JP2002309573A - Mouth pipe of ground anchor and method of forming slit therein - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent pressurized water and ejected sand from flowing out of the mouth of an anchor hole when a ground anchor is driven into the ground below the level of underground water for the construction of an earth retaining wall or the like. SOLUTION: A plurality of inflow slits 12 are provided in the mid position of a mouth pipe 10 buried into the ground at the back of an earth retaining wall 1 in order to prevent the collapse of the wall of the anchor hole in the ground anchor. Underground water around the mouth pipe 10 is forced into the pipe via the slits 12 and discharged.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a mouth pipe of a ground anchor and a method of forming a slit on the surface of the pipe to allow groundwater to flow into the pipe, and more particularly to a back face acting on the mouth pipe of a ground anchor installed on a retaining wall. BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a mouth pipe of a ground anchor and a method for forming a slit in the pipe, which reduce water pressure to prevent sand from being generated from the mouth of the anchor hole.

[0002]

2. Description of the Related Art In earth retaining work, there is a case where a sandy soil layer having a high groundwater level behind a mountain retaining wall is excavated while being supported by a ground anchor (also referred to as a ground anchor). In this case, if the anchor hole is drilled in the retaining wall without taking measures against water spouting at the mouth of the anchor hole, the pressurized water and sand may flow back through the anchor hole and spout from the mouth at the same time as drilling. There is. As a result, the ground behind the retaining wall is disturbed, and a cavity or the like is generated in the rear ground, which may cause a subsidence of the ground surface behind the retaining wall.

Therefore, conventionally, a steel pipe having a diameter slightly larger than an anchor hole called a mouth pipe (diameter of a drilled rod) is buried in the anchor hole over a predetermined range from the mouth, and a hole wall formed by jetting sand and a back ground are formed. To prevent collapse. Generally, in order to enhance the effect of the mouth pipe, a water stop box is provided at the tip of the mouth pipe on the yard space side. FIG.
Is the water stop box 50 and the mouth pipe 5 of the ground anchor
It is the fragmentary sectional view which expanded and showed one part. As shown in the figure, a steel pipe having an inner diameter slightly larger than the outer diameter of the drilling rod 52 and having a length of about 1 to 4 m is used as the mouth pipe 51, and a water stop box is provided at the tip protruding from the retaining wall 53. 50
Is attached. The water stop box 50 is provided with a hole 54 through which the drilling rod 52 penetrates.
A water blocking member 55 such as a rubber packing is attached to the surrounding area, and groundwater is prevented from flowing out from this portion. Also, a cock 55 is provided to drain the groundwater in the box 50. Normally, since the cock 55 is closed, the water stopping effect at the time of placing the ground anchor is ensured.

[0004]

At the time of drilling, however, as shown in FIG.
It is necessary to send drilling water into the drilling rod 52 with the hole 5 open to drain return water (muddy water) mixed with excavated soil outside the anchor hole. At this time, the relatively high water pressure of the groundwater flowing from the end 51b of the mouth pipe 51 mixes with the drilling earth and sand and spouts out of the cock 56. For this reason, even when the water stop box 50 is used, the cavity 57 is likely to be formed in the ground above the mouth pipe tip 51b, and there is a possibility that the ground surface 58 may sink.

[0005] As a countermeasure, a method of mixing cement with drilling water and increasing the specific gravity of water to balance with pressurized water has been taken. However, even in this case, sufficient results were not obtained at a depth where the pressure of the pressurized water exceeded the pressure of the drilling water.

Therefore, an object of the present invention is to solve the above-mentioned problems of the prior art and to provide a drainage function in the mouth pipe,
An object of the present invention is to provide a mouth pipe of a ground anchor and a method for forming a slit in the pipe, which minimize the inflow of sand from the tip of the mouth pipe by lowering the pressure of the water to be pressurized at the mouth pipe position.

[0007]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention relates to a mouth pipe buried in the ground near a retaining wall to prevent the anchor hole wall of a ground anchor from collapsing. , A plurality of inflow slits, and groundwater around the pipe is caused to flow into the pipe through the inflow slit.

It is preferable that a part of the inflow slit is plastically deformed after the mouth pipe is buried, so that a width of a slit previously formed on the pipe surface is increased.

At this time, it is preferable that the inflow slit is made to expand the slit width by applying an external force to the pipe head to plastically deform the pipe at the slit position.

As a method of forming the slit, a mouth pipe having a slit formed at an intermediate position of the pipe is buried to a predetermined depth of the ground near the retaining wall in order to prevent the anchor hole of the ground anchor from collapsing. A pipe deforming force is applied to the head, the pipe is plastically deformed at the slit position, and the width of the slit is widened to form an inflow slit for allowing groundwater around the mouth pipe to flow into the pipe.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the mouth pipe of a ground anchor and a method of forming a slit of the pipe according to the present invention will be described below with reference to the accompanying drawings. FIG. 1 is an enlarged cross-sectional view showing the configuration of a mouth pipe according to the present invention and a water stop box 20 attached to the mouth pipe 10. As shown in the figure, the mouth pipe 10 has a plurality of inflow slits 1 at an intermediate position on the pipe surface along the pipe longitudinal direction and circumferential direction.
2 are formed. As will be described later, the slits 12 are formed in advance at a middle position on the surface of a circular steel pipe used as the mouth pipe 10 by machining a plurality of strip-shaped slits 11 along a longitudinal direction and a circumferential direction of the pipe by a cutter or the like. After the pipe is cast at a predetermined position, an external force such as a blow is applied from the head to compress the pipe in the longitudinal direction, thereby causing plastic deformation of the pipe to increase the slit width.

In the present embodiment, each dimension (manufacturing dimension) of the mouth tube 10 at the time of driving is 3000 to 4000 mm in total length.
Thus, a streak slit 11 is formed in a range of 2000 to 3000 mm at an intermediate position of the entire length. This streak slit 1
It is preferable that the formation range of 1 is appropriately determined from the set total length of the mouth tube 10, the thickness of the retaining wall, and the like. In the present specification, a slit formed by cutting or the like on a pipe surface during pipe manufacturing is referred to as a “streak slit”, and a slit in which the width of the streak slit is increased after the pipe is embedded is referred to as an “inflow slit”.
And will be described separately.

The procedure for installing the mouth pipe 10 will be described with reference to FIGS. Based on the anchoring design, in order to drill an anchor hole set at a predetermined position and angle using the drill rod 2, the mouth pipe 10 is formed at a predetermined angle on the mountain retaining wall 1 at a predetermined angle. It is buried to a predetermined depth by a drilling machine such as a rotary percussion not shown. Using the mouth tube 10 as a guide, a plurality of unit length drilling rods 2 are connected to perform drilling up to a predetermined depth (FIG. 2).
(A)). At this time, prior to the drilling of the anchor hole, the head of the mouth tube 10 (the tip of the protruding portion from the retaining wall) is hit in the direction of the arrow with a hitting hammer (not shown), thereby being formed on the peripheral surface in advance. The pipe in the portion of the streak-shaped slit 11 is plastically deformed, the slit width is widened, and the inflow slit 12 through which the groundwater can pass is formed (FIG. 2B). Thereafter, a water stop box 20 having the same configuration as the conventional one is attached to the head of the mouth pipe 10 (FIG. 2C), and drilling using the drill rod 2 can be performed through the water stop box 20.

According to the mouth pipe 10 installed in the anchor hole as described above, as shown in FIG. 3, the groundwater acting on the mouth pipe 10 of the anchor hole drilled deeper than the groundwater level,
As shown by the streamline of the arrow, the water mainly flows into the mouth pipe 10 not only through the tip of the mouth pipe 10 but also through the inflow slit 12 at the middle position of the pipe having a large inflow area. At this time, since the water depth at the position of the inflow slit 12 is shallower than the position of the mouth end 10b of the mouth, the flow velocity of the groundwater drained from the water stop box 20 through the inside of the mouth pipe 10 decreases, and the movement of sand at the end of the tube Is weakened. For this reason, the amount of sand taken into the inside of the pipe is reduced, and the ejection of sand from the cock 21 of the water stop box 20 can be suppressed.

Next, a method of forming the inflow slit 12 of the mouth tube 10 will be described with reference to FIGS. FIG.
FIG. 2 is an explanatory view showing a mouth tube 10 and an inflow slit 12 thereof described in the present embodiment. As shown in the figure,
A streak-like slit 11 extending in the pipe axis direction is formed on the pipe surface of the mouth pipe 10 in a predetermined range in the pipe longitudinal direction over the entire circumference. In the present embodiment, the initial streak-shaped slit 11 is set to have a width of about 0.5 mm and a length of about 50 mm, and is formed by performing a cut processing in advance by a cutter or the like at a factory. When the head 10a of the lip 10 is hit, as shown in FIG. 2B, the lip 10 is compressed in the longitudinal direction of the pipe while its periphery is restrained by the ground, and each of the slits is formed. At 11 positions, the pipe is compressed and plastically deformed so as to expand laterally, and the width of each slit expands to about 1 to 2 mm.
In addition, the tip 10b of the mouth pipe 10 is finished in a sagittal shape in which a plurality of blades 31 are continuous in the circumferential direction to facilitate press-fitting into the ground. It is preferable that the slit width of the inflow slit is appropriately set according to the amount of groundwater and the ground at which the mouth pipe is installed.

Further, the amount of plastic deformation of the pipe varies depending on the magnitude of the acting force when forming the inflow slit 12, the size of the slit, and the number of the slits. By determining the relationship experimentally, the sum of the slit areas of the inflow slits 12 can be controlled, and the amount of groundwater flowing into the mouth pipe 10,
That is, the amount of drainage from the water stop box 20 can be appropriately adjusted. In addition, the inflow of sand can be reliably prevented by mounting a thin mesh strainer in advance at the slit position.

As a method for forming the inflow slit, a predetermined torque is applied to the head while the tip of the buried mouth tube is fixed, and the width of the streak-like slit is widened by twisting the tube so that the inflow slit is formed. By forming a slit or applying a tensile force to the head of the mouth tube to which the tip is fixed to slightly expand the tube, it is also possible to increase the width of the streak-like slit to form the inflow slit. .

On the other hand, in the case of a ground in which the mouth pipe can be relatively easily driven into the ground, and there is no fear of buckling of the pipe in the axial direction when the mouth pipe is driven, It is also possible to previously form a slit having a width approximately equal to the slit width of the inflow slit at the time of production of the tube, and to cast a mouth tube with this inflow slit (see FIG. 5). In this case, the slit forming operation after the mouth pipe is buried can be omitted, and the conventional problem can be solved similarly.

[0019]

As described above, according to the present invention,
By injecting groundwater into the mouth pipe at an intermediate position of the mouth pipe, it is possible to suppress the sudden inflow of groundwater from the tip of the mouth pipe, prevent the discharge of groundwater with disturbed sand, and prevent the ground from collapsing behind the retaining wall. This has the effect that it can be prevented.

[Brief description of the drawings]

FIG. 1 is a partially enlarged sectional view showing one embodiment of a mouth pipe of a ground anchor according to the present invention.

FIG. 2 is a construction sequence diagram schematically showing a procedure of a method of forming a slit of a mouth pipe of a ground anchor according to the present invention.

FIG. 3 is an explanatory view schematically showing the flow of groundwater along an anchor hole provided with a mouth pipe according to the present invention.

FIG. 4 is a perspective view showing an example of forming an inflow slit of a mouth tube.

FIG. 5 is a partially enlarged sectional view showing another embodiment of the mouth pipe of the ground anchor according to the present invention.

FIG. 6 is a partially enlarged sectional view showing an example of the configuration of a conventional mouth tube.

FIG. 7 is an explanatory view schematically showing the situation of the spouting of groundwater and sand at the anchor hole provided with the mouth pipe shown in FIG. 6;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Mountain retaining wall 2 Drilling rod 10 Mouth pipe 11 Streak slit 12 Inflow slit 20 Water stop box 21 Cock

Claims (4)

[Claims] 1. A mouth pipe buried in the ground near a retaining wall for preventing the anchor hole wall of a ground anchor from collapsing, having a plurality of inflow slits at an intermediate position of the pipe, and through the inflow slit. A mouth pipe of a ground anchor, wherein groundwater around the pipe is caused to flow into the pipe. 2. The inflow slit according to claim 1, wherein a part of the mouth pipe is plastically deformed after the mouth pipe is buried, and a width of a slit previously formed on the pipe surface is widened. Item 2. A mouth tube of the ground anchor according to Item 1. 3. The mouth pipe of a ground anchor according to claim 2, wherein the inflow slit is formed by applying an external force to the pipe head to plastically deform the pipe at the slit position to widen the slit width. . 4. A pipe having a slit formed at an intermediate position of the pipe is buried up to a predetermined depth of the ground near the retaining wall to prevent the anchor hole of the ground anchor from collapsing, and the pipe is deformed at the pipe head of the pipe. A slit forming method for a mouth pipe, wherein a force is applied to deform the pipe plastically at the slit position, the width of the slit is widened, and an inflow slit for flowing groundwater around the mouth pipe into the pipe is formed.