JPH1195074A - Embedded optical cable and work execution method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To eliminate movement of an optical cable inside embedding material due to coming off the embedding material by specifying the relation between the total elasticity of the optical cable and frictional force per unit length between the surface of the optical cable and the embedding material covering it in contact. SOLUTION: An embedded optical cable is provided with a coated optical fiber in a center position inside its cross section, for instance, and a sheath is formed surrounding inclusion filled around the coated optical fiber. The total elasticity EA of each member of this embedded optical cable is defined by an expression, where (n) is the number of members constituting the optical cable, Ei is the elastic modulus of each member, Ai is the cross-sectional area of each member. The sheath is formed of polyethylene, and protects the coated optical fiber and fixes the embedded optical cable in embedding material by frictional force F generated by contact with the embedding material. It is so constituted as to satisfy the relation of F>=Af(Δt) (f(Δt)=α.Δt, where α is the linear expansion coefficient of the embedded optical cable, and Δt is temperature variation.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a buried optical cable for directly burying an optical cable comprising a plurality of members such as an optical fiber core wire and a sheath for covering the same, and a method of constructing the same. is there.

[0002]

2. Description of the Related Art Generally, when laying an optical cable directly in a buried material such as concrete and laying it in the ground, a buried groove is excavated in advance along a position where the optical cable is laid, and concrete is inserted into the buried groove. Then, an optical cable is laid directly on the concrete foundation, and concrete, which is an embedding material, is cast and buried around the optical cable.

[0003]

However, after the optical cable is buried in concrete as described above, a temperature distortion occurs in the optical cable due to a change in ambient temperature. If this temperature distortion force is greater than the frictional force per unit length generated between the optical cable and the buried material, the optical cable is peeled from the surrounding concrete by the temperature distortion force and moves inside the buried material. The phenomenon occurs.

By the way, when an optical cable is used as an optical sensor to detect a physical quantity such as a temperature or a load in a remote place,
The optical cable must be in close contact with the surrounding concrete, and if the optical cable is separated from the concrete as described above, there arises a problem that accurate information cannot be detected.

Accordingly, the present invention has been devised to solve the above-mentioned problems, and an object of the present invention is to provide a buried optical cable in which the optical cable does not peel off inside the buried material and does not move, and a method of constructing the same.

[0006]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention relates to a method for directly embedding an optical cable composed of a plurality of members such as an optical fiber core wire and a sheath covering the same into an embedding material such as concrete. For embedded optical cables,

[0007]

(Equation 1)

(Where n is the number of members constituting the optical cable, Ei is the elastic modulus of each member, Ai is the cross-sectional area of each member) and the total elastic force EA of the optical cable is expressed by And the frictional force F per unit length between the surface of the optical cable and the buried material covering the optical cable, F ≧ EA
The relational expression of f (Δt) (f (Δt) = α · Δt, where α represents the coefficient of linear expansion of the buried optical cable and Δt represents the amount of temperature change) is established.

When an optical cable composed of a plurality of members such as an optical fiber core wire and a sheath covering the optical fiber core is directly embedded in an embedding material such as concrete, the following equation 1 is used.

[0010]

(Equation 1)

(Where n is the number of members constituting the optical cable, Ei is the elastic coefficient of each member, Ai is the cross-sectional area of each member), and the total elastic force EA of the optical cable is expressed by And the frictional force F per unit length between the surface of the optical cable and the buried material covering the optical cable, F ≧ EA
A buried optical cable that satisfies a relational expression of f (Δt) (f (Δt) = α · Δt, where α is a coefficient of linear expansion of the buried optical cable, and Δt is a temperature change amount) is laid in a buried groove excavated in advance. This is a construction method in which the surrounding area is backfilled with a buried material.

[0012] A jacket material forming the surface of the buried optical cable is formed of PE (polyethylene) and has an outer diameter of 5 mm.
And the temperature distortion force EAf (Δt) (where EA is the total elastic force of the optical cable, f (Δt) = α · Δt, where α is the linear expansion coefficient of the buried optical cable, and Δt is the temperature change amount. (Indicated below) is 5 kgf or less, and a method for constructing a buried optical cable in which the burying material is mortar is preferable.

Further, the burying material may be a caulking material having a frictional force F per unit length of 5 kgf / m or more with a jacket material made of PE forming the surface of the buried optical cable.

According to the above construction and construction method, when the optical cable is directly buried in the buried material such as concrete, even if the temperature distortion of the optical cable acts on the buried material, the optical cable and the surrounding buried material are not affected. Since the frictional force of the optical cable is larger, it is possible to prevent the optical cable from being separated from the embedded material and moving inside the embedded material.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

First, the configuration of a buried optical cable according to the present invention will be described.

As shown in FIG. 2, an embedded optical cable 1 to be embedded is provided with an optical fiber core wire 2 at a center position inside the cross section, for example, and an intervention 3 made of high tensile strength fiber is provided around the core. Is filled. A sheath 4 which is a covering material of the embedded optical cable 1 is formed so as to surround the interposition 3. The total elastic force EA of each member of the buried optical cable 1 is represented by the following equation (1).

[0018]

(Equation 1)

The sheath 4 is made of PE (polyethylene), protects the optical fiber core 2 inside, and uses the buried optical cable 1 by the frictional force F generated by contact with the buried material 5 covering the periphery of the buried optical cable 1. 1 for buried material 5
It is designed to be fixed inside.

The embedded optical cable 1 has an outer diameter L of 5 mm or less, and has an elastic force EA,
That is, the elastic force E2 A2 of the optical fiber 2, the elastic force E3 A3 of the interposition 3, and the elastic force E4 A4 of the sheath 4 are summed up and the amount of expansion due to the temperature change of the embedded optical cable 1 is shown. EAf (Δ
t) (f (Δt) = α · Δt, where α is the coefficient of linear expansion of the buried optical cable and Δt is the amount of temperature change) is set to 5 kgf or less, and the temperature distortion force EAf (Δ
t) is smaller than the frictional force F per unit length generated between the sheath 4 made of PE and the embedding material 5. Although the buried optical cable 1 is an example of a single-core optical cable, the same applies to a multi-core optical cable.

Next, the procedure for burying the buried optical cable 1 in the ground will be described.

First, a buried groove 6 having a predetermined depth and width is excavated at a position where the buried optical cable 1 is buried such as a road made of asphalt or the like. Next, mortar is cast at the bottom of the buried groove 6 so that the base 7 along the buried groove 6 is formed.
After curing, the optical fiber cable 1 is laid directly on the base 7 of the mortar, and the mortar, which is the burying material 5, is cast around the optical cable 1 and buried.

The buried optical cable 1 buried by the above procedure is fixed by a buried material 5 around it. Even if a temperature distortion EAf (Δt) occurs in the optical cable due to a change in ambient temperature, the temperature distortion EAf (Δt) is set to be 5 kgf or less, and the sheath 4 and the embedding material 5 Since the frictional force F generated between the mortar and the mortar has 5 kgf or more, the temperature distortion force EAf (Δt) becomes smaller than the frictional force F.
Therefore, the buried optical cable 1 is reliably fixed by the frictional force F generated between the buried optical cable 1 and the surrounding buried material 5, and the buried optical cable 1 is peeled off from the buried material 5 around the buried material 5, and is embedded inside the buried material 5. It can be prevented from moving.

In the above embodiment, mortar is used as the embedding material 5, but concrete may be used. Instead of mortar and concrete, a sheath 4 made of PE constituting the surface of the embedded optical cable 1 may be used. The buried groove 6 may be filled with a caulking material 8 having a frictional force F of 5 kgf or more, and the buried optical cable 1 may be buried, and the same effect as described above can be obtained.

The buried cable 1 to be buried is not limited to the one described above. For example, as shown in FIG. 3, the optical fiber core wire 2 is placed in a metal tube 9 provided inside its cross section. Even if the sheath 4 which is a sheath material of the embedded optical cable 1 is formed so as to surround the metal tube 9 through the metal tube 9, the total elastic force EA of each member of the embedded optical cable 1 is equal to the sheath force. It is only necessary that the frictional force F per unit length generated between the material 4 and the buried material 5 be smaller.

[0026]

In summary, according to the present invention, the sheath and the buried material are so arranged that the temperature distortion force EAf (Δt) is smaller than the frictional force F generated between the sheath and the mortar constituting the buried material. Is set, the excellent effect that the embedded optical cable can be prevented from being separated from the surrounding embedded material and moved inside the embedded material can be prevented.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a buried state of a buried optical cable according to the present invention.

FIG. 2 is an enlarged sectional view showing an embodiment of a buried optical cable according to the present invention.

FIG. 3 is an enlarged sectional view showing another embodiment of the buried optical cable according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Buried optical cable 2 Optical fiber core wire 3 Interposition 4 Sheath 5 Buried material 6 Groove 7 Base part 8 Caulking material

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Kato Kato 880 Sunazawa-cho, Hitachi City, Ibaraki Prefecture Inside the Takasago Plant of Hitachi Cable, Ltd.

Claims (4)

[Claims] A buried optical cable for directly burying an optical cable comprising a plurality of members such as an optical fiber core wire and a sheath covering the same in a buried material such as concrete. (Where n is the number of members constituting the optical cable, Ei is the elastic modulus of each member, and Ai is the cross-sectional area of each member).
And the frictional force F per unit length between the surface of the optical cable and the buried material covering and covering the optical cable, F ≧ EAf (Δt)
A buried optical cable characterized in that a relational expression of (f (Δt) = α · Δt, where α is a linear expansion coefficient of the buried optical cable and Δt is a temperature change amount) is established. 2. When an optical cable composed of a plurality of members such as an optical fiber core wire and a sheath covering the optical fiber core is directly embedded in an embedding material such as concrete, the following expression is used. (Where n is the number of members constituting the optical cable, Ei is the elastic modulus of each member, and Ai is the cross-sectional area of each member).
And the frictional force F per unit length between the surface of the optical cable and the buried material covering and covering the optical cable, F ≧ EAf (Δt)
(F (Δt) = α · Δt, where α is the coefficient of linear expansion of the embedded optical cable, and Δt is the amount of temperature change).
A method of constructing a buried optical cable, characterized by backfilling the surrounding area with a buried material. 3. A jacket material forming a surface of the buried optical cable is formed of PE (polyethylene) and has an outer diameter of 5 m.
m and its temperature distortion force EAf (Δt) (where EA is the total elastic force of the optical cable, f (Δt) = α · Δt,
3. The method according to claim 2, wherein α is a coefficient of linear expansion of the buried optical cable, Δt is a temperature change amount) is 5 kgf or less, and the burying material is mortar. 4. The frictional force F per unit length between the buried material and a jacket material made of PE forming the surface of the buried optical cable.
4. The method for constructing a buried optical cable according to claim 3, wherein said cable comprises a caulking material having a weight of 5 kgf / m or more.