can be displaced, which has not been possible
previously. Any remaining soil will collapse naturally by gravity, vibration or
other means, even if the pitch between the auger shafts is made longer. Thus the
pitch between the auger shafts can be increased by the use of the present invention,
which can reduce the time and labor involved in forming a continuous wall.
When a guide shaft is provided at one end of a line of auger shafts
centers, a guide hole is drilled first which receives the guide shaft while holes
are being drilled by the auger shafts. As a result, a number of successive holes
can be drilled with good linearity, since the guide shaft receives the reaction
force. Additionally, since a hole at the end of a series can be used as a guide
hole when a first drilling operation is completed, continuity to a second drilling
operation can be achieved. Also, if the unit is provided with jet nozzles as aforesaid,
a cross section of subsoil can be drilled in a wall shape and a drilling blade
can be washed.
An embodiment of the present invention will now be described with
reference to the accompanying drawings, in which:-
- Fig. 1 is a schematic front view of a relevant part of an embodiment of the
- Fig. 2 is a side view of Fig. 1.
- Fig. 3 is a horizontal section view showing further details.
- Fig. 4 is a section view on the line A-B-C-E of Fig. 3.
- Fig. 5 is a side view of a known unit.
- Fig. 6 is a front view of an auger shaft of the machine of Fig. 5.
In Figs. 1 and 2, the pitch between the auger shafts 5A, 5B and 5C
is maintained by the housing 11 of a cutter drive unit 10 provided with bearings.
Two pairs of cutters 22, described below, are provided on the unit 10 with their
planes parallel to a straight line L connecting the centers of the auger shafts
As seen in Figs. 3 and 4, the housing 1 of the cutter drive unit
10 is formed in an H-shape by a primary part 12 located on the center line L and
two secondary parts 13 which cross the center line L orthogonally between the
A primary gear 14 (the first transfer means) is connected to the
auger shaft 5B by serrations. The primary gear is engaged with a pair of secondary
gears 15 (the second transfer means) which are arranged on the center line L in
the primary part 12. Each secondary gear 15 is keyed to a shaft 17 which extends
vertically and carries on its upper portion a primary bevel gear 18 (the third
transfer means) projecting into the secondary part 13. A rotary shaft 19 is located
in the secondary part 13 by three pairs of bearings 20. A secondary bevel gear
21 (the fourth transfer means) engaging with the primary bevel gear 18 is keyed
to the shaft 19 on one side of two of the bearings 20, and a cutter 22 is fixed
on each end of the shaft 19. Each cutter 22 is of truncated conical shape, expanding
outwardly, so as to cut an outer triangular convex area A which is generated on
both sides of the center line L by the outer rotation loci D of the drilling cutters
6 (Fig. 6) which overlap alternately.
Consequently, when the auger shafts 5 rotate in the directions of
the arrows in Fig. 1 during drilling, due to the interaction of the four transfer
means, the pairs of cutters 22 will rotate in opposite directions as shown by
the arrows, to cut the outer part A. As a result, an area of subsoil S (Fig. 3),
of which the ends form semicircles and the sides form straight lines, is drilled
by the three outer rotation loci D and the outer surfaces of the four cutters,
to form a continuous wall U. Since the cutters rotate in opposite directions, the
rotary reaction force is relieved and good balance is achieved. Although parts
Al are not cut, these parts are very small and thus negligible. Also, the outer
auger shafts 5A and 5C can be moved on the center line L as indicated by arrow
E to minimise the other uncut parts A2.
Since the cutters are of truncated conical shape, almost all of part
A can be drilled and any remaining part which the cutters do not reach will readily
collapse under gravity, vibration or by other means, even if the pitch between
the auger shafts is made greater. Therefore, the time, labor and the other costs
involved in forming a continuous wall unit can be reduced by lengthening the pitch
between the auger shafts.
Some advantageous effects of the present invention, at least in its
preferred forms, are as follows:
- (1) A wall shaped continuous wall can be formed.
- (2) Since the cutter reaction force is relieved, the balance is good.
- (3) Various costs in forming a continuous wall may be decreased by lengthening
the pitch between the auger shafts.
- (4) The drilling range can be expanded by moving the auger shafts on both sides
- (5) The reliability is much higher as compared with a chain drive, since a
gear drive can be employed.