Soil pressure-strain-temperature fiber grating sensor for transparent soil arching effect and distributed monitoring system

Abstract

The invention discloses a soil pressure-strain-temperature fiber bragg grating sensor for a soil arching effect of transparent soil and a distributed monitoring system. The soil pressure-strain-temperature fiber bragg grating sensor and the distributed monitoring system are used in a spring movable door soil arching effect transparency model test device. In the monitoring system, a plurality of gratings with different reflection center wavelengths are inscribed in an optical fiber in an optical fiber grating sensing array at intervals, and the plurality of gratings are packaged in a packaging shell. The packaging shell comprises a packaging shell I, a packaging shell II, a packaging shell III and a packaging shell IV. When the optical gratings are packaged in the packaging shells I, II, III and IV, the optical gratings are used as different sensors respectively. Compared with a traditional soil pressure sensor and a strain gauge, the volume is smaller, and the influence on a soil body is reduced; meanwhile, the optical fiber grating sensor is used in series connection, multiple point positions and multiple physical quantity data can be measured only through one optical fiber, the optical fiber grating has high electromagnetic signal interference resistance, and the problems that a traditional sensor is complex in circuit and prone to being affected by electromagnetic interference, and data are affected are solved.

Description

Technical Field

[0001] This invention relates to the field of geotechnical engineering foundation treatment technology, specifically to a soil pressure-strain-temperature fiber optic grating sensor and distributed monitoring system for the soil arching effect in transparent soil. Background Technology

[0002] When constructing engineering structures on foundations with poor geological conditions, soft soil foundations, characterized by poor permeability, high compressibility, and low bearing strength, require necessary treatment methods. Pile-supported embankments can effectively reduce the occurrence of problems such as total foundation settlement and differential settlement. Furthermore, compared to other soft soil foundation treatment methods such as vacuum preloading consolidation, drainage board consolidation, and flexible pile composite foundations, pile-supported embankments, due to the soil arching effect, possess the characteristics of high strength, small deformation, and high economy, and are widely used in the construction of engineering structures on soft soil foundations.

[0003] The soil arching effect is caused by the difference in stiffness between the pile and the soil, resulting in a settlement difference between them. During the settlement process, the embankment fill transfers part of its own weight to the pile. Traditional soil arching effect model test devices require the embedding of a large number of sensors to monitor the stress and strain data inside the soil. The large number and size of the sensors lead to overly complicated measurement circuits, which can easily affect the stress and strain data inside the soil. Summary of the Invention

[0004] The purpose of this invention is to provide a soil pressure-strain-temperature fiber optic grating sensor and distributed monitoring system for the soil arching effect in transparent soil. This sensor is used in a transparent model test device for the soil arching effect of a spring-loaded door. The model test device includes a support frame, a support plate, a model groove, a movable door, a movable door fixing device, a lifting system, and a monitoring system. A support plate is positioned above the support frame. A model groove is positioned above the support plate. The support frame, support plate, and model groove together form a space for housing the movable door, the movable door fixing device, and the lifting system. The movable door includes two fixed blocks and one movable block. The fixed blocks simulate pile foundations. The movable block simulates soil between piles and is located between the two fixed blocks. The movable door fixing device is located inside the support frame to support the fixed blocks. The lifting system drives the movable block to move vertically up and down within the space. The monitoring system includes a CCD camera and a laser to monitor the displacement and strain fields inside the soil. During the test, transparent sand is filled into the model groove.

[0005] The monitoring system also includes a fiber Bragg grating sensor array and a demodulator. The fiber Bragg grating sensor array is embedded in transparent sand, with one end extending out of the sand and connected to the demodulator.

[0006] The fiber grating sensing array includes an optical fiber, a fiber grating soil pressure sensor, a fiber grating pore water pressure sensor, a fiber grating strain sensor, and a fiber grating temperature sensor.

[0007] The optical fiber has several gratings inscribed internally at intervals, and each grating has a different reflection center wavelength. These gratings are encapsulated in a housing. The housing includes housing I, housing II, housing III, and housing IV.

[0008] When the grating is encapsulated inside the housing I, it is used as a fiber optic grating earth pressure sensor to measure changes in earth pressure at the top of a movable door.

[0009] When the grating is encapsulated inside the housing II, it is used as a fiber optic grating pore water pressure sensor to measure the effective stress value when the soil pressure changes.

[0010] When the grating is encapsulated inside the housing III, it is used as a fiber optic strain sensor to measure the deformation trend of the soil during the soil arch evolution process.

[0011] When the grating is encapsulated inside the housing IV, it is used as a fiber optic grating temperature sensor to measure the temperature change caused by frictional heat generation between particles during the soil arch evolution process.

[0012] Furthermore, the fiber optic grating earth pressure sensor includes a grating and a housing I.

[0013] The encapsulation housing I includes a housing body I and a pressure-sensitive diaphragm I. The pressure-sensitive diaphragm I is fixed to one end face of the housing body I, so that one side of the pressure-sensitive diaphragm I is in direct contact with the soil, and the other side faces inward into the housing body I. A boss is provided at the center of the side of the pressure-sensitive diaphragm I facing the housing body I. The grating is attached to the boss, and the optical fibers at both ends of the grating extend out of the housing body I.

[0014] Furthermore, the fiber optic grating pore water pressure sensor includes a grating and a housing II.

[0015] The encapsulation shell II includes a shell body II, a pressure-sensitive diaphragm II, and a permeable stone. The permeable stone is fixed to one end face of the shell body II, so that one side of the permeable stone is in direct contact with the soil, and the other side faces inward into the shell body II. The pressure-sensitive diaphragm II is installed inside the shell body II, dividing the shell body II into two chambers. The chamber closer to the permeable stone is designated as the saturation chamber, and the other is designated as the grating chamber.

[0016] The saturation cavity is filled with saturated water. The grating is located in the grating cavity and is attached to the pressure-sensitive diaphragm II.

[0017] Furthermore, the fiber optic strain sensor includes a grating and a housing Ⅲ.

[0018] The encapsulation housing III includes a base layer and a protective layer. The grating is attached between the base layer and the protective layer. The base layer and the protective layer are metal sheets.

[0019] Furthermore, the fiber optic temperature sensor includes a grating and a housing IV.

[0020] The encapsulation shell IV is a sleeve, and the grating is located inside the sleeve.

[0021] The technical effects of this invention are undeniable, and its beneficial effects are as follows:

[0022] Compared to traditional earth pressure sensors and strain gauges, the fiber Bragg grating sensor of this invention is smaller in size, reducing its impact on the soil. At the same time, the fiber Bragg grating sensor can be used in series, and multiple points and multiple physical quantities can be measured with only one optical fiber. Furthermore, the fiber Bragg grating has a strong resistance to electromagnetic signal interference, avoiding the problems of complex circuitry and susceptibility to electromagnetic interference that plague traditional sensors. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of an axial loading device;

[0024] Figure 2 Schematic diagram of the transparent model test device for the soil arch effect of a spring-loaded movable door;

[0025] Figure 3 Schematic diagram of the transparent model test device for the soil arch effect of a spring-loaded movable door;

[0026] Figure 4 Schematic diagram of the door fixing device;

[0027] In the diagram: Support frame 1, base plate 101, top plate 102, column I 103, support plate 2, model groove 3, movable door 4, fixing block 401, movable block 402, movable door fixing device 5, pull rod 501, support plate 502, fixing hole I 5021, fixing hole II 5022, spring 503, pin 504, lifting system 6, electric lift 601. Detailed Implementation

[0028] The present invention will be further described below with reference to embodiments, but it should not be construed that the scope of the present invention is limited to the following embodiments. Various substitutions and modifications made based on ordinary technical knowledge and common practices in the art without departing from the above-described technical concept of the present invention should be included within the scope of protection of the present invention.

[0029] Example 1:

[0030] A soil pressure-strain-temperature fiber optic grating sensor and distributed monitoring system for the soil arching effect in transparent soil are disclosed. This system is used in a transparent model test device for the soil arching effect of a spring-loaded movable door. The model test device includes a support frame 1, a support plate 2, a model groove 3, a movable door 4, a movable door fixing device 5, a lifting system 6, and a monitoring system. The support plate 2 is positioned above the support frame 1. The model groove 3 is positioned above the support plate 2. The support frame 1, support plate 2, and model groove 3 form a space for accommodating the movable door 4, the movable door fixing device 5, and the lifting system 6. The movable door 4 includes two fixed blocks 401 and one movable block 402. The fixed blocks 401 simulate pile foundations. The movable block 402 simulates the soil between piles and is located between the two fixed blocks 401. The movable door fixing device 5 is located inside the support frame 1 and supports the fixed blocks. The lifting system drives the vertical movement of the movable block 402 within the accommodating space. The monitoring system includes a CCD camera and a laser for monitoring the displacement and strain fields within the soil. During the test, the model trough 3 was filled with transparent sand.

[0031] The monitoring system also includes a fiber Bragg grating sensor array and a demodulator. The fiber Bragg grating sensor array is embedded in transparent sand, with one end extending out of the sand and connected to the demodulator.

[0032] The fiber grating sensing array includes an optical fiber, a fiber grating soil pressure sensor, a fiber grating pore water pressure sensor, a fiber grating strain sensor, and a fiber grating temperature sensor.

[0033] The optical fiber has several gratings inscribed internally at intervals, and each grating has a different reflection center wavelength. These gratings are encapsulated in a housing. The housing includes housing I, housing II, housing III, and housing IV.

[0034] When the grating is encapsulated inside the housing I, it is used as a fiber optic grating earth pressure sensor to measure changes in earth pressure at the top of the movable door 4.

[0035] When the grating is encapsulated inside the housing II, it is used as a fiber optic grating pore water pressure sensor to measure the effective stress value when the soil pressure changes.

[0036] When the grating is encapsulated inside the housing III, it is used as a fiber optic strain sensor to measure the deformation trend of the soil during the soil arch evolution process.

[0037] When the grating is encapsulated inside the housing IV, it is used as a fiber optic grating temperature sensor to measure the temperature change caused by frictional heat generation between particles during the soil arch evolution process.

[0038] Example 2:

[0039] The main structure of this embodiment is the same as that of Embodiment 1. Furthermore, the fiber optic grating earth pressure sensor includes a grating and a packaging shell I.

[0040] The encapsulation housing I includes a housing body I and a pressure-sensitive diaphragm I. The pressure-sensitive diaphragm I is fixed to one end face of the housing body I, so that one side of the pressure-sensitive diaphragm I is in direct contact with the soil, and the other side faces inward into the housing body I. A boss is provided at the center of the side of the pressure-sensitive diaphragm I facing the housing body I. The grating is attached to the boss, and the optical fibers at both ends of the grating extend out of the housing body I.

[0041] Example 3:

[0042] The main structure of this embodiment is the same as any one of embodiments 1 to 2. Furthermore, the fiber optic grating pore water pressure sensor includes a grating and a packaging shell II.

[0043] The encapsulation shell II includes a shell body II, a pressure-sensitive diaphragm II, and a permeable stone. The permeable stone is fixed to one end face of the shell body II, so that one side of the permeable stone is in direct contact with the soil, and the other side faces inward into the shell body II. The pressure-sensitive diaphragm II is installed inside the shell body II, dividing the shell body II into two chambers. The chamber closer to the permeable stone is designated as the saturation chamber, and the other is designated as the grating chamber.

[0044] The saturation cavity is filled with saturated water. The grating is located in the grating cavity and is attached to the pressure-sensitive diaphragm II.

[0045] Example 4:

[0046] The main structure of this embodiment is the same as any one of embodiments 1 to 3. Furthermore, the fiber optic strain sensor includes a grating and a packaging shell III.

[0047] The encapsulation housing III includes a base layer and a protective layer. The grating is attached between the base layer and the protective layer. The base layer and the protective layer are metal sheets.

[0048] Example 5:

[0049] The main structure of this embodiment is the same as any one of embodiments 1 to 4. Furthermore, the fiber optic temperature sensor includes a grating and a packaging shell IV.

[0050] The encapsulation shell IV is a sleeve, and the grating is located inside the sleeve.

[0051] In this embodiment, the sleeve is a stainless steel tube or a ceramic tube.

[0052] Example 6:

[0053] The main structure of this embodiment is the same as any one of embodiments 1 to 5. Furthermore, the monitoring system is applied to the transparent model test device of the soil arch effect of the spring movable door.

[0054] The model test device also includes an axial loading device, which includes a loading reaction frame 7, an actuator 8, a hydraulic device 9, a frame 10, and a loading plate 11.

[0055] The loading reaction frame includes four columns and four crossbars.

[0056] One end of the column is fixed to the working platform, and the other end is perpendicularly connected to the crossbar. The four crossbars are connected perpendicularly in sequence to form a square ring frame structure.

[0057] The loading reaction frame is internally equipped with an actuator 8, a hydraulic device 9, a frame 10, a loading plate 11, and a model testing device.

[0058] The hydraulic device 9 is fixed to the working platform. The telescopic end of the hydraulic device 9 is connected to the bottom of the frame 10. Driving the hydraulic device 9 allows the frame 10 to move up and down along the loading reaction frame 7, thereby driving the actuator 8 fixed thereon to move up and down. After the frame 10 moves to the target position, it is fixed to the loading reaction frame 7. The telescopic end of the actuator 8 points vertically downwards, facing the model groove 3. A loading plate is placed on the transparent sand. During loading, the telescopic end of the actuator, driven by a motor, applies pressure to the loading plate, thereby compacting the transparent sand.

[0059] The reaction frames on both sides of the present invention can control the actuator to move up and down, can adapt to acrylic model tanks of different sizes, and realize the control of the relative density of transparent sand model test.

[0060] The axial loading device is used to control the compaction of sand during the backfilling process. Loading stops once the sand compaction reaches a specified value. During the test, a water-filled bladder with a cross-sectional size of a model trench is placed on top of the soil. The axial loading device then applies load to the water-filled bladder through its loading plate, thereby applying confining pressure to the soil.

[0061] Example 7:

[0062] The main structure of this embodiment is the same as any one of embodiments 1 to 6. Furthermore, this device introduces an axial loading device and a fiber optic grating sensor in the movable door test.

[0063] The axial loading device can control the relative density of transparent sand in the model trench.

[0064] Fiber Bragg grating (FBG) sensors solve the problem that traditional transparent soil model tests can only obtain soil displacement field data, but cannot obtain internal stress data of transparent soil. At the same time, FBG sensors also avoid the problem that the large size of traditional sensors affects the data on internal stress of the soil.

[0065] See Figure 1 It includes a loading reaction frame, actuator, model slot, movable door device, fiber Bragg grating sensor, and fiber Bragg grating demodulator.

[0066] Working principle:

[0067] ① The reaction frame is similar to a forklift at both ends, with a hydraulic device to control the up and down movement of the middle blue frame. The actuator of the middle loading device can also move up and down. With a loading plate slightly smaller than the size of the model trough, the relative density of the sand can be controlled.

[0068] ② Fiber Bragg grating sensors are embedded inside the model trench and connected to a demodulator via optical fiber. This allows for the measurement of soil pressure, pore water pressure, and strain within the soil. The fiber Bragg grating sensors and the demodulator are connected in series on the same optical fiber. Pressure, strain, and temperature are calculated by converting changes in the center wavelengths of multiple sensors.

[0069] Example 8:

[0070] The main structure of this embodiment is the same as any one of embodiments 1 to 7. Furthermore, a soil pressure-strain-temperature fiber optic grating sensor and distributed monitoring system for the soil arching effect of transparent soil are used in the transparent model test device of the soil arching effect of spring movable door.

[0071] The model testing device includes a support frame 1, a support plate 2, a model slot 3, a movable door 4, a movable door fixing device 5, and a lifting system 6.

[0072] The supporting frame 1 includes a base plate 101, a top plate 102, and several columns 1103. The bottom of each column 1103 is connected to the upper surface of the base plate 101, and the top is connected to the lower surface of the top plate 102, forming a hexahedral frame structure. A supporting plate 2 is installed on the upper surface of the top plate 102. Both the supporting plate 2 and the top plate 102 are square annular plates, and the inner holes of the supporting plate 2 and the top plate 102 communicate with the interior of the supporting frame 1. A model groove 3 is fixed on the upper surface of the supporting plate 2. The model groove 3 is a hexahedral structure that is hollow inside and open at both ends.

[0073] The movable door 4 is disposed within the inner hole of the support plate 2 and the top plate 10. The movable door 4 includes two fixed blocks 401 and one movable block 402. In this embodiment, the fixed blocks 401 and the movable block 402 are made of P-type steel. The fixed blocks 401 are used to simulate pile foundations. The movable block 402 is used to simulate soil between piles and is located between the two fixed blocks 401. The tops of the fixed blocks 401 and the movable block 402 are higher than the bottom of the model groove 3.

[0074] The movable door fixing device 5 is installed inside the support frame 1 and is used to support the fixing block 401. The movable door fixing device 5 includes a pull rod 501, a support plate 502, a spring 503, and a pin 504. The support plate 502 is located inside the frame of the support frame 1 and is suspended on the top plate 102. The support plate 502 has a fixing hole I 5021 at its center, and fixing holes II 5022 are also provided on the support plate 502 at intervals around the fixing hole I. The pull rod 501 is threaded. One end of the pull rod 501 passes through the fixing hole I 5021 and abuts against the bottom surface of the fixing block 401, and the other end is locked by a nut. The pin 504 is threaded. One end of the pin 504 passes through the fixing hole II 5022 and abuts against the bottom surface of the fixing block 401, and the other end is locked by a nut. A spring 503 is fitted on the pin 504.

[0075] The movable door fixing device 5 has two support methods.

[0076] Method 1: Fix the fixing block 401 using pin 504 and pull rod 501.

[0077] Method 2: Adjust the position of pin 504 and fix the fixing block 401 by spring 503 and pull rod 501.

[0078] The lifting system 6 is used to drive the movable block 402 to move vertically within the accommodating space. The lifting system 6 includes an electric lift 601 and a lift displacement controller. The lift displacement controller is connected to the electric lift 601 and is used to control the lifting of the electric lift 601. The electric lift 601 is located inside the support frame 1, and the telescopic end of the electric lift 601 abuts against the lower surface of the movable block 402.

[0079] During the test, the model trough 3 was filled with transparent sand.

[0080] The model testing device is also equipped with a data acquisition and processing system. This system includes a laser emitter, a CCD industrial camera, and a computer. The laser emitter is used to emit a light source to illuminate the interior of the soil, and the CCD industrial camera is used to synchronously capture dynamic images and transmit them to the computer.

Claims

1. A soil pressure-strain-temperature fiber optic grating sensor and distributed monitoring system for the soil arching effect in transparent soil, used in a transparent model test device for the soil arching effect of a spring-loaded movable door, the model test device comprising a support frame (1), a support plate (2), a model groove (3), a movable door (4), a movable door fixing device (5), a lifting system (6), and a monitoring system; the support plate (2) is provided above the support frame (1); the model groove (3) is provided above the support plate (2); the support frame (1), the support plate (2), and the model groove (3) form a receiving space for placing the movable door (4), the movable door fixing device (5), and the spring-loaded movable door (6). 5) and lifting system (6); the movable door (4) includes two fixed blocks (401) and one movable block (402); the fixed block (401) is used to simulate pile foundation; the movable block (402) is used to simulate soil between piles and is located between the two fixed blocks (401); the movable door fixing device (5) is set inside the support frame (1) to support the fixed block; the lifting system is used to drive the movable block (402) to move vertically within the accommodating space; the monitoring system includes a CCD camera and a laser to monitor the displacement field and strain field inside the soil; during the test, the model trench (3) is filled with transparent sand, characterized in that: The monitoring system also includes a fiber optic grating sensor array and a demodulator; the fiber optic grating sensor array is embedded in transparent sand, and one end extends out of the transparent sand and is connected to the demodulator. The fiber grating sensing array includes an optical fiber, a fiber grating soil pressure sensor, a fiber grating pore water pressure sensor, a fiber grating strain sensor, and a fiber grating temperature sensor. The optical fiber has several gratings etched inside at intervals, and each grating has a different reflection center wavelength; the several gratings are encapsulated in an encapsulation shell; The encapsulation housing includes encapsulation housing I, encapsulation housing II, encapsulation housing III, and encapsulation housing IV; When the grating is encapsulated inside the encapsulation housing I, it is used as a fiber optic grating earth pressure sensor to measure the change in earth pressure at the top of the movable door (5); When the grating is encapsulated inside the housing II, it is used as a fiber optic grating pore water pressure sensor to measure the effective stress value when the soil pressure changes. When the grating is encapsulated inside the housing III, it is used as a fiber optic strain sensor to measure the deformation trend of the soil during the soil arch evolution process. When the grating is encapsulated inside the housing IV, it is used as a fiber optic grating temperature sensor to measure the temperature change caused by frictional heat generation between particles during the soil arch evolution process.

2. The soil pressure-strain-temperature fiber optic grating sensor and distributed monitoring system for the soil arching effect in transparent soil according to claim 1, characterized in that: The fiber optic earth pressure sensor includes a grating and a housing I; The encapsulation shell I includes the shell body I and the pressure-sensitive diaphragm I; the pressure-sensitive diaphragm I is fixed to one end face of the shell body I, so that one side of the pressure-sensitive diaphragm I is in direct contact with the soil and the other side faces the inside of the shell body I; a boss is provided at the center of the side of the pressure-sensitive diaphragm I facing the shell body I; the grating is attached to the boss, and the optical fibers at both ends of the grating extend out of the shell body I.

3. The soil pressure-strain-temperature fiber optic grating sensor and distributed monitoring system for the soil arching effect in transparent soil according to claim 1, characterized in that: The fiber optic grating pore water pressure sensor includes a grating and a housing II; The encapsulation shell II includes a shell body II, a pressure-sensitive diaphragm II, and a permeable stone; the permeable stone is fixed on one end face of the shell body II, so that one side of the permeable stone is in direct contact with the soil and the other side faces the interior of the shell body II; the pressure-sensitive diaphragm II is installed inside the shell body II, and the pressure-sensitive diaphragm II divides the shell body II into two chambers, the chamber near the permeable stone is denoted as the saturation chamber, and the other is denoted as the grating chamber; The saturation cavity is filled with saturated water; the grating is located in the grating cavity and is attached to the pressure-sensitive diaphragm II.

4. The soil pressure-strain-temperature fiber optic grating sensor and distributed monitoring system for the soil arching effect in transparent soil according to claim 1, characterized in that: The fiber optic strain sensor includes a grating and a housing III; The encapsulation shell III includes a base layer and a protective layer; the grating is attached between the base layer and the protective layer; the base layer and the protective layer are metal sheets.

5. The soil pressure-strain-temperature fiber optic grating sensor and distributed monitoring system for the soil arching effect in transparent soil according to claim 1, characterized in that: The fiber optic temperature sensor includes a grating and a housing IV; The encapsulation shell IV is a sleeve, and the grating is located inside the sleeve.

Images