STEEL PIPE FOR REINFORCING GROUND, METHOD OF REINFORCING GROUND USING THE SAME, AND METHOD OF REINFORCING STRUCTURE

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A steel pipe ground reinforcement of the present invention is driven into a ground and injects a grouting material into the ground. The steel pipe ground reinforcement includes: a recess portion and a smooth portion that are arranged on an outer peripheral surface thereof; and a plurality of through-holes that are arranged in the recess portion or the smooth portion that communicates between the inside and outside of the steel pipe ground reinforcement.

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Description
TECHNICAL FIELD

The present invention relates to a steel pipe ground reinforcement suitable for use in a forepoling method in a tunnel construction and the like, and in a method of reinforcing a excavation wall surface. The present invention also relates to a method of reinforcing the ground using the same and a method of reinforcing a structure such as a concrete foundation using the same.

Priority is claimed on Japanese Patent Application No. 2008-009570, filed on Jan. 18, 2008, the contents of which are incorporated herein by reference.

BACKGROUND ART

For example, in a tunnel construction in the soft natural ground, a forepoling method of burying steel pipes is often adopted to reinforce the natural ground. In this method, drilling is performed with a steel pipe being fitted onto a drilling rod whose forward end portion is attached with a bit. Then, after a hole with a predetermined depth is drilled, the drilling rod is pulled out with the steel pipe left where it is. Subsequently, a grouting material such as mortar is injected into the steel pipe. A number of through-holes communicating between the inside and outside of the steel pipe are bored in a body of the steel pipe. The injected grouting material permeates into the natural ground through the through-holes, and then becomes solidified. As a result, the soft natural ground is reinforced. As for the forepoling method, a multitude of patent applications have been filed (for example, see Japanese Unexamined Patent Application, First Publication No. 2000-204870 and No. 2001-020657).

The steel pipes used in the aforementioned forepoling method are buried in the natural ground. Therefore, steel pipes with a material having high strength at comparatively low cost are used. In injecting the grouting material, it is required for the grouting material flowing out through the through-holes to sufficiently permeate into the natural ground and also to be densely filled in the gap between the natural ground and the steel pipe. Furthermore, for the buried steel pipe to be securely fixed, it is desirable that the steel pipe and the layer of the grouting material around the outer periphery of the steel pipe be securely integrated.

However, a conventional steel pipe has its outer surface formed as a smooth surface, providing no hooking between itself and the layer of the grouting material outside it. Therefore, it is not correct to say that both are secured with each other. As an improvement on this, there is a method of subjecting an outer surface of a steel pipe to a sandblast treatment or the like to make the surface rough. This method offers a close contact effect in its own way. However, in terms of securely fixing the steel pipe in the natural ground, it leaves something to be desired.

Furthermore, Japanese Unexamined Patent Application, First Publication No. 2006-022501 (JPA 2006-022501) discloses a steel pipe ground reinforcement in which a protruded spiral strip is formed on its outer periphery and a plurality of through-holes, which communicates between the inside and outside of the steel pipe for allowing a grouting material to flow out of the steel pipe, are provided in a space between the protruded spiral strip.

However, the steel pipe disclosed in the above JPA 2006-022501 has a protruded portion on its outer periphery. The protruded portion functions as an obstacle when the steel pipe is driven. In addition, the protruded portion functions as an obstacle when earth and sand are exhausted from the outer surface side of the steel pipe. This prevents the protruded portion from being formed in a large shape, resulting in difficulty to secure sufficient close contact. Furthermore, to provide a protruded portion on the outer periphery of a steel pipe, an additional step of providing a protruded portion is required after the manufacture of the steel pipe. This leads to a problem of waning productivity and higher cost.

The present invention is for solving the above problems, and has an object to provide a steel pipe ground reinforcement that, without increased manufacturing cost, offers low resistance when buried in the ground and causes itself and its surroundings to be securely in close contact with each other when a grouting material is poured. The present invention has a further object to provide a method of reinforcing the ground using the steel pipe ground reinforcement and a method of reinforcing a structure.

DISCLOSURE OF INVENTION

To solve the above problems and achieve such objects, the present invention adopts the following.

(1) A steel pipe ground reinforcement of the present invention is driven into a ground and injects a grouting material into the ground. The steel pipe includes: a recess portion and a smooth portion that are arranged on an outer peripheral surface thereof; and a plurality of through-holes that are arranged in the recess portion or the smooth portion that communicates between the inside and outside of the steel pipe ground reinforcement.

(2) The recess portion may have a cross-sectional shape with a depth of the recess portion of 0.005 D to 0.2 D and a width of the recess portion of 0.015 D to 2D where D is an outer diameter of the steel pipe, that the recess portion have a triangular shape in cross-section, and that B/H=3 to 20 where B is the width of the recess portion and H is the depth of the recess portion.

(3) The recess portion may have a cross-sectional shape with a depth of the recess portion of 0.005 D to 0.2 D and a width of the recess portion of 0.015 D to 2D where D is an outer diameter of the steel pipe, that the recess portion have a rectangular shape in cross-section, and that B/H=4 to 20 where B is the width of the recess portion and H is the depth of the recess portion.

(4) The recess portion may have a cross-sectional shape with a depth of the recess portion of 0.005 D to 0.2 D and a width of the recess portion of 0.015 D to 2D where D is an outer diameter of the steel pipe, that the recess portion have a semicircular or trapezoidal shape in cross-section, and that B/H=3 to 20 where B is the width of the recess portion and H is the depth of the recess portion.

(5) A plurality of the recess portions may be provided on a same periphery of the steel pipe.

(6) A plurality of the recess portions may be provided in a circumferential direction of the steel pipe, and that at least the recess portions that face each other be provided so as to avoid being on a same periphery of the steel pipe.

(7) A plurality of the recess portions may be provided diagonally with respect to an axis of the steel pipe.

(8) A plurality of the recess portions may be provided in parallel with respect to an axis of the steel pipe.

(9) A plurality of the recess portions may be provided in a circular shape when seen from front.

(10) Plating or resin coating may be provided on the surface of the steel pipe.

(11) A method of reinforcing the ground of the present invention includes: when reinforcing a ground, driving the steel pipe ground reinforcement according to the above (1) while drilling the ground; and after driving of the steel pipe ground reinforcement, injecting a grouting material into an inside of the steel pipe ground reinforcement to thereby inject the grouting material into an outside of the steel pipe ground reinforcement through the plurality of through-holes.

(12) A minimum inner diameter of the steel pipe ground reinforcement may be larger than an outer diameter of an inner bit that is used when the ground is drilled.

(13) A maximum outer diameter of the steel pipe ground reinforcement may be smaller than an outer diameter of an outer bit that is used when the ground is drilled.

(14) A method of reinforcing a structure of the present invention including concrete includes: when reinforcing a structure, driving the steel pipe ground reinforcement according to claim 1 while drilling the structure; and after driving of the steel pipe ground reinforcement, injecting a grouting material into an inside of the steel pipe ground reinforcement to thereby inject the grouting material into an outside of the steel pipe ground reinforcement through the plurality of through-holes.

ADVANTAGEOUS EFFECTS OF INVENTION

The steel pipe ground reinforcement according to the above (1) has a recess portion formed in an outer peripheral surface of a steel pipe. Therefore, when buried in the ground, the recess portion will not function as a resistance (an obstacle). Furthermore, when poured around the outer peripheral surface of the steel pipe, a grouting material is filled also in the recess portion, improving close contact between the steel pipe and the ground. As a result, it is possible to reduce the number of the steel pipes to be buried at the time of construction work, and hence, to reduce the construction cost and the period of construction work.

Furthermore, the steel pipe ground reinforcement according to the above (1) is provided only with a recess portion in its outer peripheral surface. Therefore, for example, after fabricating a steel pipe, the steel pipe is only passed (as it is) between the rolls provided with a protruded portion, to thereby make it possible to manufacture the steel pipe ground reinforcement. As a result, it is also possible to reduce the manufacturing cost more than the case of the conventional method without lowering production efficiency.

Furthermore, it is possible to use the steel pipe ground reinforcement according to the above (1) similarly for reinforcement of a structure such as a concrete foundation of a building. Therefore, it is possible to reinforce the structure at low cost.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a front view showing an embodiment of a steel pipe ground reinforcement according to the present invention.

FIG. 2A is a diagram showing an embodiment of a steel pipe ground reinforcement according to the present invention.

FIG. 2B is a diagram showing a modification of the steel pipe ground reinforcement according to the present invention.

FIG. 2C is a diagram showing a modification of the steel pipe ground reinforcement according to the present invention.

FIG. 2D is a diagram showing a modification of the steel pipe ground reinforcement according to the present invention.

FIG. 2E is a diagram showing a modification of the steel pipe ground reinforcement according to the present invention.

FIG. 2F is a diagram showing a modification of the steel pipe ground reinforcement according to the present invention.

FIG. 2G is a diagram showing a modification of the steel pipe ground reinforcement according to the present invention.

FIG. 2H is a diagram showing a modification of the steel pipe ground reinforcement according to the present invention.

FIG. 2I is a diagram showing a modification of the steel pipe ground reinforcement according to the present invention.

FIG. 2J is a diagram showing a modification of the steel pipe ground reinforcement according to the present invention.

FIG. 2K is a diagram showing a modification of the steel pipe ground reinforcement according to the present invention.

FIG. 3A is a diagram showing a specific example of a recess portion of a steel pipe ground reinforcement according to the present invention.

FIG. 3B is a diagram showing another specific example of a recess portion of a steel pipe ground reinforcement according to the present invention.

FIG. 3C is a diagram showing another specific example of a recess portion of a steel pipe ground reinforcement according to the present invention.

FIG. 3D is a diagram showing another specific example of a recess portion of a steel pipe ground reinforcement according to the present invention.

FIG. 4 is a diagram showing a relationship between a width and a depth of a recess portion of a steel pipe ground reinforcement according to the present invention.

FIG. 5 is a diagram showing a production line for a typical forge-welded steel pipe.

FIG. 6 is an example of a production line for forge-welded steel pipes that manufactures a steel pipe ground reinforcement according to the present invention.

FIG. 7A is a conceptual diagram of rolls used for manufacturing a steel pipe according to the present invention.

FIG. 7B is a conceptual diagram of the rolls used for manufacturing a steel pipe according to the present invention.

FIG. 8 is another example of a production line for forge-welded steel pipes that manufactures a steel pipe ground reinforcement according to the present invention.

FIG. 9 is a partial cross-sectional view of a forward end portion of a steel pipe ground reinforcement into which a drilling rod with a bit is inserted.

FIG. 10A is a diagram showing an evaluation method of a close contact force in an example.

FIG. 10B is a diagram showing an evaluation method of a close contact force in comparative examples.

FIG. 11 is a diagram comparing the effects in examples.

 DESCRIPTION OF THE REFERENCE SYMBOLS

    • 1: steel pipe
    • 2: recess portion
    • 3: through-hole
    • 4: outer bit
    • 5: steel pipe ground reinforcement

EMBODIMENTS OF THE INVENTION

Hereunder is a specific description of the present invention with reference to the drawings.

FIG. 1 schematically shows a steel pipe ground reinforcement 5 according to the present invention. The steel pipe ground reinforcement 5 includes a steel pipe 1 and recess portions 2 provided in an outer peripheral portion of the steel pipe 1. The recess portions 2 are circumferentially provided there in a regularly spaced manner. With the recess portions 2, a frictional force between the steel pipe 1 and the ground, concrete, or the like is increased.

In addition, over the whole peripheral surface of the steel pipe 1, there are arranged a plurality of through-holes 3 that communicate between the inside and outside of the steel pipe 1. A grouting material injected into the steel pipe 1 flows out to the outer surface of the steel pipe through the through-holes 3. Some of the grouting material is filled between the natural ground and the steel pipe 1 to fix the natural ground with the steel pipe 1. Some of the grouting material permeates into the natural ground and becomes solidified, to thereby reinforce the natural ground. At this time, the recess portions 2 are brought into a state of being buried in a layer of the solidified grouting material. This securely integrates both. Therefore, even if a force in the axial direction of the steel pipe 1 acts on the steel pipe 1, engagement between the recess portions 2 and the grouting material layer produces hooking resistance, preventing the movement of the steel pipe 1.

As described above, with the steel pipe ground reinforcement 5 of the present embodiment, it is possible to improve the close contact between the steel pipe 1 and the natural ground. This can fix the steel pipe 1 with the natural ground more securely. In FIG. 1, reference numeral 4 denotes an outer bit.

The manufacturing method of the steel pipe ground reinforcement 5 requires only that, after fabrication of a steel pipe 1 on a steel pipe production line, recess portions 2 be provided in the surface of the steel pipe 1 by means of a pressing device under hot or warm conditions. Therefore, productivity is substantially the same as that of an ordinary pipe fabrication step.

FIGS. 2A to 2K show specific examples of another shape of the recess portions 2.

In FIGS. 2A, 2B, and 2C, the steel pipe 1 has a plurality of recess portions 2A to 2C, respectively, in the circumferential direction. The recess portions 2A to 2C are formed in a regularly spaced manner in the axis direction. The steel pipe ground reinforcement 5 of FIG. 2A is an example in which a plurality of (two in an opposing manner, in the figure) recess portions 2A are provided on the same circumference of the steel pipe 1. The steel pipe ground reinforcement 5 of FIG. 2B is one in which the recess portions 2 formed not by mill rolls but by a reciprocal-type pressing apparatus capable of moving closer to or further away from the steel pipe 1A. The recess portion 2B has substantially the same depth on the circumference of the steel pipe 1. The steel pipe ground reinforcement 5 of FIG. 2C is an example in which a plurality of recess portions 2C are provided in the circumferential direction of the steel pipe 1 and at least facing recess portions 2C of these do not exist on the same circumference.

With the facing recess portions 2C being arranged in a staggered manner so as not to exist on the same circumference as is the case with the steel pipe 1 of FIG. 2C, it is possible to improve the strength of the steel pipe 1 at positions where the recess portions 2C are arranged compared with the case of the steel pipe 1 of FIG. 2A. The steel pipe 1 shown in FIG. 2C is suitable for the case in which higher strength of the steel pipe ground reinforcement 5, especially at portions where the recess portion 2 are arranged, is required. In the example of the staggered arrangement of the recess portions 2C, it is desirable that the recess portions 2C be formed so that their opposing portions do not overlap with each other by the whole width.

FIGS. 2D to 2G are diagrams showing a steel pipe 1 in which recess portions 2D to 2G with long edges in directions diagonal to the axis of the steel pipe 1 are formed, respectively. FIG. 2H and FIG. 2I are diagrams showing a steel pipe 1 in which recess portions 2H, 2I with long edges in a direction parallel to the axis of the steel pipe 1 are formed, respectively. FIG. 2J and FIG. 2K are diagrams showing a steel pipe 1 in which round spot-like (circular) recess portions 2J, 2K are formed, respectively. It is possible to freely select the shape of the spot-like recess portions 2J, 2K from an ellipse, a polygon, and the like depending on easiness of their formation and the like. Furthermore, it is possible to freely select whether to arrange the recess portions 2D to 2G on the same periphery, or whether to arrange them in a staggered manner.

Here, the shape of the recess portions 2D to 2G is limited only in height. The only requirement is that space large enough to allow a drilling bit to pass through the inside of the steel pipe 1 is secured.

In the steel pipe ground reinforcement 5 of the present invention, the recess portions 2 are formed under hot or warm conditions as will be described later. Therefore, it is possible to manufacture the steel pipe 1 with ease even if it has a thickness of, for example, 2 mm or greater. Consequently, when a thick steel pipe ground reinforcement 5 is manufactured and is driven into, for example, the ground while being rotated a twisting force does not act on the steel pipe ground reinforcement 5 to be bent or to cause its forward end to be crushed. In addition, it is possible to easily manufacture a steel pipe with an outer diameter of 50 mm or greater that can be put to practical use as a steel pipe ground reinforcement 5.

In the case where the steel pipe ground reinforcement 5 according to the present invention is used for applications in which especially corrosion resistance is required, it is desirable that a surface of the steel pipe 1 provided with the recess portions 2 be subjected to plating or resin coating, to thereby deliver favorable corrosion resistance.

As for the recess portion 2 of the steel pipe 1, its conceivable cross-sectional shape is basically a triangle or a rectangle, as shown in FIGS. 3A to 3D. A semicircle or a trapezoid may be regarded as substantially a triangle. In any case, a depth H of the recess portion 2 (which denotes a depth at its deepest point) requires 0.005×D (where D is an outer diameter of the steel pipe) or greater in order to obtain a frictional force between the peripheral surface of the steel pipe 1 and the ground, concrete, or the like. However, an effect of improving a frictional force is saturated above 0.2×D. Therefore, the depth H of the recess portion 2 is set to 0.005×D to 0.2×D. Furthermore, a width B of the recess portion 2 requires 0.015×D or greater to obtain the frictional force. However, above 2×D, an effect of improving a frictional force is small. Consequently, the depth H is required to be set to 2×D or less.

Furthermore, for optimizing the shape of the recess portion 2 under the above preconditions, it is important to meet the following requirements. That is, when the cross-sectional shape of the recess portion 2 is a triangle, B/H=3 to 20. When the cross-sectional shape of the recess portion 2 is a rectangle, B/H=4 to 20. When the cross-sectional shape of the recess portion 2 is a semicircle or a trapezoid, B/H=3 to 20.

Hereunder is a description of how the above relationship of B/H is derived with reference to FIG. 4. As a precondition, a fracture mode for the recess portion 2 is determined by either the shear strength of the soil cement outside the recess portion 2, that is, at the base of the triangle (the width B of the recess portion 2) in FIG. 4 or the bearing strength of soil cement inside the recess portion 2. At this time, if a first of the fracture modes obviously precedes a second fracture mode, it is conceived that the strength is decreased because the strength is determined by the first fracture mode. Therefore, to consider the optimum shape of the recess portion 2, it is necessary to determine such a shape to allow for simultaneous occurrence of the above two fracture modes.

As a result, in the optimum shape of the recess portion 2, it is required that a bearing pressure P imparting a bearing strength and a shearing force S imparting a shear strength satisfy a conditional equation for equilibrium expressed as equation (1) as follows:


S=Pcosθ  (1)

where θ is an angle formed by the surface of the steel pipe 1 and the entry side surface of the recess portion 2.

Here the shearing force S is defined by (area on which the shearing force acts)×(shearing force). Therefore, the shearing force S is formulated as an equation (2) shown below. Here, it is assumed that the recess portions 2 are arranged over the whole periphery of the steel pipe 1. A shear area is expressed by a product of a peripheral length 1D of the steel pipe 1 and a width B of the recess portion 2 (base portion of the triangle) as follows:


S=tτ·B·π·D  (2).

On the other hand, the bearing pressure P is a bearing stress multiplied by an area on which the bearing stress acts, which is formulated as an equation (3) as follows:


P=H·σb·cosθ·π·D  (3)

where τ is a shear stress, D is an outer diameter of the steel pipe, and σb is a bearing pressure (bearing stress, dimension of force/area).

Substitution of the equations (2), (3) into the equation (1) yields equations (4), and hence (4′), as follows:


τ·B=(H·σb·cosθ)cosθ  (4)


∴B/H=σb·cos2θ/τ  (4′).

The equation (4′) is a modification of the conditional equation of force equilibrium when the optimum shape is provided to the recess portion 2. Here, the equation (4′) is solved for the case where an angle (θ) formed by a side surface of the recess portion 2, that is, an oblique surface of the triangle in FIG. 4 and a surface of the steel pipe 1 is 45 degrees (hereinafter, referred to as a triangular shape) and 90 degrees (hereinafter, referred to as a rectangular shape).

Letting 0=90° (the recess portion 2 have a rectangular shape),


B/H=σb/τ  (5).

For example, substitution of the soil cement's bearing strength σb=1 N/mm2 and its shear strength τ=0.1 N/mm2 into the equation (5) yields B/H=10 (the width of recess portion 2 is ten times its height). As a result, the recess portion 2 has a shape of a rectangle with a length of 10H and a height of H.

On the other hand, if the final shape of the recess portion 2 is a triangular shape and also the triangle is isosceles, then B, H, and θ satisfy a relational expression (6) as follows:


tan θ=2·H/B  (6).

Substituting this into the equation (4′) yields


2/(sin θ·cosθ)=σb/τ  (7).

Substitution of the soil cement's bearing strength σb=1 N/mm2 and its shear strength τ=0.1 N/mm2 into this equation (7) yields


sin θ·cos θ=⅕  (8)


sin 2θ=⅖=0.4  (8′).


∴θ=11.8

Letting the relationship between the soil cement's (concrete's) bearing strength σb and its shear strength τ be


1/20≦Σ/σb≦ 2/9 (typically, τ/σb=approximately 1/10),

(a) if the recess portion 2 has a shape of a triangle, the relationship between the width B and the depth H of the recess portion 2 is obtained from the equation (5) as:


4.5≦B/H≦20.0

(b) if the recess portion 2 has a shape of a triangle, a proper range of 0 is obtained from the equation (7) as:


5.8≦θ≦31.4

At this time, the relationship between the width B and the depth H of the recess portion 2 is obtained from the equation (6) as:


3.3≦B/H≦19.8

Here, in the case of the recess portions 2 with a shape diagonal or parallel to the axis direction of the steel pipe 1 or the spot-like recess portions 2 as shown in FIGS. 2D to 2K, the aforementioned equations may be applied also to the A-A cross-section of FIG. 2D, the H-H cross-section of FIG. 2H, and the C-C cross-section of FIG. 2J.

As described above, in the present invention, B/H is prescribed as follows:

(1) If the cross-section of the recess portion 2 has a triangular shape, B/H=3 to 20

(2) If the cross-section of the recess portion 2 has a rectangular shape, B/H=4 to 20

(3) If the cross-section of the recess portion 2 has a semicircular or trapezoidal shape, B/H=3 to 20.

Next is a description of a manufacturing method of the steel pipe ground reinforcement 5 according to the present invention.

In the present invention, any of the following steps of a), b), c), and d) may be used. The present invention will be described for the case of a production line for forge-welded steel pipes by way of representative example.

a) After being welded by electric resistance welding on a steel pipe production line for electric resistance welding, a steel pipe is heated and its surface is pressed by a pressing device.

b) After a steel pipe is welded on a steel pipe production line for hot or warm welding, its surface is pressed by a pressing device.

c) After a steel pipe is butt-welded on a steel pipe production line for forge-welding, its surface is pressed by a pressing device.

d) After a tube is fabricated on a seamless steel pipe production line, its surface is pressed by a pressing device.

FIG. 5 is a diagram showing a typical production line for forge-welded pipes.

Steel belts 10 that are cut into a desired width are formed in a circular cross-section by rolls 21. After that, both corresponding ends thereof are heated to high temperatures, pressed to each other, and butt-welded by rolls 22 into a pipe. By narrowing the butt-welded pipe down with following rolls 23 to 34, the pipe is reduced in diameter to a predetermined size. The pipe is then cut by a cutter 38 into predetermined lengths, and their shapes are adjusted by following rolls 35 to 37. Thus, forge-welded pipes 11 (steel pipes 1) are manufactured.

FIG. 6 is an embodiment of a production line for forge-welded pipes.

A difference from a conventional production line lies in that only the final rolls 34 of the reduction rolls before the cutter 38 are modified. As shown in FIGS. 7A, 7B, in the roll 34, one or more protruded portions α are provided on the peripheral surface of the roll 34 in the roll axis direction. The protruded portion a functions as a pressing device. The roll 34 provided with the protruded portions α is used on one or both of the upper and lower sides. FIGS. 6, 7A, and 7B show a set of two rolls 34a, 34b on the upper and lower sides, respectively. However, a set of more than three rolls may be provided. By the rolls 34 with such protruded portions α, a pressure is applied to a forge-welded pipe 11 at high temperatures (approximately 1200 to 1300° C.). Therefore, in portions of the forge-welded pipe 11 brought into contact with the protruded portions α, recess portions 2 are formed with ease. In addition, compared with cold working, a shape of the recess portion 2 is formed in accordance with the shape of the protruded portion a of the roll 34. Consequently, it is possible to obtain recess portions 2 with an acuter angle. After that, the forge-welded pipe 11 is cut into predetermined lengths and sized. Thus, a steel pipe ground reinforcement 5 with recess portions 11a of the present invention is completed.

Here, to modify the recess portions 2 on the forge-welded pipe 11 in their height, width, or pitch, the protruded portions a of the roll 34 may be modified in their shape or pitch. Furthermore, in order to form recess portions 2 on the forge-welded pipe 11 at the same location, protruded portions a may be provided on both of the upper and lower rolls 34a, 34b, and the positions of protruded portions a of the upper and lower rolls 34a, 34b may be matched at an initial stage. In this condition, the upper and lower rolls 34a, 34b may be coupled via, for example, a single drive source and a single universal joint or the like, to thereby synchronously drive the upper and lower rolls 34a, 34b

It is desirable that the protruded portion a formed on the roll 34 be shaped so as to be highest at its central portion and be lower as it is closer to the edge portions of the roll 34, as shown in FIG. 7B. The reason is this. The central portion and edge portion of the roll 34 have different peripheral velocities. The edge portion, which has a larger diameter, has a higher peripheral velocity. Accordingly, the roll 34 rotates faster than the passing pipe, applying an unnecessary force on the forge-welded pipe 11. As a result, excessive deformation or distortion is produced in the forge-welded pipe 11.

FIG. 8 shows another example of a production line for forge-welded pipes.

This production line is an example in which a dedicated pressuring apparatus (pressing device) 39 for applying pressure to the forge-welded pipe 11 (steel pipe 1) is provided between the reduction rolls 34 and the cutter 38. As the pressurizing apparatus 39, the aforementioned roll 34 with protruded portions a may be used. Alternatively, one of a type that applies pressure to the forge-welded pipe 11 from top and bottom may be used. It is desirable that the pressurizing apparatus 39 have a mechanism capable of moving forward and backward with respect to the forge-welded pipe 11 or capable of moving forward and backward with respect to the moving direction of the forge-welded pipe 11.

With the pressurizing apparatus 39 being capable of moving closer to and away from the forge-welded pipe 11, it is possible to form the recess portion 2 at an optional position of the forge-welded pipe 11. Even when the pitch between the recess portions 2 is to be modified, the rolls 34 need not be replaced. Furthermore, with this function, it is possible for the recess portions 2 to be controlled by control portions so as not to be placed at cut positions of the forge-welded pipe 11 that are previously recognized by the control portion. When the recess portions 2 coincide with the end portions of the forge-welded pipes 11, different forge-welded pipes 11 have end faces different in diameter and shape. This makes it difficult, for example, to connect the forge-welded pipes 11 to each other.

Furthermore, with the pressurizing apparatus 39 being capable of moving in the moving direction of the forge-welded pipe 11, it is possible to move the reduced-diameter formation apparatus in synchronization with a movement of the forge-welded pipe 11. This makes it possible to unboundedly form of the shape of the recess portion 2 without excessive distortion of the forge-welded pipe 11 produced by a difference in peripheral velocity between the central portion and edge portion of the roll 34 as described above.

While description has been for the dedicated apparatus, the functions of the dedicated apparatus may be provided to rolls 34, which are existing final reduction rolls with protruded portions α.

As described above, the pipe fabrication method may be any of the pipe fabrication method by electric resistance welding, the pipe fabrication method in which pipes are hot- or cold-welded, the pipe fabrication method by forge-welding, and the seamless pipe fabrication method. The surface of the fabricated pipe may be pressed by a pressing device under warm or hot conditions that are brought about by heating or the like during or after the pipe fabrication. This enables online manufacture of a steel pipe 1 with recess portions 2.

The steel pipe 1 manufactured by any of the manufacturing methods has the recess portions 2 formed under hot conditions. Therefore, it is possible to easily manufacture the steel pipe 1 even if the steel pipe 1 has a thickness of 2 mm or greater. For example, when the steel pipe 1 is rotated to be driven into the ground as a steel pipe pile, it does not occur that a twisting force acts on the steel pipe 1 to cause the steel pipe 1 to be bent or its forward end to be crushed, because the steel pipe 1 is thick. Furthermore, it is also possible to easily manufacture a pipe with an outer diameter of 50 mm or greater that can be put to practical use as a steel pipe ground reinforcement 5. In addition, its production efficiency is the same as that when typical forge-welded steel pipes are manufactured.

With a steel pipe being manufactured by dedicated roll(s) provided with protrusion(s) on a production line for typical steel pipes by the steel pipe manufacturing method as described above, it is possible to continuously provide recess portions 2 simultaneously with the manufacture of the steel pipe. Furthermore, with modification in shape of the protruded portion(s) α of the dedicated roll(s) 34, it is possible to provide recess portions 2 with optional shape, pitch, and arrangement. In addition, this eliminates the necessity of working in another step, making it possible to provide a steel pipe 1 with recess portions 2 at a very low cost.

In the steel pipe ground reinforcement 5 of the present invention, not externally-protruded shapes but internally-protruded shapes (that is, recess portions 2) are provided in the surface of the steel pipe 1. Thereby, when the steel pipe 1 is driven, the recess portions 2 do not function as obstacles. Furthermore, it is possible to manufacture a steel pipe ground reinforcement 5 with large recess portions 2 capable of securing sufficient close contact, at a low cost without reducing productivity

Then, in the steel pipe 1 provided with the recess portions 2, a plurality of through-holes 3 are bored. The through-holes 3 may be provided in the recess portions 2 on the periphery of the steel pipe 1 or in a smooth portion outside the recess portions 2. Alternatively, through-holes 3 may be provided in both. The diameter and arrangement of through-holes 3 are required only to allow the grouting material to spread over the whole length of the steel pipe 1, and hence may be optionally determined according to the characteristic and condition of the grouting material and to the condition of the ground.

FIG. 9 is a diagram showing a positional relationship among drilling bits 4, 7 and the steel pipe ground reinforcement 5. The outer bit 4, while rotating by the motive force transmitted from the rod 6 and the inner bit 7, drills the ground and the like ahead. Behind the outer bit 4, the steel pipe ground reinforcement 5 of the present invention is arranged. Therefore, the outer diameter of the steel pipe ground reinforcement 5 is required only to be smaller than the outer diameter of the outer bit 4.

The rod 6 and the inner bit 7 extend through the inside of the steel pipe ground reinforcement 5. Therefore, the minimum inner diameter of the steel pipe 1 is required to be larger than the maximum outer diameter of the inner bit 7. So long as the above conditions are met, the recess portion 2 on the periphery of the steel pipe 1 can be made deeper.

To use the steel pipe ground reinforcement 5, the drilling rod 6 with the inner bit 7 attached to its forward end portion is inserted through the steel pipe 1, as shown in FIG. 9. In this condition, the rearward end portions of the drilling rod 6 and the steel pipe 1 are connected to a rock drill (not shown in the figure) such that the inner bit 7 of the forward end portion is set to protrude past the outer bit 4 of the steel pipe 1. Then, boring is performed while strike, rotation, and thrust are being applied to the drilling rod 6 and the steel pipe 1 from the rock drill. During the boring, water or compressed air is supplied from the rock drill, and is discharged from the forward end portion of the outer bit 4. Most of the cuttings produced by the boring pass through the inside of the steel pipe 1 and are discharged. However, part of them pass over the outside of the steel pipe 1 and are discharged backwardly.

After completion of boring a hole with a predetermined depth and the steel pipe 1 is buried into the natural ground, the drilling rod 6 together with the inner bit 7 is pulled out backwardly from the steel pipe 1. After that, an injection apparatus (not shown in the figure) is attached to the rearward end portion of the steel pipe 1, and a grouting material is injected into the steel pipe 1. The grouting material fills the steel pipe 1, and flows to the outside through the multitude of through-holes 3 provided in the steel pipe 1. Then, while flowing along the outer surface of the steel pipe 1, the grouting material permeates into the natural ground and becomes solidified. Thereby, the natural ground is reinforced.

The steel pipe 1 has the recess portions 2 formed in its outer peripheral portion. Therefore, the recess portions 2 are brought into a state of being buried in a layer of the solidified grouting material. This securely integrates both. As a result, even if a force in the axis direction acts on the steel pipe 1, engagement between the recess portions 2 and the grouting material layer produces hooking resistance, preventing movement of the steel pipe 1. Thus, the steel pipe 1 is securely fixed in the natural ground. The recess portions 2 have a predetermined cross-sectional shape. Therefore, it is possible to improve both hooking resistance for preventing displacement and fluidity of grouting material and cuttings.

The recess portions 2 are typically formed by milling rolls. Therefore, their cross-sectional shape is a smooth shape without an edge or a corner. Therefore, the cuttings and the grouting material smoothly flow, preventing the partial formation of clogging or a gap. As a result, not only a discharge state of the cuttings is favorable, but also close contact between the grouting material and the steel pipe 1 improves. Thereby, it is possible to achieve excellent ground enforcement. In the above description, a combination of the ring-like outer bit 4 affixed to the forward end portion of the steel pipe 1 and the inner bit 7 attached to the forward end portion of the drilling rod 6 is adopted as a bit. However, an expandable bit capable of expanding and shrinking its diameter may be used. During boring, a hole of the bit may be bored so that its diameter is larger than the outer diameter of the steel pipe 1. At the end of boring, the diameter of the expandable bit may be shrunk so that it is smaller than the inner diameter of the steel pipe 1, and the bit may be pulled out backwardly. When the expandable bit is used, the ring bit (outer bit) 4 need not be fixed to the forward end portion of the steel pipe 1.

EXAMPLES

Next is a description of a comparison of close contact forces on the following levels. The number of the levels is three as shown in Table 1. Size: 76.3 mmφ×3.2 mm t×6 m L, Standard: JIS G 3444 STK

TABLE 1 Comparative Example 1 Straight pipe Typical straight pipe Comparative Steel pipe with Externally spiral deposit-welded steel pipe Example 2 protrusions (equivalent to Japanese Unexamined Patent Application, First Publication No. 2006-022501) <Deposit dimension> height: 5 mm × width: 5 mm × lead: 300 mm, lead angle: 30 degrees Present Steel pipe with Steel pipe provided with recesses Example recesses <Step shape> Step shape: triangular step portions provided in circumferential direction, equally spaced in pipe axis direction (space between steps: 200 mm) depth: 8 mm × width: 40 mm

In the evaluation method of the close contact forces, the steel pipe ground reinforcement 5 is buried in a soil cement 100 and a load is applied thereon by an upper portion 101, as shown in FIGS. 10A, 10B. Thereby, a maximum load was measured (Degree of close contact was measured at a maximum load). FIG. 10A is a diagram schematically showing an evaluation method when the steel pipe ground reinforcement 5 of the present invention is buried. FIG. 10B is a diagram schematically showing an evaluation method when a steel pipe 102 provided with protruded portions 103 is buried as a comparative example 2.

As the soil cement 100, a mixture of soil and solidification material was used. Two types of soil were used: cohesive soil and sandy soil. The cohesive soil had a particle size of 0.001 to 0.005 mm. The sandy soil had a particle size of 0.074 to 2.000 mm. As a result, it has been recognized that the present invention has a heavier push-out load, that is, a greater close contact force than Comparative Examples, as shown in FIG. 11.

The manufacturing cost of the steel pipe ground reinforcement formed with the recess portions of the present invention is substantially the same as the Comparative Example 1. On the other hand, for the steel pipe with protrusions of Comparative Example 2, a deposit welding cost for forming the protruded portions is added to a pipe fabrication cost. This results in a higher cost. Therefore, it is understood that the present invention is excellent also in cost.

INDUSTRIAL APPLICABILITY

As is clear from the above description, the steel pipe ground reinforcement according to the present invention is one in which recess portions are formed in an outer peripheral surface of a conventional steel pipe, and is capable of reinforcing the ground in a tunnel construction and the like or capable of reinforcing a structure such as a concrete foundation at a low cost with efficiency.

Claims

1. A steel pipe ground reinforcement that is driven into a ground and injects a grouting material into the ground, the steel pipe ground reinforcement comprises:

a recess portion and a smooth portion that are arranged on an outer peripheral surface thereof; and
a plurality of through-holes that are arranged in the recess portion or the smooth portion that communicates between an inside and an outside of the steel pipe ground reinforcement.

2. The steel pipe ground reinforcement according to claim 1,

wherein the recess portion has a cross-sectional shape with a depth of the recess portion of 0.005 D to 0.2 D and a width of the recess portion of 0.015 D to 2D where D is an outer diameter of the steel pipe, and
wherein the recess portion has a triangular shape in cross-section, and B/H=3 to 20 where B is the width of the recess portion and H is the depth of the recess portion.

3. The steel pipe ground reinforcement according to claim 1,

wherein the recess portion has a cross-sectional shape with a depth of the recess portion of 0.005 D to 0.2 D and a width of the recess portion of 0.015 D to 2D where D is an outer diameter of the steel pipe, and
wherein the recess portion has a rectangular shape in cross-section, and B/H=4 to 20 where B is the width of the recess portion and H is the depth of the recess portion.

4. The steel pipe ground reinforcement according to claim 1,

wherein the recess portion has a cross-sectional shape with a depth of the recess portion of 0.005 D to 0.2 D and a width of the recess portion of 0.015 D to 2D where D is an outer diameter of the steel pipe, and
wherein the recess portion has a semicircular or trapezoidal shape in cross-section, and B/H=3 to 20 where B is the width of the recess portion and H is the depth of the recess portion.

5. The steel pipe ground reinforcement according to claim 1,

wherein a plurality of the recess portions are provided on a same periphery of the steel pipe.

6. The steel pipe ground reinforcement according to claim 1,

wherein a plurality of the recess portions are provided in a circumferential direction of the steel pipe, and
wherein at least the recess portions that face each other are provided so as to avoid being on a same periphery of the steel pipe.

7. The steel pipe ground reinforcement according to claim 1,

wherein a plurality of the recess portions are provided diagonally with respect to an axis of the steel pipe.

8. The steel pipe ground reinforcement according to claim 1,

wherein a plurality of the recess portions are provided in parallel with respect to an axis of the steel pipe.

9. The steel pipe ground reinforcement according to claim 1,

wherein a plurality of the recess portions are provided in a circular shape when seen from front.

10. The steel pipe ground reinforcement according to claim 1,

wherein plating or resin coating is provided on the surface of the steel pipe.

11. A method of reinforcing a ground, comprising:

when reinforcing a ground, driving the steel pipe ground reinforcement according to claim 1 while drilling the ground; and
after driving of the steel pipe ground reinforcement, injecting a grouting material into an inside of the steel pipe ground reinforcement to thereby inject the grouting material into an outside of the steel pipe ground reinforcement through the plurality of through-holes.

12. The method of reinforcing a ground according to claim 11,

wherein a minimum inner diameter of the steel pipe ground reinforcement is larger than an outer diameter of an inner bit that is used when the ground is drilled.

13. The method of reinforcing a ground according to claim 11,

wherein a maximum outer diameter of the steel pipe ground reinforcement is smaller than an outer diameter of an outer bit that is used when the ground is drilled.

14. A method of reinforcing a structure including concrete, comprising:

when reinforcing a structure, driving the steel pipe ground reinforcement according to claim 1 while drilling the structure; and
after driving of the steel pipe ground reinforcement, injecting a grouting material into an inside of the steel pipe ground reinforcement to thereby inject the grouting material into an outside of the steel pipe ground reinforcement through the plurality of through-holes.
Patent History
Publication number: 20110038675
Type: Application
Filed: Oct 1, 2009
Publication Date: Feb 17, 2011
Applicant:
Inventors: Tomohiro Nakaji (Tokyo), Yuki Motegi (Tokyo), Tatsuya Yamamoto (Tokyo), Tetsu Satoh (Tokyo)
Application Number: 12/863,134
Classifications
Current U.S. Class: Columnar Structure (e.g., Pier, Pile) (405/231); Injector (405/269)
International Classification: E02D 3/12 (20060101);