MULTI-SHAFT EXCAVATING DEVICE

Abstract: A reliable multi-shaft excavating device for forming a linear continuous wall unit comprises three mixing shafts (5A, 5B, 5C) for use in forming in the ground a continuous wall, and a housing (11) for maintaining intervals between said mixing shafts (5A, 5B, 5C) provided therein with first transfer means (14) rotated by the middle mixing shaft (5B), second transfer means (15) in engagement with said first transfer means (14), third transfer means (18) that is integral with said first transfer means (14), fourth transfer means (21) in mesh engagement with said third transfer means (18) and secured to a rotating shaft (19) perpendicular to a straight line connecting the centers of said mixing shafts, and sideward expanded cone-shape cutters (22) securely provided on the ends of said rotating shaft (19). According to the present invention, all the triangular projecting portions that have been left uncut are cut by cutters, and it is possible to form in the ground a continuous wall unit having semi-circular ends and linear sides. Here, since the above mentioned cutters are in a cone shape such as a frustoconical shape, even if the distances between the mixing shafts are long, most of the triangular projecting portions (portions that have not been excavated) can be excavated, and portions left uncut disintegrate naturally by their self weights, vibrations, and others. In other words, according to the present invention, it is possible to make longer portions between the mixing shafts. In addition, it is possible to reduce time and labor to be spent for forming a continuous wall unit by making longer portions between the mixing shafts.

Description: The present invention relates to a multi-shaft drilling apparatus having three rotatable auger shafts, for use in forming a continuous wall under the ground. 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 4. 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 truncated cones. 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 guide shaft. 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 shaft. 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 invention. 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 5. 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 shafts 5. 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 slightly outwards. (5) The reliability is much higher as compared with a chain drive, since a gear drive can be employed.

Claims: A multi-shaft drilling apparatus having three auger shafts (5), for forming a continuous wall under the ground, said apparatus including a housing (11) arranged to maintain the pitch between said auger shafts, said housing incoporating: first drive transfer means (14) rotatable around the central one of said auger shafts; a pair of second drive transfer means (15,17) engaging with said first transfer means; third drive transfer means (18) integral with said second drive transfer means (17) ; fourth drive transfer means (21) engaging with said third drive transfer means and being fixed to a rotary shaft (19) which crosses at right angles a straight line (L) connecting the center of said auger shafts; and cone-shaped cutters (22) fixed on both end of said rotary shaft, the cutter diameters increasing in the direction away from the said straight line (L).

Inventors: KOTAKI HIROSHI, SHIBASAKI MITSUHIRO, KOTAKI, HIROSHI, SHIBASAKI, MITSUHIRO
Applicants: CHEMICAL GROUT CO, CHEMICAL GROUTING COMPANY LTD.
Application year: 1993
Main classification: E02D5
IPC codes: E21B17, E02D17, E21B7, E02D5