JP2002081061A - Load control method for ground anchor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for holding a long-time superior performance for detecting elongation of a ground anchor caused by a tensile force, for example, in a slope, a retaining wall, etc. SOLUTION: This detection method detects the extension/contraction of the ground anchor by fixing optical sensors to parts for measuring strain of the ground anchor and connecting the optical fiber from the optical sensors to an observation device on the ground for detecting the extension/contraction of the ground anchor.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for managing the load of a ground anchor by detecting elongation of a ground anchor on a slope, a retaining wall or the like due to a tensile load.

[0002]

2. Description of the Related Art Conventionally, as a method of controlling the load of a ground anchor installed on a slope or the like, a method of installing a load cell on an anchor head, or a method using a strand made of a PC steel strand made of a synthetic resin (such as PE) is used. In the tendon coated with (1), a method is known in which a part of the PE coating is peeled off, a strain gauge is fixed thereto, and the load is controlled by periodically measuring the elongation of the strand.

[0003]

However, since the ground anchor is buried in the hole in the slope, the strain gauge and the connection line, which are instruments for observing strain over a long period of time, must maintain the initial state. However, there is a problem that rust is generated due to water infiltration due to cracking of the grout material filled in the hole. In addition, since a part of the tendon is peeled off, it is necessary to prevent the strand from being scratched and to perform a rust-preventive treatment on that part, which requires a great deal of trouble in setting the equipment. In addition, deterioration of observation instruments due to aging also poses a problem. Further, in the conventional measurement method using electricity, there is a possibility that the measurement cannot be performed due to a lightning strike or a stray current.

[0004] In such a conventional load control method of a ground anchor, there is no method using an optical sensor. A ground anchor according to the present invention is proposed to solve the above-mentioned problem.

[0005]

The gist of the present invention for solving the above-mentioned problems is to fix an optical sensor to a strain measuring point of the ground anchor and to detect a load of the ground anchor. An optical fiber from an optical sensor is connected to a ground-based observer to detect expansion and contraction of the ground anchor.

[0006] The light sensor is directly fixed to the covering member of the tendon of the ground anchor without removing the covering member by a fixing tool.

[0007] According to the method of controlling the load on the ground anchor according to the present invention, there is no fear of rusting or deterioration due to the use of an optical sensor, it is excellent as a long-term observation device, and the covering member of tendon does not peel off. Therefore, workability is improved and the need for rust prevention treatment is eliminated. Since an optical fiber is used, non-guided and long-distance measurement can be performed, and there is no electrical influence. Remote monitoring and control can be performed using a communication line, and load information can be obtained in real time.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A ground anchor load management method according to the present invention will be described below with reference to the drawings. As shown in FIG. 1 and FIG. 2, the configuration of the observation device in the load control method of the ground anchor is such that the tendon 1 in which the strand is covered with a covering member made of a synthetic resin (for example, PE) is provided with an adhesive or a fixing tool. One or a plurality of sensors 4, 4,... Are directly attached to the covering member at required intervals. Therefore, the troublesome work of peeling the covering member to expose the strand and mounting the strain gauge thereon is omitted.

In the free length portion 5 of the tendon 1 on the moving ground side, as shown in FIG. 1 and FIGS. Has been fixed. The sensors 4, 4,... Are connected by an optical fiber 7.

The sensor 4 is a sensor called an FBG sensor. As shown in FIG. 5, a refractive index of a core portion 9 covered by a cladding portion (coating portion) 8 changes periodically. The diffraction grating portion (grating portion) 10 has a Bragg wavelength (λB = 2n).
0S: n0 is the average refractive index of the core of the grating section)
When a strain is applied to this portion by an external force, the Bragg wavelength shifts, so that the local strain can be quantitatively measured, and functions as a sensor capable of measuring the tension and compression sides. Therefore, the sensors 4 can be arranged at multiple points in series.

The optical fiber 7 is connected to a remote measuring instrument (not shown) on the ground, and the measuring instrument is connected to a computer (not shown). For example, the system is configured to issue an alarm or the like when a load change (distortion) exceeding a predetermined value occurs.

In this embodiment, for example, when a tensile force is applied to the tendon 1, a strain is simultaneously generated in the strand and the covering member, and the strain is grasped at each measurement point by the Bragg wavelength.

As shown in FIG. 6, a second embodiment of the ground anchor load management method according to the present invention includes a sensor 4a called an OSMOS sensor for quantitatively measuring the strain of the whole structure during fixing. , Fixed to the tendon 1 via a fixture.

The sensor 4a is, as shown in FIG.
Detects deformation (distortion) of a structure by measuring the change in light intensity (the amount of change in light leaking from the stranded wire) of an optical fiber stranded wire (both reciprocating multimode fibers) with both ends fixed to the object Things. Therefore, serial multipoint measurement cannot be performed.

In order to fix the sensor 4a to the tendon 1, for example, at an interval of 1 m to 10 m, the end boxes 11, 11 at both ends are fixed by bolts, adhesives, clamps or the like. Also in this case, the cover member of the tendon 1 is directly fixed to the end box 11 as a fixing tool without peeling. This sensor 4a can also measure the tension and compression sides.

A protection pipe 12 for the sensor is installed in a portion where the sensor 4a is installed, and a sealing material is used in a connection portion with the deformed joints 13 (13a, 13b), so that a sufficient water stopping process is performed. And connected. The optical fiber 7 drawn from the sensor portion is inserted into a link cable protection pipe 14 and connected to, for example, a site box 15 such as a site personal computer at a slope site, and converts a change in light intensity into an electric signal therefrom. The transmitted data is transmitted to the monitoring personal computer 16 via a communication modem or the like, and monitored by a monitor.

According to the second embodiment, a load is measured by passing the infrared ray through the optical fiber 7 and measuring the change in the intensity of the light, so that the tendon 1 of the ground anchor expands and contracts. Since the change in light intensity is measured, complicated data processing is not required, and the displacement of the tendon 1 is monitored quickly and in real time.

[0018]

As described above, according to the load control method for the ground anchor according to the present invention, in order to detect the load on the ground anchor, an optical sensor is fixed to the strain measurement point of the ground anchor and the light sensor is fixed. The optical fiber from the sensor is connected to the ground observation device to detect the expansion and contraction of the ground anchor and manage the load. This is an excellent effect that a good observational attitude is maintained.

Since the optical sensor is directly fixed to the covering member at the tendon of the ground anchor without peeling off the covering member by the fixing tool, the necessity of the peeling operation is eliminated, and the work efficiency is improved, and the strand is scratched. There is no fear of attachment, and safety is ensured.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing an embodiment of a load control method for a ground anchor according to the present invention.

FIG. 2 is a cross-sectional view of FIG. 1 when the sensor is fixed with an adhesive.

FIG. 3 is a side view of FIG. 1 in a case where the sensor is fixed with a fixture.

FIG. 4 is a cross-sectional view of FIG. 1 when the sensor is fixed by a fixing tool.

FIG. 5 is a detailed enlarged view of a sensor unit.

FIG. 6 is an explanatory diagram of a ground anchor expansion / contraction detection method according to a second embodiment of the present invention.

FIG. 7 is a block diagram showing a configuration of a sensor according to the second embodiment.

[Explanation of symbols]

1 tendon, 2 holes, 4,4a sensor, 5 free length section, 6 fixture, 7 optical fiber, 8 clad section, 9 core section, 10 diffraction grating section, 11 end box, 12 protective pipe, 13 deformed joint, 14
Link cable protection pipe, 15 site box,
16 Personal computer for monitoring.

Claims (2)

[Claims] 1. An optical sensor is fixed to a strain measuring point of the ground anchor to control a load of the ground anchor, and an optical fiber from the optical sensor is connected to a ground-based observer. Detecting the expansion and contraction of the ground anchor, and controlling the load of the ground anchor. 2. The load management of a ground anchor according to claim 1, wherein the optical sensor is directly fixed to the covering member at the tendon of the ground anchor without peeling the covering member by a fixing tool. Method.