Positive and negative triaxial fiber bragg grating space strain sensor for flow-state solidified soil

Abstract

The invention provides a positive and negative triaxial fiber bragg grating spatial strain sensor suitable for flow-state solidified soil. The device comprises six fiber bragg grating strain sensing units which are respectively arranged in six axial directions of a positive X axial direction, a negative X axial direction, a positive Y axial direction, a negative Y axial direction, a positive Z axial direction and a negative Z axial direction in a space, and all-directional measurement of positive strain and shear strain in a target space is realized by directly measuring positive strain in the three directions and indirectly deducing shear strain in the three directions. And meanwhile, a temperature compensation unit is arranged for eliminating the influence of temperature change on strain measurement. Compared with a traditional space strain sensor, the device has the following advantages that the device is compact and stable in structure and can be directly buried in flow-state solidified soil or other flow-state environments, and the mechanical behavior of the device is not affected; six-direction symmetrical arrangement ensures that the sensor senses external force more uniformly, and the sensor adapts to a complex stress field.

Description

Technical Field

[0001] The invention belongs to the technical field of fiber grating sensor measurement, and relates to a positive and negative triaxial fiber grating sensor for measuring spatial strain in fluidized solidified soil. Background Art

[0002] In modern engineering, strain monitoring is a crucial tool for assessing structural health and is widely used for health monitoring and fault diagnosis of structures such as bridges, tunnels, aircraft, and spacecraft. Strain sensors play a crucial role in high-precision applications, particularly in fields like aerospace and civil engineering. Traditional strain measurement methods typically rely on electrical strain gauges or fiber Bragg grating (FBG) sensors, which provide strain data in a single direction.

[0003] In the field of civil engineering, especially in infrastructure construction, fluidized solidified soil, as a new type of soil reinforcement material, has become an important technical means to improve engineering quality and safety. By introducing a curing agent, fluidized solidified soil can significantly improve the physical and mechanical properties of the soil and is widely used in engineering projects such as soft soil foundation reinforcement and building foundation stability improvement. However, the strength and stability of fluidized solidified soil are affected by various factors during the construction process, which may cause soil strain changes in different directions, thereby affecting the curing effect and the safety of the structure. Therefore, accurately monitoring the strain distribution of fluidized solidified soil during construction and use, especially the strain changes in multiple directions, is the key to ensuring engineering quality.

[0004] Currently, some fiber Bragg grating (FBG) technologies have been applied to multi-axis strain monitoring, but most existing technologies still have some limitations. For example, while traditional triaxial strain sensors can monitor strain in three perpendicular directions, they cannot fully cover all possible strain directions. Moreover, in complex environments, temperature changes often affect the accuracy of strain measurements, leading to measurement errors. In addition, the strain sensors used in existing technologies are relatively complex in structure, making it difficult to achieve simple installation and long-term stability in engineering. Therefore, designing a spatial fiber Bragg grating (FBG) strain sensing device that is easy to install, has strong serviceability, and is stable over the long term has become an urgent problem in the current technical field. Summary of the Invention

[0005] To address the problems of existing strain monitoring technology in complex engineering projects, particularly in fluidized solidified soil applications, such as a single monitoring direction, significant temperature influence, and insufficient monitoring accuracy, the present invention provides a fiber Bragg grating strain sensing device capable of precise strain monitoring in multiple directions and effective temperature compensation. The device features easy installation, strong serviceability, and can stably perform three-dimensional strain detection on fluidized solidified soil over a long period of time. Furthermore, temperature compensation improves strain measurement accuracy.

[0006] According to the above invention objectives, the present invention adopts the following technical solutions:

[0007] A positive and negative triaxial fiber Bragg grating spatial strain sensor for fluidized solidified soil, comprising six strain fiber sensing units, one temperature fiber sensing unit, and a bracket.

[0008] A spatial XYZ three-axis rectangular coordinate system can be established with the center of the sensor as the origin, including the X-axis, Y-axis, and Z-axis; with the origin as the starting point of the coordinate position, strain fiber optic sensing units are respectively set in the six axes of the positive and negative directions of each coordinate axis, namely the positive X-axis direction, the negative X-axis direction, the positive Y-axis direction, the negative Y-axis direction, and the positive Z-axis direction, to monitor the strain signals of the fluidized solidified soil in the six axial directions; the temperature fiber optic sensing unit and each of the strain fiber optic sensing units are respectively connected to the signal processor via optical fibers;

[0009] A temperature fiber optic sensing unit is set at the center position of the sensor to detect the temperature of the fluidized solidified soil. The temperature fiber optic sensing unit is connected to the signal processor to form a temperature compensation system. During the strain measurement process of the fluidized solidified soil, temperature compensation is performed through the temperature compensation system.

[0010] Preferably, the overall contour of the sensor is a double tetrahedral pyramid combination grid structure, which has a bracket consisting of 12 edges and 6 vertices; external connecting supports are arranged between adjacent vertices as edges, and each vertex is formed by a common point in which 4 external connecting supports are connected to each other; inside the double tetrahedral pyramid combination grid structure, internal connecting members are arranged along 6 axial directions respectively; a hollow connecting block assembly is arranged at the center position inside the double tetrahedral pyramid combination grid structure, and the center of the hollow connecting block assembly is used as the origin of the spatial XYZ three-axis rectangular coordinate system; the strain fiber optic sensing units are respectively arranged on the 6 axially arranged internal connecting members, and the temperature fiber optic sensing unit is arranged in the internal cavity of the hollow connecting block; an external connecting support and the internal connecting members connected at both ends of the external connecting support constitute a triangular support structure, and there are a total of 12 triangular support structures, and the triangular support structures connect the strain fiber optic sensing units in a symmetrically distributed form.

[0011] Preferably, the hollow connection block assembly is provided with optical fiber mounting holes in six axial directions; in each axial direction, a sealing assembly is provided corresponding to each optical fiber mounting hole of the hollow connection block assembly to seal the optical fiber mounting hole; in each axial direction, a fixing member is provided near the common connection point of the four external connection supports at the same vertex, and the external connection supports and the fixing member are fastened together to form a rigid frame; in the same axial direction, an intermediate section of soft protective tube is provided between the sealing assembly and the fixing member, and the sealing assembly is connected to the hollow connection block assembly and the intermediate section of soft protective tube through interfaces at both ends, respectively; a strain optical fiber sensing unit is provided in the middle section of the intermediate section of the soft protective tube, and the signal end of the strain optical fiber sensing unit is connected to the built-in optical fiber in the armored cable;

[0012] A packaging assembly and a cover plate are provided inside the hollow connecting block assembly. The packaging assembly is provided with an optical fiber mounting hole, and the cover plate is used to encapsulate the optical fiber mounting hole of the hollow connecting block assembly; the armored wire with the built-in optical fiber passes through the optical fiber mounting hole of the sealing assembly, the cover plate and the packaging assembly, so that one end of the optical fiber is connected to the signal end of the temperature optical fiber sensing unit, and the armored wire is also nested inside the soft protective tube in the middle section. The outlet end of the armored wire passes through the inner hole of the fixing part, so that the temperature optical fiber sensing unit and each of the strain optical fiber sensing units are connected to the signal processor through the optical fiber.

[0013] The hollow connecting block assembly, sealing assembly, external connecting support, middle section soft protective tube, fixing parts, packaging assembly and cover plate can all be 3D printed and formed, and are easy to design and manufacture.

[0014] The hollow connecting block assembly described in the present invention is located at the center of the sensor, serving as a connecting core, and is connected to the strain fiber optic sensing unit through a sealing assembly; the triangular support structure connects the strain sensing units in a symmetrically distributed manner to form a rigid frame, ensuring that the sensor unit can maintain a fixed position under different loads or external interference, avoiding measurement errors caused by displacement or vibration; the fixing part is installed at the connection between the strain fiber optic sensing unit and the triangular support structure, for fixing and dispersing external forces; the packaging assembly is arranged inside the hollow connecting block assembly, and the temperature fiber optic sensing unit is packaged therein, so that the packaged temperature fiber optic sensing unit in the cavity is only affected by temperature and not by external force, ultimately forming the temperature sensing unit of the sensor.

[0015] Preferably, the strain optical fiber sensing unit is located at the center of the middle section of the soft protective tube between the sealing assembly and the fixing member, and the strain optical fiber sensing unit is fixed to the inner wall of the middle section of the soft protective tube by filling a fixing agent.

[0016] Preferably, the hollow connecting block assembly adopts a spherical hollow module structure.

[0017] Preferably, the packaging component adopts a square packaging module structure.

[0018] Preferably, the sealing assembly adopts a cylindrical packaging module structure.

[0019] Preferably, the fixing member adopts a disc-shaped fixing module structure.

[0020] Preferably, an adhesive is injected into the soft protective tube to fix the armor wires.

[0021] Preferably, the armor wire is led out from the end of the soft protective tube, and the armor wire is sheathed on the optical fiber.

[0022] Preferably, the internal cavity of the hollow connecting block assembly is filled with polyurethane as a damping material to form a vibration-damping material layer.

[0023] Preferably, the hollow connection block adopts any one of a hollow spherical node, a hollow short cylindrical connector, and a hollow short prism connector.

[0024] Preferably, the strain optical fiber sensing unit adopts a strain optical fiber Bragg grating (FBG) sensor.

[0025] The calculation of the positive and negative triaxial fiber Bragg grating spatial strain sensor of the present invention is based on the mathematical model of the strain tensor and fiber Bragg grating technology. The strain signal measured by the sensor, namely the wavelength change of the fiber Bragg grating, needs to be converted according to the relationship between strain and wavelength change to obtain the actual strain value. The core principles of the present invention are as follows:

[0026] The relationship between fiber Bragg grating and strain:

[0027] Where: ε is strain, a dimensionless parameter; Δλ is the wavelength change of the fiber Bragg grating; k is the calibration coefficient of the fiber Bragg grating, obtained in the experiment; λ0 is the initial wavelength of the fiber Bragg grating.

[0028] The six fiber Bragg grating strain sensing units are installed in the six directions of space. The six directions of the sensor can be marked as ε xx , ε yy , ε zz , ε -xx , ε -yy , ε -zz .

[0029] Among them, ε xx , ε yy , ε zz is the normal strain along the X, Y, and Z directions, ε -xx , ε -yy , ε -zz is the strain in the opposite direction.

[0030] The strain tensor in space is usually represented by a symmetric 3×3 matrix, which represents the strain state of a point in three-dimensional space. It contains three normal strain components and three shear strain components:

[0031]

[0032] The normal strain is directly measured by the wavelength change of the fiber Bragg grating, and the wavelength change Δλ measured by each sensing unit is i Corresponding to the strain ε in the corresponding direction i The shear strain is obtained through multi-point measurement and calculated by the relative displacement between strain units in different directions. The specific calculation principle is as follows:

[0033] By using known positive strain in the negative direction (such as ε -xx ), can be integrated to get the displacement (u x ):

[0034]

[0035] Where C1 is a constant determined by boundary conditions or known displacement states. Displacement u along the y and z directions y 、u z The same logic applies.

[0036]

[0037] By displacement u in the x and y directions x 、u y The shear strain γ along the xy plane can be obtained xy :

[0038]

[0039] Similarly, γ xz and γ yz It can be obtained by normal strain in two orthogonal directions.

[0040]

[0041] At this time, the normal strain in any direction can be calculated using the strain data in the six directions of the orthogonal beam structure.

[0042] For strain in any direction Assumptions is a unit vector, and the strain calculation formula in any direction is:

[0043]

[0044] The unit vector The length is 1, for any direction Satisfy n x 2 +n y 2 +n z 2 =1.

[0045] Assume that the coordinates of the target point are (x, y, z), where the direction component is calculated as follows:

[0046]

[0047] In order to eliminate the influence of temperature fluctuation on strain measurement, temperature compensation is introduced:

[0048] ε r =ε m -T c

[0049] Among them, ε r is the actual strain value, which has taken temperature compensation into account; ε m is the uncompensated strain value; T c is the temperature compensation value, calculated based on the data provided by the temperature sensor.

[0050] Compared with the prior art, the present invention has obvious outstanding substantive features and significant advantages:

[0051] The present invention's positive and negative triaxial fiber Bragg grating spatial strain sensor includes six identically structured strain sensing units arranged in six spatial directions: positive X, negative X, positive Y, negative Y, and positive Z, negative Z. Furthermore, the device includes a temperature sensing unit located within the spherical mold at the center of the sensor. This unit performs temperature compensation during strain measurement, eliminating the effects of temperature changes on measurement results and enabling precise stress detection in multiple directions.

[0052] 2. The hollow connecting block assembly of the present invention is filled with polyurethane as a damping material to reduce the interference of construction vibration on measurement accuracy. Polyurethane is elastic and wear-resistant, and can provide a strong damping effect, making it suitable for long-term use.

[0053] 3. The sensor of the present invention can more comprehensively cover all possible strain directions and, in complex environments, can eliminate the interference of temperature changes on strain measurement, effectively eliminating measurement errors. The strain sensor of the present invention has a simple structure, which can achieve easy installation and long-term stability in engineering. BRIEF DESCRIPTION OF THE DRAWINGS

[0054] Figure 1 It is a schematic diagram of a positive and negative triaxial fiber Bragg grating spatial strain sensor for fluidized solidified soil according to a preferred embodiment of the present invention.

[0055] Figure 2 Schematic diagram of the structure of a strain optical fiber sensing unit according to a preferred embodiment of the present invention.

[0056] Figure 3 It is a structural schematic diagram of a temperature optical fiber sensing unit according to a preferred embodiment of the present invention.

[0057] As shown in the figure: 1-hollow connecting block assembly, 2-sealing assembly, 3-external connecting support, 4-middle section soft protective tube, 5-fixing part, 6-armored wire, 7-optical fiber, 8-packaging assembly, 9-cover plate, 10-temperature optical fiber sensing unit, 11-strain optical fiber sensing unit. DETAILED DESCRIPTION

[0058] The preferred embodiment of the present invention adopts the following principles:

[0059] The calculation of the positive and negative triaxial fiber Bragg grating spatial strain sensor of the present invention is based on the mathematical model of the strain tensor and fiber Bragg grating technology. The strain signal measured by the sensor, namely the wavelength change of the fiber Bragg grating, needs to be converted according to the relationship between strain and wavelength change to obtain the actual strain value. The core principles of the present invention are as follows:

[0060] The relationship between fiber Bragg grating and strain:

[0061] Where: ε is strain, a dimensionless parameter; Δλ is the wavelength change of the fiber Bragg grating; k is the calibration coefficient of the fiber Bragg grating, obtained in the experiment; λ0 is the initial wavelength of the fiber Bragg grating.

[0062] The six fiber Bragg grating strain sensing units are installed in the six directions of space. The six directions of the sensor can be marked as ε xx , ε yy , ε zz , ε -xx , ε -yy , ε -zz .

[0063] Among them, ε xx , ε yy , ε zz is the normal strain along the X, Y, and Z directions, ε -xx , ε -yy , ε -zz is the strain in the opposite direction.

[0064] The strain tensor in space is usually represented by a symmetric 3×3 matrix, which represents the strain state of a point in three-dimensional space. It contains three normal strain components and three shear strain components:

[0065]

[0066] The normal strain is directly measured by the wavelength change of the fiber Bragg grating, and the wavelength change Δλ measured by each sensing unit is i Corresponding to the strain ε in the corresponding direction i The shear strain is obtained through multi-point measurement and calculated by the relative displacement between strain units in different directions. The specific calculation principle is as follows:

[0067] By using known positive strain in the negative direction (such as ε -xx ), can be integrated to get the displacement (u x ):

[0068]

[0069] Where C1 is a constant determined by boundary conditions or known displacement states. Displacement u along the y and z directions y 、u z The same logic applies.

[0070]

[0071] By displacement u along the x and y directions x 、u y The shear strain γ along the xy plane can be obtained xy :

[0072]

[0073] Similarly, γ xz and γ yz It can be obtained by normal strain in two orthogonal directions.

[0074]

[0075] At this time, the normal strain in any direction can be calculated using the strain data in the six directions of the orthogonal beam structure.

[0076] For strain in any direction Assumptions is a unit vector, and the strain calculation formula in any direction is:

[0077]

[0078] The unit vector The length is 1, for any direction Satisfy n x 2 +n y 2 +n z 2 =1.

[0079] Assume that the coordinates of the target point are (x, y, z), where the direction component is calculated as follows:

[0080]

[0081] In order to eliminate the influence of temperature fluctuation on strain measurement, temperature compensation is introduced:

[0082] ε r =ε m -T c

[0083] Among them, ε r is the actual strain value, which has taken temperature compensation into account; ε m is the uncompensated strain value; T c is the temperature compensation value, calculated based on the data provided by the temperature sensor.

[0084] The above solution is further described below with reference to specific implementation examples. The preferred embodiments of the present invention are described in detail as follows:

[0085] Example 1

[0086] like Figure 1-3 As shown, a positive and negative triaxial fiber Bragg grating spatial strain sensor for fluidized solidified soil includes six strain fiber sensing units 11, one temperature fiber sensing unit 10 and a bracket portion;

[0087] A spatial XYZ three-axis rectangular coordinate system, including the X-axis, Y-axis, and Z-axis, can be established with the center of the sensor as the origin. With the origin as the starting point of the coordinate position, strain fiber optic sensing units 11 are respectively provided in the six axial directions of the positive and negative directions of each coordinate axis, namely, the positive X-axis direction, the negative X-axis direction, the positive Y-axis direction, the negative Y-axis direction, and the positive Z-axis direction, and the negative Z-axis direction, for monitoring the strain signals of the fluidized solidified soil in the six axial directions. The temperature fiber optic sensing unit 10 and each of the strain fiber optic sensing units 11 are respectively connected to the signal processor via optical fibers 7.

[0088] A temperature fiber optic sensing unit 10 is set at the center position of the sensor to detect the temperature of the fluidized solidified soil. The temperature fiber optic sensing unit 10 is connected to the signal processor to form a temperature compensation system. During the strain measurement process of the fluidized solidified soil, temperature compensation is performed through the temperature compensation system.

[0089] This embodiment of the positive and negative triaxial fiber Bragg grating spatial strain sensor for fluidized solidified soil achieves omnidirectional measurement of the positive and shear strains within the target space by directly measuring the positive strains in three directions and indirectly inferring the shear strains in three directions. It is also equipped with a temperature compensation unit to eliminate the effects of temperature changes on strain measurement. Compared with traditional spatial strain sensors, the sensor of this embodiment has the following advantages: the device structure is compact and stable, and can be directly buried in fluidized solidified soil or other fluid environments without affecting its mechanical behavior; the six-way symmetrical arrangement ensures that the sensor perceives external forces more uniformly, adapts to complex force fields, and has high measurement accuracy.

[0090] Example 2

[0091] This embodiment is basically the same as the first embodiment, with the following special features:

[0092] like Figure 1-3 As shown, the overall outline of the sensor is a double tetrahedral pyramid combination grid structure, which has a bracket consisting of 12 edges and 6 vertices; external connecting supports 3 are set between adjacent vertices as edges, and each vertex is formed by a common point where four external connecting supports 3 are connected to each other; inside the double tetrahedral pyramid combination grid structure, internal connecting members are set along 6 axial directions respectively; a hollow connecting block assembly 1 is set at the center position inside the double tetrahedral pyramid combination grid structure, and the center of the hollow connecting block assembly 1 is used as the origin of the spatial XYZ three-axis rectangular coordinate system; the strain fiber optic sensing unit 11 is respectively set on the 6 axially set internal connecting members, and the temperature fiber optic sensing unit 10 is set in the internal cavity of the hollow connecting block 1; an external connecting support 3 and the internal connecting members connected at both ends thereof form a triangular support structure, and there are a total of 12 triangular support structures, which connect the strain fiber optic sensing units 11 in a symmetrically distributed form.

[0093] This embodiment adopts a device structure with a symmetrical geometric structure, which is easy to design and manufacture, has a simple structure, and a six-way symmetrical arrangement to ensure that the sensor perceives external forces more uniformly, adapts to complex force fields, and has high measurement accuracy.

[0094] Example 3

[0095] This embodiment is basically the same as the above embodiment, with the following special features:

[0096] like Figure 1-3As shown, in the positive and negative triaxial fiber Bragg grating spatial strain sensor for fluidized solidified soil, the hollow connecting block assembly 1 is provided with fiber mounting holes in six axial directions; in each axial direction, a sealing assembly 2 is provided corresponding to each fiber mounting hole of the hollow connecting block assembly 1 to seal the fiber mounting hole; in each axial direction, a fixing member 5 is provided near the common connection point of the four external connecting supports 3 at the same vertex, and the external connecting supports 3 and the fixing member 5 are fastened together to form a rigid frame; in the same axial direction, an intermediate section soft protective tube 4 is provided between the sealing assembly 2 and the fixing member 5, and the sealing assembly 2 is connected to the hollow connecting block assembly 1 and the intermediate section soft protective tube 4 through interfaces at both ends respectively, and a strain fiber optic sensing unit 11 is provided in the middle section of the intermediate section soft protective tube 4, and the signal end of the strain fiber optic sensing unit 11 is connected to the built-in optical fiber 7 in the armored wire 6;

[0097] In this embodiment, a packaging component 8 and a cover plate 9 are provided inside the hollow connecting block component 1. The packaging component 8 is provided with an optical fiber mounting hole, and the cover plate 9 is used to encapsulate the optical fiber mounting hole of the hollow connecting block component 1; the armored wire 6 with the built-in optical fiber 7 passes through the sealing component 2, the cover plate 9 and the optical fiber mounting hole of the packaging component 8, so that one end of the optical fiber 7 is connected to the signal end of the temperature optical fiber sensing unit 10, and the armored wire 6 is also nested inside the middle section soft protective tube 4, and the outlet end of the armored wire 6 passes through the inner hole of the fixing member 5, so that the temperature optical fiber sensing unit 10 and each of the strain optical fiber sensing units 11 are connected to the signal processor through the optical fiber 7.

[0098] In this embodiment, the strain optical fiber sensing unit 11 is located at the center of the middle section of the soft protective tube 4 between the sealing assembly 2 and the fixing member 5 , and the strain optical fiber sensing unit 11 is fixed to the inner wall of the middle section of the soft protective tube 4 by filling a fixing agent.

[0099] In this embodiment, the hollow connecting block assembly 1 adopts a spherical hollow module structure; the packaging assembly 8 adopts a square packaging module structure; the sealing assembly 2 adopts a cylindrical packaging module structure; and the fixing member 5 adopts a disc-shaped fixing module structure.

[0100] In this embodiment, adhesive is injected into the soft protective tube 4 to fix the armor wires 6 .

[0101] In this embodiment, the armored wire 6 is led out from the end of the soft protective tube 4 , and the armored wire 6 is sleeved on the optical fiber 7 .

[0102] In this embodiment, the internal cavity of the hollow connecting block assembly 1 is filled with polyurethane as a damping material to form a vibration-damping material layer to reduce the interference of construction vibration on measurement accuracy.

[0103] In this embodiment, the hollow connection block 1 adopts any one of a hollow spherical node, a hollow short cylindrical connector, and a hollow short prism connector.

[0104] In this embodiment, the strain optical fiber sensing unit 11 adopts a strain optical fiber Bragg grating (FBG) sensor.

[0105] In this embodiment, a spherical hollow connecting block assembly 1 is located at the center of the sensor as the connection core, and is connected to the strain fiber sensing unit 11 through a cylindrical packaging assembly 2; the cylindrical packaging assembly 2 is connected to the spherical hollow connecting block assembly 1 and the middle section soft protective tube 4 through interfaces at both ends; the triangular support structure connects the strain sensing units in a symmetrical distribution to form a rigid frame, ensuring that the strain fiber sensing unit 11 can maintain a fixed position under different loads or external interference, avoiding measurement errors caused by displacement or vibration; the disc-shaped fixing member 5 is installed at the connection between the strain fiber sensing unit 11 and the triangular support structure to fix and disperse external forces; the square packaging assembly 8 is arranged inside the spherical mold 1, and the temperature measurement fiber grating unit 10 is encapsulated therein, so that the encapsulated temperature measurement FBG in the cavity is only affected by temperature and not by external forces, ultimately forming the temperature fiber sensing unit 10 of the sensor.

[0106] In addition, except for the strain fiber optic sensing unit 11, the temperature fiber optic sensing unit 10, the armored wire 6 and the optical fiber 7, all can be formed by 3D printing of corrosion-resistant nylon, which is easy to design and manufacture.

[0107] In this embodiment, the armored wire 6 is threaded through the intermediate soft tube 4 and secured with epoxy resin adhesive. A strain gauge fiber grating (FBG) is affixed to the central inner wall of the intermediate soft tube 4. The spherical hollow connecting block assembly 1 and the intermediate soft tube 4 are connected via interfaces at both ends of the cylindrical packaging assembly 2. Each set of optical fiber strain sensing units is arranged along the six directions of positive X, negative X, positive Y, negative Y, positive Z, and negative Z, and connected to the triangular support structure via a disc-shaped fixture 5. This results in a stable structure, evenly distributed stress detection points, and minimal measurement error.

[0108] In this embodiment, the temperature-measuring FBG is embedded in a square packaging component 8, which is then installed in the internal cavity of a spherical hollow connecting block component 1 and sealed with a cover plate 9. Finally, polyurethane is injected into the interior of the spherical hollow connecting block component 1, which forms a damping layer after curing. Finally, the cylindrical packaging component 2 completes the airtight packaging, achieving excellent airtightness and waterproof sealing, avoiding further measurement errors and achieving high detection accuracy.

[0109] Example 4

[0110] This embodiment is basically the same as the above embodiment, with the following special features:

[0111] like Figure 1-3As shown, this embodiment adopts the positive and negative triaxial fiber Bragg grating spatial strain sensor for fluidized solidified soil of the above-mentioned embodiment 3, and its operation method is as follows:

[0112] Drill a hole vertically at the measurement location to the designed burial depth, with the hole diameter matching the guide sleeve. Insert the guide sleeve into the hole to ensure that the gap between the sleeve and the hole wall is uniform to prevent displacement during the pouring of fluidized solidified soil. Fix the sensor of the present invention on the positioning bracket and adjust it to a vertical state using an electronic level. Ensure that the orthogonal directions (X, Y, Z axes) of the six strain sensing units are aligned with the engineering coordinate system. Slowly push the sensor into the guide sleeve to avoid bending of the armored wire 6 and the optical fiber 7. Monitor the optical fiber signal in real time to ensure that there is no abnormal wavelength drift during the lowering of the sensor.

[0113] After securing the sensor, pour fluidized soil to the target height and then cover with a waterproof sealant to prevent external moisture infiltration. Lead the armored cable 6 and optical fiber 7 through the pre-buried PVC protective pipe to the surface monitoring station. The surface-end optical fiber connector is encapsulated with a waterproof connector to prevent signal attenuation caused by humid environments.

[0114] After the burial is completed, the optical fiber demodulator is immediately started to monitor the wavelengths of the six strain FBGs and the temperature measurement FBG10 in real time and calculate the strain value in any direction.

[0115] This embodiment is suitable for a positive and negative three-axis fiber Bragg grating spatial strain sensor for fluidized solidified soil, comprising six fiber Bragg grating strain sensing units, which are respectively arranged in six directions in space (positive X, negative X, positive Y, negative Y, positive Z, negative Z). By directly measuring the positive strain in three directions and indirectly deducing the shear strain in three directions, omnidirectional measurement of the positive strain and shear strain in the target space is achieved. At the same time, a temperature compensation unit is provided to eliminate the influence of temperature changes on strain measurement. Compared with traditional spatial strain sensors, the present invention has the following advantages: the device structure is compact and stable, and can be directly buried in fluidized solidified soil or other fluid environments without affecting its mechanical behavior; the six-way symmetrical arrangement ensures that the sensor's perception of external force is more uniform and adapts to complex force fields.

[0116] The above embodiments, combined with the accompanying drawings, provide a detailed description of the specific implementation methods of the present invention. However, it should be noted that the technical solutions covered by the present invention are not limited to the above embodiments. Based on the design purpose and core principles of the present invention, any improvement and extension of the technical solution made by any person skilled in the art through logical adjustment, modification, equivalent replacement, functional combination or structural simplification, etc., as long as it does not deviate from the technical principles and inventive concepts of the present invention and does not exceed the scope of protection defined by the claims, shall be regarded as an equivalent implementation method of the present invention and fall within the scope of legal protection of this patent.

Claims

1. A positive and negative triaxial fiber Bragg grating spatial strain sensor for fluidized solidified soil, characterized by: It includes six strain optical fiber sensing units (11), one temperature optical fiber sensing unit (10) and a bracket part; A spatial XYZ three-axis rectangular coordinate system can be established with the center of the sensor as the origin, including the X-axis, the Y-axis and the Z-axis; with the origin as the starting point of the coordinate position, strain optical fiber sensing units (11) are respectively set in the six axial directions of the positive and negative directions of each coordinate axis, namely, the positive X-axis direction, the negative X-axis direction, the positive Y-axis direction, the negative Y-axis direction, the positive Z-axis direction and the negative Z-axis direction, for monitoring the strain signals of the fluidized solidified soil in the six axial directions; the temperature optical fiber sensing unit (10) and each of the strain optical fiber sensing units (11) are respectively connected to the signal processor via optical fibers (7); A temperature optical fiber sensing unit (10) is arranged at the center of the sensor to detect the temperature of the fluidized solidified soil. The temperature optical fiber sensing unit (10) is connected to a signal processor to form a temperature compensation system. During the strain measurement process of the fluidized solidified soil, temperature compensation is performed through the temperature compensation system.

2. The positive and negative triaxial fiber Bragg grating spatial strain sensor for fluidized solidified soil according to claim 1, characterized in that: The overall outline of the sensor is a double tetrahedral pyramid combination grid structure, which has a bracket consisting of 12 edges and 6 vertices; external connection supports (3) are arranged between adjacent vertices as edges, and each vertex is formed by a common point where four external connection supports (3) are connected to each other; internal connection members are arranged along six axial directions inside the double tetrahedral pyramid combination grid structure; a hollow connection block assembly (1) is arranged at the center position inside the double tetrahedral pyramid combination grid structure, and the center of the hollow connection block assembly (1) is used as the origin of the spatial XYZ three-axis rectangular coordinate system; the strain optical fiber sensing units (11) are respectively arranged on the six axially arranged internal connection members, and the temperature optical fiber sensing unit (10) is arranged in the internal cavity of the hollow connection block (1); an external connection support (3) and the internal connection members connected at both ends thereof form a triangular support structure, and there are a total of 12 triangular support structures, and the triangular support structures connect the strain optical fiber sensing units (11) in a symmetrically distributed form.

3. The positive and negative triaxial fiber Bragg grating spatial strain sensor for fluidized solidified soil according to claim 1, characterized in that: The hollow connection block assembly (1) is provided with optical fiber installation holes in six axial directions; in each axial direction, a sealing assembly (2) is provided corresponding to each optical fiber installation hole of the hollow connection block assembly (1) to seal the optical fiber installation hole; in each axial direction, a fixing member (5) is provided near the common connection point of four external connection supports (3) at the same vertex, and the external connection supports (3) and the fixing member (5) are fastened together to form a rigid frame; in the same axial direction, an intermediate section soft protective tube (4) is provided between the sealing assembly (2) and the fixing member (5); the sealing assembly (2) is connected to the hollow connection block assembly (1) and the intermediate section soft protective tube (4) through interfaces at both ends; a strain optical fiber sensing unit (11) is provided in the intermediate section of the intermediate section soft protective tube (4); the signal end of the strain optical fiber sensing unit (11) is connected to the built-in optical fiber (7) in the armored wire (6); A packaging assembly (8) and a cover plate (9) are provided inside the hollow connection block assembly (1); the packaging assembly (8) is provided with an optical fiber installation hole, and the cover plate (9) is used to package the optical fiber installation hole of the hollow connection block assembly (1); an armored wire (6) with a built-in optical fiber (7) passes through the sealing assembly (2), the cover plate (9) and the optical fiber installation hole of the packaging assembly (8), so that one end of the optical fiber (7) is connected to the signal end of the temperature optical fiber sensing unit (10); the armored wire (6) is also nested inside the intermediate soft protective tube (4), and the outlet end of the armored wire (6) passes through the inner hole of the fixing member (5), so that the temperature optical fiber sensing unit (10) and each of the strain optical fiber sensing units (11) are connected to the signal processor through the optical fiber (7).

4. The positive and negative triaxial fiber Bragg grating spatial strain sensor for fluidized solidified soil according to claim 3, characterized in that: The strain optical fiber sensing unit (11) is located at the center of the middle section soft protective tube (4) between the sealing component (2) and the fixing member (5), and the strain optical fiber sensing unit (11) is fixed to the inner wall of the middle section soft protective tube (4) by filling a fixing agent.

5. The positive and negative triaxial fiber Bragg grating spatial strain sensor for fluidized solidified soil according to claim 3, characterized in that: The hollow connecting block assembly (1) adopts a spherical hollow module structure; Alternatively, the packaging component (8) adopts a square packaging module structure; Alternatively, the sealing component (2) adopts a cylindrical packaging module structure; Alternatively, the fixing member (5) adopts a disc-shaped fixing module structure.

6. The positive and negative triaxial fiber Bragg grating spatial strain sensor for fluidized solidified soil according to claim 3, characterized in that: Adhesive is injected into the soft protective tube (4) to fix the armor wire (6).

7. The positive and negative triaxial fiber Bragg grating spatial strain sensor for fluidized solidified soil according to claim 3, characterized in that: The armored wire (6) is led out from the end of the soft protective tube (4), and the armored wire (6) is sleeved on the optical fiber (7).

8. The positive and negative triaxial fiber Bragg grating spatial strain sensor for fluidized solidified soil according to any one of claims 1 to 7, characterized in that: The internal cavity of the hollow connecting block assembly (1) is filled with polyurethane as a damping material to form a vibration-damping material layer.

9. The positive and negative triaxial fiber Bragg grating spatial strain sensor for fluidized solidified soil according to any one of claims 1 to 7, characterized in that: The hollow connection block (1) adopts any one of a hollow spherical node, a hollow short cylindrical connector, and a hollow short prism connector.

10. The positive and negative triaxial fiber Bragg grating spatial strain sensor for fluidized solidified soil according to any one of claims 1 to 7, characterized in that: The strain optical fiber sensing unit (11) adopts a strain optical fiber Bragg grating (FBG) sensor.

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