CN101915552A - The Method of Measuring the Deformation and Stress of Geogrid Using Fiber Bragg Grating - Google Patents

Abstract

The invention discloses a method for measuring the deformation and stress of a geogrid by using an optical fiber grating. Lay temperature compensation sensing optical fiber on the warp grid or the adjacent warp grid or weft grid of the geogrid; make the armored structure of the sensing fiber; after the sensing fiber is laid on the geogrid to be tested, wrap and lay it with rubber strips The warp grid or weft grid of the geogrid of the sensing fiber; the geogrid that has laid the sensing fiber and completed the protection structure is laid and installed in place, and one end of the sensing fiber grating is connected to the fiber jumper connector to prepare for entering the distributed fiber measuring system. The invention is simple and easy to implement, has low cost, can accurately measure the deformation and stress of the geogrid, and the measurement accuracy meets the actual measurement needs of engineering.

Description

The Method of Measuring the Deformation and Stress of Geogrid Using Fiber Bragg Grating

technical field

The invention relates to a kind of deformation and force monitoring of geogrid used in soil reinforcement work of civil engineering, water conservancy, electric power, transportation and other projects, especially relates to a method of using optical fiber grating to measure the deformation and force of geogrid Methods.

Background technique

At present, geogrids are widely used in soil reinforcement work in civil engineering, water conservancy, electric power, transportation and other projects, but the function of geogrids in soil reinforcement cannot be accurately quantified due to the lack of effective measurement methods Therefore, the design of geogrid in soil reinforcement can only be designed according to relevant regulations and specifications using empirical methods. In the past, measurement methods such as strain gauges were used to try to measure the deformation of reinforced geogrid in soil. However, due to the rigidity of the monitoring instrument structure itself, such as traditional strain gauges, is much greater than that of reinforced geogrids, there is a large error between the measurement results and the actual situation, resulting in the reinforcement of the soil in such projects. Attempts to measure the deformation and force of the grid ended in failure, and the current measurement methods for the deformation and force of the soil-reinforced grid are basically blank.

Contents of the invention

purpose of invention

In order to overcome the deficiencies of the prior art, the present invention proposes a method for measuring the deformation and stress of the geogrid by using an optical fiber grating.

Technical solutions

In order to realize the foregoing invention object, the present invention adopts following technical scheme:

A method for measuring geogrid deformation and stress by using fiber gratings, comprising the following steps:

1) Clean the surface of the geogrid under test, and connect the strain-sensing optical fiber with the warp or weft grid of the geogrid under test by structural glue and binding, so that the strain-sensing optical fiber and the geogrid under test The warp grating or weft grating becomes a whole with consistent deformation; the temperature compensation sensing optical fiber is laid on the adjacent warp grating or weft grating of the measured geogrid to measure the temperature of the measured value of the strain sensing fiber. Correction, the structural schematic diagram of the measurement method is shown in Figure 1, and the connection mode of the sensing grating and the geogrid is shown in Figure 2;

2) Make the armored structure of the sensing fiber according to the deformation characteristics of the geogrid to be tested. Different grating fillers and sheath structures are used. The stiffness of the sensing fiber formed by the armor must be much smaller than the stiffness of the geogrid to be tested. The stiffness of the geogrid after bundling and cementing the sensing fiber does not change greatly due to the addition of the sensing fiber and its structural force is mainly borne by the grid itself. The structure of the sensing fiber is shown in Figure 3;

3) After laying the sensing optical fiber on the geogrid under test, wrap the warp or dimension grid of the geogrid on which the sensing optical fiber is laid with adhesive strips to protect the sensing optical fiber laid on it;

4) Lay and install the geogrid that has laid the sensing fiber and completed the protection structure in place, and one end of the sensing fiber grating is connected to the fiber jumper connector to prepare for entering the distributed fiber optic measurement system;

5) The sensing fiber grating is docked with the connecting optical cable and connected to the detection instrument. The most advanced distributed optical fiber sensing technology is used to measure the strain characteristics of the geogrid. The distributed optical fiber sensing technology can realize automatic measurement. The strain characteristics of the grid can be calculated point by point to obtain the deformation characteristics of the geogrid, combined with the deformation modulus of the geogrid to calculate its stress.

The beneficial effects of the present invention are:

1) The existing distributed fiber grating measurement technology is applied to the deformation and force measurement of geogrid. The present invention is simple and easy to implement, low in cost, and can accurately measure the deformation and force of geogrid, and the measurement accuracy meets the engineering practice measurement needs;

2) The sensing fiber grating is small in size. The present invention adopts a specially processed sensing fiber grating. After laying and installing the sensing fiber grating, it basically does not affect the deformation and stress of the geogrid under test, and the measurement results accurately reflect the geotechnical The actual deformation and stress state of the grating, and multiple groups of optical fibers or gratings can be used for data comparison and analysis to improve measurement accuracy;

3) Expand the application field of distributed fiber grating sensing technology measurement.

The distributed optical fiber sensing monitoring technology based on Brillouin scattering is different from the conventional monitoring technology principle. It has the characteristics of distributed, long distance, real-time, high precision and long durability, and can monitor every project facility. Compared with the traditional monitoring technology, the distributed optical fiber sensing technology has the following characteristics: (1) The fiber grating integrates the sensor and the transmission medium, which is easy to install, easy to form an automatic monitoring system, and has high cost performance. (2) It can Continuous measurement of space at any point along the optical fiber, long measurement distance, large range, and large amount of information, greatly reducing the missed detection rate of traditional point method detection. (3) The fiber grating sensor has a simple structure and small size. According to the needs of the measured object, distributed fiber grating sensors with various diameters (diameter 1mm-20mm) and different stiffnesses are made, which have little influence on the physical properties of the installation and buried parts, high measurement sensitivity, anti-electromagnetic interference, anti-lightning strike, and reliable high sex.

Description of drawings

Fig. 1, is the geogrid deformation of the present invention and the measuring method structural representation of stressed;

Fig. 2 is a schematic diagram of the connection between the fiber grid and the geogrid of the present invention;

Fig. 3 is a schematic diagram of the structure of the sensing optical fiber of the present invention.

Detailed ways

In order to better understand the present invention, the content of the present invention is further illustrated below in conjunction with the examples, but the content of the present invention is not limited only to the following examples.

The technical problem to be solved by the present invention is to aim at the blank status of the current reinforced geogrid deformation and force measurement method, fully utilize the characteristics of distributed fiber Bragg grating sensing measurement technology, and provide a method that utilizes the current advanced distributed fiber Bragg grating sensing technology. The method of measuring the deformation and force of geogrid with sensing technology, including the structure type of distributed sensing fiber grating for geogrid deformation and force measurement, the installation and arrangement structure type of distributed sensing fiber grating on the surface of geogrid, the strain The sensor fiber temperature compensation correction method, the connection and cementation method of the sensor fiber grating and the geogrid. The method is simple and easy to implement, and the cost is very low. It is suitable for measuring the deformation and stress of any structural geogrid, and can realize automatic measurement. The test results show that its measurement precision and accuracy are high.

The diameter of the sensing optical fiber in the present invention is 4-6mm, the ultimate tensile strength is not less than 1000N, the ultimate deformation capacity is not less than 1%, and the deformation modulus is less than 10% of the geogrid to be tested; the sensing optical fiber and geogrid The binding structure is plastic strapping; the structural glue is epoxy resin glue or structural glue with similar characteristics.

The present invention utilizes fiber grating to measure geogrid deformation and force bearing method, utilizes current advanced distributed optical fiber measurement technology to have high measurement accuracy (measurement accuracy can reach 1με), and distributed measurement (minimum measurement point distributed distance is 0.05m) ), strong anti-interference ability, long measurement distance (up to 30km), very suitable for long-distance geogrid deformation and force measurement in reinforced geotechnical engineering, fast measurement speed, low sensor cost, etc. The rapid and accurate measurement of the deformation and stress of the soil reinforced geogrid can fill in the blank of the deformation and stress measurement method of the geogrid. Carry out the geogrid deformation and force measurement test indoors with the present invention, the geogrid is loaded with a fully automatic press, and the fully automatic press automatically records the geogrid deformation and force, and at the same time adopts the distribution method of the present invention. The fiber-optic measuring system was used to measure the geogrids synchronously. There were 16 comparison tests in total, using biaxially stretched plastic geogrids, glass fiber geogrids, steel-plastic composite geogrids and polyester warp-knitted polyester geogrids. For each type of geogrid, two sets of comparative tests were completed, one of which was a single geogrid, and the other was a 3-grid geogrid. The lengths of the geogrid samples were 50cm and 70cm respectively. All the test results show that the absolute error of the geogrid strain value measured by the present invention and the measured value of the automatic press machine are less than 15 με, and the relative error is less than 2%, which shows that the present invention has a higher accuracy in measuring geogrid deformation and stress. The measurement accuracy can fully meet the actual measurement needs of the project.

Example 1:

As shown in Figure 1, Figure 2 and Figure 3, the method of measuring the deformation and stress of the geogrid using fiber gratings includes the following steps:

1) After the geogrid is laid on the project site, clean the surface of the grid at the position of the grid to be tested, lay strain and temperature compensation sensing fibers on the grid to be tested, and bind the sensing fibers to the grid with plastic strapping tape. On the surface, after the strain sensing optical fiber is bundled, the structural glue is applied to the optical fiber and the foundation surface of the geogrid to make the two tightly bonded together to ensure that the deformation of the two is consistent, as shown in Figure 1 and Figure 2;

2) The sensing optical fiber is led out from one end and connected to the optical fiber jumper connector to prepare for entering the distributed optical fiber measurement system;

3) Connect the jumper connector of the strain and temperature compensation sensing optical fiber to the connecting optical cable, the optical cable is connected to the distributed optical fiber measuring instrument, and the current advanced distributed optical fiber grating measurement technology is used to measure the strain and deformation of the geogrid. Grid strain to calculate geogrid force.

Example 2:

It is basically the same as Embodiment 1, except that the sensing optical fiber and the geogrid are bundled and cemented indoors and then transported to the site for laying of the geogrid.

Example 3:

It is basically the same as Embodiment 1, except that the sensing optical fiber is first implanted into the glass fiber geogrid and then transported to the site for laying of the geogrid.

Example 4:

It is basically the same as in Example 1, except that the measured geogrid is changed from a biaxially stretched plastic geogrid to a steel-plastic geogrid.

Example 5:

It is basically the same as Example 1, except that the measured geogrid is changed from biaxially stretched plastic geogrid to polyester warp-knitted polyester geogrid.

Claims (2)

1. utilize fiber grating to measure geogrid deformation and stressed method, it is characterized in that, may further comprise the steps:

1) the tested GSZ of cleaning surface, adopt structure glue and the mode of tying up links together the Ascension or Declination Bar of strain sensing optical fiber and tested GSZ, make the Ascension or Declination Bar of strain sensing optical fiber and tested survey GSZ become the consistent integral body of compatibility of deformation; On the adjacent Ascension or Declination Bar of the Ascension or Declination Bar of tested GSZ, lay the temperature compensation sensor fibre, so that strain sensor fibre measured value is carried out the temperature correction;

2) make the sensor fibre sheathed structure, according to the deformation characteristic different mining of tested GSZ with different grating filler and jacket structure, the rigidity of the sensor fibre that armouring forms must guarantee to tie up with the later GSZ rigidity of glued sensor fibre and mainly do not born by grid itself with its structure stress because of big change takes place additional sensor fibre much smaller than the rigidity of tested GSZ;

3) on the tested GSZ sensor fibre lay finish the back adopt the adhesive tape parcel lay sensor fibre GSZ through grid or dimension grid, to protect the sensor fibre of laying on it;

4) GSZ that will lay sensor fibre and finish the protection structure is laid and to be in place, and sensor fibre grating one end is drawn and connected the optical patchcord joint in order to entering the distribution type fiber-optic measuring system;

5) the sensor fibre grating be connected optical cable butt joint and insert detecting instrument, adopt the emergent property of distributing optical fiber sensing commercial measurement GSZ, the distributing optical fiber sensing technology can realize automatic measurement, can pointwise calculate the deformation characteristic of GSZ by tested geogrid strain characteristic, calculate its stressing conditions in conjunction with the deformation modulus of GSZ.

2. utilize fiber grating to measure geogrid deformation and stressed method, it is characterized in that described sensor fibre diameter 4～6mm; Ultimate tensile strength (UTS) is not less than 1000N; The ultimate deformation ability is not less than 1%; Deformation modulus is less than 10% of tested GSZ; The binder structure of described sensor fibre and GSZ is a plastic strapping tape; Described structure glue is epoxide-resin glue or similar characteristics structure glue.

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