JP2807869B2 - Construction method of ground anchor in soft ground - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for constructing a ground anchor which can be constructed on soft ground.

[0002]

2. Description of the Related Art Conventionally, ground anchors can be constructed only on the ground where there is a tight sand layer or gravel layer that can be used as anchor anchoring layers. The ground anchor according to the prior art uses such a strong layer as a fixing layer to secure the pull-out resistance of the ground anchor.

[0003]

As described above, the conventional ground anchor is premised on the existence of a strong layer. Therefore, it is considered that the anchor cannot be fixed with a loose sand layer or a viscous soil layer. Was.

The present invention has been made in order to solve the above-mentioned conventional problems, and can be applied to a loose sand layer, a viscous soil layer, etc., which could not be used as a fixing layer. An object of the present invention is to provide a construction method of a ground anchor in soft ground.

[0005]

Means for Solving the Problems In order to achieve the above object, the method of installing a ground anchor in soft ground according to the present invention is to improve the ground around the ground anchor anchoring portion, and to improve the ground. In the improvement process, using a casing, drilling is performed by rotating the casing in a state where the surrounding soil and sand are prevented from collapsing by this casing, and when drilling is completed, the casing is pulled out only the ground improvement section, and then Then, insert the injection rod inside the casing, and from the deepest end of the injection rod,
While injecting the hardening material at high pressure, rotate the injection rod gradually and gradually pull up, after the hardening of the ground improvement area, insert the anchor material and fix it, performing ground anchoring method on soft ground It is.

Further, in the method of installing a ground anchor in soft ground according to the present invention, a casing is used in a ground improvement process, and drilling is performed by rotating the casing in a state where the surrounding soil and sand are prevented from being collapsed by the casing. When drilling is completed, insert the injection rod into the casing, pull out the casing slightly, fix it so that the tip of the injection rod is exposed from the tip of the casing by an appropriate length, and in the state exposed from the tip of the casing, From the tip of the injection rod, inject the hardening material, rotate the casing and the injection rod together and gradually pull up, after hardening the ground improvement area, insert the anchor material and fix it, the ground anchor in soft ground It features a construction method.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a method for installing a ground anchor in soft ground according to the present invention will be described below with reference to the drawings.

<A> Order of Construction In the construction method of the present invention, construction is performed by the following two steps. Locally improve the ground in the area where the anchor is to be constructed. Install anchors on the improved ground. In this way, when the target is soft ground, it is a natural combination to improve the ground in the area where the anchor is placed and make the ground strong, and then perform the anchor construction. However, in actuality, if the conventional ground improvement method is used as it is for the ground anchor construction method in soft ground, the following problems exist.

<B> Conventional ground improvement method. First, a conventional method for improving the ground into a cylindrical shape will be described. Various methods have been developed, but basically, as shown in FIG. 6, a hardening material a pumped by a high-pressure pump d is jetted at a high pressure, and the ground is cut with the energy of the hardening material a. At the same time, the hardening material and the local soil are mixed and stirred. The hardening material is supplied through a small-diameter rod b and is ejected from a nozzle. By moving the rod b up and down while rotating, the ground improvement area c stirred in a coil shape or a cylindrical shape can be formed.

<C> Problems of local ground improvement of ground. When the injection rod is inserted into the ground, if the drilling direction is vertical as in the example of FIG. 6, there is little possibility that the drilling direction is bent. However, in general, the anchor is often installed diagonally. Then, as shown in FIG. 7, since the ground improvement is performed with the injection rod having a small diameter, the drilling direction is likely to bend. FIG. 7 shows an example of a state where the ground improvement range c is bent downward. If the direction of the drilling is bent in the ground improvement process, the cylindrical ground improvement range c cannot be constructed as designed. Then anchor d to be performed after that
May be displaced from the middle, and the anchoring portion of the important anchor tip may fall out of the ground improvement range c to a range where the ground has not been improved. The following can be considered as causes of the deviation of the cylindrical ground improvement range c from the planned line.

[0011] When the hardening material is injected from the rod tip,
The surrounding ground is in a fluid state in which earth and sand and a liquid of the hardening material are mixed. On the other hand, a jet rod having a small diameter and low rigidity is used. Such a rod is likely to move inside the fluid, causing the tip of the injection rod to tend to flex downward due to the weight of the injection rod itself, resulting in bending of the hole. Slime accumulates below the hole being drilled. Then, the tip of the rod is pushed upward by the slime, and the hole is bent. When the soil quality of the ground changes on the way, the soft layer is easily collapsed by the injection, and the hard side is unlikely to collapse. Therefore, the ground improvement area is likely to bend toward the side of the soft layer. Due to the low rigidity of the rod, if the tip hits a locally hard object such as gravel, it is likely to bend in a direction to avoid it.

<D> The ground improvement method of the present invention. The ground improvement of the present invention is performed by the following method so as to avoid the above problems and to facilitate the subsequent installation of the anchor.

Use of a casing. First, the feature is that the casing 1 to be used for the ground anchor in the subsequent process is also used for ground improvement.

Drilling. (FIG. 1) In a state where the surrounding soil and soil are prevented from being collapsed by the casing 1, the casing 1 is drilled by rotation. Holes are drilled to the deepest part of the ground improvement section with the casing 1, but unlike the conventional injection rod, the casing 1 is made of a material having high rigidity, so that bending of the hole hardly occurs.

[0015] Pulling out of the casing 1. (FIG. 2) When drilling in the protected state is completed, the casing 1 is also pulled out. However, the casing 1 is not pulled out of the entire length, but is pulled out only of the ground improvement section. As a result, only the hole drilled by the casing 1 remains in the ground improvement section, and the casing 1 is located on the hole opening side.

Insertion of injection rod. After that, the injection rod 3 is inserted. The injection rod 3 can be easily inserted into the drilling tip by using the casing 1 remaining in the ground and the hole remaining in the ground improvement area at the tip as a guide. Therefore, even if the injection rod 3 is low in rigidity and small in diameter, it is not drilled by the rod itself, and there is no possibility that bending of the hole occurs as in the related art.

Injection of hardener. (FIG. 3) While injecting the hardening material 4 at a high pressure from the deepest end of the injection rod 3, the rod is rotated and gradually pulled up.
As a result, the ground improvement area 5 at the correct position in the planned section
Can be installed.

<E> Ground improvement method. (Part 2) The ground improvement before anchor construction of the present invention can also be performed by the following method.

Use of the casing 1. Also in this method, the casing 1 to be used for the ground anchor, which is a subsequent step, is used for ground improvement as in the above-described method.

Drilling. In a state where the surrounding earth and sand are prevented from collapsing by the casing 1, the casing 1 is drilled by rotating the casing 1. Holes are drilled to the deepest part of the ground improvement section with the casing 1, but unlike the conventional injection rod 3, the casing 1 is made of a material having high rigidity, so that the hole hardly bends.

Insertion of the injection rod 3. Next, the injection rod 3 is inserted into the casing 1.
Then, the casing 1 is slightly pulled out and fixed so that the tip of the injection rod 3 is exposed from the tip of the casing by an appropriate length. Also in this case, even if the injection rod 3 is low in rigidity and small in diameter, it is not drilled by the rod itself, so there is no possibility that the hole is bent unlike the conventional case.

Injection of hardening material 4 With the injection rod 3 exposed from the end of the casing 1,
, The hardening material 4 is injected at a high pressure. Then, the casing 1 and the injection rod 3 are integrally rotated and gradually pulled up. According to this method, as a result, the ground at the exact position of the scheduled section can be improved.

<F> Construction of Ground Anchor In any of the above-described methods, since the hole does not bend, the ground at an accurate position is improved. Moreover, since the casing 1 remains in the ground up to the entrance of the ground improvement area 5, its direction and position can be easily determined from the ground. Therefore, after a certain period, the ground improvement area 5
When a predetermined design strength is developed, the ground improvement portion is drilled using the casing 1 left in the ground. (FIG. 4) After the drilling, the anchor anchor 6 is inserted into the inside, and the ground anchor is constructed by using various known methods such as fixing by grouting from the front end side while pulling out the casing 1. (Fig. 5)

[0024]

[Effects of the present invention] Since the method of installing a ground anchor in soft ground according to the present invention is as described above, the following effects can be obtained. <a> When drilling holes in a soft ground in an oblique direction, bending of the holes cannot be avoided by the conventional method. Therefore, there is a possibility that the anchoring portion at the tip of the anchor may be out of the ground improvement area where the ground has been improved. However, according to the method of the present invention, the ground improvement in an accurate range became possible by using the casing 1 used for anchor installation in the subsequent step in the previous step. For this purpose, the anchor has improved ground around the anchorage, so it improves the compressive fracture strength of the anchor body, increases the frictional resistance between the anchor body and the surrounding ground, and secures the required anchor pull-out strength. It became possible. <B> When the injection rod 3 is pulled up while injecting the hardening material 4 at a high pressure, a sludge-like mixture of earth and sand and the hardening material 4 blows out to the ground. The disposal of the sludge-like mixture was costly. However, in the method of the present invention, drilling is performed once before the injection step,
That space is secured. Therefore, the amount of soil blown to the ground, that is, the amount of industrial waste, can be reduced by the volume of the drilled holes. Further, the operation process of breaking the earth wall with the energy of the injection can be omitted by the volume of the drilled holes, so that the operation time can be reduced.

[Brief description of the drawings]

FIG. 1 is an explanatory view of a construction order of ground anchors on soft ground.

FIG. 2 is an explanatory view of a construction order of ground anchors on soft ground.

FIG. 3 is an explanatory view of a construction order of ground anchors on soft ground.

FIG. 4 is an explanatory view of a construction order of ground anchors on soft ground.

FIG. 5 is an explanatory view of a construction order of ground anchors on soft ground.

FIG. 6 is an explanatory view of a conventional ground improvement method.

FIG. 7 is an explanatory view of a problem on construction of a conventional ground anchor.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-49-57618 (JP, A) JP-A-62-143747 (JP, A) JP-A-9-143975 (JP, A) JP-A 61-143975 113924 (JP, A) JP-A-5-214726 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) E02D 5/80 E02D 3/12 101

Claims (2)

(57) [Claims] In a ground improvement process, a casing is used, and in a state where the surrounding soil and sand are prevented from collapsing, drilling is performed by rotating the casing. When the drilling is completed, the casing is replaced with a ground improvement. Pull out only the section, then insert the injection rod equipped with a high-pressure injection structure at the tip inside the casing, rotate the rod gradually while spraying the hardening material at high pressure from the deepest end of the injection rod The ground anchor is inserted into the ground improvement section, and after the ground improvement area is hardened, the anchor material is inserted and settled. 2. A casing is used in a ground improvement process, and drilling is performed by rotating the casing in a state where the surrounding soil and sand are prevented from being collapsed by the casing. When the drilling is completed, the injection rod is inserted into the casing. Then, pull out the casing a little, fix it so that the tip of the injection rod is exposed from the tip of the casing by an appropriate length, and with the tip of the injection rod exposed from the tip of the casing, remove the hardening material from the tip of the injection rod. The ground anchor is installed on soft ground by injecting a predetermined section by rotating the casing and the injection rod together and gradually pulling it up and injecting it into a predetermined section. Method