Rock mass deformation monitoring device and method based on radial and axial displacement conversion

Abstract

The application discloses a kind of rock mass deformation monitoring device and method based on radial and axial displacement conversion, belong to ground stress measurement device technical field, and the rock mass deformation monitoring device based on radial and axial displacement conversion of this application includes protective sleeve, transmission optical cable, radial displacement monitoring unit and ground data demodulation system.Wherein, radial displacement monitoring unit includes two contact plates, cantilever beam and fiber grating strain sensor, contact plate is elastically abutting to the inner wall of protective sleeve, cantilever beam extends along the axial direction of protective sleeve, the second end of cantilever beam is drivingly connected with another contact plate, fiber grating strain sensor is attached to the surface of cantilever beam and is connected with transmission optical cable.The application realizes the structure separation of force path and sensing path, avoids irreversible chirp distortion, fiber core fracture or adhesive layer peeling of fiber grating due to direct stress, fundamentally solves the problem of permanent failure of sensor, meets the long-term dynamic monitoring demand under the condition of large deformation of soft rock mass.

Description

Technical Field

[0001] This invention relates to the field of geostress measurement device technology, and in particular to a rock mass deformation monitoring device and method based on radial and axial displacement conversion. Background Technology

[0002] In-situ stress is a core fundamental parameter for the stability analysis and disaster prevention of surrounding rock in underground engineering. As engineering projects in energy, transportation, and other fields continue to extend deeper, adverse geological conditions such as weak, fractured rock masses and fault zones are becoming increasingly common under high in-situ stress conditions. These rock masses have low strength and poor self-stability, making them highly susceptible to sustained, large-scale plastic flow or fracture after excavation and unloading—typical large deformation disasters in underground engineering that seriously threaten project safety.

[0003] It should be noted that the underground borehole environment is complex, often containing groundwater, corrosive media, and rock cuttings, which imposes numerous limitations on the installation of traditional sensors. Specifically, traditional sensor installation requires complex sealing and waterproofing treatments, and the more connection points there are, the higher the risk of seal failure. Once the seal fails, the sensor will quickly become unusable due to short circuits and corrosion. Furthermore, borehole diameters are typically only tens of millimeters, with very limited space. If multiple monitoring points need to be deployed, each sensor requires its own power supply and signal lines, forming a large wiring harness that is difficult to fit into the confined space of the borehole. In addition, electrical signals attenuate significantly over long distances, requiring additional relay amplification equipment, which further increases the complexity of the entire monitoring system. Therefore, traditional precision sensors have limitations in measurement range and impact resistance, making it difficult to meet the needs of effective long-term monitoring during periods of large rock deformation.

[0004] As a passive optical element, fiber Bragg gratings possess the following characteristics: First, their core components are made of glass, requiring no external power supply and exhibiting excellent waterproof and corrosion-resistant properties, effectively adapting to the harsh environment inside boreholes. Second, fiber Bragg grating signals are transmitted in optical form, with minimal signal attenuation in the optical fiber. Furthermore, dozens of fiber Bragg gratings of different wavelengths can be connected in series on a single fiber, each grating corresponding to a monitoring point. The signals from each monitoring point are independent of each other, perfectly solving the problem of limited borehole space. Therefore, fiber Bragg grating strain sensors, with their unique advantages, have become an ideal choice for long-term monitoring in underground engineering.

[0005] However, in existing borehole stress monitoring technologies based on fiber Bragg gratings, fiber Bragg grating strain sensors are typically directly bonded to the surface of the load-bearing element. In this integrated load-bearing and sensing design, the optical fiber not only performs strain sensing but also directly bears the mechanical tensile and compressive loads from rock deformation. When the monitored object is a weak rock mass or a fault fracture zone, the rock mass often undergoes continuous, centimeter-level radial deformation after engineering disturbances. This large deformation acts directly on the optical fiber and its bonding interface through the force transmission mechanism, easily leading to irreversible chirping distortion, core breakage, or permanent damage such as peeling of the adhesive layer from the substrate to the fiber Bragg grating. Once such damage occurs, the sensor permanently fails, thus failing to meet the requirements for long-term dynamic monitoring. Summary of the Invention

[0006] This invention aims to solve at least one of the technical problems existing in the prior art. To this end, this invention proposes a rock mass deformation monitoring device and method based on radial and axial displacement conversion, which can realize the physical separation of the mechanical bearing path of the radial displacement of the rock mass and the fiber optic strain sensing path, avoiding irreversible damage to the fiber optic grating due to direct mechanical tensile and compressive loads.

[0007] This invention also proposes a rock mass deformation monitoring method based on radial and axial displacement conversion.

[0008] According to a first aspect of the present invention, a rock mass deformation monitoring device based on radial and axial displacement conversion includes: a protective sleeve; a transmission optical cable extending axially along the protective sleeve; a radial displacement monitoring unit disposed inside the protective sleeve, the radial displacement monitoring unit including two contact plates, a cantilever beam, and a fiber Bragg grating strain sensor, the two contact plates elastically abutting against the inner wall of the protective sleeve in opposite directions, the cantilever beam extending axially along the protective sleeve, a first end of the cantilever beam being fixedly connected to one of its contact plates, a second end of the cantilever beam being drively connected to the other contact plate, the fiber Bragg grating strain sensor being attached to the surface of the cantilever beam and connected to the transmission optical cable, the fiber Bragg grating strain sensor being configured to measure the bending strain of the cantilever beam; and a ground data demodulation system connected to the transmission optical cable, the ground data demodulation system being configured to demodulate the wavelength signal transmitted by the transmission optical cable.

[0009] The invention offers at least the following advantages: It physically separates the load-bearing path of the radial load on the rock mass from the sensing path. When changes in ground stress cause the rock mass to compress inward or expand outward, resulting in radial displacement, the contact plate directly bears the radial load and undergoes displacement. This displacement is then transmitted to the free end of the cantilever beam, causing it to bend. During this mechanical transmission process, the energy of the rock mass deformation is absorbed step-by-step by the contact plate and the cantilever beam. Because the fiber optic strain sensor is attached to the surface of the cantilever beam, the relationship between them is strain-following rather than a rigid load-bearing connection. Therefore, the fiber optic strain sensor does not need to bear any tensile or compressive loads from the rock mass deformation, thus avoiding irreversible chirping distortion, fiber core breakage, or adhesive peeling caused by direct force on the fiber optic strain sensor. This solves the problem of sensor damage and failure under large deformation conditions. Based on the above structure, when the rock mass is in the elastic deformation stage, this invention can calculate the magnitude and direction of the two-dimensional principal stress in the plane where the measuring point is located by measuring the radial displacement. That is, when the rock mass enters the plastic large deformation stage, this invention can still work stably, and its continuously output displacement detection data can be used as a judgment index for surrounding rock stability evaluation and disaster early warning. Thus, the technical solution of this invention achieves full-process monitoring coverage from elastic deformation to plastic large deformation, meeting the needs of long-term dynamic monitoring and disaster early warning under complex geological conditions such as weak rock masses.

[0010] According to some embodiments of the present invention, multiple radial displacement monitoring units are provided, and the multiple radial displacement monitoring units are arranged at intervals along the axial direction of the protective sleeve. The contact plates of the multiple radial displacement monitoring units are respectively oriented in different directions to measure radial displacement components in different directions.

[0011] According to some embodiments of the present invention, the radial displacement monitoring unit further includes a housing, the axial direction of which is parallel to the axial direction of the protective sleeve. The housing has two oppositely arranged clearance holes, and two contact plates are respectively slidably inserted into the two clearance holes. The contact plates are provided with stop members, which are located inside the housing and are configured to limit the maximum stroke of the contact plates extending out of the corresponding clearance holes.

[0012] According to some embodiments of the present invention, the radial displacement monitoring unit further includes a displacement transmission rod disposed at the second end, the displacement transmission rod being drively connected to the contact plate, and the displacement transmission rod being configured to transmit the radial displacement of the contact plate to the cantilever beam.

[0013] According to some embodiments of the present invention, the radial displacement monitoring unit further includes a first limiting member disposed on the contact plate, the first limiting member being fixedly connected to the cantilever beam, the position of the first limiting member corresponding to the position of the displacement transmission rod, and the first limiting member being configured to prevent the cantilever beam from bending excessively.

[0014] According to some embodiments of the present invention, a grouting pipe is also included, which is inserted into the housing along the axial direction of the protective sleeve. The grouting pipe is connected to a plurality of grouting branch pipes along its extension direction. The grouting branch pipes are configured to fill the annular space between the protective sleeve and the wall of the monitoring hole with grouting material.

[0015] According to some embodiments of the present invention, the end of the contact plate is provided with a guide slope, and when the contact plate abuts against the inner wall of the protective sleeve, the guide slope drives the two contact plates to move closer to each other.

[0016] According to a second aspect of the present invention, a rock mass deformation monitoring method based on radial and axial displacement conversion is applied to a rock mass deformation monitoring device based on radial and axial displacement conversion as described in the first aspect of the present invention. The method includes: S1: Perform laboratory calibration on the radial displacement monitoring unit, establish a calibration curve between the center wavelength drift of the fiber grating and the radial displacement, and record the calibration coefficients of each radial displacement monitoring unit. S2: Obtain the preset installation orientation of the radial displacement monitoring unit, install multiple radial displacement monitoring units into the protective sleeve according to the preset installation orientation, pass the transmission optical cable through all the radial displacement monitoring units, and connect all the fiber optic strain sensors to the transmission optical cable to form a series of measurement points. S3: Obtain the design orientation and design inclination, drill a monitoring hole according to the design orientation and design inclination, and lower the measuring point string to the predetermined depth in the monitoring hole; S4: Use the grouting pipe to inject grouting material into the annular space between the protective casing and the borehole wall, so that the outer wall of the protective casing is consolidated and coupled with the rock mass; S5: Continuously monitor the wavelength drift of the fiber optic grating strain sensor through the ground data demodulation system, convert the wavelength drift into radial displacement according to the calibration curve, and record the change data of radial displacement of each measuring point over time. S6: Based on the changing data, establish a set of equations relating radial displacement and far-field stress components, solve the set of equations, and obtain the magnitude and direction of the two-dimensional principal stress in the plane where the measuring point is located.

[0017] It has at least the following beneficial effects: This rock mass deformation monitoring method based on radial and axial displacement conversion has all the beneficial effects brought by the aforementioned rock mass deformation monitoring device based on radial and axial displacement conversion, which will not be repeated here.

[0018] According to some embodiments of the present invention, in S2, before the radial displacement monitoring unit is installed into the protective sleeve, the stop abuts against the inner wall of the housing to limit the maximum outward stroke of the contact plate, and the cantilever beam generates initial bending deformation under the preload of the displacement transmission rod.

[0019] According to some embodiments of the present invention, in S2, multiple radial displacement monitoring units are installed into the protective sleeve according to a preset orientation, including: Install the first radial displacement monitoring unit into the first section of the protective sleeve, aligning the monitoring direction of the first radial displacement monitoring unit with the preset positioning mark on the first section of the protective sleeve; The transmission optical cable is passed through the housing of the first radial displacement monitoring unit and connected to the fiber optic strain sensor of the first radial displacement monitoring unit. Connect the second protective sleeve to the end of the first protective sleeve, and install the second radial displacement monitoring unit inside the second protective sleeve, so that the monitoring direction of the second radial displacement monitoring unit is aligned with the preset positioning mark on the second protective sleeve. Repeat this process until all protective sleeves and all radial displacement monitoring units are connected in series.

[0020] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0021] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which: Figure 1 This is a front view of the rock mass deformation monitoring device based on radial and axial displacement conversion in this specific embodiment; Figure 2 for Figure 1 AA section view in the middle; Figure 3 for Figure 1 A schematic diagram of the structure; Figure 4 for Figure 3 A schematic diagram of the structure after the shell has been concealed. Figure 5 for Figure 2 Installation diagram of the radial displacement monitoring unit; Figure 6 This is a schematic flowchart of the rock mass deformation monitoring method based on radial and axial displacement conversion in this specific embodiment.

[0022] Figure label: Protective sleeve 1; 2. Transmission optical cable; Radial displacement monitoring unit 3, housing 31, clearance hole 311, third limiting member 312, contact plate 32, stop member 321, guide slope 322, push rod 323, limiting groove 324, second limiting member 325, first limiting member 33, preload spring 34, cantilever beam 35, displacement transmission rod 36, fiber optic strain sensor 37, sleeve 38; Ground data demodulation system 4; Grouting pipe 5. Detailed Implementation

[0023] In the description of this invention, it should be understood that the orientation descriptions, such as up, down, left, right, front, back, etc., are based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limiting this invention.

[0024] In the description of this invention, "several" means one or more, "multiple" means two or more, "greater than," "less than," "exceeding," etc. are understood to exclude the stated number, and "above," "below," "within," etc. are understood to include the stated number. If "first," "second," etc. are used in the description, they are only configured to distinguish technical features and should not be construed as indicating or implying relative importance or implicitly indicating the number of indicated technical features or the order of the indicated technical features.

[0025] In the description of this invention, unless otherwise explicitly defined, terms such as "set", "install", and "connect" should be interpreted broadly, and those skilled in the art can reasonably determine the specific meaning of the above terms in this invention in conjunction with the specific content of the technical solution.

[0026] Please refer to Figures 1 to 5This embodiment discloses a rock mass deformation monitoring device based on radial and axial displacement conversion, including a protective sleeve 1, a transmission optical cable 2, a radial displacement monitoring unit 3, and a ground data demodulation system 4. The transmission optical cable 2 extends axially along the protective sleeve 1; the radial displacement monitoring unit 3 is disposed inside the protective sleeve 1 and includes two contact plates 32, a cantilever beam 35, and a fiber Bragg grating strain sensor 37. The two contact plates 32 elastically abut against the inner wall of the protective sleeve 1 in opposite directions. The cantilever beam 35 extends axially along the protective sleeve 1, with its first end fixedly connected to one contact plate 32 and its second end connected to the other contact plate 32. The fiber Bragg grating strain sensor 37 is attached to the surface of the cantilever beam 35 and connected to the transmission optical cable 2, and is configured to measure the bending strain of the cantilever beam 35. The ground data demodulation system 4 is connected to the transmission optical cable 2 and is configured to demodulate the wavelength signal transmitted by the transmission optical cable 2.

[0027] Reference Figures 1 to 5 The protective sleeve 1 is lowered into the monitoring hole to provide mechanical protection and installation support for the internal components. Its outer diameter is slightly smaller than the diameter of the monitoring hole to form an annular space for filling with grouting material. The transmission optical cable 2 extends along the axial direction of the protective sleeve 1. Several radial displacement monitoring units 3 are arranged at intervals along the axial direction of the protective sleeve 1. One end of the transmission optical cable 2 is connected to the ground data demodulation system 4, and the other end is connected to the fiber optic strain sensor 37 of the radial displacement monitoring unit 3 to transmit the wavelength signal output by the fiber optic strain sensor 37 to the ground. The ground data demodulation system 4 then demodulates the wavelength signal and calculates the ground stress parameters.

[0028] Reference Figures 2 to 4The radial displacement monitoring unit 3 includes two contact plates 32, a cantilever beam 35, and a fiber optic strain sensor 37. Both contact plates 32 can elastically float in the vertical direction. Specifically, a preload spring 34 is provided between the two contact plates 32, applying radially outward pressure to both contact plates 32 simultaneously, causing them to extend in opposite directions and press against the inner wall of the protective sleeve 1 to accurately sense the radial displacement of the rock mass. The cantilever beam 35 has a fixed end at one end and a free end at the other. The fixed end of the cantilever beam 35 is fixedly mounted on one of the contact plates 32, while the free end extends axially along the protective sleeve 1 and is connected to the other contact plate 32 via a transmission connection. It should be noted that, in the initial state, when the preload spring 34 drives the two contact plates 32 to press against the inner wall of the protective sleeve 1, the cantilever beam 35 undergoes initial bending deformation under the preload of the contact plates 32. When the contact plates 32 slide inward under the radial pressure of the rock mass, they drive the free end of the cantilever beam 35 to move downward, thereby causing further bending deformation of the cantilever beam 35. The fiber optic strain sensor 37 is attached to the tension surface of the cantilever beam 35 and connected to the transmission optical cable 2. When the cantilever beam 35 undergoes bending deformation, the fiber optic strain sensor 37 generates axial strain, causing its center wavelength to drift, thereby converting the bending strain of the cantilever beam 35 into a wavelength signal. This wavelength signal is transmitted to the ground data demodulation system 4 for processing via the transmission optical cable 2.

[0029] This invention physically separates the load-bearing path of the radial load on the rock mass from the sensing path. When the rock mass undergoes radial displacement due to inward compression or outward expansion of the monitoring borehole wall caused by changes in ground stress, the contact plate 32 directly bears the radial load of the rock mass and undergoes displacement. The contact plate 32 transmits this displacement to the free end of the cantilever beam 35, causing the cantilever beam 35 to bend and deform. In this mechanical transmission process, the energy of the rock mass deformation is absorbed step by step by mechanical components such as the contact plate 32 and the cantilever beam 35. Since the fiber optic strain sensor 37 is attached to the surface of the cantilever beam 35, the relationship between it and the cantilever beam 35 is strain-following rather than a rigid load-bearing connection. Therefore, the fiber optic strain sensor 37 does not need to bear any tensile or compressive loads from the rock mass deformation, thereby avoiding irreversible chirping distortion, fiber core breakage, or adhesive peeling caused by direct force on the fiber optic strain sensor 37. This solves the problem of easy damage and failure of the sensor under large deformation conditions. Based on the above structure, when the rock mass is in the elastic deformation stage, this invention can calculate the magnitude and direction of the two-dimensional principal stress in the plane where the measuring point is located by measuring the radial displacement. That is, when the rock mass enters the plastic large deformation stage, this invention can still work stably, and its continuously output displacement detection data can be used as a judgment index for surrounding rock stability evaluation and disaster early warning. Thus, the technical solution of this invention achieves full-process monitoring coverage from elastic deformation to plastic large deformation, meeting the needs of long-term dynamic monitoring and disaster early warning under complex geological conditions such as weak rock masses.

[0030] In some specific embodiments of the present invention, a push rod 323 is provided at one end of the housing 31 for the contact plate 32, and the two push rods 323 of the two contact plates 32 are coaxially arranged and extend in the same direction. A sleeve 38 is sleeved on the outer side of the two push rods 323, and a preload spring 34 is disposed between the two push rods 323. The elastic structure composed of the push rods 323, the sleeve 38 and the preload spring 34 is a conventional design in the art, and its specific limiting method will not be described in detail here. An optical cable channel is opened in the middle of the sleeve 38. The optical cable channel is a tubular channel located on the same horizontal line as the cantilever beam 35, and the transmission optical cable 2 passes through the tubular channel.

[0031] Furthermore, there are two pre-tension springs 34, which are arranged side by side between the two push rods 323. The two pre-tension springs 34 are spaced apart by a preset distance to form a clearance space for the optical cable to pass through. The optical cable channel is located between the two pre-tension springs 34, and the transmission optical cable 2 passes through the gap between the two pre-tension springs 34, thereby avoiding interference with the compression stroke of the pre-tension springs 34.

[0032] In some specific embodiments of the present invention, there are multiple radial displacement monitoring units 3, which are arranged at intervals along the axial direction of the protective sleeve 1. The contact plates of the multiple radial displacement monitoring units 3 are oriented in different directions to measure radial displacement components in different directions.

[0033] Please refer to Figure 1 The number of radial displacement monitoring units 3 is selected according to measurement needs, such as two, three, four, or more. Each radial displacement monitoring unit 3 is arranged at a predetermined spacing within the protective sleeve 1. This spacing can be determined based on the required density of measuring points and the geological conditions of the rock mass. The contact plates of each radial displacement monitoring unit 3 face different azimuth angles. Taking three radial displacement monitoring units 3 as an example, the contact plate of the first unit can face 0°, the contact plate of the second unit can face 120°, and the contact plate of the third unit can face 240°, meaning that each contact plate forms a 120° angle with each other in the circumferential direction. Of course, other angle intervals can also be selected according to actual measurement needs, such as 45°, 60°, or 90°, as long as the contact plates of each radial displacement monitoring unit 3 face different azimuths. Through the above arrangement, when radial displacement occurs in the rock mass of the monitoring borehole wall, the contact plates at different azimuths can independently sense the radial displacement components in their respective directions, thereby obtaining radial displacement data in multiple different directions. These multi-directional data can be used for subsequent two-dimensional geostress inversion calculations to determine the maximum principal stress, minimum principal stress, and their orientation angles in the plane where the measuring point is located.

[0034] In some specific embodiments of the present invention, the radial displacement monitoring unit 3 further includes a housing 31, the axial direction of the housing 31 being parallel to the axial direction of the protective sleeve 1, the housing 31 having two oppositely arranged clearance holes 311, two contact plates 32 being slidably inserted into the two clearance holes 311 respectively, the contact plates 32 being provided with a stop member 321, the stop member 321 being located inside the housing 31, the stop member 321 being configured to limit the maximum stroke of the contact plate 32 extending out of the corresponding clearance hole 311.

[0035] Reference Figures 2 to 4The axis of the housing 31 extends in the left-right direction. The housing 31 has two clearance holes 311 arranged opposite each other in the up-down direction, penetrating the side wall of the housing 31 radially. Two contact plates 32 are respectively arranged corresponding to the two clearance holes 311, sliding through the corresponding clearance holes 311. Both contact plates 32 can float in the up-down direction. In the initial state, the preload spring 34 applies radial outward pressure to the two contact plates 32, causing them to pass through the corresponding clearance holes and extend outward. When the housing 31 is fitted with the protective sleeve 1 to further contract the preload spring 34, the preload spring 34 can drive the two contact plates 32 to press against the inner wall of the protective sleeve 1. The stop member 321 is a protruding ridge extending in the up-down direction. The top arc of the protruding ridge matches the curvature of the inner wall of the housing 31. Several protruding ridges are evenly arranged around the periphery of the contact plates 32. In the initial state, the housing 31 is not yet fitted with the protective sleeve 1. When the contact plate 32 extends outward to a predetermined position under the drive of the preload spring 34, the stop 321 abuts against the inner wall of the housing 31, thereby limiting the contact plate 32 from moving further outward, i.e., limiting the maximum stroke of the contact plate 32 extending out of the clearance hole 311. Thus, by setting the stop 321, the contact plate 32 can be effectively prevented from over-extending under the drive of the preload spring 34 and detaching from the housing 31, thereby ensuring the reliability of the device.

[0036] In some specific embodiments of the present invention, the radial displacement monitoring unit 3 further includes a displacement transmission rod 36 disposed at the second end, the displacement transmission rod 36 being connected to the contact plate 32 in a transmission manner, and the displacement transmission rod 36 being configured to transmit the radial displacement of the contact plate 32 to the cantilever beam 35.

[0037] like Figure 2 As shown, the displacement transmission rod 36 extends vertically and is disposed at the second end of the cantilever beam 35. The upper end of the displacement transmission rod 36 is connected to the contact plate 32. When the preload spring 34 drives the two contact plates 32 to press against the inner wall of the protective sleeve 1, the end of the displacement transmission rod 36 abuts against the bottom of the limiting groove 324, so that the cantilever beam 35 undergoes initial bending deformation under the preload of the displacement transmission rod 36. When the contact plate 32 slides inward under the radial pressure of the rock mass, the displacement transmission rod 36 drives the free end of the cantilever beam 35 to move downward, thereby causing the cantilever beam 35 to undergo bending deformation.

[0038] Furthermore, the contact plate 32 is provided with a limiting groove 324, which can accommodate the end of the displacement transmission rod 36 and limit the end of the displacement transmission rod 36 to prevent it from slipping off the contact plate 32 during movement, so as to ensure the reliability of the transmission cooperation between the displacement transmission rod 36 and the contact plate 32.

[0039] In some specific embodiments of the present invention, the cantilever beam 35, the displacement transmission rod 36, and the contact plate 32 located below are integrally formed. In other embodiments, the cantilever beam 35 can also be fixed to the contact plate 32 by other means. Exemplarily, the fixed end of the cantilever beam 35 can be pressed and fixed to the contact plate 32 by fixing screws, and the fixing screws can be coated with thread-locking adhesive to prevent loosening; or, the fixed end of the cantilever beam 35 can be fixed to the contact plate 32 by laser welding to form a non-removable rigid connection.

[0040] It is worth noting that when the monitored object is a weak rock mass or a fault fracture zone, the rock mass may experience unexpectedly large deformations. Without limit protection, excessive radial displacement can cause excessive bending deformation of the cantilever beam 35, which in turn causes the fiber Bragg grating strain sensor 37 attached to its surface to bear excessive tensile strain, resulting in irreversible damage or breakage of the fiber Bragg grating. In some specific embodiments of the present invention, the radial displacement monitoring unit 3 further includes a first limiting member 33 disposed on the contact plate 32. The first limiting member 33 is fixedly connected to the cantilever beam 35, and the position of the first limiting member 33 corresponds to the position of the displacement transmission rod 36. The first limiting member 33 is configured to prevent the cantilever beam 35 from excessive bending. By setting the first limiting member 33, when the deflection of the cantilever beam 35 reaches a preset threshold, the first limiting member 33 contacts the free end and forms a mechanical block, thereby limiting the maximum deflection of the cantilever beam 35 and preventing it from bending further, effectively protecting the fiber Bragg grating strain sensor 37 from overload damage.

[0041] Specifically, such as Figure 2 As shown, the first limiting member 33 is located below the free end of the cantilever beam 35, and its position corresponds vertically to that of the displacement transmission rod 36. When the cantilever beam 35 bends under the drive of the displacement transmission rod 36, the free end moves in the direction of the first limiting member 33. When the deflection of the cantilever beam 35 reaches the preset maximum allowable value, the free end abuts against the first limiting member 33, and the first limiting member 33 prevents the cantilever beam 35 from bending further, thereby limiting the maximum deflection of the cantilever beam 35.

[0042] Specifically, the first limiting member 33 can be a fixed limiting block, a limiting post, or other structural forms with limiting functions. In this embodiment, the limiting member is an adjustable limiting screw, that is, the limiting member is installed on the contact plate 32 by a threaded connection, and its extension length can be adjusted as needed. By adjusting the extension length of the first limiting member 33, the initial gap between the first limiting member 33 and the free end of the cantilever beam 35 can be changed, thereby setting the maximum allowable deflection value of the cantilever beam 35.

[0043] In some specific embodiments of the present invention, the contact plate 32 is provided with a second limiting member 325, and the housing 31 is provided with a third limiting member 312. The second limiting member 325 and the third limiting member 312 cooperate to limit the radial displacement of the contact plate 32.

[0044] like Figures 3 to 5 As shown, the second limiting member 325 is a protrusion extending in the vertical direction, and the third limiting member 312 is a groove formed on the inner wall of the housing 31 and cooperating with the protrusion. The protrusion is slidably embedded in the groove, and the two cooperate to limit the sliding direction of the contact plate 32. Through the sliding cooperation between the protrusion and the groove, the contact plate can be guided to slide smoothly in the radial direction, preventing circumferential deflection or shaking, thereby improving the monitoring efficiency of the device.

[0045] Furthermore, the stop 321 and the second limiting member 325 are integrally formed. Specifically, the raised strip integrates the function of a raised ridge. In other words, the raised structure on the contact plate 32 serves both as the second limiting member 325 slidingly engaging with the groove on the housing 31 to guide the sliding direction of the contact plate 32, and as the stop 321 abutting against the inner wall of the housing 31 when extended to its limit position to limit the maximum extension stroke of the contact plate 32. This integrated design simultaneously realizes both guiding and limiting functions on a single component, simplifying the part structure, reducing processing and assembly costs, and improving the reliability of the device.

[0046] In some specific embodiments of the present invention, a grouting pipe 5 is also included. The grouting pipe 5 passes through the housing 31 along the axial direction of the protective sleeve 1. The grouting pipe 5 is connected to a plurality of grouting branch pipes along its extension direction. The grouting branch pipes are configured to fill the annular space between the protective sleeve 1 and the monitoring hole wall with grouting material.

[0047] Please refer to Figure 1 , Figure 3 and Figure 4 The grouting pipe 5 is a long, slender pipe that extends axially along the protective sleeve 1 and sequentially passes through the housing 31 of each radial displacement monitoring unit 3. One end of the grouting pipe 5 extends to the outside of the orifice for connection to the ground grouting pump, while the other end can be closed or opened as needed. Multiple grouting branch pipes are provided along the extension direction of the grouting pipe 5. Preferably, the position of each grouting branch pipe corresponds to that of each radial displacement monitoring unit 3, meaning that each radial displacement monitoring unit 3 has one or more grouting branch pipes inside its housing 31. The grouting branch pipes sequentially penetrate the housing 31 and the protective sleeve 1, extending to the outside of the protective sleeve 1, and guide the grout to the predetermined grouting position.

[0048] After the monitoring device is lowered to the predetermined depth within the monitoring borehole, grouting material is pumped into the grouting pipe 5 via a ground grouting pump. The grouting material flows along the grouting pipe 5, exits through each grouting branch pipe, and enters the annular space between the protective sleeve 1 and the borehole wall. After the grouting material solidifies, a continuous solidified body is formed between the protective sleeve 1 and the borehole wall. It should be noted that this solidified body can bind the monitoring device to the surrounding rock mass, allowing the deformation and stress of the rock mass to be reliably transmitted to the protective sleeve 1 and the internal radial displacement monitoring unit 3 through the solidified body, ensuring the accuracy and continuity of the measurement signal and eliminating measurement errors caused by poor contact. On the other hand, the solidified body can fix and support the protective sleeve 1 and its internal components, preventing the monitoring device from loosening or shifting during long-term use. Furthermore, the dense structure formed after solidification can effectively isolate the monitoring device from groundwater, corrosive media, and other corrosive substances, thereby improving the long-term durability of the system.

[0049] Preferably, the grouting material is a micro-expansion cement-based grout, whose elastic modulus after curing is similar to that of the surrounding rock mass, thereby forming a continuous force transmission medium with matching elastic modulus between the rock mass, the solidified body and the monitoring device, avoiding stress transmission distortion due to excessive material stiffness differences.

[0050] In some specific embodiments of the present invention, the end of the contact plate 32 is provided with a guide slope. When the contact plate 32 abuts against the inner wall of the protective sleeve 1, the guide slope drives the two contact plates 32 to move closer to each other.

[0051] like Figure 2 As shown, a guide ramp 322 is provided at the left end of the contact plate 32, and the cross-sectional area of ​​the guide ramp 322 gradually decreases from right to left. During the process of installing the radial displacement monitoring unit 3 into the protective sleeve 1, when the guide ramp 322 contacts the edge of the port of the protective sleeve 1, the oblique compression of the two guide ramps 322 on the port of the protective sleeve 1 generates a radial component force. This component force drives the two contact plates 32 to move closer to each other, that is, drives the two contact plates 32 to retract into the housing 31, so that the radial displacement monitoring unit 3 can be smoothly pushed into the protective sleeve 1, avoiding the contact plates 32 from being stuck at the port of the protective sleeve 1 due to protrusion. After the radial displacement monitoring unit 3 is fully inserted into the protective sleeve 1, the two contact plates 32 extend outward under the action of the pre-tension spring 34 and press against the inner wall of the protective sleeve 1.

[0052] It should be noted that before the radial displacement monitoring unit 3 is installed into the protective sleeve 1, the displacement transmission rod 36 is either in contact with or not in contact with the bottom of the limiting groove 324. During the installation process, the two guide ramps 322 contact the ends of the protective sleeve 1, driving the two contact plates 32 to move closer to each other. The displacement transmission rod 36 then moves towards the bottom of the limiting groove 324 and contacts it, thus preloading the cantilever beam 35. After installation, the preload spring 34 drives the two contact plates to extend outward, but constrained by the inner wall of the protective sleeve 1, the displacement transmission rod 36 remains in contact with the bottom of the groove, and the cantilever beam 35 maintains a stable preload state.

[0053] Furthermore, the inner wall of the protective sleeve 1 is provided with a guide groove along the axial direction, and the guide groove matches the end shape of the contact plate 32. When the monitoring unit is installed into the protective sleeve 1, the ends of the two contact plates 32 are respectively embedded in the corresponding guide grooves, thereby guiding the radial displacement monitoring unit 3 to smoothly advance along the axial direction of the protective sleeve 1, while restricting the circumferential rotation of the monitoring unit within the protective sleeve 1.

[0054] Furthermore, the circumferential position of the guide groove on the inner wall of the protective sleeve 1 corresponds to the preset orientation of the contact plate. Since multiple radial displacement monitoring units 3 are arranged at intervals along the axial direction of the protective sleeve 1, and the contact plates of each unit need to face different directions, by setting multiple sets of guide grooves at different circumferential positions on the inner wall of the protective sleeve 1, and setting different positioning features on the housing 31 of each radial displacement monitoring unit 3, it can be ensured that the contact plate 32 of each radial displacement monitoring unit 3 is automatically aligned with the preset orientation when it is installed, thereby achieving precise control of the orientation of the contact plate 32.

[0055] Reference Figure 6 This embodiment discloses a rock mass deformation monitoring method based on radial and axial displacement conversion, which is applied to a rock mass deformation monitoring device based on radial and axial displacement conversion. The method includes: S1: Perform laboratory calibration on radial displacement monitoring unit 3, establish calibration curve between fiber optic grating center wavelength drift and radial displacement, and record calibration coefficients for each radial displacement monitoring unit 3. S2: Obtain the preset installation position of the radial displacement monitoring unit 3, install multiple radial displacement monitoring units 3 into the protective sleeve 1 according to the preset installation position, pass the transmission optical cable 2 through all the radial displacement monitoring units 3, and connect all the fiber optic strain sensors 37 to the transmission optical cable 2 to form a series of measuring points. S3: Obtain the design orientation and design inclination, drill a monitoring hole according to the design orientation and design inclination, and lower the measuring point string to the predetermined depth in the monitoring hole; S4: Use grouting pipe 5 to inject grouting material into the annular space between protective casing 1 and the borehole wall, so that the outer wall of protective casing 1 is consolidated and coupled with the rock mass; S5: The wavelength drift of the fiber optic grating strain sensor 37 is continuously monitored through the ground data demodulation system 4. The wavelength drift is converted into radial displacement according to the calibration curve, and the radial displacement of each measuring point is recorded over time. S6: Based on the changing data, establish a set of equations relating radial displacement and far-field stress components, solve the set of equations, and obtain the magnitude and direction of the two-dimensional principal stress in the plane where the measuring point is located.

[0056] In some specific embodiments of the present invention, in S2, before the radial displacement monitoring unit 3 is installed into the protective sleeve 1, the stop 321 abuts against the inner wall of the housing 31 to limit the maximum outward stroke of the contact plate 32, and the cantilever beam 35 generates initial bending deformation under the preload of the displacement transmission rod 36.

[0057] In some specific embodiments of the present invention, in S2, multiple radial displacement monitoring units 3 are installed into the protective sleeve 1 according to a preset orientation, including: Install the first radial displacement monitoring unit 3 into the first protective sleeve 1, so that the monitoring direction of the first radial displacement monitoring unit 3 is aligned with the preset positioning mark on the first protective sleeve 1. The transmission optical cable 2 is passed through the housing 31 of the first radial displacement monitoring unit 3 and connected to the fiber optic strain sensor 37 of the first radial displacement monitoring unit 3. Connect the second section of protective sleeve 1 to the end of the first section of protective sleeve 1, and install the second radial displacement monitoring unit 3 into the second section of protective sleeve 1, so that the monitoring direction of the second radial displacement monitoring unit 3 is aligned with the preset positioning mark on the second section of protective sleeve 1. Repeat this process until all protective sleeves 1 and all radial displacement monitoring units 3 are connected in series.

[0058] In some specific embodiments of the present invention, the radial displacement is derived from monitoring data at least three different azimuth angles.

[0059] Reference Figures 1 to 6 This embodiment discloses a rock mass deformation monitoring method based on radial and axial displacement conversion. This method is applied to a rock mass deformation monitoring device based on radial and axial displacement conversion, and includes the following steps: S1: Perform laboratory calibration on each radial displacement monitoring unit 3. Specifically, in the laboratory, apply a known radial displacement to each radial displacement monitoring unit 3. Simultaneously, the center wavelength drift of the fiber optic strain sensor 37 is recorded. A calibration curve was established between the center wavelength drift and radial displacement of the fiber grating, and the calibration coefficients of each element were determined. It satisfies the following relationship:

[0060] In the formula, These are radial displacement observations. This is the center wavelength shift of the fiber grating. This is the inherent calibration constant of the sensing unit.

[0061] S2: Obtain the preset installation orientation of the radial displacement monitoring unit 3, install multiple radial displacement monitoring units 3 into the protective sleeve 1 according to the preset installation orientation, pass the transmission optical cable 2 through the housing 31 of all radial displacement monitoring units 3, and connect the fiber optic strain sensor 37 of each radial displacement monitoring unit 3 to the transmission optical cable 2 in sequence to form a series of measuring points.

[0062] Specifically, the process of installing multiple radial displacement monitoring units 3 into the protective sleeve 1 according to a preset orientation is as follows: First, the first radial displacement monitoring unit 3 is installed inside the first protective sleeve 1, aligning its monitoring direction with the pre-set positioning mark on the first protective sleeve 1. During insertion, the guide ramp 322 contacts the edge of the protective sleeve 1. The ramp's oblique compression of the sleeve port generates a radial force, which drives the two contact plates 32 to move closer together, allowing the radial displacement monitoring unit 3 to be smoothly pushed into the protective sleeve 1, preventing the contact plates from sticking to the sleeve port due to overextension. Simultaneously, the stop 321 limits the maximum extension stroke of the contact plates 32, preventing them from overextension during installation.

[0063] Next, the transmission optical cable 2 is passed through the optical cable channel opened inside the housing 31 of the first radial displacement monitoring unit 3, and the transmission optical cable 2 is connected to the fiber optic strain sensor 37 of the first radial displacement monitoring unit 3 using an optical fiber connector.

[0064] Then, the second protective sleeve 1 is connected to the end of the first protective sleeve 1 by means of threaded connection, snap connection or other reliable mechanical connection, and the second radial displacement monitoring unit 3 is installed in the second protective sleeve 1 so that the monitoring direction of the second radial displacement monitoring unit 3 is aligned with the preset positioning mark on the second protective sleeve 1.

[0065] It should be noted that the contact plates of different radial displacement monitoring units 3 are oriented in different directions. In this specific embodiment, the contact plate of the first unit is oriented at 0°, the contact plate of the second unit is oriented at 120°, the contact plate of the third unit is oriented at 240°, and so on, to obtain radial displacement components in different directions.

[0066] Repeat the above process until all protective sleeves 1 and all radial displacement monitoring units 3 are connected in series to form a complete measuring point string.

[0067] It should be further explained that the monitoring direction refers to the direction of the line connecting the two contact plates in the radial displacement monitoring unit 3, that is, the sensitive direction of the radial displacement that this unit can sense. By aligning the monitoring direction with the positioning mark on the protective sleeve 1, it can be ensured that the contact plates of each radial displacement monitoring unit 3 are arranged according to the preset azimuth angle, thereby obtaining the radial displacement components in different directions, providing a data basis for the subsequent inversion of the magnitude and direction of the two-dimensional principal stress in the plane where the measuring point is located based on the theory of elasticity.

[0068] S3: Obtain the design azimuth and inclination angle, and drill a monitoring hole according to the design azimuth and inclination angle. The diameter of the monitoring hole is slightly larger than the outer diameter of the protective sleeve 1 to ensure that the measuring point string can be lowered smoothly. After drilling, clean the bottom of the hole to remove rock cuttings and debris. Slowly and steadily lower the assembled measuring point string to the predetermined depth in the monitoring hole. Because the pre-tensioning spring 34 drives the two contact plates 32 to press against the inner wall of the protective sleeve 1, even if the space between the protective sleeve 1 and the hole wall has not yet been filled with grouting material, this pre-tensioning force can ensure the initial positioning of the measuring point string in the hole.

[0069] S4: Inject grouting material into the annular space between the protective casing 1 and the borehole wall using the grouting pipe 5. Specifically, connect the ground grouting pump to the grouting pipe 5, and start the pump to pump a cured micro-expansion cement-based grout with an elastic modulus similar to the surrounding rock mass into the grouting pipe 5. The micro-expansion cement-based grout flows along the grouting pipe 5, flows out through each grouting branch pipe, and enters the annular space between the protective casing 1 and the monitoring borehole wall. As the micro-expansion cement-based grout is continuously injected, the annular space is gradually filled. Grouting is stopped when the micro-expansion cement-based grout completely fills the entire annular space and returns from the borehole opening.

[0070] S5: After the grouting material has cured, the wavelength data of each fiber optic strain sensor 37 is continuously monitored by the ground data demodulation system 4. The ground data demodulation system 4 reads the wavelength data of each fiber optic strain sensor 37 and calculates the center wavelength drift of each sensor. And according to the calibration curve of equation (1), the wavelength shift amount Converted into radial displacement changes of the monitoring holes in various directions Record the radial displacement of each measuring point over time.

[0071] S6: Based on the theory of elasticity, establish a model relating radial displacement to stress at the far-field point. For a two-dimensional stress field, displacement data in at least three different directions are required. For any direction... The relationship between the radial displacement of the borehole wall and the stress at the far field is shown in equation (2):

[0072] In the formula, These are radial displacement observations. To monitor the borehole radius, The elastic modulus of the rock mass. Poisson's ratio of the rock mass , To measure the normal stress components in the x and y directions in the coordinate system, This represents the shear stress component.

[0073] Boundary conditions of the hole wall Below, a set of polar coordinate displacement observation equations is established, with each equation corresponding to a displacement-stress relationship at a specific azimuth angle. The matrix form of the polar coordinate observation system is constructed as shown in equation (3):

[0074] Finally, the principal stresses are calculated, and the stress components are converted into principal stress parameters that are more meaningful for engineering purposes, as shown in equation (4):

[0075] In the formula, For the maximum and minimum principal stresses, The principal stress direction angle.

[0076] By following the steps above, the magnitude and direction of the two-dimensional principal stress in the plane where the measuring point is located can be obtained, enabling long-term, continuous, and high-precision monitoring of rock mass stress.

[0077] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0078] Of course, the present invention is not limited to the above-described embodiments. Those skilled in the art can make equivalent modifications or substitutions without departing from the spirit of the present invention. All such equivalent modifications or substitutions are included within the scope defined by the claims of this application.

Claims

1. A rock mass deformation monitoring device based on radial and axial displacement conversion, characterized in that, include: Protective sleeve (1); The transmission optical cable (2) extends along the axial direction of the protective sleeve (1); A radial displacement monitoring unit (3) is disposed inside the protective sleeve (1). The radial displacement monitoring unit (3) includes two contact plates (32), a cantilever beam (35), and a fiber optic strain sensor (37). The two contact plates (32) are elastically pressed against the inner wall of the protective sleeve (1) in opposite directions. The cantilever beam (35) extends along the axial direction of the protective sleeve (1). The first end of the cantilever beam (35) is fixedly connected to one of the contact plates (32), and the second end of the cantilever beam (35) is drivenly connected to the other contact plate (32). The fiber optic strain sensor (37) is attached to the surface of the cantilever beam (35) and connected to the transmission optical cable (2). The fiber optic strain sensor (37) is configured to measure the bending strain of the cantilever beam (35). A ground data demodulation system (4) is connected to the transmission optical cable (2), and the ground data demodulation system (4) is configured to demodulate the wavelength signal transmitted by the transmission optical cable (2); The radial displacement monitoring unit (3) is provided in multiple ways. The multiple radial displacement monitoring units (3) are arranged at intervals along the axial direction of the protective sleeve (1). The contact plates (32) of the multiple radial displacement monitoring units (3) are respectively oriented in different directions to measure radial displacement components in different directions. The radial displacement monitoring unit (3) further includes a housing (31), the axial direction of which is parallel to the axial direction of the protective sleeve (1). The housing (31) has two oppositely arranged clearance holes (311), and the two contact plates (32) are respectively slidably inserted into the two clearance holes (311). The contact plate (32) is provided with a stop (321), the stop (321) is located inside the housing (31), and the stop (321) is configured to limit the maximum stroke of the contact plate (32) extending out of the corresponding clearance hole (311).

2. The rock mass deformation monitoring device based on radial and axial displacement conversion according to claim 1, characterized in that, The radial displacement monitoring unit (3) further includes a displacement transmission rod (36) disposed at the second end. The displacement transmission rod (36) is connected to the contact plate (32) in a transmission manner. The displacement transmission rod (36) is configured to transmit the radial displacement of the contact plate (32) to the cantilever beam (35).

3. The rock mass deformation monitoring device based on radial and axial displacement conversion according to claim 2, characterized in that, The radial displacement monitoring unit (3) further includes a first limiting member (33) disposed on the contact plate (32). The first limiting member (33) is fixedly connected to the cantilever beam (35). The position of the first limiting member (33) corresponds to the position of the displacement transmission rod (36). The first limiting member (33) is configured to prevent the cantilever beam (35) from bending excessively.

4. The rock mass deformation monitoring device based on radial and axial displacement conversion according to claim 3, characterized in that, It also includes a grouting pipe (5), which is inserted into the housing (31) along the axial direction of the protective sleeve (1). The grouting pipe (5) is connected to a plurality of grouting branch pipes along its extension direction. The grouting branch pipes are configured to fill the annular space between the protective sleeve (1) and the monitoring hole wall with grouting material.

5. The rock mass deformation monitoring device based on radial and axial displacement conversion according to claim 4, characterized in that, The end of the contact plate (32) is provided with a guide slope (322). When the contact plate (32) abuts against the inner wall of the protective sleeve (1), the guide slope (322) drives the two contact plates (32) to move closer to each other.

6. A method for monitoring rock mass deformation based on radial and axial displacement conversion, characterized in that, The method applied to the rock mass deformation monitoring device based on radial and axial displacement conversion as described in claim 5 includes: S1: Perform laboratory calibration on the radial displacement monitoring unit (3), establish a calibration curve between the center wavelength drift of the fiber grating and the radial displacement, and record the calibration coefficients of each radial displacement monitoring unit (3). S2: Obtain the preset installation position of the radial displacement monitoring unit (3), install multiple radial displacement monitoring units (3) into the protective sleeve (1) according to the preset installation position, pass the transmission optical cable (2) through all the radial displacement monitoring units (3), and connect all the fiber optic strain sensors (37) to the transmission optical cable (2) to form a series of measuring points; S3: Obtain the design orientation and design inclination angle, drill a monitoring hole according to the design orientation and design inclination angle, and lower the measuring point string to a predetermined depth in the monitoring hole; S4: Use the grouting pipe (5) to inject grouting material into the annular space between the protective sleeve (1) and the hole wall, so that the outer wall of the protective sleeve (1) is solidified and coupled with the rock mass; S5: The wavelength drift of the fiber optic strain sensor (37) is continuously monitored by the ground data demodulation system (4), and the wavelength drift is converted into radial displacement according to the calibration curve. The radial displacement of each measuring point is recorded over time. S6: Based on the change data, establish a set of equations relating the radial displacement to the far-field stress components, solve the set of equations, and obtain the magnitude and direction of the two-dimensional principal stress in the plane where the measuring point is located.

7. The rock mass deformation monitoring method based on radial and axial displacement conversion according to claim 6, characterized in that, In S2, before the radial displacement monitoring unit (3) is installed into the protective sleeve (1), the stop (321) abuts against the inner wall of the housing (31) to limit the maximum outward stroke of the contact plate (32), and the cantilever beam (35) undergoes initial bending deformation under the preload of the displacement transmission rod (36).

8. The rock mass deformation monitoring method based on radial and axial displacement conversion according to claim 6, characterized in that, In S2, multiple radial displacement monitoring units (3) are installed into the protective sleeve (1) according to a preset orientation, including: The first radial displacement monitoring unit (3) is installed inside the first section of the protective sleeve (1) so that the monitoring direction of the first radial displacement monitoring unit (3) is aligned with the preset positioning mark on the first section of the protective sleeve (1). The transmission optical cable (2) is passed through the housing (31) of the first radial displacement monitoring unit (3) and connected to the fiber optic strain sensor (37) of the first radial displacement monitoring unit (3). Connect the second section of the protective sleeve (1) to the end of the first section of the protective sleeve (1), and install the second radial displacement monitoring unit (3) into the second section of the protective sleeve (1) so that the monitoring direction of the second radial displacement monitoring unit (3) is aligned with the preset positioning mark on the second section of the protective sleeve (1). Repeat this process until all the protective sleeves (1) and all the radial displacement monitoring units (3) are connected in series.

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