Device for pre-embedding distributed optical fibers in similar material model and use method

Abstract

The invention discloses a device for pre-embedding distributed optical fibers in a similar material model and a use method, and belongs to the technical field of geotechnical engineering, the device comprises a similar material model frame, an optical fiber horizontal positioning mechanism, an optical fiber height positioning mechanism, a temperature-strain monitoring mechanism and a data acquisition and analysis system; protrusions at the two ends of the optical fiber horizontal positioning mechanism are clamped on the two sides of a front plate and a rear plate of the similar material model frame, the upper end of the optical fiber height positioning mechanism penetrates through an optical fiber positioning rod hole reserved in the optical fiber horizontal positioning mechanism, and the lower end of the optical fiber height positioning mechanism is connected with the temperature-strain detection mechanism. The temperature-strain detection mechanism is connected with the data acquisition and analysis system to reflect detection data; accurate positioning of the height, the length and the direction of the distributed optical fiber is achieved, the problems of damage, bending, displacement and the like of the distributed optical fiber in the pouring process are avoided, the testing method is simple, and the testing result is accurate and reliable.

Description

Technical Field

[0001] The invention relates to the technical field of geotechnical engineering, and in particular to a device for pre-embedding distributed optical fibers in a similar material model and a use method thereof. Background Art

[0002] Similar material simulation test is a commonly used research method in geotechnical engineering. This method is based on the similarity theorem and uses special similar materials to build models to study mechanical phenomena in engineering practice. Since geotechnical engineering focuses on studying the stress-strain laws during the destruction and movement of similar material models, monitoring the internal stress and strain of similar material models is an important part of geotechnical engineering research.

[0003] Distributed fiber optic sensing (DFOS) is a new optoelectronic technology based on communication technology and developing rapidly with the transformation of optical materials. Compared with the current mainstream monitoring technology, it has the advantages of corrosion resistance, anti-electromagnetic, strong sensitivity, high precision and distribution, and can realize real-time automatic remote monitoring. It has become an important means of monitoring rock deformation and damage in the field of geotechnical engineering. Using distributed fiber optic sensing technology to test the internal stress-strain law of similar material models has become a hot issue in the field of similar material simulation test research.

[0004] The sensing element used in distributed fiber optic sensing technology is distributed optical fiber. In the process of stress and strain testing inside similar material models, the reasonable, effective and precise layout of distributed optical fiber is the prerequisite for the success of the experiment, and determines the reliability of the experimental data to a certain extent. The literature on the experimental study of fault activity detection based on distributed optical fiber method, the distributed optical fiber sensing technology for crack positioning in small-scale gypsum models of arch dams, and the application of BOTDR distributed optical fiber sensing technology in filling mining model tests mentioned the layout method of distributed optical fiber, but the problem of precise positioning was not considered in the process of laying distributed optical fiber, and the soft and easy-to-bend characteristics of distributed optical fiber were ignored, which easily led to changes in the position and bending of distributed optical fiber, resulting in errors in the test results.

[0005] A key issue of distributed optical fiber sensing technology is the temperature compensation problem in monitoring. During the monitoring process, the strain and temperature of the object to be measured will be sensed at the same time. Therefore, temperature compensation is required when monitoring the deformation of rock and soil in an environment with a large temperature difference to eliminate the influence of temperature on the monitoring results. At present, the temperature compensation method commonly used in distributed optical fiber sensing technology is mainly the reference optical fiber method, that is, while laying the distributed optical fiber, a single temperature measuring optical fiber is laid next to it, and the optical fiber is kept from contacting the object to be measured, so that the temperature impact value can be obtained. This method requires an additional set of reference optical fibers to be laid, and it is difficult to achieve that the temperature measuring optical fiber is completely free of force, so the cost is high, and the test results need to be corrected. CN115127513A patent document discloses a temperature compensation method, which realizes temperature self-compensation of distributed optical fiber sensor devices by placing a white sleeve with embedded free distributed optical fiber under the distributed optical fiber. This method is simple to operate and reduces the test cost, but inside the similar material model, due to the gap between the white sleeve and the distributed optical fiber, the similar material will enter the white sleeve from the gap during the pouring process, and it cannot be guaranteed that the distributed optical fiber inside the white sleeve cannot be guaranteed to be unaffected by strain, which will cause errors in the measured results.

[0006] In summary, the existing distributed optical fiber deployment method in similar material models does not take into account the precise positioning and soft and flexible characteristics of the distributed optical fiber, and the test results are prone to errors. In addition, there is currently no efficient and low-cost method to achieve temperature compensation inside the similar material model. Summary of the invention

[0007] In order to solve the technical problems existing in the layout of distributed optical fibers and temperature compensation in the above-mentioned similar material models, the present invention provides a device and a method for using distributed optical fibers pre-embedded in a similar material model, so as to achieve precise positioning of the distributed optical fibers during the test and realize temperature compensation inside the similar material model efficiently and at low cost.

[0008] In order to achieve the above object, the technical solution of the present invention is:

[0009] A device for pre-embedding distributed optical fibers in a similar material model comprises a similar material model frame, an optical fiber horizontal positioning mechanism, an optical fiber height positioning mechanism, a temperature-strain monitoring mechanism and a data acquisition and analysis system; the projections at both ends of the optical fiber horizontal positioning mechanism are clamped on both sides of the front and rear plates of the similar material model frame to form a mechanical interlock; the upper end of the optical fiber height positioning mechanism passes through the optical fiber positioning rod hole reserved on the optical fiber horizontal positioning mechanism, and the lower end is connected to the temperature-strain detection mechanism; the temperature-strain detection mechanism is connected to the data acquisition and analysis system to react detection data.

[0010] Furthermore, the similar material model frame is composed of a front side panel, a rear side panel, a left side panel, a right side panel and a bottom plate. The bottom plate is placed at the bottom, the front side panel is attached to the front end of the bottom plate, the rear side panel is attached to the rear end of the bottom plate, the left side panel is attached to the bottom plate, the front side panel and the left end of the rear side panel, the right side panel is attached to the bottom plate, the front side panel and the right end of the rear side panel, and the front side panel, the rear side panel, the left side panel, the right side panel and the bottom plate are connected at their junctions by bolts.

[0011] Furthermore, the optical fiber horizontal positioning mechanism includes a fixed optical fiber positioning plate, a rotatable optical fiber positioning plate, a fine screw and a nut matching the fine screw; the fixed optical fiber positioning plate and the rotatable optical fiber plate are double-layer plates, a fine screw hole for the fixed optical fiber positioning plate is reserved on the fixed optical fiber positioning plate, and a fine screw hole for the rotatable optical fiber positioning plate is reserved on the rotatable optical fiber plate, the upper plate of the rotatable optical fiber plate is placed on the upper surface of the fixed optical fiber positioning plate, and the lower plate of the rotatable optical fiber plate is placed between the double-layer plates of the fixed optical fiber positioning plate, the fixed optical fiber positioning plate and the rotatable optical fiber positioning plate are fixed by fine screws and nuts, protrusions are installed at both ends of the upper plate of the fixed optical fiber positioning plate, and optical fiber positioning rod holes and distributed optical fiber holes are reserved on the rotatable optical fiber positioning plate; the distance between the distributed optical fiber holes is the length of the distributed optical fiber test section; the distributed optical fiber hole matches the size of the distributed optical fiber and is used to lead out the free section of the distributed optical fiber; the angle between the rotatable optical fiber positioning plate and the fixed optical fiber positioning plate can be adjusted according to the requirements of the test plan.

[0012] Furthermore, the optical fiber height positioning mechanism includes a long screw, a hexagonal nut, and a gasket, and the long screw is sequentially mounted with the gasket and the hexagonal nut; during installation, the long screw passes through the optical fiber positioning rod hole on the rotatable optical fiber positioning plate and is locked by the hexagonal nut and the gasket; there are size markings on the long screw, which is convenient for adjusting the height according to the test design during use, and the length of the long screw is adjusted according to the height of the distributed optical fiber layout.

[0013] Furthermore, the temperature-strain monitoring mechanism includes a tee pipe main pipe, a tee pipe branch pipe, a short capillary, a temperature-compensating distributed optical fiber, and a strain-distributed optical fiber; the tee pipe main pipe is installed on the upper surfaces of both ends of the tee pipe branch pipe, and the interior of the tee pipe main pipe is a threaded structure, which matches the long screw in the optical fiber height positioning mechanism; the outer diameter of the short capillary matches the inner diameter of the tee pipe branch pipe, and the inner diameter matches the diameter of the temperature-compensating distributed optical fiber; the short capillary passes through the tee pipe branch pipe, the temperature-compensating distributed optical fiber penetrates into the short capillary pipe, and the strain-distributed optical fiber is installed on the lower surface of the tee pipe branch pipe; during the test, the temperature-compensating distributed optical fiber in the tee pipe branch pipe does not contact similar materials, so the measured strains are all affected by temperature.

[0014] Furthermore, the data acquisition and analysis system includes a distributed optical fiber jumper, a distributed optical fiber demodulator, and a distributed optical fiber laptop computer; the free end of the optical fiber in the temperature-strain detection mechanism is connected to the distributed optical fiber demodulator through a distributed optical fiber jumper, and the distributed optical fiber demodulator is connected to the distributed optical fiber laptop computer.

[0015] Furthermore, one or more rotatable optical fiber positioning plates are arranged on the fixed optical fiber positioning plate, and one or more distributed optical fibers are arranged on the same level, which are reasonably configured according to the test items and test contents.

[0016] A method for using a device for pre-embedding distributed optical fibers in a similar material model comprises the following steps:

[0017] Step 1: Assemble the Model Mold of Similar Materials

[0018] Place the base plate on the ground, and fasten the left side plate, the right side plate, the front side plate, and the rear side plate around the base plate by bolts to assemble into a similar material model mold;

[0019] Step 2: Assemble the fiber optic horizontal positioning mechanism

[0020] Place the upper plate of the rotatable optical fiber positioning plate on the upper surface of the fixed optical fiber positioning plate, place the lower plate between the fixed optical fiber positioning plates, and pass the thin screw through the thin screw hole of the rotatable optical fiber positioning plate and the thin screw hole of the fixed optical fiber positioning plate, rotate the rotatable optical fiber positioning plate, and when the angle between the fixed optical fiber positioning plate and the rotatable optical fiber positioning plate reaches the angle required by the test design, screw in nuts from both ends of the thin screw to fasten the fixed optical fiber positioning plate and the rotatable optical fiber positioning plate;

[0021] Step 3: Install the fiber height positioning mechanism

[0022] Pass the two long screws through the fiber optic positioning rod holes on the rotatable fiber optic positioning plate, screw the lower ends into the tee pipe main pipe, and adjust the lowering height of the long screws by observing the size marks on the long screws above the rotatable fiber optic positioning top plate. After reaching the corresponding position, screw in the gasket and nut from above the long screws and tighten them;

[0023] Step 4: Assemble the Temperature-Strain Monitoring Mechanism

[0024] Press the short capillary into the tee branch, and pass the temperature-compensated distributed optical fiber test section through the short capillary, and at the same time drip adhesive into the gap between the short capillary and the temperature-compensated distributed optical fiber test section to ensure that there is no gap between the short capillary and the temperature-compensated distributed optical fiber test section; take another strain-distributed optical fiber test section and place it under the tee branch, tighten the strain-distributed optical fiber test section to make it close to the tee branch, and apply a small amount of adhesive between the two ends of the tee branch and the strain-distributed optical fiber test section to ensure that the strain-distributed optical fiber is straight so that it will not shift or bend during the pouring of similar materials; finally, pass the temperature-compensated distributed optical fiber free section and the strain-distributed optical fiber free section through the distributed optical fiber hole on the rotatable optical fiber positioning plate;

[0025] Step 5: Install the fiber optic horizontal positioning mechanism

[0026] Install the optical fiber horizontal positioning mechanism, the optical fiber height positioning mechanism and the temperature-strain monitoring mechanism on the similar material model mold; during installation, the protrusions at both ends of the fixed optical fiber positioning plate in the optical fiber horizontal positioning mechanism are clamped at both ends of the front side plate and the rear side plate of the similar material model mold to form a mechanical interlock with the front side plate and the rear side plate;

[0027] Step 6: Pour similar material slurry

[0028] Based on the parameter ratio set in the test, weigh the corresponding similar material raw materials, stir them evenly to form similar material slurry, and then pour them into the similar material model mold ； The pouring process is divided into three steps. The first step is to pour the similar material slurry until it covers the main pipe of the three-way pipe and vibrate it with a vibrating rod; the second step is to loosen the nut on the long screw rod, rotate it in the opposite direction to unscrew the optical fiber positioning rod from the main pipe of the three-way pipe, and take out the optical fiber horizontal positioning mechanism together with the optical fiber height positioning mechanism for reuse; the third step is to continue pouring the similar material slurry until it reaches the top of the similar material model mold, and then vibrate it;

[0029] Step 7: Demolding

[0030] After the similar material slurry solidifies, the left side plate, the right side plate, the front side plate, the rear side plate and the bottom plate of the similar material model mold are removed by removing the bolts to remove the similar material model;

[0031] Step 8: Curing and testing

[0032] The similar material model is placed in a curing room for curing. After a period of curing, the similar material model is taken out to carry out experiments. In the experiment, the temperature-compensated distributed optical fiber and the strain-distributed optical fiber free segment are connected to the distributed optical fiber demodulator through distributed optical fiber jumpers, and the distributed optical fiber demodulator is connected to a distributed optical fiber laptop computer. The collected signal and strain are converted in real time through the built-in software of the distributed optical fiber laptop computer.

[0033] Step 9: Calculate stress distribution

[0034] Based on the monitoring results of the distributed optical fiber laptop computer, the internal stress distribution of similar materials is calculated according to the following formula:

[0035] σ=E·(ε2-ε1)

[0036] Where: σ-stress, MPa; E-elastic modulus of similar material, GPa; ε2-strain distributed optical fiber monitoring strain; ε1-temperature compensation distributed optical fiber monitoring strain.

[0037] Beneficial effects of the present invention:

[0038] (1) The present invention realizes the precise positioning of the height, length and direction of the distributed optical fiber, and avoids the problems of damage, bending and displacement of the distributed optical fiber caused during the casting process. The test method is simple and the test results are accurate and reliable.

[0039] (2) The present invention realizes the arrangement of multiple distributed optical fibers at multiple angles, multiple levels, and multiple strain measurements.

[0040] (3) The present invention realizes the internal temperature measurement of the similar material model based on distributed optical fiber, and performs temperature compensation on the distributed optical fiber monitoring results inside the similar material model through the strain distribution under the influence of temperature, so as to obtain the strain results under the influence of pure stress, thereby obtaining accurate stress distribution results.

[0041] (4) The similar material model mold, optical fiber horizontal positioning mechanism, and optical fiber height positioning mechanism in the present invention are simple in structure and can be reused at low cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 It is a structural schematic diagram of the device provided by the present invention;

[0043] Figure 2 It is a three-dimensional schematic diagram of the similar material model framework provided by the present invention;

[0044] Figure 3 It is a three-dimensional schematic diagram of the connection between the fixed optical fiber positioning plate and the rotatable optical fiber positioning plate provided by the present invention;

[0045] Figure 4 It is a three-dimensional schematic diagram of arranging a plurality of rotatable optical fiber positioning plates on a fixed optical fiber positioning plate provided by the present invention;

[0046] Figure 5 It is a three-dimensional schematic diagram of the connection relationship of the devices when multiple temperature-strain optical fiber monitoring mechanisms are arranged according to the present invention;

[0047] Figure 6Schematic diagram of the longitudinal section of the temperature-strain optical fiber monitoring mechanism provided by the present invention

[0048] Figure 7 is a side-section schematic diagram of the temperature-strain optical fiber monitoring mechanism provided by the present invention;

[0049] Figure 8 It is a schematic diagram of the data acquisition and analysis system structure provided by the present invention;

[0050] Fig. 9 The stress distribution curve in the cement mortar specimen under the expansion effect of the self-expanding anchor rod is measured by using the device of the present invention.

[0051] The reference numerals in the drawings of the specification include:

[0052] 1. Similar material model frame, 1-1. Front side plate, 1-2. Rear side plate, 1-3. Left side plate, 1-4. Right side plate, 1-5. Bottom plate, 1-6. Bolts, 2. Fiber optic horizontal positioning mechanism, 2-1. Fixed fiber optic positioning plate, 2-2. Rotatable fiber optic positioning plate, 2-3. Fine screw, 2-4. Nut, 2-5. Fine screw hole for fixed fiber optic positioning plate, 2-6. Protrusion, 2-7. Fine screw hole for rotatable fiber optic positioning plate, 2-8. Fiber optic positioning rod hole, 2- 9. Distributed optical fiber hole, 3. Optical fiber height positioning mechanism, 3-1. Long screw, 3-2. Hexagonal nut, 3-3. Gasket, 4. Temperature-strain monitoring mechanism, 4-1. Three-way pipe main pipe, 4-2. Three-way pipe branch pipe, 4-3. Short capillary, 4-4. Temperature-compensated distributed optical fiber, 4-5. Strain distributed optical fiber, 5. Data acquisition and analysis system, 5-1. Distributed optical fiber jumper, 5-2. Distributed optical fiber demodulator, 5-3. Distributed optical fiber laptop computer. DETAILED DESCRIPTION

[0053] The technical solutions in the embodiments of the present invention will be described clearly and completely below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments.

[0054] The test plan formulated in the embodiment of the present invention is to reserve a 40mm drill hole in a 300mm*300mm*250mm cement mortar specimen, and arrange a distributed optical fiber at a height of 125mm from the bottom. After the cement mortar specimen is cured for 28 days, a self-expanding anchor rod is installed in the drill hole, and the device and method of the present invention are used to test the stress distribution in the cement mortar specimen under the expansion and extrusion action of the self-expanding anchor rod.

[0055] like Figures 1 to 8As shown, a device for pre-embedding distributed optical fibers in a similar material model comprises: a similar material model frame 1, an optical fiber horizontal positioning mechanism 2, an optical fiber height positioning mechanism 3, a temperature-strain monitoring mechanism 4 and a data acquisition and analysis system 5; the protrusions at both ends of the optical fiber horizontal positioning mechanism 2 are stuck on both sides of the front and rear plates of the similar material model frame 1 to form a mechanical interlock, the upper end of the optical fiber height positioning mechanism 3 passes through the optical fiber positioning rod hole 2-8 reserved on the optical fiber horizontal positioning mechanism 2, and the lower end is connected to the temperature-strain detection mechanism 4, and the temperature-strain detection mechanism 4 is connected to the data acquisition and analysis system 5 to react detection data.

[0056] The similar material model frame is composed of a front side plate 1-1, a rear side plate 1-2, a left side plate 1-3, a right side plate 1-4 and a bottom plate 1-5. The bottom plate 1-5 is placed at the bottom, the front side plate 1-1 is attached to the front end of the bottom plate 1-5, the rear side plate 1-2 is attached to the rear end of the bottom plate 1-5, the left side plate 1-3 is attached to the bottom plate 1-5 and the left ends of the front side plate 1-1 and the rear side plate 1-2, the right side plate 1-4 is attached to the bottom plate 1-5, the front side plate 1-1 and the right ends of the rear side plate 1-2, the front side plate 1-1, the rear side plate 1-2, the left side plate 1-3, the right side plate 1-4 and the bottom plate 1-5 are connected at their intersections by bolts. In this embodiment, the plate is made of high-strength alloy steel, and the internal dimensions of the frame are 300mm*300mm*250m.

[0057] The optical fiber horizontal positioning mechanism 2 is composed of a fixed optical fiber positioning plate 2-1, a rotatable optical fiber positioning plate 2-2, a fine screw 2-3 and a nut 2-4 matching the fine screw 2-3; the fixed optical fiber positioning plate 2-1 and the rotatable optical fiber plate 2-2 are double-layer plates, a fixed optical fiber positioning plate fine screw hole 2-5 is reserved on the fixed optical fiber positioning plate 2-1, and a rotatable optical fiber positioning plate fine screw hole 2-7 is reserved on the rotatable optical fiber plate 2-2, the upper plate of the rotatable optical fiber plate 2-2 is placed on the upper surface of the fixed optical fiber positioning plate 2-1, and the lower plate of the rotatable optical fiber plate 2-2 is placed between the double-layer plates of the fixed optical fiber positioning plate 2-1, and the fixed optical fiber is fixed to the optical fiber horizontal positioning mechanism 2. The fiber positioning plate 2-1 and the rotatable fiber positioning plate 2-2 are fixed by a fine screw 2-3 and a nut 2-4, protrusions 2-6 are installed on both ends of the upper plate of the fixed fiber positioning plate 2-1, and fiber positioning rod holes 2-8 and distributed fiber holes 2-9 are reserved on the rotatable fiber positioning plate 2-2; the distance between the distributed fiber holes 2-9 is the length of the distributed fiber test section; the distributed fiber holes 2-9 match the size of the distributed optical fiber and are used to lead out the free section of the distributed optical fiber; the angle between the rotatable fiber positioning plate and the fixed fiber positioning plate can be adjusted according to the requirements of the test plan; in this embodiment, the plate is based on PLA consumables using ANYCUBIC Printed by a 3D printer, during the test, the protrusions 2-6 at both ends of the fixed optical fiber positioning plate 2-1 are stuck at the two ends of the front side plate 1-1 and the rear side plate 1-2 of the similar material model frame 1, forming a mechanical interlock with the front side plate 1-1 and the rear side plate 1-2. The diameter of the fine screw hole 2-5 of the fixed optical fiber positioning plate reserved in this embodiment is 4mm, and the protrusion 2-6 has a length of 10mm, a width of 50mm, and a height of 10mm; the diameter of the fine screw hole 2-7 of the rotatable optical fiber positioning plate reserved in this embodiment is 4mm, the diameter of the optical fiber positioning rod hole 2-8 is 1.65mm, and two holes are reserved at 20mm and 120mm on the same side of the center of the rotatable optical fiber positioning plate 2-2, and the diameter of the distributed optical fiber hole 2-9 is 3mm, and two holes are reserved at 140mm and 145mm from the center on the same side of the rotatable optical fiber positioning plate 2-2;

[0058] The optical fiber height positioning mechanism 3 is composed of a long screw 3-1, a hexagonal nut 3-2 and a gasket 3-3; during the test, the long screw 3-1 passes through the optical fiber positioning rod hole 2-8 on the rotatable optical fiber positioning plate 2-2, and is locked by the hexagonal nut 3-2 and the gasket 3-3; there are size marks on the long screw 3-1, which is convenient for adjusting the height according to the test design during use; during the test, the length of the long screw is adjusted according to the height of the distributed optical fiber layout; in this embodiment, the long screw 3-1 is made of stainless steel, is threaded, has a length of 250mm, a diameter of 3mm, and has size marks every 1cm.

[0059] The temperature-strain monitoring mechanism 4 is composed of a three-way pipe main pipe 4-1, a three-way pipe branch pipe 4-2, a short capillary 4-3, a temperature compensation distributed optical fiber 4-4, and a strain distributed optical fiber 4-5; the three-way pipe main pipe 4-1 is installed on the upper surfaces of both ends of the three-way pipe branch pipe 4-2, and the interior of the three-way pipe main pipe 4-1 is a threaded structure, which matches the long screw 3-1 in the optical fiber height positioning mechanism 3; the outer diameter of the short capillary 4-3 matches the inner diameter of the three-way pipe branch pipe 4-2, and the inner diameter matches the diameter of the temperature compensation distributed optical fiber, the short capillary passes through the three-way pipe branch pipe, the temperature compensation distributed optical fiber penetrates into the short capillary, and the strain distributed optical fiber 4-5 is installed on the lower surface of the three-way pipe branch pipe 4-2; During the test, the temperature-compensated distributed optical fiber 4-4 in the tee branch 4-2 does not contact similar materials, so the measured strains are all affected by temperature; in this embodiment, the tee main pipe 4-2 is made of stainless steel, 3 cm high and 5 cm in outer diameter; the tee branch 4-2 is a hollow stainless steel capillary, 100 mm long, 2.4 mm in inner diameter and 1.3 mm in thickness; the short capillary 4-3 is made of stainless steel, 2 mm in length, 2.5 mm in outer diameter and 0.2 mm in thickness. Both the temperature-compensated distributed optical fiber 4-4 and the strain distributed optical fiber 4-5 use NZS-DSS-C07 high-transmission tight-sheathed strain sensing optical cable with a diameter of 2 mm and a length of 1 m.

[0060] The data acquisition and analysis system 5 is composed of a distributed optical fiber jumper 5-1, a distributed optical fiber demodulator 5-2, and a distributed optical fiber laptop computer 5-3; the free end of the optical fiber in the temperature-strain detection mechanism 4 is connected to the distributed optical fiber demodulator 5-2 through the distributed optical fiber jumper 5-1, and the distributed optical fiber demodulator 5-2 is connected to the distributed optical fiber laptop computer 5-3. During the test, the distributed optical fiber laptop computer 5-3 collects and records the signal of the distributed optical fiber in real time, and converts the collected signal and strain in real time through the built-in software OBR v3.12.1; the distributed optical fiber jumper 5-1 used in this embodiment is an FC / APC jumper, the distributed optical fiber demodulator 5-2 used is an OBR4600 demodulator, and the distributed optical fiber laptop computer 5-3 used is an OBR notebook.

[0061] A method for using a device for pre-embedding distributed optical fibers in a similar material model comprises the following steps:

[0062] Step 1: Assemble similar material model mold 1

[0063] Place the bottom plate 1-5 on the ground, and fasten the left side plate 1-3, the right side plate 1-4, the front side plate 1-1, and the rear side plate 1-2 around the bottom plate by bolts 1-6 to form a similar material model mold with an internal size of 300mm*300mm*250mm;

[0064] Step 2: Assemble the optical fiber horizontal positioning mechanism 2

[0065] Print the fixed optical fiber positioning plate 2-1 and the rotatable optical fiber positioning plate 2-2 based on the ANYCUBIC 3D printer. After printing, place the upper plate of the rotatable optical fiber positioning plate 2-2 on the upper surface of the fixed optical fiber positioning plate 2-1, place the lower plate of the rotatable optical fiber positioning plate 2-2 between the plates of the fixed optical fiber positioning plate 2-1, and pass the fine screw 2-3 through the fine screw hole 2-7 of the rotatable optical fiber positioning plate and the fine screw hole 2-5 of the fixed optical fiber positioning plate, rotate the rotatable optical fiber positioning plate 2-2, and when it is rotated to an angle of 90° with the fixed optical fiber positioning plate 2-1, screw the nuts 2-4 from both ends of the fine screw 2-3 to fasten the fixed optical fiber positioning plate 2-1 and the rotatable optical fiber positioning plate 2-2;

[0066] Step 3: Install the fiber height positioning mechanism 3

[0067] Pass the two long screws 3-1 through the fiber positioning rod holes 2-8 on the rotatable fiber positioning plate 2-2, and screw the lower ends into the three-way pipe main pipe 4-1. By observing the size marks on the long screws 3-1 on the rotatable fiber positioning plate 2-2, adjust the lowering height of the long screws 3-1. When the lowering length is 100mm, screw the gasket 3-3 and the hexagonal nut 3-2 from the top of the long screws 3-1 and tighten them.

[0068] Step 4: Assemble the Temperature-Strain Monitoring Mechanism 4

[0069] The short capillary 4-3 is pressed into the tee branch 4-2, the temperature compensation distributed optical fiber 4-4 is selected as the NZS-DSS-C07 high transmission tight sheath strain sensing optical cable and passed through the short capillary 4-3, and epoxy resin is dripped between the short capillary 4-3 and the temperature compensation distributed optical fiber 4-4 to ensure that there is no gap between the short capillary 4-3 and the temperature compensation distributed optical fiber 4-4; another NZS-DSS-C07 high transmission tight sheath strain sensing optical cable is taken as the strain distributed optical fiber 4-5 and placed under the tee branch 4-2, the strain distributed optical fiber 4-5 is tightened to make it close to the tee branch 4-2, and a small amount of epoxy resin is applied between the two ends of the tee branch 4-2 and the strain distributed optical fiber 4-5; finally, the free sections of the temperature compensation distributed optical fiber 4-4 and the strain distributed optical fiber 4-5 are passed through the distributed optical fiber hole 2-9 in the rotatable optical fiber positioning plate 2-2;

[0070] Step 5: Install the optical fiber horizontal positioning mechanism 2

[0071] The optical fiber horizontal positioning mechanism 2, together with the optical fiber height positioning mechanism 3 and the temperature-strain monitoring mechanism 4, are installed on the similar material model mold 1. During installation, the protrusions 2-6 at both ends of the fixed optical fiber positioning plate 2-1 in the optical fiber horizontal positioning mechanism 2 are clamped at both ends of the front side plate 1-1 and the rear side plate 1-2 of the similar material model frame 1 to form a mechanical interlock with the front side plate 1-1 and the rear side plate 1-2;

[0072] Step 6: Pour similar material slurry

[0073] According to the mass ratio of cement: coarse sand: fine sand: water = 50:57:114:25, weigh the similar material raw materials, mix them evenly to form cement mortar slurry, and then pour them into the similar material model mold 1. The pouring process is divided into three steps. The first step is to pour the cement mortar slurry until it covers the three-way pipe main pipe 4-1, and vibrate it with a vibrating rod; the second step is to loosen the hexagonal nut 3-2 on the long screw 3-1, and then rotate the long screw 3-1 out of the three-way pipe main pipe 4-1 by rotating it in the opposite direction, and take out the optical fiber horizontal positioning mechanism 2 together with the optical fiber height positioning mechanism 3 for reuse; the third step is to continue pouring the cement mortar slurry until it reaches the top of the similar material model mold 1, and then vibrate it;

[0074] Step 7: Demolding

[0075] After the cement mortar paste solidifies, the left side plate 1-3, the right side plate 1-4, the front side plate 1-1, the rear side plate 1-2 and the bottom plate 1-5 of the similar material model mold are removed by removing the bolts 1-6, so as to remove the cement mortar specimen.

[0076] Step 8: Curing and testing

[0077] The cement mortar specimen was placed in a curing room for curing. After 28 days of curing, the cement mortar specimen was taken out and a hole with a diameter of 40 mm was drilled in the center of the cement mortar specimen by a drilling rig for placing the self-expanding anchor rod. After that, the free sections of the temperature-compensated distributed optical fiber 4-4 and the strain-distributed optical fiber 4-5 were connected to the OBR 4600 demodulator 5-2 through the FC / APC jumper 5-1, and the OBR 4600 demodulator 5-2 was connected to the OBR notebook 5-3. After the above work was completed, the self-expanding anchor rod was placed in the borehole and data monitoring was started. The collected signal and strain were converted in real time through the OBR v3.12.1 software built into the distributed optical fiber laptop. After 24 hours of reaction, the monitoring was terminated.

[0078] Step 9: Calculate stress distribution

[0079] Based on the monitoring results of the distributed optical fiber laptop computer, the internal stress distribution of similar materials is calculated according to the following formula:

[0080] σ=E·(ε2-ε1)

[0081] Where: σ-stress, MPa; E-elastic modulus of similar material, GPa; ε2-strain distributed optical fiber monitoring strain; ε1-temperature compensation distributed optical fiber monitoring strain.

[0082] like Fig. 9 Shown is the calculated stress distribution curve of each measuring point in the cement mortar specimen under the expansion action of the self-expanding anchor.

Claims

1. A device for pre-embedding distributed optical fibers in a similar material model, characterized in that: include: Similar material model frame, optical fiber horizontal positioning mechanism, optical fiber height positioning mechanism, temperature-strain monitoring mechanism and data acquisition and analysis system; the protrusions at both ends of the optical fiber horizontal positioning mechanism are stuck on both sides of the front and rear plates of the similar material model frame to form a mechanical interlock, the upper end of the optical fiber height positioning mechanism passes through the optical fiber positioning rod hole reserved on the optical fiber horizontal positioning mechanism, and the lower end is connected to the temperature-strain detection mechanism, and the temperature-strain detection mechanism is connected to the data acquisition and analysis system to react to the detection data.

2. The device for pre-embedding distributed optical fiber in a similar material model according to claim 1, characterized in that: The similar material model frame consists of a front side plate, a rear side plate, a left side plate, a right side plate and a bottom plate, the bottom plate is placed at the bottom, the front side plate is attached to the front end of the bottom plate, the rear side plate is attached to the rear end of the bottom plate, the left side plate is attached to the bottom plate, the front side plate and the left end of the rear side plate, the right side plate is attached to the bottom plate, the front side plate and the right end of the rear side plate, and the front side plate, the rear side plate, the left side plate, the right side plate and the bottom plate are connected at their intersections by bolts.

3. The device for pre-embedding distributed optical fiber in a similar material model according to claim 1, characterized in that: The optical fiber horizontal positioning mechanism comprises a fixed optical fiber positioning plate, a rotatable optical fiber positioning plate, a fine screw and a nut matched with the fine screw; the fixed optical fiber positioning plate and the rotatable optical fiber plate are double-layer plates, a fine screw hole for the fixed optical fiber positioning plate is reserved on the fixed optical fiber positioning plate, and a fine screw hole for the rotatable optical fiber positioning plate is reserved on the rotatable optical fiber plate, the upper plate of the rotatable optical fiber plate is placed on the upper surface of the fixed optical fiber positioning plate, and the lower plate of the rotatable optical fiber plate is placed between the double-layer plates of the fixed optical fiber positioning plate, the fixed optical fiber positioning plate and the rotatable optical fiber positioning plate are fixed by fine screws and nuts, protrusions are installed at both ends of the upper surface of the fixed optical fiber positioning plate, and optical fiber positioning rod holes and distributed optical fiber holes are reserved on the rotatable optical fiber positioning plate; the distance between the distributed optical fiber holes is the length of the distributed optical fiber test section; the distributed optical fiber hole matches the size of the distributed optical fiber and is used to lead out the free section of the distributed optical fiber; the angle between the rotatable optical fiber positioning plate and the fixed optical fiber positioning plate can be adjusted according to the requirements of the test plan.

4. The device for pre-embedding distributed optical fiber in a similar material model according to claim 1, characterized in that: The optical fiber height positioning mechanism includes a long screw, a hexagonal nut, and a gasket, and the long screw is sequentially mounted with the gasket and the hexagonal nut; during installation, the long screw passes through the optical fiber positioning rod hole on the rotatable optical fiber positioning plate and is locked by the hexagonal nut and the gasket; there are size markings on the long screw, which is convenient for adjusting the height according to the test design during use, and the length of the long screw is adjusted according to the height of the distributed optical fiber layout.

5. The device for pre-embedding distributed optical fiber in a similar material model according to claim 1, characterized in that: The temperature-strain monitoring mechanism includes a tee pipe main pipe, a tee pipe branch pipe, a short capillary, a temperature-compensating distributed optical fiber, and a strain-distributed optical fiber; the tee pipe main pipe is installed on the upper surfaces of both ends of the tee pipe branch pipe, and the interior of the tee pipe main pipe is a threaded structure, which matches the long screw in the optical fiber height positioning mechanism; the outer diameter of the short capillary matches the inner diameter of the tee pipe branch pipe, and the inner diameter matches the diameter of the temperature-compensating distributed optical fiber; the short capillary passes through the tee pipe branch pipe, the temperature-compensating distributed optical fiber penetrates into the short capillary pipe, and the strain-distributed optical fiber is installed on the lower surface of the tee pipe branch pipe; during the test, the temperature-compensating distributed optical fiber in the tee pipe branch pipe does not contact with similar materials, so the measured strains are all affected by temperature.

6. The device for pre-embedding distributed optical fiber in a similar material model according to claim 1, characterized in that: The data acquisition and analysis system includes a distributed optical fiber jumper, a distributed optical fiber demodulator, and a distributed optical fiber laptop computer; the free end of the optical fiber in the temperature-strain detection mechanism is connected to the distributed optical fiber demodulator through the distributed optical fiber jumper, and the distributed optical fiber demodulator is connected to the distributed optical fiber laptop computer.

7. The device for pre-embedding distributed optical fiber in a similar material model according to claim 1, characterized in that: One or more rotatable optical fiber positioning plates are arranged on the fixed optical fiber positioning plate, and one or more distributed optical fibers are arranged on the same level, which are reasonably configured according to the test items and test contents.

8. A method for using a device for pre-embedding distributed optical fibers in a similar material model, characterized in that: The following steps are involved: Step 1: Assemble the Model Mold of Similar Materials Place the base plate on the ground, and fasten the left side plate, the right side plate, the front side plate, and the rear side plate around the base plate by bolts to assemble into a similar material model mold; Step 2: Assemble the fiber optic horizontal positioning mechanism Place the upper plate of the rotatable optical fiber positioning plate on the upper surface of the fixed optical fiber positioning plate, place the lower plate between the fixed optical fiber positioning plates, and pass the thin screw through the thin screw hole of the rotatable optical fiber positioning plate and the thin screw hole of the fixed optical fiber positioning plate, rotate the rotatable optical fiber positioning plate, and when the angle between the fixed optical fiber positioning plate and the rotatable optical fiber positioning plate reaches the angle required by the test design, screw in nuts from both ends of the thin screw to fasten the fixed optical fiber positioning plate and the rotatable optical fiber positioning plate; Step 3: Install the fiber height positioning mechanism Pass the two long screws through the fiber optic positioning rod holes on the rotatable fiber optic positioning plate, screw the lower ends into the tee pipe main pipe, and adjust the lowering height of the long screws by observing the size marks on the long screws above the rotatable fiber optic positioning top plate. After reaching the corresponding position, screw in the gasket and nut from above the long screws and tighten them; Step 4: Assemble the Temperature-Strain Monitoring Mechanism Press the short capillary into the tee branch, and pass the temperature-compensated distributed optical fiber test section through the short capillary, and at the same time drip adhesive into the gap between the short capillary and the temperature-compensated distributed optical fiber test section to ensure that there is no gap between the short capillary and the temperature-compensated distributed optical fiber test section; take another strain-distributed optical fiber test section and place it under the tee branch, tighten the strain-distributed optical fiber test section to make it close to the tee branch, and apply a small amount of adhesive between the two ends of the tee branch and the strain-distributed optical fiber test section to ensure that the strain-distributed optical fiber is straight so that it will not shift or bend during the pouring of similar materials; finally, pass the temperature-compensated distributed optical fiber free section and the strain-distributed optical fiber free section through the distributed optical fiber hole on the rotatable optical fiber positioning plate; Step 5: Install the fiber optic horizontal positioning mechanism Install the optical fiber horizontal positioning mechanism, the optical fiber height positioning mechanism and the temperature-strain monitoring mechanism on the similar material model mold; during installation, the protrusions at both ends of the fixed optical fiber positioning plate in the optical fiber horizontal positioning mechanism are clamped at both ends of the front side plate and the rear side plate of the similar material model mold to form a mechanical interlock with the front side plate and the rear side plate; Step 6: Pour similar material slurry Based on the parameter ratio set in the test, the corresponding similar material raw materials are weighed, uniformly stirred to form similar material slurry, and then poured into the similar material model mold; the pouring process is divided into three steps, the first step: pouring the similar material slurry to cover the main pipe of the three-way pipe, and vibrating it with a vibrating rod; Step 2: After loosening the nut on the long screw, rotate it in the opposite direction to unscrew the optical fiber positioning rod from the main three-way pipe, and take out the optical fiber horizontal positioning mechanism together with the optical fiber height positioning mechanism for reuse; Step 3: Continue pouring the similar material slurry until it reaches the top of the similar material model mold, and then vibrate it; Step 7: Demolding After the similar material slurry solidifies, the left side plate, the right side plate, the front side plate, the rear side plate and the bottom plate of the similar material model mold are removed by removing the bolts to remove the similar material model; Step 8: Curing and testing The similar material model is placed in a curing room for curing. After a period of curing, the similar material model is taken out to carry out experiments. In the experiment, the temperature-compensated distributed optical fiber and the strain-distributed optical fiber free segment are connected to the distributed optical fiber demodulator through distributed optical fiber jumpers, and the distributed optical fiber demodulator is connected to a distributed optical fiber laptop computer. The collected signal and strain are converted in real time through the built-in software of the distributed optical fiber laptop computer. Step 9: Calculate stress distribution Based on the monitoring results of the distributed optical fiber laptop computer, the internal stress distribution of similar materials is calculated according to the following formula: σ=E·(ε2-ε1) Where: σ-stress, MPa; E-elastic modulus of similar materials, GPa; ε2-strain distributed optical fiber monitoring strain; ε1-temperature compensation distributed optical fiber monitoring strain.

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