JP7081940B2 - Micro pile method using a gap blocker - Google Patents

Description

The present invention relates to a micropile construction method using a gap closing tool.

The micropile method is a general term for cast-in-place piles with a small diameter of 300 mm or less, because it can be constructed with compact construction equipment, can be constructed in a narrow space, and can be constructed without stopping the function of the existing structure. It is used for various purposes such as seismic reinforcement of existing structures, ground reinforcement, and slope stabilization.
In the micropile method, first, the first rod to which a drill is attached to the tip is inserted into the inside of the first casing segment whose outer peripheral portion is a cutter for outer drilling, and the first rod is inserted. A process of drilling while rotating the casing segment and the rod and injecting water is performed.

Then, at each predetermined depth, the next casing segment is detachably connected to the end of the casing segment via a joint member and added, and the next rod is detachably connected to the end of the rod. The process of adding, rotating the casing segment and the rod, and drilling holes while injecting water is performed.
The outer diameter of the outer drilling cutter is larger than the outer diameter of the casing segment in consideration of the outer diameter of the joint member, and after drilling, there is an annular gap between the drilling wall surface and the outer peripheral surface of the casing segment. It is formed.
A casing is constructed by connecting a plurality of casing segments, and when the drilled holes pass through the soft layer and reach a predetermined depth of the load bearing layer, a drill is drilled from the inside of the casing together with the rod. The process of pulling out is performed.
Then, if necessary, a reinforcing material such as a reinforcing bar is arranged inside the casing over the entire length of the casing.

Next, the inside of the casing is filled with the grout material using a grout hose.
As the grout material, cement milk, mortar material, and concrete material mixed with small-diameter aggregate can be used.
Next, a step of pulling out the casing, that is, a step of pulling out the casing segment is performed while pressure-injecting the grout material into the inside of the casing.
It is desirable that the pressurization of the grout material is performed at a pressure such that the grout material adheres to the wall surface of the drilled hole and the joint state between the grout material and the ground is strengthened.
The extraction of the casing ends when the plurality of casing segments located above are removed together with the joint member and the lower end of the first casing segment located at the lowest position approaches the uppermost portion of the load bearing layer.

Next, a step of pushing back a predetermined amount of the grout material into the grout material pressure-filled with the grout material is performed, and the portion surrounded by the casing and the portion not surrounded by the casing are formed. Create a part with an intermediate structure between.
Then, by hardening the grout material, a pile body in which a ground joint portion made of the grout material is formed in the load bearing layer can be obtained.
Next, a steel bearing plate is joined to the upper end of the casing by welding to form a connecting structure for connecting the pile head of the pile body to the structure.

By the way, when the ground is soft ground, the wall surface of the hole drilled by the outer drilling cutter at the outer peripheral portion of the tip of the first casing segment and the drilling drill collapses at the time of drilling, and the hole is drilled. Since the annular gap between the inner peripheral surface of the hole and the outer peripheral surface of the casing is closed, pressure can be applied to the grout material inside the casing in the final step.

Patent No. 4010383

However, when the location to be drilled is cohesive soil or rock, the inner peripheral surface of the drilled hole is less likely to collapse, and after drilling, the inner peripheral surface of the drilled hole and the casing segment. An annular gap is always secured between the outer peripheral surface and the outer peripheral surface of the clay.
Therefore, in the final step, pressure cannot be applied to the grout material, and a joint portion in which the grout material and the ground are firmly bonded cannot be formed directly under the casing including the periphery of the lower end of the casing.
In order to solve such a situation, conventionally, the grout material is injected once, and when the grout material is about to harden, the grout material is injected again to apply pressure to the grout material. There was a problem that the time could not be shortened and the micro pile method could not be performed efficiently.
In order to solve this situation, it is possible to use a highly viscous grout material, but in this case, the conventional pump cannot be used and the cost increases, such as the need to introduce a large pump. A problem occurs.

The present invention has been devised in view of the above circumstances, and an object of the present invention is to include holes drilled by a simple structure when the location to be drilled is cohesive ground or rock. In the final process of the micropile method, a micropile method using a gap closing tool that can efficiently perform pressure injection of grout material can be used to reliably close the annular gap between the peripheral surface and the outer peripheral surface of the casing. To provide.

In order to achieve the above-mentioned object, the present invention comprises a drilling step of passing through a soft layer and drilling to a predetermined depth of a load supporting layer while adding a casing segment, and adding the casing segment. It has a filling step of filling the inside of the casing with a grout material, a pulling step of pulling out the casing until the lower end of the casing approaches the uppermost portion of the load supporting layer, and a pushing back step of pushing back the casing by a predetermined amount. However, in the micropile method of forming a joint in which the grout material and the load support layer are firmly joined at the position of the load support layer directly under the casing, in a plane orthogonal to the extending direction of the drilled hole. From the reduced state of the contour whose cut cross-sectional shape is larger than the cross-sectional shape of the casing and smaller than the cross-sectional shape of the drilled hole, the entire circumference of the outer peripheral surface of the casing and the inner circumference of the drilled hole. A gap closing tool provided with a gap closing member that is variable to an expanded state that is in close contact with the entire circumference of the surface and an expansion means that changes the gap closing member from the reduced state to the expanded state is provided, and is positioned on the ground surface by the pulling step. The gap closing member is attached to the portion of the casing to bring the gap closing member into the reduced state, and the gap closing member is positioned in the drilled hole in the push-back step, and then by the expansion means. The gap closing member is expanded, the annular gap between the inner peripheral surface of the drilled hole and the outer peripheral surface of the casing is closed, and the grout material is pressurized and injected into the inside of the casing segment. It is characterized by.
Further, in the present invention, the gap closing member is composed of a bag body formed of a foldable material and formed in an annular bag shape through which the casing is inserted, and the casing is located on the ground surface by the pulling step. When the bag body is attached to the position and the bag body is brought into the reduced state, a member that allows the change of the bag body from the reduced state to the expanded state is wound on the reduced state. It is characterized in that it is turned to maintain the reduced state of the bag body on the casing.
Further, the present invention is configured such that the expansion means includes a filler that expands the bag by being supplied to the inside of the bag, and a tube that supplies the filler to the bag. The filler is the same grout material as the grout material filled inside the casing in the filling step.

According to the present invention , when the location to be drilled is a clay-based ground or bedrock, a desired pressure can be applied to the grout material in the final step of the micropile method, and the ground is solid due to the grout material. It is possible to reliably obtain a pile body having a joint portion.
According to the present invention , if the gap closing tool is composed of a bag body and a tube body having a simple structure, it can be manufactured inexpensively and easily, and can be easily attached to the casing in a short time. It is advantageous in increasing efficiency.
According to the present invention , it is advantageous in surely closing the annular gap between the inner peripheral surface of the drilled hole and the outer peripheral surface of the casing segment.
According to the present invention , when the location to be drilled is a clay-based ground or bedrock, a desired pressure can be applied to the grout material in the final step of the micropile method, and the ground is solid due to the grout material. It is possible to reliably obtain a pile body having a joint portion.
According to the present invention , it is advantageous to reliably arrange the gap closing member inside the drilled hole.
According to the present invention , the grout material to be injected into the casing, the pump for injecting the grout material, or the like can be used as it is, and the expanded state of the bag body can be formed inexpensively and in a short time.

(A) is a front view with a half portion of the expanded bag body as a cross section, and (B) is a BB cross-sectional view of (A). It is a front view which made the bag body in a reduced state and attached to a casing. It is a partial cross-sectional front view of the bag body expanded in the drilled hole. (A) to (I) are explanatory views of the micropile construction method using the gap closing tool.

Hereinafter, embodiments of the gap closing tool used in the micropile method according to the present invention will be described with reference to the accompanying drawings.
As shown in FIG. 4 (F), the casing C is configured by connecting a plurality of casing segments 12 by a joint 14, and the gap closing tool 20 of the present invention is used for the casing C.
As shown in FIGS. 1A and 1B, the gap closing tool 20 includes a gap closing member 22 and an expansion means 24.

In the present embodiment, the gap closing member 22 is composed of a bag body 26 formed of a foldable material in a bag shape, and FIG. 1 shows the bag body 26 in an expanded state.
As the foldable material, any material sufficient to prevent leakage of the filler filled inside the bag body 26 may be used, and various conventionally known materials can be used. However, in the present embodiment, the cloth is used. Is used.
The bag body 26 has an annular shape surrounding the casing C, and has a central hole 2602 in the center thereof.
In the present embodiment, the bag body 26 includes an inner peripheral portion 2604 located around the central hole 2602 and an outer peripheral portion 2606 located outside the inner peripheral portion 2604.
Further, on the outer peripheral portion 2606 of the bag body 26, a plurality of large diameter portions 2606A and small diameter portions 2606B are alternately provided at intervals in the axial direction of the central hole 2602 in a state where the bag body 26 is expanded. ..
With this configuration, as shown in FIG. 3, in the expanded state of the bag body 26, the bag body 26 effectively adheres to the inner peripheral surface of the hole 16 drilled by the casing C, and the ground is made of cohesive soil. In some cases, the outer peripheral portion 2606 bites into the inner peripheral surface of the drilled hole 16 and more reliably closes the annular gap S between the inner peripheral surface of the drilled hole 16 and the outer peripheral surface of the casing C. It is designed so that it can be done.

As shown in FIG. 2, the bag body 26 has a cross-sectional shape of a hole 16 in which a cross-sectional shape cut in a plane orthogonal to the extending direction of the drilled hole 16 is folded on the outer peripheral surface of the casing C and the hole 16 is drilled. As shown in FIG. 3, the contour is reduced to a smaller size, and as shown in FIG. 3, it is in an expanded state in which it is in close contact with the entire circumference of the outer peripheral surface of the casing C and is in close contact with the entire circumference of the inner peripheral surface of the drilled hole 16. Is formed in.
Therefore, in the reduced state, the cross-sectional shape of the bag body 26 cut in a plane orthogonal to the extending direction of the drilled hole 16 is larger than the cross-sectional shape of the casing C and larger than the cross-sectional shape of the drilled hole 16. It has a small contour.

As shown in FIG. 1A, the expansion means 24 includes a filler that expands the bag 26 by being supplied to the inside of the bag 26, and a pipe body 28 that supplies the filler to the bag 26. It is configured to include.
The filler may be any material such as water or air that changes the bag body 26 from the reduced state to the expanded state. In the present embodiment, the holes 16 drilled in the load-bearing layer, which will be described later, and the grout material G to be filled inside the casing C are used as the filler.
The tube body 28 penetrates the upper end of the bag body 26, and the lower end opening of the tube body 28 is located inside the bag body 26.
At the position where the tube body 28 penetrates the upper end of the bag body 26, the tube body 28 and the bag body 26 are connected via a sealing member 2802 so that the filler does not leak to the bag body 26, and the tube body 28 is connected to the bag body 26 via a sealing member 2802. The pipe body 28 and the bag body 26 are connected so as to move integrally with the downward movement of the casing C.

Next, a micropile method using the gap closing tool 20 will be described with reference to FIG.
As shown in FIG. 4A, when the micropile method is applied, the tip is inside the first elongated hollow cylindrical steel casing segment 12 in which the outer peripheral portion of the tip is the outer drilling cutter 1202. The first rod 18 to which the drilling drill 1802 is attached is inserted into the cylinder, and the casing segment 12 and the rod 18 are rotated, and water is injected into the outer drilling cutter 1202 and the drilling drill 1802. A step of drilling a hole 16 in the soft layer 30 is performed.
In the present embodiment, the soft layer 30 is a cohesive soil system, and when a hole is drilled, the inner peripheral surface of the drilled hole 16 does not collapse and the contour of the hole 16 is maintained.

As shown in FIGS. 4 (B) and 4 (C), each time the hole 16 reaches a predetermined depth, the next elongated hollow cylindrical steel casing segment 12 is connected to the end of the casing segment 12 via the joint 14. The next rod 18 is detachably connected and added to the end of the rod 18, the casing segment 12 and the rod 18 are rotated, and the outer surface is drilled while injecting water. A step of drilling the hole 16 is performed by the hole cutter 1202 and the drill drill 1802.

The casing C is configured by connecting the plurality of casing segments 12.
As shown in FIG. 4C, when the drilled hole 16 passes through the soft layer 30 and reaches a predetermined depth of the load bearing layer 32, the drilling drill 1802 is inserted into the casing C together with the rod 18. The process of pulling out from is performed.
Next, if necessary, a reinforcing material such as a reinforcing bar is arranged inside the casing C over the entire length of the casing C.

Next, as shown in FIG. 4D, the grout material G is filled inside the casing C using a grout hose (not shown).
As the grout material G, a concrete material mixed with cement milk, a mortar material, and a small-diameter aggregate can be used.
Next, as shown in FIG. 4E, a step of pulling out the casing segment 12 while injecting the grout material G into the inside of the casing C, that is, a step of pulling out the casing C is performed.

When the casing C is pulled out, the lower casing segment 12 is rotatably gripped at a position where the upper end of the lower casing segment 12 is located near the ground among the casing segments 12 adjacent to the upper and lower sides, and the upper casing is pulled out. This is done by rotating the segment 12 and removing the upper casing segment 12 together with the joint 14 with respect to the lower casing segment 12.
A plurality of casing segments 12 located above are removed together with the joint 14, and as shown in FIG. 4 (E), the lower end of the first casing segment 12 located at the lowest position is at the uppermost portion of the load support layer 32. When approaching, the pulling out of the casing C is completed.

Here, as shown in FIGS. 2 and 4 (F), the bag body 26 of the gap closing tool 20 is attached to the casing segment 12 located on the ground.
That is, the casing segment 12 is inserted into the central hole 1602 of the annular bag body 26, and the lower end of the bag body 26 is fastened to the outer peripheral surface of the casing C by the fastener 34 so that the tube body 28 projects upward. As the fastener 34, various conventionally known members such as a belt can be used.

Then, as shown in FIG. 2, the bag body 26 is brought into the reduced state, and the member 36 that allows the change from the reduced state to the expanded state of the bag body 26 is wound around the bag body 26 in the reduced state, and the bag body 26 is wound. It is attached to the casing C while maintaining the reduced state of.
As a result, when the casing C is moved downward, the bag body 26 is maintained in a reduced state even if it comes into contact with the inner peripheral surface of the drilled hole 16, and the inside of the drilled hole 16 of the bag body 26 is maintained. It is designed so that the movement can be done smoothly.
The member 36 that allows the change of the bag body 26 from the contracted state to the expanded state is, for example, a string-shaped member made of breakable paper or stretchable rubber, or the bag body 26 in the reduced state. Various conventionally known materials and forms such as a bag-shaped member covering the rubber can be used.
The gap closing tool 20 may be attached to the casing segment 12 in advance at the time of drilling, but it is better to attach the gap closing tool 20 when the casing C is pulled out as in the present embodiment to reduce the size of the bag body 26. It is advantageous in maintaining the state.

Next, as shown in FIG. 4 (G), a step of pushing the casing C to which the gap closing tool 20 is attached back into the already injected grout material G by a predetermined amount is performed.
If the casing C is pushed back by a predetermined amount, the bag body 26 is located inside the drilled hole 16 below the ground surface.

Next, as shown in FIGS. 3 and 4 (H), the grout material G is supplied from the tubular body 28 as a filler into the bag body 26, the bag body 26 is changed from the reduced state to the expanded state, and the bag body 26 is used. 2604 is brought into close contact with the entire outer peripheral surface of the casing C, and the outer peripheral portion 2606 of the bag body 26 is brought into close contact with the entire inner peripheral surface of the drilled hole 16.
In the present embodiment, since the soft layer 30 is a cohesive soil system, in the expanded state of the bag body 26, as shown in FIG. 3, the outer peripheral portion 2606 of the bag body 26 is the inner peripheral surface of the drilled hole 16. The annular gap S formed in the soft layer 30 and the load support layer 32 is completely closed and is surely shielded from the atmosphere.

Next, the grout material G is pressurized and injected into the casing C to create a portion having an intermediate structure between the portion surrounded by the casing C and the portion not surrounded by the casing C.
The pressure injection of the grout material G into the casing C is such that the grout material G is in close contact with the wall surface of the drilled hole 16 and the joint state between the grout material G and the ground is strengthened. It is desirable to be done.
In the present embodiment, the annular gap S formed in the soft layer 30 and the load support layer 32 is completely and surely shielded from the atmosphere by the expanded bag body 26, so that the grout material G is pressed at a desired pressure. Can be applied, and the joint state between the grout material G and the ground can be as strong as designed.
Then, as shown in FIG. 4 (I), the grout material G is cured to obtain a pile body 40 having a ground joint 38 formed by the grout material G.
Next, a steel bearing plate 42 is joined to the upper end of the casing C by welding to form a connecting structure for connecting the pile head of the pile body 40 to the structure.

Therefore, according to the present embodiment, when the portion to be drilled is a cohesive ground or rock, the inner peripheral surface of the drilled hole 16 is less likely to collapse, and the drilled hole 16 is drilled after the drilling. Although an annular gap S is always secured between the inner peripheral surface of the hole 16 and the outer peripheral surface of the casing segment 12, a desired pressure can be applied to the grout material G in the final step of the micropile method. , It is possible to reliably obtain a pile body 40 having a strong ground joint 38 made of grout material G.
Moreover, since the gap closing member 22 is composed of a bag body 26 and a pipe body 28 having a simple structure, it can be easily manufactured at low cost, and can be easily attached to the casing C in a short time, and is a micro pile. It is extremely advantageous in improving the work efficiency of the construction method.

Further, since the grout material G is used as the filler for changing the bag body 26 from the reduced state to the expanded state, the existing equipment such as the grout material G to be injected into the inside of the casing C and the pump for injecting the grout material G can be used. It can be used as it is, and the expanded state of the bag body 26 can be formed inexpensively and in a short time as compared with the case where water or air is used as the filler.
Further, the bag body 26 and the tube body 28 which are filled with the grout material G and are in an expanded state are buried and killed, which is advantageous in securing the lateral resistance of the pile body 40 as compared with the case where water or air is used as the filling material. Will be.

In the present embodiment, the case where the bag body 26 is made of cloth has been described, but the bag body 26 is made of an elastic rubber material and is not filled with water, air, or the grout material G. The elasticity may cause it to shrink and shrink around the casing C, and the filler may be supplied to expand and expand it.
Further, in the present embodiment, the case where the bag body 26 is attached to the casing C by the fastener 34 has been described, but the bag body 26 in a reduced state is formed, and the bag body 26 is drilled by the tube body 28. The bag body 26 may be expanded in a predetermined position by hanging it in the hole 16.
Further, the place where the gap closing member 22 is arranged may be a place where pressure can be applied to the grout material G in the final step, and therefore, at a place above the ground joint 38 between the ground surface and the ground joint 38. It suffices, and it is not limited to the place of the embodiment.
Further, in the present embodiment, the case where the gap closing member 22 is composed of the bag body 26 has been described, but the gap closing tool 20 may have a structure capable of closing the annular gap S, for example, the gap closing member 22. As an annular shutter composed of a plurality of wings and capable of opening and closing the annular gap S, and using an actuator for opening and closing the shutter as the expanding means 24, various conventionally known mechanical structures such as the gap closing tool 20 are also available. It can be adopted.

12 Casing segment 14 Joint 20 Gap closing tool 22 Gap closing member 24 Expansion means 26 Bag body 2602 Center hole 2604 Inner peripheral part 2606 Outer peripheral part 2606A Large diameter part 2606B Small diameter part 28 Tube body 30 Soft layer 32 Load support layer 34 Fastener 38 Ground joint 40 Pile body C Casing G Grout material S Circular gap

Claims (3)

A drilling step of passing through the soft layer and drilling to a predetermined depth of the load-bearing layer while adding a casing segment, and a filling step of filling the inside of the casing formed by adding the casing segment with a grout material. It has a pull-out step of pulling out the casing to a point where the lower end of the casing approaches the uppermost portion of the load-bearing layer, and a push-back step of pushing back the casing by a predetermined amount. In the micropile method, which forms a joint in which the casing and the load bearing layer are firmly joined.
The outer circumference of the casing is from a reduced state where the cross-sectional shape cut in a plane orthogonal to the extending direction of the drilled hole is larger than the cross-sectional shape of the casing and smaller than the cross-sectional shape of the drilled hole. It is provided with a gap closing member that is variable to an expanded state that is in close contact with the entire circumference of the surface and the entire circumference of the inner peripheral surface of the drilled hole, and an expansion means that changes the gap closing member from the reduced state to the expanded state. Provide a gap blocker
The gap closing member is attached to the casing located on the ground surface by the pulling step to bring the gap closing member into the reduced state.
After the gap closing member is positioned in the drilled hole in the push-back step, the gap closing member is expanded by the expanding means, and the inner peripheral surface of the drilled hole and the outer periphery of the casing are made. Block the annular gap between the faces and
Pressurizing and injecting the grout material into the casing segment.
A micro pile construction method characterized by this. The gap closing member is made of a foldable material and is composed of an annular bag-shaped bag through which the casing is inserted.
A member that allows a change from the reduced state to the expanded state of the bag when the bag is attached to the location of the casing located on the ground surface by the pulling step to bring the bag into the reduced state. Was wound around the bag body in the reduced state so as to maintain the reduced state of the bag body on the casing.
The micropile method according to claim 1 , wherein the method is characterized by the above. The expansion means is configured to include a filler that expands the bag by being supplied to the inside of the bag, and a tube that supplies the filler to the bag.
The filler is the same grout material as the grout material filled inside the casing in the filling step.
The micropile method according to claim 2 , wherein the method is characterized by the above.

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