CN110031138B - Direct measurement method of geogrid force based on fiber grating technology - Google Patents
Direct measurement method of geogrid force based on fiber grating technology Download PDFInfo
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- CN110031138B CN110031138B CN201910331200.8A CN201910331200A CN110031138B CN 110031138 B CN110031138 B CN 110031138B CN 201910331200 A CN201910331200 A CN 201910331200A CN 110031138 B CN110031138 B CN 110031138B
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01L—MEASURING FORCE, STRESS, TORQUE, WORK, MECHANICAL POWER, MECHANICAL EFFICIENCY, OR FLUID PRESSURE
- G01L1/00—Measuring force or stress, in general
- G01L1/24—Measuring force or stress, in general by measuring variations of optical properties of material when it is stressed, e.g. by photoelastic stress analysis using infrared, visible light, ultraviolet
- G01L1/242—Measuring force or stress, in general by measuring variations of optical properties of material when it is stressed, e.g. by photoelastic stress analysis using infrared, visible light, ultraviolet the material being an optical fibre
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01L—MEASURING FORCE, STRESS, TORQUE, WORK, MECHANICAL POWER, MECHANICAL EFFICIENCY, OR FLUID PRESSURE
- G01L1/00—Measuring force or stress, in general
- G01L1/24—Measuring force or stress, in general by measuring variations of optical properties of material when it is stressed, e.g. by photoelastic stress analysis using infrared, visible light, ultraviolet
- G01L1/247—Measuring force or stress, in general by measuring variations of optical properties of material when it is stressed, e.g. by photoelastic stress analysis using infrared, visible light, ultraviolet using distributed sensing elements, e.g. microcapsules
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- Investigating Strength Of Materials By Application Of Mechanical Stress (AREA)
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Abstract
本发明公开了一种基于光纤光栅技术的土工格栅受力的直接测量方法。本方法包含两个步骤：光纤光栅半紧套结构的封装以及土工格栅受力参数直接测量的标定方法；结合不同规格与粗糙度的套管，实现半紧套封装结构，在保证变形协调性的同时，保护光栅；通过一种用于测得土工格栅受力参数的标定方法，通过半紧套传感结构土工格栅的系统拉伸试验，实现受力参数的直接测量；对光栅区段的套管进行粗糙度处理，实现格栅表面与护套间的界面相容性。本发明在土工格栅受力直接测量的基础上，提高光纤使用寿命，防止结构胶对格栅强度的改变，提高套管与土工格栅表面间紧紧咬合的界面相容性，保证套管与土工格栅的协调变形，易于操作、成本低廉、便于推广使用。
The invention discloses a method for directly measuring the force of a geogrid based on fiber grating technology. The method includes two steps: encapsulation of the fiber grating semi-tight-sleeve structure and a calibration method for direct measurement of the force parameters of the geogrid; the semi-tight-sleeve encapsulation structure is realized by combining casings of different specifications and roughnesses to ensure the deformation coordination. At the same time, the grating is protected; through a calibration method for measuring the force parameters of the geogrid, the direct measurement of the force parameters is realized through the systematic tensile test of the semi-tight-sleeve sensing structure geogrid; The casing of the section is roughened to realize the interface compatibility between the grid surface and the sheath. On the basis of the direct measurement of the force of the geogrid, the invention improves the service life of the optical fiber, prevents the structural adhesive from changing the strength of the grid, improves the interface compatibility between the casing and the surface of the geogrid, and ensures the casing The coordinated deformation with the geogrid is easy to operate, low in cost, and easy to popularize and use.
Description
Technical Field
The invention relates to the fields of civil engineering monitoring, water conservancy, traffic, electric power and the like, in particular to a method for directly measuring the stress of a geogrid based on a fiber grating technology, which comprises a semi-tight fiber grating packaging design method for measuring the deformation and the stress of the geogrid in reinforced soil and a calibration method for directly measuring the stress of the geogrid.
Background
In recent years, geogrids have been widely applied in geotechnical engineering to perform reinforcement treatment on soil, especially in traffic engineering and civil engineering. With the development of high polymer materials, geogrids are used as novel reinforced materials, are greatly applied and popularized in the field of civil engineering, and meanwhile, the continuous improvement of the whole geosynthetic material system is promoted.
The scholars at home and abroad carry out a lot of researches on the reinforcement mechanism, loose sandy soil can be piled into a slope with a natural angle of repose under the action of self weight, if reinforcement materials are embedded in the sandy soil in a layering manner, the reinforced sandy soil can not collapse into the slope and keeps a certain vertical state, the geogrid reinforcement action just utilizes the principle, and the composite soil body formed after reinforcement can improve the mechanical property. However, for the deformation and the stress value of the reinforcing materials such as geogrids in the reinforcing process, due to the lack of effective tools for assisting experimental research, a relatively accurate theorem is not obtained at present. For the measurement of deformation and stress of the geogrid, when an indoor model test of civil engineering is carried out, the deformation is small, and the sensing precision of the traditional sensor cannot meet the requirement easily; when the sensor is applied to actual engineering, the rigidity of a traditional sensor such as a strain gauge is far larger than the rigidity of the geogrid, so that the measurement error is large, the accumulation of errors can cause the distortion of a monitoring result, the traditional sensor made of metal can be rapidly aged and failed in severe environment, even if the strain value is measured, the stress value of the geogrid still needs to be converted by combining the elastic modulus, and if the engineering data is incomplete, the stress value cannot be obtained when the elastic modulus of a reinforcement material is not available. In view of the above, there is a need for a measuring tool and method with long life and capable of direct measurement in practical engineering.
Disclosure of Invention
The invention aims to provide a method for directly measuring the stress of a geogrid based on an optical fiber grating technology, aiming at the defects of the prior art, which can be popularized and applied, provides a reference for the research of the reinforcement effect of the geogrid, provides a new angle for the related research in the fields of geosynthetics and reinforced earth, and provides a reference for the application effect of the optical fiber grating in other fields.
In order to achieve the purpose, the technical scheme adopted by the invention is as follows:
a method for directly measuring the stress of a geogrid based on a fiber grating technology is characterized by comprising the following specific operation steps: the method comprises the following steps that firstly, sleeves with different specifications and different roughness are used, the optical fibers and ribs of the geogrid are connected together in a point-mode fixing mode, coordinated deformation is achieved, and a semi-tight sleeve packaging structure of the optical fiber grating is realized, so that the fixing mode that the grating is directly wrapped by the rubber strip type in the prior art is improved, the service life of the grating is prolonged, and meanwhile, the influence of the rubber strip on the integral strength of the geogrid is prevented; and the second step is that according to a calibration test method, the stress value of the geogrid is directly measured in actual measurement through a calibration result obtained in advance, the condition that stress parameters cannot be obtained due to lack of related physical property indexes of the reinforced material in actual engineering or geotechnical tests can be compensated through the operation, the calculation step of conversion of the elastic modulus of the geogrid is avoided, and meanwhile, the processing of data after work is simplified.
The method for directly measuring the stress of the geogrid based on the fiber grating technology is characterized by comprising the following steps of: the half-tight-sleeve packaging structure of the fiber bragg grating in the first step is composed of a thin sleeve (a heat-shrinkable tube with the diameter of 1 mm), a thick sleeve (a heat-shrinkable tube with the diameter of 2-3 mm), structural adhesive (structural adhesive similar to epoxy resin), a geogrid and the fiber bragg grating, as shown in figures 1, 2 and 3, wherein the length of the thin sleeve is as long as that of a grating section and is about 10mm, after the grating section is placed in the middle of the thin sleeve, the structural adhesive is used for adhering the front end of the thin sleeve and the rear end of the thin sleeve, and the thin sleeve is small in size, so that the phenomenon that the optical fiber is damaged due to the fact that the thin sleeve is pushed by soil particles when the grating section is used in an actual soil body is avoided, and the position where the thin sleeve is in contact with the surface of the geogrid is fixed by the structural adhesive so as to ensure that the thin sleeve does not shift and protect the grating section; the mode that the point type is fixed can reduce the use amount that the structure was glued when avoiding glue direct contact grating district, has prevented that the structure from gluing the influence to the grating wavelength change, prevents the ageing of structure glue in actual engineering to the destruction of grating, prevents that the adhesive tape is glued to the change of geogrid reinforced strength, increase of service life to the large dose structure.
The method for directly measuring the stress of the geogrid based on the fiber grating technology is characterized by comprising the following steps of: the grating of the sensing section in the first step is protected by a thin sleeve, the optical fiber of the transmission section is protected by a thick sleeve, the thin sleeve of the sensing section enables the grating to be close to the geogrid sufficiently, the accuracy of data is guaranteed, the thick sleeve of the transmission section enables a space to be reserved between the sleeve and the optical fiber, the stability of optical path transmission is guaranteed, and the optical fiber is prevented from being bent; the two sleeves respectively play respective advantages and protective effects and are combined to form a semi-tight sleeve packaging structure.
The method for directly measuring the stress of the geogrid based on the fiber grating technology is characterized by comprising the following steps of: in the first step, because the diameters of the thick sleeve and the thin sleeve are different, gaps (A and B) with the width of about 1mm appear at the joint of the thick sleeve and the thin sleeve in the fixed semi-tight sleeve packaging structure, and therefore structural glue is used for sealing the gap A and the gap B in the last step of completing the packaging structure, and connection between the sleeves with two different sizes is guaranteed.
The method for directly measuring the stress of the geogrid based on the fiber grating technology is characterized by comprising the following steps of: in the first step, the thin sleeve of the protective grating section is subjected to roughness treatment, so that the effects of meshing and embedding between fibers at the mutual contact position of the thin sleeve and the surface of the geogrid are achieved, and the coordinated deformation between the optical fibers and the geogrid is ensured; because the length of the grating section casing pipe subjected to rough treatment is only 10mm, the length is far smaller than the sizes of soil body and reinforcing materials in geotechnical tests or actual engineering, and therefore the movement of soil particles in the soil body and the reinforcement effect cannot be influenced.
The method for directly measuring the stress of the geogrid based on the fiber grating technology is characterized by comprising the following steps of: in the second step, the instrument and equipment required by the calibration method for measuring the stress parameters of the geogrid are a universal machine, an optical fiber demodulator and a computer, and the calibration test comprises the steps of firstly placing the geogrid packaged with the optical fiber grating on the universal machine, then stretching the geogrid to obtain the change data of the wavelength of the optical fiber and the change data of the tension of the universal machine, and finally drawing a relation curve of the tension value and the wavelength of the optical fiber; when the force value is measured in actual geotechnical tests and engineering, the force value of the geogrid can be directly obtained by directly applying the calibration relation curve, and the situation that the force value cannot be measured under the condition that the elasticity modulus of the geogrid is difficult to measure or unknown in the actual engineering is compensated while the data processing after work is simplified.
Compared with the prior art, the invention has the following advantages:
1. the invention fully utilizes the advantages of stable physical properties of the optical fiber, difficult corrosion and integration of transmission and sensing, because the grating of the sensing area is a section of processed optical fiber, the sensing area is completely compatible with the transmission area, the processing and customization can be carried out, the space and the number of the sensing gratings are designed according to the actual requirement, a plurality of grating sensing areas are distributed on one optical fiber, the quasi-distributed measurement is realized, and the condition of damage caused by excessive lead-out cables can be reduced when the optical fiber is used in the actual engineering;
2. the semi-tight sleeve packaging structure design can reduce the use amount of structural adhesive, avoid the change of the large-dose adhesive on the strength and the reinforcement performance of the geogrid, and improve the traditional use mode of the large-area long-strip-shaped structural adhesive into a point-type structural adhesive fixing method, thereby not only avoiding the wavelength reflection influence of the adhesive on the grating, but also prolonging the service life;
3. the thin sleeve for protecting the grating selected in the invention has small volume, can not influence the soil particles in the soil body and the stress and deformation of the geogrid, is close to the geogrid, can accurately sense the deformation and stress of the geogrid, carries out roughness treatment on the thin sleeve, improves the interface compatibility between the sleeve and the geogrid, leads the sleeve and the geogrid to deform cooperatively, has low price and low cost, and can meet the large-batch requirements of actual engineering;
4. the calibration method for directly measuring the geogrid stress can make up for the situation that the physical parameters of the geotechnical reinforcement material are lost in the actual engineering, and simultaneously simplifies the analysis steps of data after the engineering.
Drawings
Fig. 1 is a schematic diagram (top view) of a semi-tight package sensing structure of the present invention.
Fig. 2 is a schematic diagram (side view) of a semi-tight package sensing configuration of the present invention.
Fig. 3 is a schematic diagram (cross-sectional view) of a semi-tight package sensing structure of the present invention.
FIG. 4 is a schematic view of the measurement of the present invention.
FIG. 5 is a schematic drawing of the calibration test of the present invention.
Detailed description of the preferred embodiments
The technical solutions of the present invention will be described in further detail below with reference to the accompanying drawings and preferred embodiments, but the scope of application of the present invention is not limited thereto.
The first embodiment is as follows:
referring to fig. 1 to 5, the method for directly measuring the stress of the geogrid based on the fiber grating technology is characterized by comprising the following specific operation steps: the method comprises the following steps that firstly, sleeves with different specifications and different roughness are combined, point-type fixation is carried out on the fiber grating through structural adhesive and the sleeves, a semi-tight sleeve packaging structure of the fiber grating is realized, and the effect of protecting the grating is achieved while deformation coordination is ensured; and secondly, directly measuring the stress parameters by stretching the geogrid (1) through a calibration method for measuring the stress parameters of the geogrid (1).
Example two:
this embodiment is substantially the same as the first embodiment, and is characterized in that:
the semi-tight sleeve packaging structure of the fiber grating comprises the following components: carry out point type through pasting thin sleeve pipe (3) front end (6) and thin sleeve pipe (3) rear end (10) and fix grating district (4), for preventing that thin sleeve pipe (3) the aversion in the in-service use from damaging grating (5), fix position (8) that contact between thin sleeve pipe (3) and geogrid (1) surface with the protection grating, this kind avoids the adhesive tape directly to wrap up the fixed mode of grating district (4) and geogrid (1), can improve the life of optic fibre, prevent that the structure from gluing from to the change of geogrid reinforced strength. The semi-tight sleeve packaging structure of the fiber grating comprises the following components: the sensing section grating is protected through the thin sleeve (3), the grating is guaranteed to be close to the geogrid (1) sufficiently, the transmission section optical fiber (5) is protected through the thick sleeve, the thin sleeve (3) is subjected to roughness treatment, the interface compatibility of tight occlusion between the thin sleeve (3) and the surface of the geogrid (1) is achieved, the spare part between the thick sleeve (2) and the optical fiber (5) can guarantee the stability of optical path transmission, and the transmission section optical fiber (5) is prevented from being bent. The calibration method for measuring the stress parameters of the geogrid comprises the following steps: the stress value of the geogrid is obtained in advance without elastic modulus conversion, the calibration relation curve of stress and wavelength change is obtained, the stress value of the geogrid (1) can be directly measured in actual measurement according to the calibration result, the condition that the stress value cannot be measured due to lack of related physical property indexes such as elastic modulus of the geogrid (1) in actual engineering is made up, and meanwhile, the processing of data after chemical engineering can be simplified.
Example three:
the invention aims to solve the problem of directly measuring the stress of the geogrid, and comprises the first step of packaging a semi-tight sleeve packaging structure of the fiber grating, and the second step of combining a calibration method for measuring the stress parameter of the geogrid to obtain the change relation between the tension of the geogrid and the wavelength of an optical fiber in advance. The semi-tight sleeve packaging method in the first step is easy to operate, low in price and good in effect, and is almost suitable for deformation and stress measurement of the geogrids in any structure. The invention composed of the two key steps improves the fixing mode of the adhesive tape type direct wrapping in the prior art, improves the existing stress measurement method through elastic modulus conversion, can prolong the service life of the fiber bragg grating, ensures the measurement precision and accuracy, directly measures the stress value, simplifies the processing of the data after chemical engineering, can realize the automatic distributed measurement effect, and meets the requirement of actual engineering.
The invention is used for carrying out an indoor geogrid reinforcement slope model test of civil engineering, the geogrid with known elasticity modulus is used as a reinforcement material, 4 groups of tests are set, 2 layers of reinforcement (1 group of the reinforcement material with the distance of 50mm and 100 mm), 3 layers of reinforcement and 4 layers of reinforcement are respectively adopted, 2 optical fiber measuring points are distributed on each layer of geogrid, each point is named as 'X layer 1 #' and 'X layer 2 #', and the distribution schematic diagram is shown in figure 4.
For each measuring point, according to the design of the step 1 in the invention, a thin sleeve is adopted to protect a sensing grating section, a thick sleeve is adopted to protect a transmitted optical fiber section, structural adhesive is used to stick and fix the front end (the number is I) of the thin sleeve, the rear end (the number is II) of the thin sleeve and the contact surface (the number is III), the structural adhesive is used to seal a gap A and a gap B (the structural adhesive used here is epoxy resin, and other structural adhesives with similar properties can be used), and the packaging of the optical fiber grating semi-tight sleeve structure is completed. By the improved packaging structure, the using amount of the structural adhesive is reduced, and the change of the geogrid reinforcement strength caused by a large amount of adhesive can be avoided; meanwhile, the direct wrapping contact mode of the adhesive tape and the sensing part of the fiber bragg grating is avoided, the influence of glue on the accuracy and long-term stability of grating measurement is prevented, and the service life of the optical fiber is prolonged.
In the invention, the rough treatment of the protective sleeve in the grating area can be carried out in a sand blasting mode, so that the adhesive force between the protective sleeve and the geogrid is increased, and the interface compatibility between the sleeve and the geogrid is improved; the sand blasting particles can be selected from glass sand, steel sand, quartz and the like, and can be selected according to the strength of the geogrid and matched with the roughness of the surface of the geogrid as much as possible.
When a calibration test is carried out, the geogrid with the same type as that in a slope test is selected for stretching, stretching equipment is a universal machine, the universal machine can directly record a stretching force value and a deformation value, and a demodulator can automatically record change data of wavelength, so that a change relation curve of stress and wavelength can be obtained; it should be noted that, the grid with the same width as the universal machine clamp is selected here, and about 3 ribs are selected, as shown in fig. 5, one third of the tension of the universal machine clamp is needed when the tension of the rib is calculated later.
Burying the packaged geogrid according to the test working condition, burying the geogrid packaged with the fiber grating in a side slope, wherein the upper load of the side slope soil body comes from the loading function of a universal machine, the universal machine can automatically acquire pressure and top displacement data, and a demodulator can automatically record the change data of the wavelength. And (3) finishing the test after the slope damage, obtaining the deformation value of the geogrid according to the wavelength change recorded in the slope test process, and obtaining the stress value of the geogrid by calibrating the relation curve obtained by the test in advance. The theoretical calculation value of the stress is calculated according to the elastic modulus and the deformation value of the geogrid known in the test, and is compared with the actually measured stress value obtained through the calibration relation curve, and the result is shown in table 1.
The relative error between the actually measured stress value and the theoretical calculated value calculated by the method is within 5 percent, and by the calibration method, the data distortion caused by the lack of the related physical property indexes of the reinforced material in the actual engineering or geotechnical model test can be compensated without the conversion of the elastic modulus of the geogrid. In addition, after the unloading and sample dismantling work after the test is finished, the fiber bragg grating in the soil body is still intact, and the packaging structure has a strong protection effect, and the measurement precision and accuracy of the stress value also meet the engineering requirements.
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| DE10012291C1 (en) * | 2000-03-14 | 2001-09-20 | Reinhausen Maschf Scheubeck | Process for fiber optic temperature measurement and fiber optic temperature sensor |
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| CN2183561Y (en) * | 1994-02-25 | 1994-11-23 | 清华大学 | Optical-fiber mechanical quantity transducer |
| CN1329716A (en) * | 1998-12-04 | 2002-01-02 | 塞德拉公司 | Strain-isolated bragg grating temperature sensor |
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