JPH0410527B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of introducing prestress into underground walls such as continuous underground walls.

<> Purpose of the invention [Industrial application field] construction technology.

[Conventional technology] In a construction method in which an underground wall, which is a concrete structure, is built underground and one side of the underground wall is cut and excavated to form an earth retaining wall, the purpose of this method is to improve the horizontal strength of the earth retaining wall. There is a construction method that applies prestress to the above underground walls.

This construction method applies a certain tension to steel materials such as prestressed steel rods, prestressed steel wires, and prestressed steel strands placed vertically inside the basement wall after the concrete has hardened. It provides compressive force and strengthens the load-bearing capacity of underground walls.

Specifically, as shown in Fig. 5, an anchoring part 11' of the steel material 1' is provided at the lower end of the underground wall 4', and the space between it and the upper tension end part 12' is unbonded, and after the concrete hardens. This method introduces prestress from the upper end of the underground wall 4'.

[Problems to be solved by the present invention] The above method has the following problems.

(b) Prestress is introduced by a prestressing steel material that has an anchorage at the lower end of the basement wall and a tension end at the upper end of the basement wall.

However, even after excavation, one side is in contact with the ground over a large area, so the frictional force between the underground wall surface and the surrounding ground is large, making it difficult to introduce prestressing sufficiently.

(b) If several levels of horizontal struts are installed after excavation, a moment as shown in the moment diagram in Figure 4 will occur.

In other words, a large moment acts on the intermediate portion of each shoring, but the moment on the shoring portion is small, and furthermore, there are differences in moments between each shoring.

Therefore, it is extremely uneconomical to uniformly apply prestress to the entire wall surface.

[Object of the Invention] The present invention has been made to solve the above-mentioned problems. The purpose is to provide a method for introducing prestress into walls.

<> Structure of the Invention [Means for Solving the Problems] Next, the method of introducing prestress into underground walls according to the present invention will be explained with reference to the drawings.

Cutting and excavating the ground on one side of the constructed underground wall,
It is known that, as mentioned above, a bending moment as shown in FIG. 4 acts on an underground wall when it is supported by supports such as struts.

According to this, the maximum moment is acting between the upper and lower supports.

Therefore, in the present invention, instead of inserting a single continuous prestressing steel member in the vertical direction of the underground wall 4, as shown in Fig. Use methods that cause stress.

This will be explained in detail below.

(a) Steel material (Fig. 2) The steel material 1 used in the present invention is the same material as the conventional PC steel material.

A fixing portion 11 is provided at the tip of each steel material 1, and a tensioning end portion 12 is provided at the other end.

The space between the fixing part 11 and the tension end part 12 is of an unbonded type so that concrete does not directly adhere thereto.

The total length is such that two steel members 1 can be positioned between the upper and lower supports 3 as described later.

(B) Pedestal (Fig. 2) Pedestal 2 is a member for taking reaction force when applying tension to the steel material 1.

The shape is, for example, a prismatic body, and two through holes 21 are provided that penetrate through a pair of opposing surfaces.

Each through hole 21 is a hole into which the steel material 1 is inserted.

The through hole 21 does not open perpendicularly to the surface to be penetrated,
Two through holes 21 when viewed from the cross-sectional direction of the wall
open diagonally so that they intersect with each other.

(c) Drilling holes and installing steel materials (Fig. 2) In the present invention, two steel materials 1 are used as a set, and each steel material 1 is temporarily fixed to a reinforcing rod or the like inserted into a deep trench A of an underground wall.

The temporary fixing position is determined by cutting and excavating one side of the ground B, and then positioning the anchoring part 11 of each steel member 1 on the ground B side at the position where the exposed underground wall 4 is supported by the shoring 3. The pedestal 2 is located in the middle part of the upper and lower supports 3 on the side where the support is to be carried out.

At this time, the tensioned ends 12 of each steel material 1 are fitted into the through holes 21 of the pedestal 2 and exposed to the other surface.

Since the two through holes 21 are opened so as to intersect with each other when viewed from the cross-sectional direction of the wall,
Each steel material 1 will be inserted diagonally, and the two steel materials 1 will intersect in a V-shape.

Next, the two steel members 1 fitted into the pedestal 2 are erected at predetermined positions in the deep groove A for underground walls together with the reinforcing bar cage.

The part where the pedestal 2 is located is surrounded by a formwork material 5 or the like so that, when concrete is poured, a hollow part in the form of, for example, a rectangular parallelepiped is created on the wall surface of the underground wall 4.

(d) Concrete pouring (Figure 3) After the steel material 1 is placed in the predetermined location of the underground wall trench A, concrete is poured into the underground wall trench A and allowed to cure.

At this time, the pedestal 2 portion is protected by the formwork material 5, and there is no concrete adhesion.

Furthermore, since the space between the fixing portion 11 and the tension end portion 12 of each steel material 1 is also of an unbonded type, concrete does not adhere directly to the steel material 1.

(E) Root cutting and excavation After concrete curing, when sufficient strength is obtained, root cutting is excavated on one side of the ground, and the anchorage part 11 of the steel material 1 of the underground wall 4 is buried with the support 3 made of struts etc. Support your position.

(f) Applying prestress (Fig. 3) The pedestal 2 portion is in a boxed state by the formwork material 5.

Then, a jack J is installed on the tensile end portions 12 of the two steel members 1 exposed on the pedestal 2 portion, and tension force is applied simultaneously by sandwiching the pedestal 2 from both directions.

[Function] As shown in FIG. 4, the maximum moment acts on the underground wall 4 between the respective shorings 3, so that bends and cracks are likely to occur on the wall surface on the excavation side in that part.

However, when prestress is applied using the method of this embodiment, the excavated side of the underground wall 4 contracts, so that the above stress can be resisted.

<> Effects of the Invention Since the present invention has been described above, the following effects can be expected.

(b) Rather than using steel that runs vertically through the entire basement wall, this method uses steel only in partial sections.

Therefore, it is possible to reduce the influence of frictional resistance between the ground and the wall surface of the basement wall, which are in contact over a wide area, and to introduce prestress individually into each small area.

(b) The jacks for applying tension to each steel material between each shoring do not need to have a large capacity.

(c) Since prestress can be applied individually to the necessary parts, it is possible to introduce prestress of the optimal size at the optimal location according to the design stress, which is extremely economical.

(d) If there is only one steel member, tension can only be applied from the upper end of the steel member, but since the steel member applies tension independently between each support, it is possible to reliably apply prestress to each part. Can be introduced.

[Brief explanation of drawings]

Figures 1 to 3: An explanatory diagram of the prestress introduction method of the present invention, Figure 4: An explanatory diagram of the moment acting on the underground wall, Figure 5: An explanatory diagram of the conventional prestress introduction method 1: Steel material, 2: Pedestal , 3: Shoring, 4: Underground wall, A: Deep trench for underground wall, B: Ground, J: Jacket.

Claims (1)

[Scope of Claims] 1. In a construction method for introducing prestress into an underground wall constructed while supporting it with horizontal supports, there is
This is a prestress introduction method that is characterized by placing prestressing steel materials, tensioning the prestressing steel materials after the concrete has hardened, and introducing prestress individually between the shoring structures.