Distributed fiber bragg grating measuring device for displacement of deep soil body and mounting method of distributed fiber bragg grating measuring device

Abstract

The invention discloses a distributed fiber bragg grating measuring device for deep soil displacement and an installation method. The device comprises a chained fiber bragg grating detection part formed by connecting a sensor pipe joint and an optical fiber in series; each section of cross-layer optical fiber is provided with a pay-off box; the pay-off box is provided with two rolling shafts, the upper section of each cross-layer optical fiber is wound on the upper rolling shaft to form an upper wire roller and connected with the upper sensor pipe section, the lower section of each cross-layer optical fiber is wound on the lower rolling shaft to form a lower wire roller and connected with the lower sensor pipe section, and the middle section of each cross-layer optical fiber is a loose section; two electromagnets used for tying the corresponding wire rollers are further arranged in the pay-off box. The lower end of the chained fiber grating detection part is anchored at the bottom end of the measurement hole; the installation method comprises the following steps: anchoring the bottom end of the chain type fiber grating detection part at the bottom of a measurement hole; the protection tube is screwed out of the measuring hole, and the chain type fiber grating detection part is buried in the collapsed hole soil; and then the electromagnet core shaft is retracted, and the wire roller is unlocked. According to the device and the method, the constraint effect on the free horizontal displacement of the sensor pipe joint in the large-displacement stratum can be eliminated.

Description

Technical Field

[0001] This invention relates to the field of deep soil displacement monitoring technology, specifically to a distributed fiber optic grating measuring device for monitoring deep soil displacement and a method for installing the measuring device. Background Technology

[0002] When pile driving or foundation pit excavation is carried out in areas where the soil is prone to horizontal displacement due to disturbance, and when there are buildings or facilities such as subway tunnels, cultural heritage buildings, old and dilapidated buildings, or precision instrument factories nearby, the horizontal displacement of the soil can easily cause the buildings or facilities to tilt, be damaged, or even be destroyed. Therefore, it is necessary to conduct deep horizontal displacement monitoring of the strata between the work area and sensitive buildings and facilities. Once the horizontal displacement of the soil is detected to exceed the safety standard, work must be stopped immediately, and reinforcement, repair, and other protective measures must be taken.

[0003] Distributed fiber Bragg grating (FBG) measurement devices are a mature existing technology. They consist of multiple FBG sensor segments (hereinafter referred to as sensor segments), connected by an optical fiber. All sensor segments are connected in series via multiple optical fiber segments to form a chain-like FBG detection unit deployed within the measurement area. The first sensor segment is connected to a grating sensor analyzer via the first optical fiber segment. The grating sensor analyzer is connected to the main controller, which in turn is connected to an alarm. All components, including the grating sensor analyzer, main controller, and alarm, are located outside the measurement area. This allows each sensor segment along the entire fiber optic detection line to transmit its sensing signal to the grating sensor analyzer via optical fiber. This measurement device is widely used in deep ground horizontal displacement monitoring due to its advantages, including small size, strong anti-interference capability, ease of embedding in the soil, wide dynamic range, high sensitivity, continuous measurement of displacement, strain, and other sensing parameters along the fiber optic line, long transmission distance, and stable transmission performance.

[0004] The existing technology for installing and deploying a distributed fiber optic grating measurement device for monitoring deep soil displacement involves workers drilling vertical measurement holes at ground measurement points using a tracked stepping drill rig. A protective tube is then inserted into the measurement hole using the same rig. A chain-type fiber optic grating detection unit, consisting of sensor sections and optical fibers connected in series, is lowered into the protective tube, enabling monitoring. When horizontal displacement occurs in the soil layer, it causes horizontal displacement of each sensor section. The displacement data of each sensor section is transmitted via optical fiber to a grating sensor analyzer on the ground outside the measurement hole. This allows for the measurement of the horizontal displacement at various depths for each sensor section along a vertical fiber optic detection line. The main controller monitors in real time, taking the largest horizontal displacement value from each sensor section and comparing it to a set alarm value. If the horizontal displacement value of the sensor section with the largest amplitude exceeds the alarm value, an alarm is triggered.

[0005] The aforementioned distributed fiber Bragg grating measurement device and deployment method have the following drawbacks. Due to the complex geological environment in actual construction, multiple strata are often distributed from top to bottom, such as backfill soil layer, silt layer, gravel layer, and rock layer. The horizontal displacement of different strata varies, and the frictional resistance of different strata to the measuring device varies greatly. Specifically, the silt layer has the largest horizontal displacement, while the backfill soil layer and gravel layer have smaller horizontal displacements. Therefore, the middle section of the protective pipe located in the silt layer will exert a pulling effect on the upper section of the protective pipe located in the backfill soil layer and the lower section of the protective pipe located in the gravel layer. This pulls the upper and lower sections of the protective pipe towards the middle section to meet the horizontal displacement of the middle section. However, the backfill soil layer and gravel layer have a large frictional resistance on the upper and lower sections of the protective pipe, preventing the upper and lower sections of the protective pipe from moving towards the silt layer. This significantly hinders and reduces the horizontal displacement amplitude of the middle section of the protective pipe in the silt layer, resulting in the measurement device's detection result being underestimated. For example, the actual lateral displacement of the silt layer is 10cm, but the middle section of the protective pipe, hindered by the backfill soil layer and gravel layer, only displaces 8cm laterally. The current method's relatively small detection results have little impact on normal buildings and facilities. However, for buildings or facilities that are sensitive to horizontal soil movement, such as tunnels, cultural heritage buildings, old and dilapidated buildings, and precision instrument factories, the hazards of small monitoring results, insensitive alarms, and untimely reinforcement and remediation are more obvious. For example, if there are oil tanks around an excavated foundation pit, once the soil shifts horizontally to the pit side to a certain extent, it is easy to cause the oil tanks to tilt, resulting in leakage due to the pulling of oil tank pipelines and joints.

[0006] Furthermore, because the chain-type fiber optic grating detection unit is confined within a protective tube, and the bending deformation range of the protective tube is limited (e.g., the middle section can be bent to a maximum of 120 degrees), the maximum horizontal displacement of the sensor section within the protective tube is also limited. For example, the maximum displacement of the middle sensor section is 12cm. Once the horizontal displacement of the silt layer exceeds 12cm, the sensor section cannot continue to move horizontally, thus limiting the overall range of the existing measuring device. In actual operation, when the horizontal displacement of the silt layer triggers an alarm and technicians intervene to take reinforcement measures, the lateral displacement of the soil often continues. However, because it exceeds the overall range of the measuring device, the horizontal displacement of the silt layer cannot be measured after reinforcement and protection measures are implemented.

[0007] Of course, some industry professionals have also noticed the aforementioned drawbacks of existing devices. To eliminate the constraints imposed by the protective tubes on each sensor section, they have proposed the idea of ​​directly placing the chain fiber optic grating detection unit into the measuring hole without using protective tubes. However, the backfill soil and gravel layers will still cause friction, hindering the movement of the chain fiber optic grating detection unit from the upper and lower sections towards the middle section. Similarly, they will also hinder the free horizontal displacement of the chain fiber optic grating detection unit located in the silt layer. This will not solve the problems of underestimating measurement results and triggering delayed alarms. Furthermore, it will not solve the problem of the limited total range of the measuring device, which will prevent continuous operation and monitoring of deep soil after exceeding the alarm value. Summary of the Invention

[0008] One technical problem to be solved by the present invention is to provide a distributed fiber optic grating measurement device that can eliminate the constraint effect of other strata on the free horizontal displacement of sensor tube sections located in strata with large displacement such as silt layers, ensure accurate measurement results, and expand the total range of deep soil displacement.

[0009] One technical solution of the present invention is to provide a distributed fiber optic grating measurement device for deep soil displacement, comprising a chain-type fiber optic grating detection unit, a grating sensor analyzer, and an alarm; the chain-type fiber optic grating detection unit is composed of multiple sensor tube sections and multiple optical fiber segments connected in series, the chain-type fiber optic grating detection unit is located inside the measurement hole, and the grating sensor analyzer and alarm are located on the ground outside the measurement hole, the uppermost sensor tube section is connected to the grating sensor analyzer and alarm via the uppermost optical fiber segment; each optical fiber segment spanning the stratum interface is provided with a cable-laying box, which is located at the stratum interface; each cable-laying box contains two rollers, the outer ends of which are rotatably connected to the side wall of the cable-laying box; the upper section of each cross-layer optical fiber is wound around the upper roller in a... After the upper roller is formed, it extends out of the top of the pay-off box and connects to the upper sensor tube section. The lower section, after being wound around the lower roller to form the lower roller, extends out of the bottom of the pay-off box and connects to the lower sensor tube section. The middle section is the relaxation section. The dividing point between the upper and middle sections is fixed to the inner end of the upper roller, and the dividing point between the middle and lower sections is fixed to the inner end of the lower roller. The length of the relaxation section is slightly greater than the sum of the distance between the two roller shafts and the radii of the two rollers. The pay-off box is also equipped with two electromagnets. In the initial state, each electromagnet core shaft extends and hooks onto the corresponding roller. After switching between power on and off, each electromagnet core shaft retracts and unlocks from the corresponding roller. The pay-off box is also equipped with a PCB board and power supply for driving the electromagnets. A counterweight is provided at the lower end of the chain fiber optic grating detection section. The counterweight is anchored to the bottom of the measuring hole by cement grout.

[0010] Another technical problem to be solved by the present invention is to provide an installation method for a distributed fiber optic grating measurement device that can eliminate the constraint effect of other strata on the free horizontal displacement of sensor tube sections located in strata with large displacement such as silt layers, ensure accurate measurement results, and expand the total range of deep soil displacement.

[0011] Another technical solution of the present invention is to provide an installation method for a distributed fiber optic grating measurement device for deep soil displacement, which includes the following steps:

[0012] Drill measurement holes and take core samples at the measurement points in the area to be measured. Measure the specific depth of each stratum interface at the measurement point based on the soil samples after core sampling.

[0013] Each sensor tube segment is connected in series with an optical fiber to form a chain fiber optic detection unit. Cross-layer optical fibers with wire-laying boxes are laid according to the depth of the formation interface, so that the distance from each wire-laying box to the ground is equal to the corresponding depth of the formation interface. Then, an electromagnet is used to hold the wire roller of the wire-laying box with the distance already adjusted.

[0014] Drill a protective tube with spiral blades on its outer wall into the measuring hole;

[0015] The chain fiber grating detection unit is lowered into the protective tube, and grout is injected into the bottom of the protective tube to anchor the counterweight at the bottom of the chain fiber grating detection unit to the bottom of the measuring hole.

[0016] Unscrewing the protective tube out of the measuring hole and unscrewing the spiral blades will increase soil disturbance and accelerate the collapse of the measuring hole, thus burying the chain fiber optic grating detection unit in the soil.

[0017] The electromagnet core shaft of each wire feeding box is retracted, which unlocks each wire roller and allows it to feed wire freely.

[0018] Compared with existing technologies, the distributed fiber optic grating measurement device and its installation method for deep soil displacement described above have the following advantages.

[0019] First, a wire-laying box is installed at each stratum interface, and both the upper and lower rollers of the wire-laying box are unlocked, allowing for free wire laying. This solves the problem of automatic compensation for the measuring section located in strata with large horizontal displacement, such as silt layers. This allows each sensor tube section located in the silt layer to move freely horizontally with the silt layer, solving the problem in existing technologies where sensor tube sections in silt layers are pulled by gravel or backfill soil layers, resulting in constrained horizontal displacement amplitude and smaller measurement results. This improves measurement accuracy, makes alarm triggering more sensitive, and facilitates timely reinforcement and remedial measures. It is especially suitable for protecting buildings or facilities around the work area that are sensitive to horizontal soil movement.

[0020] Similarly, by eliminating the constraint effect of adjacent backfill soil layers and gravel layers with small horizontal displacement and high frictional resistance on the sensor tube sections in the silt layer, the problem of limited maximum horizontal displacement amplitude and small range of existing measuring devices is also solved. Even if the lateral displacement amplitude of the measuring device in this application exceeds the warning value and triggers an alarm, it can still continue to play the role of measurement and monitoring. In this way, it provides data support and judgment basis for judging the effect of reinforcement and remediation.

[0021] The laying-out box solves the problem of how to achieve automatic compensation, while the installation method solves the problem of how to lay the laying-out box to the corresponding depth. By taking core samples from the measuring hole, the specific depth of the stratum boundary line is accurately known, and the target depth is clarified. First, the upper and lower rollers are tightened using electromagnets to lock the relative distance between the laying-out box and the sensor tube section. During this stage, each fiber segment acts as a traction rope, allowing the chain fiber grating detection unit to be lowered steadily. After being lowered into place, the chain fiber grating detection unit is straightened by grouting and anchoring with a heavy hammer to determine the accuracy of the depth of each laying-out box and sensor. When the laying-out box and each sensor tube section reach the target depth, the drill rig is reversed to pull up the protective pipe. By rotating the spiral blades of the protective pipe, the disturbance to the surrounding soil is maximized, accelerating the collapse of the hole and burying the chain fiber grating detection, so that the depth of the laying-out box and sensor tube section in the measuring hole is completely fixed. Then, the electromagnet core shaft is retracted to unlock each roller, allowing free laying of the wire. The ingenuity of the above approach lies in first using an electromagnet to hold the wire roller, allowing the optical fiber to be precisely lowered as a traction rope and controlling the depth of the wire box. Then, after the wire box is positioned by burying it in the collapsed hole, the wire roller is unlocked to prevent the optical fiber from pulling and preventing the displacement of the sensors during the monitoring phase. This allows the optical fiber to revert from its function as a traction rope to its function of transmitting signals.

[0022] In summary, the combination and mutual reinforcement of the above-mentioned features enable the precise and deep installation of each wire box, providing length compensation for the measurement section in the silt layer, improving measurement accuracy, expanding the measurement range, and enabling continuous monitoring.

[0023] The preferred structures for fixing the boundary between the upper and middle sections of the cross-layer optical fiber to the inner end of the upper roller, and the boundary between the middle and lower sections of the cross-layer optical fiber to the inner end of the lower roller, are as follows: Each roller has an anchor hole extending from the inner side of the annular surface to the inner end face. The upper section of the cross-layer optical fiber passes through the anchor hole of the upper roller, and a wedge is inserted into the inner end of the anchor hole. The boundary between the upper and middle sections of the cross-layer optical fiber is anchored in the anchor hole of the upper roller by the wedge. The lower section of the cross-layer optical fiber passes through the anchor hole of the lower roller, and a wedge is also inserted into the inner end of the anchor hole. The boundary between the middle and lower sections of the cross-layer optical fiber is anchored in the anchor hole of the lower roller by the wedge. This structure is easy to assemble; it only requires passing the optical fiber section through the anchor hole and inserting the wedge. The wedge is inserted from the inner end of the anchor hole. Thus, when the upper and lower sections of the cross-layer optical fiber are pulled up and down, the wedge will naturally be pulled tighter and tighter, resulting in a firm and reliable anchoring effect.

[0024] Preferably, the vertical partition divides the inner cavity of the pay-off box into two chambers, left and right. Two wire rollers are located in the left chamber, and two electromagnets are located in the right chamber. A gap is left between the inner ends of the two wire rollers and the vertical partition to accommodate the slack section of the cross-layer optical fiber. In the initial state, the electromagnet core shaft passes through the vertical partition and is bolted into the bolt hole at the inner end of the corresponding wire roller. After switching between power on and off, the electromagnet core shaft retracts to the other side of the partition. After the electromagnet core shaft is de-energized, it completely retracts to one side of the partition, ensuring that the partition completely separates the core shaft and the slack section of the cross-layer optical fiber, avoiding accidental entanglement between the slack section and the core shaft when the upper and lower wire rollers are paying off, and improving the stability of the pay-off box.

[0025] As a further optimization, the PCB board and power supply are also located in the right chamber. The PCB board is equipped with a timing circuit, which switches the power on and off of the electromagnet. Accordingly, the PCB board, through the timing circuit, cuts off the power to the corresponding electromagnet 2 hours after the measuring hole is lowered by the chain fiber grating detection unit, causing its spindle to retract and unlocking the electromagnet from the corresponding wire roller. Since there is a time lag between the lowering of the chain fiber grating detection unit to the protective tube and the unscrewing of the spiral blade, the PCB board can precisely control the power on and off of the electromagnet. Setting the power off after 2 hours allows ample time for the protective tube to be unscrewed, the hole to be fully collapsed, and the wire boxes to be stably buried. The timing function is a classic and commonly used function of PCB board measuring instruments, so the above timing control process is accurate and reliable. Moreover, the PCB board with the timing circuit is inexpensive, costing only a few tens of yuan, which does not put pressure on the overall cost of the measuring device.

[0026] As a further optimization, the side wall of the pay-off box is provided with two mounting sleeves, one upper and one lower. Each mounting sleeve protrudes from the side wall at both its inner and outer ends, and each mounting sleeve is connected to the outer end of the corresponding roller via a bearing. Each roller has a hexagonal countersunk hole on its outer end face, and also a marking line on its outer end face to indicate the circumferential position of the bolt hole. Correspondingly, during the process of connecting each fiber segment to the various sensor tube sections in series to form a chain-type fiber optic grating detection unit, the hexagonal countersunk holes of the upper and lower rollers of each pay-off box are rotated with a hexagonal wrench to adjust the initial length of the fiber segment extending out of the pay-off box from the upper and lower rollers, thereby achieving precise fine-tuning of the height of the pay-off box.

[0027] The advantages of the above-mentioned preferred scheme are as follows. First, the roller is installed on one side of the pay-off box instead of on both sides. That is, the outer end of the roller is installed on the side wall of the pay-off box, and the inner end of the roller provides space for the middle slack section of the cross-layer fiber, avoiding entanglement between the slack section and the roller. Also, due to the single-sided installation, a mounting sleeve protruding from the side wall is set to increase the installation thickness of the roller and the bearing, ensuring that the single-sided roller can be rotated and firmly connected. A hexagonal countersunk hole is set on the outer end face of the roller. In this way, the approximate depth of the pay-off box depends on the number of optical fibers laid. Rotating the upper and lower rollers can change the initial length of the optical fiber segment extending out of the pay-off box, realizing fine adjustment of the depth of the pay-off box. This ensures more accurate alignment between the depth of the pay-off box and the formation interface. Moreover, the hexagonal countersunk hole on the outer end face of the roller allows the upper and lower rollers to be rotated by inserting a hexagonal wrench into the hexagonal countersunk hole without opening the pay-off box, making the fine adjustment process more convenient. Furthermore, the outer end face of the roller is marked with a line corresponding to each bolt hole. For example, if there are six bolt holes on the outer end face, six lines are set. After the roller is finely adjusted and rotated into place, it is only necessary to ensure that one line is located in the 0 point direction to ensure that the electromagnet core shaft is accurately inserted into one of the six bolt holes, and to ensure that the electromagnet is firmly bolted to the corresponding roller.

[0028] As a further optimization, all fiber segments in the chain-type fiber grating detection section, except for the interlayer fiber, are provided with four reinforcing ribs along the circumference of the fiber tube wall. In this way, the cross-section of the fiber segments other than the interlayer fiber is cross-shaped, which has two functions: first, to increase the strength of the fiber, ensuring the weight of the various cable boxes and sensor tube sections supported when used as a traction rope in the initial state; second, to increase the adhesion and synchronization with the soil layer, so that it moves more closely and synchronously with the soil layer, further ensuring the accuracy of the measurement results. Attached Figure Description

[0029] Figure 1 This is a schematic diagram of the structure of the distributed fiber optic grating measurement device for deep soil displacement of the present invention, which is installed in a row of measurement holes between the oil tank and the foundation pit.

[0030] Figure 2 yes Figure 1 A magnified structural diagram of part A in the middle.

[0031] Figure 3 yes Figure 1 A magnified structural diagram of part B.

[0032] Figure 4 yes Figure 1 A magnified structural diagram of section C.

[0033] Figure 5 yes Figure 1 A magnified structural diagram of part D in the middle.

[0034] Figure 6This is an enlarged structural diagram of the fiber segments other than the cross-layer fiber in the distributed fiber grating measurement device of the present invention.

[0035] Figure 7 This is an enlarged structural schematic diagram of the protective tube of the distributed fiber optic grating measurement device of the present invention.

[0036] Figure 8 This is a schematic diagram of the pay-off box of the distributed fiber Bragg grating measurement device of the present invention.

[0037] Figure 9 yes Figure 8 A schematic diagram of the structure of the cable box body and vertical partition after being partially cut.

[0038] Figure 10 yes Figure 9 A schematic diagram of the structure after being deflected at a certain angle.

[0039] Figure 11 This is an enlarged schematic diagram of the upper roller structure of the distributed fiber optic grating measurement device of the present invention.

[0040] Figure 12 yes Figure 11 A schematic diagram of the exploded structure after the interlayer optical fiber is hidden and the wedge is removed from the anchor hole.

[0041] Figure 13 yes Figure 12 A schematic diagram of the structure after the wedge-shaped piece is hidden and deflected at a certain angle.

[0042] Figure 14 This is a schematic diagram of the attitude distribution of the chain fiber grating detection unit after horizontal displacement of the soil. (The solid line represents the distribution attitude of the chain fiber grating detection unit in this application, while the dashed line represents the distribution attitude of the chain fiber grating detection unit in the prior art).

[0043] The diagram shows: 1. Cable box; 2. Interlayer optical fiber; 2.1. Relaxation section; 3. Upper roller; 4. Lower roller; 5. Mounting sleeve; 6. Hexagonal countersunk hole; 7. Upper wire roller; 8. Lower wire roller; 9. Anchor hole; 10. Wedge plate; 11. Electromagnet; 11.1. Mandrel; 12. Bolt hole; 13. Vertical partition; 14. Triangular bracket; 15. Counterweight; 16. Rock stratum; 17. Reinforcing rib; 18. Chain-type fiber optic grating detection section; 19. Grating sensor analyzer; 20. Sensor tube section; 21. Uppermost section of optical fiber; 22. Fixed pulley; 23. Backfill soil layer; 24. Silt layer; 25. Gravel layer; 26. Helical blade; 27. Protective tube; 28. Measuring hole. Detailed Implementation

[0044] The present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0045] like Figures 1-14As shown, the distributed fiber optic grating measurement device for deep soil displacement of the present invention includes a vertically linked fiber optic grating detection unit 18, a grating sensor analyzer 19, a main controller, a power supply, and an alarm. The linked fiber optic grating detection unit 18 is composed of multiple sensor segments 20 connected in series with multiple optical fibers. The linked fiber optic grating detection unit 18 is located inside the measurement hole 28. The uppermost sensor segment 20 of the linked fiber optic grating detection unit 18 is connected to the grating sensor analyzer 19 via the uppermost optical fiber 21. The grating sensor analyzer 19 is also called a grating demodulator. The grating sensor analyzer 19 is signal-connected to the main controller, and the main controller is connected to the alarm. The grating sensor analyzer 19, the main controller, and the alarm are all located outside the measurement area, i.e., on the ground outside the measurement hole 28. All of the above are mature existing technologies. As is common sense, the uppermost fiber optic cable 21, after being led out from the grating sensor analyzer 19, is laid loosely on the ground with a spare length. Therefore, this position itself has a free range of cable laying, and there is no need to install a cable laying box 1 at the opening of the measuring hole 28. However, in order to make the fiber optic cable laying more regular, a wheel frame with a fixed pulley 22 can be installed at this position.

[0046] Each fiber optic cable spanning a stratigraphic interface is provided with a cable delivery box 1, which is located at the stratigraphic interface; for ease of description, the fiber optic cable spanning the stratigraphic interface is referred to as the interlayer fiber optic cable 2. Each cable delivery box 1 is provided with an upper roller 3 and a lower roller 4, the outer ends of which are rotatably connected to the side wall of the cable delivery box 1; that is, one side wall of the cable delivery box 1 is provided with two mounting sleeves 5, the inner and outer ends of each mounting sleeve 5 protruding from the side wall to increase the hinge distance. The upper mounting sleeve 5 is connected to the outer end of the upper roller 3 via a bearing, and the lower mounting sleeve 5 is also connected to the outer end of the lower roller 4 via a bearing. Each roller has a hexagonal countersunk hole 6 on its outer end face, which facilitates the rotation of the corresponding roller by hand with a hexagonal wrench.

[0047] The upper segment of each cross-layer optical fiber 2 is wound multiple times on the upper roller 3 to form an upper wire roller 7, then extends out of the upper opening of the wire release box 1 and connects to the upper sensor tube section 20. The lower segment of each cross-layer optical fiber 2 is wound multiple times on the lower roller 4 to form a lower wire roller 8, then extends out of the lower opening of the wire release box 1 and connects to the lower sensor tube section 20. More specifically, each roller includes an outer shaft portion and an inner wheel portion. The diameter of the wheel portion is larger than that of the shaft portion to facilitate wire winding. The optical fiber segment of the cross-layer optical fiber 2 is wound on the wheel portion of the roller to form a wire roller. The middle segment of each cross-layer optical fiber 2 is a slack segment 2.1. The boundary point between the upper and middle segments of this cross-layer optical fiber 2 is fixed to the inner end of the upper roller 3, and the boundary point between the middle and lower segments of this cross-layer optical fiber 2 is fixed to the inner end of the lower roller 4. The length of the relaxation section 2.1 should be slightly greater than the sum of the center distance between the two rollers and the radius of the two roller wheels. For example, if the center distance between the upper roller 3 and the lower roller 4 is 10cm, and the radius of the upper roller 3 wheel and the lower roller 4 wheel is 4cm, then the sum of the three is 18cm, and the length of the relaxation section 2.1 should be 20cm. Generally, it is 1.1 to 1.3 times the center distance and the sum of the two radii.

[0048] Each segment of the interlayer optical fiber 2 has two fixing points with the upper roller 3 and the lower roller 4: one is the boundary between the upper and middle segments of the interlayer optical fiber 2, and the other is the boundary between the middle and lower segments of the interlayer optical fiber 2. Preferably, the fixing structure has an anchor hole 9 on the wheel portion of each roller, extending from the inner side of the annular surface to the inner end face. The upper segment of the interlayer optical fiber 2 passes through the anchor hole 9 of the upper roller 3, and a wedge-shaped piece 10 is inserted into the inner end of the anchor hole 9. The boundary between the upper and middle segments of the interlayer optical fiber 2 is anchored in the anchor hole 9 of the upper roller 3 by the wedge-shaped piece 10. Similarly, the lower segment of the interlayer optical fiber 2 passes through the anchor hole 9 of the lower roller 4, and a wedge-shaped piece 10 is also inserted into the inner end of the anchor hole 9. The boundary between the middle and lower segments of the interlayer optical fiber 2 is anchored in the anchor hole 9 of the lower roller 4 by the wedge-shaped piece 10.

[0049] The wire feeding box 1 also contains two electromagnets 11, one above the other. In the initial state, the spindle 11.1 of each electromagnet 11 extends out to hold the corresponding wire roller, preventing it from prematurely feeding. Specifically, the inner end face of each wire roller has one or more locking holes 12. In this embodiment, six locking holes 12 are provided. The spindle 11.1 of the electromagnet 11 is inserted into one of the locking holes 12 to securely lock the corresponding wire roller. Moreover, the outer end face of each roller is also provided with markings to indicate the circumferential position of the locking holes 12. In this way, when the roller is rotated with a hex wrench to fine-tune the initial length of the fiber segment extending out of the wire feeding box 1 of each wire roller, people can observe the markings. When the wire roller is rotated into position, as long as one marking is located in the 0 point direction, it can be ensured that the spindle 11.1 of the electromagnet 11 is accurately inserted into one of the six locking holes 12, ensuring that the electromagnet 11 securely holds the corresponding wire roller. After the power is switched on and off, the spindle 11.1 of each electromagnet 11 retracts and unlocks the corresponding wire roller. In this embodiment, for convenient control and energy saving, the spindle 11.1 is set to retract when the electromagnet 11 is de-energized and to extend and lock the corresponding wire roller when the electromagnet 11 is energized. The wire feeding box 1 is also equipped with a PCB board and power supply for driving the electromagnet 11.

[0050] In this embodiment, the wire feeding box 1 is provided with a vertical partition 13, which divides the inner cavity of the wire feeding box 1 into two chambers, left and right. The upper wire roller 7 and the lower wire roller 8 are located in the left chamber, and two electromagnets 11 are located in the right chamber. Each electromagnet 11 is fixed to one side wall of the wire feeding box 1 via a triangular bracket 14. A gap is left between the inner ends of the two wire rollers and the vertical partition 13 to accommodate the relaxation section 2.1 of the cross-layer optical fiber 2. In the initial state, the core shaft 11.1 of the electromagnet 11 passes through the vertical partition 13 and is bolted into the bolt hole 12 at the inner end of the corresponding wire roller. After switching between power on and off, the core shaft 11.1 of the electromagnet 11 will be completely retracted to the other side of the partition, which can further prevent the core shaft 11.1 from getting tangled with the relaxation section 2.1 of the cross-layer optical fiber 2 during the wire feeding state. The PCB board and power supply are also located in the right chamber. In this embodiment, a battery is used as the power source to power the electromagnets 11, and the space between the two electromagnets 11 in the right chamber is just right for setting up the battery compartment. The PCB board in this embodiment is equipped with a timing circuit, which switches the power on and off of the electromagnet 11. For example, the electromagnet 11 is de-energized 2 hours after the chain fiber optic grating detection unit 18 is lowered into the protective tube 27. Alternatively, a pressure sensor can be installed in the wire release box 1, which is also connected to the PCB board. After the hole collapses and is buried, the pressure on the wire release box 1 increases, and the pressure change is fed back to the PCB board through the pressure sensor, thus achieving precise control of the retraction of the electromagnet 11 spindle 11.1. However, considering that the cost of adding a timing circuit to the PCB board is less than that of adding a pressure sensor, this embodiment preferably uses a PCB board with a timing circuit.

[0051] To more accurately control the depth of each wire box 1, a counterweight 15 is provided at the lower end of the chain fiber optic grating detection unit 18 to tighten the chain fiber optic grating detection unit 18. The bottom end of the measuring hole 28 is drilled into the rock layer 16 as the bearing layer, and the counterweight 15 is anchored to the bottom end of the measuring hole 28 with cement grout.

[0052] Preferably, in the chain-type fiber grating detection section 18, all fiber segments except the interlayer fiber 2 are provided with four reinforcing ribs 17 along the circumferential direction of the fiber tube wall. Of course, to increase the strength and load-bearing capacity of each fiber segment and reduce its wear, the thickness of the rubber protective layer outside each fiber segment can be appropriately increased, such as by about 2 mm.

[0053] The present invention relates to an installation method for a distributed fiber optic grating measurement device for deep soil displacement, which includes the following steps.

[0054] A tracked stepping drill rig is used to drill a measuring hole 28 at the measurement point in the area to be measured, and soil samples are taken from the measuring hole 28. Based on the soil samples taken, the specific depths of the various stratigraphic boundaries at the measurement point are measured. In this embodiment, the thicknesses of the backfill soil layer 23, silt layer 24, and gravel layer 25 of the measuring hole 28 are measured to be 4 meters, 6 meters, and 7 meters, respectively. Below the gravel layer 25 is the rock layer 16, which serves as the bearing layer. Therefore, the depths of the three stratigraphic boundaries are -4 meters, -10 meters, and -17 meters, respectively. Subsequently, three cable boxes 1 need to be installed at these three depths.

[0055] Each sensor tube segment 20 is connected in series with optical fiber segments to form a chain-type fiber Bragg grating detection unit 18. Interlayer optical fibers 2 with pay-off boxes 1 are laid out according to the depth of the formation interface, ensuring that the distance from each pay-off box 1 to the ground is equal to the corresponding formation interface depth. Specifically, three pay-off boxes 1 are laid out at -4 meters, -10 meters, and -17 meters respectively. An electromagnet 11 is then used to hold the wire rollers of the pay-off boxes 1, which have been adjusted in distance. More specifically, a red mark is provided on the first optical fiber segment of the chain-type fiber Bragg grating detection unit 18. After the chain-type fiber Bragg grating detection unit 18 is inserted into the measuring hole 28, this red mark is precisely located at the opening of the measuring hole 28. Thus, the distance between the midpoint of each pay-off box 1 and the red mark is the distance from the pay-off box 1 to the ground.

[0056] During the process of connecting each fiber segment to the sensor tube section 20 in series to form a chain fiber optic detection unit 18, the hexagonal countersunk holes 6 of the upper roller 7 and lower roller 8 of each wire release box 1 are rotated with a hexagonal wrench to adjust the initial length of the fiber segment extending out of the wire release box 1 from the upper roller 7 and lower roller 8, so as to achieve precise fine adjustment of the height of the wire release box 1.

[0057] A protective pipe 27 with spiral blades 26 on its outer wall is drilled into the measuring hole 28 using a tracked stepping drill.

[0058] The chain fiber grating detection unit 18 is lowered into the protective tube 27, and grout is injected into the bottom of the protective tube 27 using the grouting pipe, thereby anchoring the weight 15 at the bottom of the chain fiber grating detection unit 18 to the bottom of the measuring hole 28; since the measuring hole 28 is generally drilled into the rock layer 16, the weight 15 is anchored in the rock layer 16.

[0059] Using a tracked stepping drill, the protective pipe 27 is unscrewed out of the measuring hole 28. The unscrewing of the spiral blade 26 will increase the disturbance of the soil around the measuring hole 28, accelerate the collapse of the measuring hole 28, and bury the chain fiber optic grating detection unit 18 in the soil.

[0060] Because the protective tube is quite long, about 20-30 meters, it is extended section by section using threads, and disassembly is also performed section by section when unscrewing it. More specifically, using a small crane makes disassembly easier. An upper clamp is installed on the crane boom to hold the uppermost fiber optic section of the chain-type fiber optic grating detection unit 18, suspending it at a height of 2 meters to flex the chain-type fiber optic grating detection unit. Then, a crawler-type stepping drill is used to unscrew the protective tube 27 about 1.5 meters out of the measuring hole. The section of the protective tube extending above ground is then unscrewed from the main body of the protective tube. A lower clamp is then used to hold the uppermost fiber optic section, suspending the chain-type fiber optic grating detection unit at ground level to flex it. The upper clamp on the boom is then released, and the first section of the unscrewed protective tube is removed from the uppermost fiber optic section. Then, the boom... The upper clamp continues to suspend the chain-type fiber optic grating detection unit at a height of 2 meters. Then, the second section of the protective tube is unscrewed. The lower clamp is then used to firmly hold the chain-type fiber optic grating detection unit at ground level. The upper clamp is then released, and the unscrewed second section of the protective tube is removed from the top fiber optic section. This process is repeated, unscrewing the entire protective tube section by section and removing it from the top fiber optic section. Throughout the removal process, the chain-type fiber optic grating detection unit is firmly clamped to prevent it from falling. After the protective tube is removed, the first end of the top fiber optic section is connected to the grating sensor analyzer, and the top fiber optic section is placed on the fixed pulley 22 at the opening of the measuring hole. The above describes the process of unscrewing and removing the protective tube section by section. Of course, if there is a large crane on the construction site, the upper clamp of the large crane arm can be used to clamp the uppermost section of optical fiber and lift it to more than 20 meters. The entire protective tube can then be completely screwed out of the opening. Then, the lower clamp on the ground can be used to clamp the chain fiber grating detection unit, and the entire protective tube can be removed from the uppermost section of optical fiber above the ground.

[0061] The electromagnet 11 spindle 11.1 of each wire feeding box 1 is retracted, thereby unlocking each wire roller and enabling it to feed wire freely. In this step, the PCB board uses a timing circuit to cut off the power supply to the corresponding electromagnet 11 2 hours after the measuring hole 28 is lowered in the chain fiber optic grating detection section 18, causing its spindle 11.1 to retract and unlocking the electromagnet 11 from the corresponding wire roller.

Claims

1. A distributed fiber optic grating measurement device for deep soil displacement, comprising a chain-type fiber optic grating detection unit, a grating sensor analyzer, and an alarm; the chain-type fiber optic grating detection unit is composed of multiple sensor tube segments and multiple optical fiber segments connected in series, the chain-type fiber optic grating detection unit is located inside the measurement hole, the grating sensor analyzer and the alarm are located on the ground outside the measurement hole, and the uppermost sensor tube segment is connected to the grating sensor analyzer and the alarm via the uppermost optical fiber segment; characterized in that: Each fiber optic segment spanning a stratigraphic boundary is equipped with a delivery box located at the boundary. Each delivery box contains two rollers, the outer ends of which are rotatably connected to the sidewall of the delivery box. The upper section of each cross-layer fiber optic segment extends from the top of the delivery box after winding around the upper roller to form an upper roller and connects to the upper sensor tube section. The lower section extends from the bottom of the delivery box after winding around the lower roller to form a lower roller and connects to the lower sensor tube section. The middle section is a relaxed section. The boundary between the upper and middle sections is located at the inner end of the upper roller. The middle and lower sections are fixed at the dividing point and the inner end of the lower roller. The length of the slack section is slightly greater than the sum of the distance between the two roller shafts and the radii of the two rollers. The wire feeding box is also equipped with two electromagnets. In the initial state, the core shaft of each electromagnet extends and hooks the corresponding wire roller. After switching on and off power, the core shaft of each electromagnet retracts and unlocks the corresponding wire roller. The wire feeding box is also equipped with a PCB board and power supply for driving the electromagnets. The lower end of the chain fiber optic grating detection section is equipped with a counterweight, which is anchored to the bottom of the measuring hole by cement grout.

2. The distributed fiber optic grating measurement device for deep soil displacement according to claim 1, characterized in that: Each roller has an anchor hole extending from the inner side of the annular surface to the inner end face. The upper section of the cross-layer fiber passes through the anchor hole of the upper roller, and a wedge is inserted into the inner end of the anchor hole. The boundary between the upper and middle sections of the cross-layer fiber is anchored in the anchor hole of the upper roller by the wedge. The lower section of the cross-layer fiber passes through the anchor hole of the lower roller, and a wedge is also inserted into the inner end of the anchor hole. The boundary between the middle and lower sections of the cross-layer fiber is anchored in the anchor hole of the lower roller by the wedge.

3. The distributed fiber optic grating measurement device for deep soil displacement according to claim 1, characterized in that: The vertical partition divides the inner cavity of the wire box into two chambers, left and right. Two wire rollers are located in the left chamber, and two electromagnets are located in the right chamber. A gap is left between the inner ends of the two wire rollers and the vertical partition to accommodate the relaxation section of the cross-layer optical fiber. In the initial state, the electromagnet core shaft passes through the vertical partition and is bolted into the bolt hole at the inner end of the corresponding wire roller. After switching on and off power, the electromagnet core shaft retracts to the other side of the partition.

4. The distributed fiber optic grating measurement device for deep soil displacement according to claim 3, characterized in that: The PCB board and power supply are also located in the right chamber; the PCB board is equipped with a timing circuit, which switches the electromagnet on and off through the timing circuit.

5. The distributed fiber optic grating measurement device for deep soil displacement according to claim 3, characterized in that: The side wall of the wire box is provided with two mounting sleeves, one above the other. Each mounting sleeve protrudes from the side wall at both the inner and outer ends. Each mounting sleeve is connected to the outer end of the corresponding roller via a bearing. Each roller has a hexagonal countersunk hole on its outer end face and a marking line for indicating the circumferential position of the bolt hole on its outer end face.

6. The distributed fiber optic grating measurement device for deep soil displacement according to claim 1, characterized in that: In the chain fiber grating detection section, except for the cross-layer fiber, all other fiber segments are provided with four reinforcing ribs along the circumferential direction of the fiber tube wall.

7. A method for installing a distributed fiber optic grating measurement device for deep soil displacement, characterized in that: It includes the following steps: Drill measurement holes and take core samples at the measurement points in the area to be measured. Measure the specific depth of each stratum interface at the measurement point based on the soil samples after core sampling. Each sensor tube segment is connected in series with each optical fiber to form a chain fiber grating detection unit. Cross-layer optical fibers with cable trays are laid according to the depth of the formation interface, so that the distance from each cable tray to the ground is equal to the corresponding depth of the formation interface. Then use an electromagnet to hold the wire roller of the wire feeding box, which has been adjusted to the correct distance; Drill a protective tube with spiral blades on its outer wall into the measuring hole; The chain fiber grating detection unit is lowered into the protective tube, and grout is injected into the bottom of the protective tube to anchor the counterweight at the bottom of the chain fiber grating detection unit to the bottom of the measuring hole. Unscrewing the protective tube out of the measuring hole and unscrewing the spiral blades will increase soil disturbance and accelerate the collapse of the measuring hole, thus burying the chain fiber optic grating detection unit in the soil. The electromagnet core shaft of each wire feeding box is retracted, which unlocks each wire roller and allows it to feed wire freely.

8. The installation method of the distributed fiber optic grating measurement device for deep soil displacement according to claim 7, characterized in that: The PCB board uses a timing circuit to cut off the power supply to the corresponding electromagnet 2 hours after the measuring hole is lowered in the chain fiber optic grating detection section, causing its spindle to retract and unlocking the electromagnet from the corresponding roller.

9. The installation method of the distributed fiber optic grating measurement device for deep soil displacement according to claim 7, characterized in that: During the process of connecting each sensor tube segment in series to form a chain fiber optic grating detection unit using various optical fiber segments, a hexagonal wrench is used to rotate the hexagonal countersunk holes of the upper and lower wire rollers of each wire box to adjust the initial length of the optical fiber segments extending out of the wire box, so as to achieve precise fine-tuning of the height of the wire box.

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