JPS6141832Y2 - - Google Patents

Description

[Detailed explanation of the idea]

The present invention relates to a boring bit used in the earth anchor construction method. The earth anchor method is a type of civil engineering method, and as shown in Figure 1, it is a construction method used by subways to construct underground structures such as building basements on soft ground. That is, (1) concrete is poured into a trench a dug in the ground to create an underground wall b (Fig. 1 A, B). (2)
The earth and sand between underground walls b are discharged, and boring is carried out from underground walls b into the ground for about 5 to 20 m using boring machine C (Fig. 1 C and D). The tip of the boring at this time is as shown in FIG. 2, and is rotated while spouting high-pressure water from the tip. After the boring is completed, as shown in FIG. 3, the wire rope e is inserted into the boring bit d and the drill pipe 5 is pulled out, leaving the boring bit d in the soil. (3) Press concrete into the bored hole along the wire rope e to create a concrete mass g with the boring bit d as the core (Fig. 1E). (4) After curing the concrete mass g, tighten the wire rope e with a hydraulic jack and fix it in that state. (5) Repeat steps (2) to (4) above several times to excavate to a predetermined depth (Fig. 1F). The conventional boring bit d used in the above-mentioned earth anchor construction method is shown in Fig. 4, and the chevron-shaped blade h provided at its tip is symmetrical in the rotational direction, and a carbide chip i is embedded in the cutting edge. Something was used. Although the conventional boring bit described above is a forged product, the groove in which the carbide tip i is embedded must be machined, and the carbide tip i is made of an expensive material, so it must be ground every time it is bored. It was uneconomical to leave it inside. The present invention was developed in consideration of the above points, and the shape of the blade has been devised to maintain sharpness without using carbide tips, reducing the unit cost per piece. The object of the present invention is to provide a boring bit that can reduce such costs. The structure of the drawing will be explained based on the embodiment shown in FIG. 5 and below. 1 in the figure is a boring bit, which is made of a cast steel product made of wear-resistant steel. A plurality of chevron-shaped blades 2 are provided radially at the tip of the boring bit 1. A bisector 3 of the apex angle of the chevron blade 2 in a cross section along the circular arc in the rotation direction of the chevron blade 2 is inclined by β in the rotation direction of the bit. Assuming that the blade surface angles on both sides of this bisector 3 are α, the appropriate angles for this blade shape were found to be 30°≦α≦40° and 60°≦β≦75° as a result of experiments. . This cutting edge is also subjected to flame hardening treatment. 4 in the diagram
is a hole for spouting water. The number of chevron-shaped blades 2 having the above shape can be set appropriately depending on the diameter of the bit, but 4
The number of pieces is good. The components of Bit 1 above are shown in the table below.

[Table] Next, the bisector 3 of the blade surface angle α and the apex angle of the chevron blade 2
Drilling efficiency (mm/s) of test results of drilling using multiple boring bits with different inclination angles β
are shown in the table below. The strata in which this test was conducted were gravel from 0 to 12.5 m, and clay from 12.5 to 18.5 m.

[Table] From the above test results, the blade surface angle α of the boring bit and the inclination angle β of the bisector of the apex angle of the chevron blade 2
The drilling efficiency was highest when 30°≦α≦40° and 60°≦β≦75°. The present invention is as described above, and in a boring bit for the earth anchor construction method in which a plurality of chevron blades 2 are provided radially on the tip surface, the cross-sectional shape of the chevron blades 2 along the circular arc in the rotational direction is
The inclination angle of the bisector 3 of the apex angle in the rotation direction is β,
When the blade surface angles on both sides of bisector 3 are α,
Since the boring bit 1 is constructed with 30°≦α≦40° and 60°≦β≦75°, rotate this boring bit 1 in the direction in which the bisector 3 of the apex angle of the chevron blade 2 is inclined. By using this, the drilling efficiency can be greatly improved compared to the case of a conventional chevron-shaped blade having a symmetrical shape in the direction of rotation. In addition, due to this high drilling efficiency, there is no need to use a carbide tip for the cutting edge as in the past, which reduces the cost per piece and reduces the cost of boring bits in the earth anchor method. can do.

[Brief explanation of the drawing]

A, B, C, D, E, and F in Fig. 1 are explanatory diagrams of the earth anchor construction method, Fig. 2 is a sectional view showing the tip of the boring in this earth anchor construction method, and Fig. 3 is an explanatory diagram of its operation. 4 is a perspective view showing a conventional boring bit, FIG. 5 is a perspective view showing a boring bit according to the present invention, and FIG. 6 is a sectional view of the chevron-shaped blade. 1 is the boring bit, 2 is the chevron blade, and 3 is the center line.

Claims (1)

[Scope of utility model registration request] In a boring bit for the earth anchor construction method in which a plurality of chevron blades 2 are provided radially on the tip surface, the cross-sectional shape of the chevron blade 2 along the circular arc in the rotation direction is defined as the bisector 3 of the apex angle of the chevron blade 2. When the inclination angle in the direction of rotation is β and the blade surface angle is α on both sides of bisector 3, 30°≦α≦40°, 60°≦β≦75
A boring bit used in the earth anchor construction method, which is characterized by the following characteristics: