Optical fiber inclination measuring device and re-measuring method for failed inclination measuring hole

Abstract

The application discloses a fiber inclinometer and a method for re-measuring a failed inclinometer hole, and the fiber inclinometer comprises an inclinometer cable installed in the failed inclinometer hole, wherein the inclinometer cable comprises a metal guide head, a multi-core optical cable and an optical cable aperture protection head; the metal guide head is located at the lowermost end of the inclinometer cable and is conical; the multi-core optical cable is composed of two ultra-weak grating optical fibers and rubber material; and the optical cable aperture protection head is fixed at the pipe opening of the failed inclinometer hole and is penetrated by the inclinometer cable when the inclinometer cable is out of the aperture. The inclinometer cable is installed in the failed inclinometer hole which still has an internal space, the displacement monitoring function of the deep part of the original hole position is recovered, new damage to the existing engineering structure is avoided, and the monitoring data of the original hole can be continued.

Description

Technical Field

[0001] This invention relates to the field of optical fiber monitoring technology, specifically to an optical fiber inclinometer and a method for retesting a failed inclinometer hole. Background Technology

[0002] Borehole inclinometers are a primary method for monitoring deep displacement in rock and soil masses. They involve drilling a borehole and installing an inclinometer tube to create an inclinometer hole for monitoring deep displacement. During measurement, an inclinometer is used to measure the inclination angle at different depths of the inclinometer tube, and finally, the horizontal displacement at these depths is calculated. Borehole inclinometers are mainly used to meet monitoring requirements during the construction phase of engineering projects. For general slope engineering, inclinometer holes are typically used for only 1-2 years of monitoring after completion. However, for large-scale hydropower projects, monitoring must serve the entire lifecycle of the project. Therefore, monitoring facilities constructed during the construction phase, if undamaged, will be used for long-term monitoring.

[0003] Currently, in large-scale hydropower projects, inclinometer boreholes used to monitor deep deformation of slope rock masses are continuously monitored if they are usable. However, inclinometer boreholes that cannot be used for monitoring due to blockage, pipe wall damage, or scaling become "failed boreholes" and are discontinued. The structural characteristics of the inclinometer boreholes themselves also determine that their failure probability increases over time. Therefore, utilizing and modifying failed boreholes to achieve re-monitoring is a crucial technical task for maintaining the integrity and continuity of the existing monitoring system.

[0004] To achieve the re-measurement of inclinometer boreholes and meet the needs of monitoring the entire life cycle of hydropower projects, the implemented technical methods need to meet two requirements:

[0005] (1) The lifespan of the sensing unit should meet the needs of long-term monitoring. Among the existing types of sensing units, the theoretical lifespan of the fiber optic sensing unit is the longest.

[0006] (2) New monitoring should make use of old monitoring holes as much as possible to ensure the consistency of the monitoring objects. This is mainly because if new monitoring holes are drilled, the geological conditions of the new monitoring hole location may differ from the original failed hole, and the inclination borehole itself has a deformation stabilization process. The monitoring data obtained after drilling new holes is difficult to form a continuous monitoring sequence with the original monitoring data.

[0007] In recent years, the monitoring systems of many large-scale hydropower projects in my country have been gradually transformed into systems suitable for long-term monitoring through technological upgrades. Improving existing monitoring systems and achieving long-term monitoring through appropriate technical means, such as modifying and utilizing failed inclinometer boreholes, aligns with the development trend of achieving full life-cycle monitoring in hydropower projects. Summary of the Invention

[0008] The technical problem to be solved by the present invention is to install a high-precision, long-life fiber optic inclinometer device in a failed inclinometer hole without damaging the main pipe wall structure, so as to realize the re-measurement of the failed inclinometer hole and meet the needs of monitoring the entire life cycle of hydropower projects.

[0009] The technical solution adopted in this invention is as follows:

[0010] A fiber optic inclinometer device includes an inclinometer cable installed in a failed inclinometer hole, the inclinometer cable including a metal guide head, a multi-core optical cable, and an optical cable hole protection head;

[0011] The metal guide head is located at the bottom of the inclinometer cable. The metal guide head is conical, and its maximum diameter is the same as that of the inclinometer cable.

[0012] Multi-core optical cables are composed of two ultra-weak grating optical fibers and rubber materials.

[0013] The optical cable aperture protection head is fixed to the opening of the failed inclinometer hole, and the optical cable passes through the optical cable aperture protection head when exiting the hole. After being installed in the failed inclinometer hole, it is fixed inside by the injected adhesive material; the optical cable aperture protection head is fixed to the opening of the failed inclinometer hole, and the optical cable passes through the optical cable aperture protection head when exiting the hole to avoid damage caused by friction with the opening.

[0014] The inclinometer optical cable consists of two ultra-weak grating optical fibers composited inside a rubber rod. The grating spacing on the two optical fibers is the same, and the grating sensing units of the two optical fibers are located at the same cross section, forming an inclinometer cross section.

[0015] The midpoint of the line connecting the centers of the two ultra-weak grating fibers on the cross-section of the multi-core optical cable coincides with the center of the cable, and the distance between the two ultra-weak grating fibers remains consistent vertically throughout the composite multi-core optical cable. The distance between the two ultra-weak grating fibers in the multi-core optical cable is a crucial parameter for calculating the lateral deformation of the cable. If a fixed distance cannot be maintained, the deformation curve of each cable segment must be measured and calibrated, which would undoubtedly involve a huge workload and severely affect the cable's applicability.

[0016] The two ultra-weak grating fibers are spaced at least 10mm apart in the multi-core optical cable, with the midpoint of their center line coinciding with the multi-core optical cable. When the multi-core optical cable experiences lateral bending deformation, the larger the distance between the two grating fibers, the greater the strain difference and the higher the accuracy of calculating the bending deformation. Therefore, the distance between the two fibers must be controlled to be no less than a certain distance. Current experiments indicate that 10mm is a suitable lower limit distance.

[0017] The ultra-weak fiber optic grating has a reflectivity of less than 0.1% and the grating spacing is the same.

[0018] The gratings on the two ultra-weak grating optical fibers appear in pairs on the same cross section of the multi-core optical cable, with a deviation of no more than 1 mm between them. The lateral deformation of the optical cable is calculated based on the strain difference of the gratings on the same cross section, which requires that a pair of gratings be in the same plane.

[0019] The optical cable aperture protection head is installed at the outlet of the inclinometer tube, through which the inclinometer optical cable passes.

[0020] The method for re-measuring failed inclinometer holes based on inclinometer cables includes the following steps:

[0021] Step 1: Use a downhole television system with a camera diameter no greater than 30mm to inspect the inner wall of the inclinometer tube in the failed inclinometer hole. The inspection includes: the maximum depth the camera can penetrate, the extent of deformation or damage to the inner wall of the inclinometer tube, and any deposits (mainly scale) on the inner wall. This method is not necessary for re-testing failed holes where the maximum depth the camera can penetrate is less than the designed depth.

[0022] Step 2: Pipe Enlargement: For locations where the cross-section of the inclinometer tube is small and the inclinometer cable cannot be lowered, the inclinometer tube is enlarged. A small or portable drilling rig can be used to press a drill rod with a diameter slightly larger than the inclinometer cable into the inclinometer tube. A tapered enlarger head is fitted to the end of the drill rod to facilitate the enlargement process.

[0023] Step 3: Scale Removal: Scale removal mainly involves cleaning the scale buildup inside the inclinometer tube. A small or portable drill can be used, with a brush roller attached to the drill rod end, to clean the scale buildup inside the inclinometer tube.

[0024] Step 4: Calibration of the inclinometer cable: During calibration, the clamp holds the inclinometer cable and distance grating. The position is L, which is the grating spacing between the two optical fibers. The other side of the grating Apply lateral deformation at the position and calculate the proportionality coefficient K between the lateral deformation S and the grating strain difference Δε.

[0025] Step 5: Installation of the Inclinometer Optical Cable: Lower the inclinometer optical cable, made according to the borehole depth, into the inclinometer hole. Fill the space around the inclinometer cable inside the inclinometer tube with cement mortar. Pass the inclinometer optical cable through the cable opening protection head, and then fit the cable opening protection head into the inclinometer tube opening for installation. After filling with cement mortar, take measurements every 7 days. Once the measurements stabilize, use the measurement value of the fourth week as the initial value and begin regular monitoring.

[0026] This invention discloses an optical fiber inclinometer and a method for re-measuring a failed inclinometer hole, with the following technical advantages:

[0027] 1) Among the existing types of sensing units, the theoretical lifespan of fiber optic sensing units is the longest. Therefore, this invention will utilize grating fiber optic sensing units to construct a sensing structure for deep displacement monitoring.

[0028] 2) The method for re-measuring failed inclinometer holes of this invention comprises four systematic steps: borehole exploration, borehole repair, and calibration and installation measurement of the inclinometer optical cable. Borehole exploration mainly involves using downhole television to examine the cause of the failed hole, determine the outer diameter of the optical cable, and implement corresponding repair measures. Borehole repair involves enlarging the inner diameter and cleaning the borehole wall of failed holes that still have space for installing inclinometer devices. Calibration of the inclinometer optical cable determines the deformation conversion coefficient for each inclinometer section. Installation of the inclinometer optical cable ensures a tight connection between the inclinometer sensor and the inclinometer tube, enabling the acquisition of actual rock mass deformation.

[0029] 3) The method for re-measuring failed inclinometer holes of the present invention can make full use of existing monitoring facilities and monitoring data, and can meet the needs of long-term engineering monitoring. Attached Figure Description

[0030] Figure 1 This is a schematic diagram of the final installation of a failed inclinometer hole, provided by an embodiment of the present invention, using an inclinometer optical cable for modification.

[0031] Figure 2(a) is Figure 1 Schematic diagram of the structure of the inclined optical cable Figure 1 ;

[0032] Figure 2(b) is Figure 1 Schematic diagram of the structure of the inclined optical cable (II);

[0033] Figure 2(c) is Figure 1 Schematic diagram of the structure of the inclined optical cable Figure 3 .

[0034] Figure 3 yes Figure 1 A schematic diagram illustrating the calibration principle of the inclined optical cable.

[0035] Figure 4 yes Figure 1 A schematic diagram illustrating the causes of failure in a failed inclinometer hole.

[0036] Figure 5 yes Figure 4 A schematic diagram of the expansion process for pipe wall deformation defects.

[0037] Figure 6 This is a flowchart illustrating the process of upgrading and utilizing failed inclinometer holes using optical fiber inclinometer technology.

[0038] The components include: 1. Inclinometer optical cable; 1-1. Ultra-weak grating optical fiber; 1-2. Rubber rod; 1-3. Inclinometer cross-section; 1-4. Grating sensing unit; 2. Metal guide head; 3. Optical cable opening protection head; 4. Inclinometer tube; 5. Consolidation mortar; 6. Deposits at the bottom of the inclinometer hole; 7. Dial gauge; 8. Clamp; 9. Deformation of the inclinometer tube wall; 10. Scale crust inside the inclinometer tube; 11. Drill rod; 12. Conical expansion head. Detailed Implementation

[0039] Figure 1 This is a schematic diagram of the final installation of a modified inclinometer cable utilizing a failed inclinometer hole. To allow the inclinometer cable 1 to be installed inside the inclinometer tube 4, the outer diameter of the inclinometer cable 1 must be smaller than the inner diameter of the inclinometer tube 4. Considering the influence of the inclinometer tube wall deformation 9 and the space required for filling with cement mortar, the maximum outer diameter of the inclinometer cable 1 should not exceed the inner diameter of the inclinometer tube 4 minus 20 mm.

[0040] Figures 2(a) to 2(c) yes Figure 1 A schematic diagram of the inclinometer cable structure. The inclinometer cable 1 consists of two ultra-weak grating optical fibers 1-1 composited within a rubber rod 1-2. The gratings on the two fibers are spaced identically, and after composite fiber bonding, the grating sensing units 1-4 of the two fibers must be located at the same cross-section, forming the inclinometer section 1-3. During measurement, the strain difference Δε between a pair of gratings at the same cross-section is measured. Based on the elastic assumption, within the elastic deformation range, the vertical deformation S of the optical cable is proportional to the grating strain difference Δε, S = K·Δε, where K is the proportionality coefficient between the vertical deformation S of the optical cable and the grating strain difference Δε.

[0041] The strain difference Δε of the grating is a key parameter that determines the deformation calculation. The greater the spacing between the two ultra-weak grating optical fibers 1-1 in the rubber rod, the higher the accuracy. Therefore, the spacing between the two ultra-weak grating optical fibers 1-1 should not be less than 10mm.

[0042] Figure 3 yes Figure 1 A schematic diagram illustrating the calibration principle of the inclinometer cable 1. During calibration, clamp 8 holds the inclinometer cable 1 at the distance grating. 1 At position 2L, L is the grating spacing between the two optical fibers. The other side of the grating... Lateral deformation is applied at the position, and the deformation is measured and recorded by dial gauge 7. At the same time, the strain difference Δε of the grating is measured and recorded.

[0043] The technical solution in this embodiment of the invention is to take certain technical measures to ensure that the fabrication, calibration and installation of the inclinometer cable conforms to the existing state of the failed inclinometer hole, under the condition that the inclinometer cable can be installed in the internal space of the failed inclinometer hole, so as to ensure that the inclinometer cable can accurately measure deep displacement data. Figure 6 A flowchart illustrating the retrofitting and utilization of failed inclinometer holes using optical fiber inclinometer technology. (Following...) Figure 6 The process ultimately obtains Figure 1 The specific steps for upgrading the inclinometer optical cable to utilize the failed inclinometer borehole are as follows:

[0044] (I) Investigation into the failure mechanism of the failed inclinometer hole:

[0045] There are many reasons for the failure of a clinometer tube. This invention is mainly applied to clinometer holes within clinometer tubes that still have clinometer cables for installation. Therefore, before re-testing and modifying a failed clinometer hole, it is necessary to investigate the cause of the failure. The investigation method is to use a downhole television system with a camera diameter of no more than 20mm to inspect the inner wall of the clinometer tube in the failed clinometer hole. If the failure is caused by severe deformation of the clinometer tube (9), technical means can be used to expand the passing radius at this point, and then the downhole television system can be used to inspect the clinometer hole again. The following conditions of the clinometer hole are determined through inspection: the maximum usable depth of the clinometer hole, the passability of the clinometer cable (whether the hole needs to be enlarged), and the condition of the deposits on the inner wall of the clinometer tube (mainly scale crust 10 inside the clinometer tube). Clinometer holes whose maximum usable depth reaches the designed hole depth and where the clinometer cable can be lowered and installed are appropriately repaired for the installation of the clinometer cable.

[0046] (2) Pipe expansion:

[0047] For locations where the cross-section of the inclinometer tube is small and the inclinometer fiber optic cable cannot pass through, the tube is expanded. The expansion can be achieved by using a small or portable drilling rig to press a drill rod 11 with a diameter slightly larger than that of the inclinometer fiber optic cable into the inclinometer tube. A tapered expansion head 12 is installed at the end of the drill rod to facilitate the expansion.

[0048] (III) Removing scale and crust:

[0049] If groundwater enters the inclinometer tube over a long period, scale will form, and in severe cases, a crust will form and detach. If this crust detaches, a large gap will remain between the remaining scale and the inclinometer tube wall. After the inclinometer cable is installed, cement mortar needs to be poured in to fix it. The gap between the remaining scale and the inclinometer tube wall will affect the transmission of external rock deformation to the inclinometer cable, reducing measurement accuracy. The cleaning method involves soaking the areas inside the borehole that need cleaning with a descaling agent for 24 hours. After soaking, a brush roller is fixed to the top of the drill rod 11, and a small or portable drill rig is used to clean the scale inside the borehole.

[0050] (iv) Fabrication and calibration of inclinometer optical cables:

[0051] Based on the investigation results of the failure mechanism of the failed inclinometer hole and the internal condition of the inclinometer hole after the inclinometer tube was expanded, the outer diameter of the inclinometer optical cable 1 was determined. Taking the commonly used inclinometer tube with an inner diameter of φ60mm as an example, the outer diameter of the manufactured inclinometer optical cable 1 should not exceed 40mm. Considering that the spacing between the two ultra-weak grating optical fibers 1-1 composited inside the optical cable should not be less than 10mm, the outer diameter of the manufactured inclinometer optical cable 1 was selected within the range of 30 to 40mm.

[0052] Because the strain difference Δε of the grating is sensitive to the calculation of deformation displacement, the scaling factor K of each pair of gratings forming the inclinometer section 1-3 needs to be calibrated. During calibration, clamp 8 holds the inclinometer cable 1 at a distance from the grating. The position is L, which is the grating spacing between the two optical fibers. The other side of the grating Lateral deformation was applied at the location, and the deformation was measured and recorded by dial gauge 7. At the same time, the strain difference Δε of the grating was measured and recorded. The lateral deformation increased from 0 mm to 5 mm in increments of 0.1 mm. The lateral deformation and grating strain difference Δε data were plotted on a two-dimensional coordinate graph, and the proportionality coefficient K between the lateral deformation S and the grating strain difference Δε was calculated.

[0053] (V) Installation and measurement of the inclination-measuring optical cable:

[0054] The inclinometer cable 1 is lowered into the inclinometer tube 4. A fiber optic demodulator can be connected to the cable to monitor the grating strain changes in real time. When the cable reaches the bottom, the strain of the grating at the lowest point can be used to determine if the cable has reached the bottom. After the cable is in place, cement mortar is poured in. The cable passes through the cable opening protection head 3, which is then fitted into the inclinometer tube 4 and installed. After pouring in the cement mortar, data is measured every 7 days. Once the measurements stabilize, the measurement value from the fourth week is used as the initial value, and regular monitoring begins.

[0055] The present invention discloses an optical fiber inclinometer device and a method for re-measuring a failed inclinometer hole, the advantages of which are:

[0056] 1. Installing the inclinometer fiber optic cable inside a failed inclinometer borehole that still has internal space restores the deep displacement monitoring function of the original borehole location without causing new damage to the existing engineering structure, and also allows for the continuation of the monitoring data from the original borehole.

[0057] 2. Ultra-weak grating optical fibers can composite thousands of gratings on a single fiber. Inclinometer cables based on ultra-weak grating optical fibers can increase the grating density on a single cable, reduce the spacing of the inclinometer sections, and improve the accuracy of the inclinometer results. The minimum spacing of the inclinometer sections in inclinometer cables based on ultra-weak grating optical fibers can be as small as 200mm, significantly smaller than the commonly used inclinometer spacing of 500mm.

[0058] 3. The basic sensing unit uses grating fiber, which ensures the durability of the sensing structure and is conducive to achieving the goal of long-term monitoring.

[0059] 4. Inclinometer optical cables can be connected to automatic data acquisition equipment to achieve online automatic data acquisition.

Claims

1. A method for re-measuring a failure survey hole based on an inclinometer cable, characterized in that, The utility model provides an inclinometer device, which comprises an inclinometer cable (1) installed in a failed inclinometer hole, the inclinometer cable (1) comprising a metal guide head (2), a multi-core optical cable and an optical cable orifice protection head (3); the metal guide head (2) is located at the lowermost end of the inclinometer cable (1) and is conical; the multi-core optical cable is composed of two ultra-weak grating optical fibers (1-1) and rubber material; The optical cable orifice protection head (3) is fixed to the pipe orifice of the failed inclinometer hole, and the inclinometer cable (1) passes through the optical cable orifice protection head (3) when it exits the orifice; The inclinometer cable (1) is composed of two ultra-weak grating optical fibers (1-1) in a rubber rod (1-2), the grating spacings of the two ultra-weak grating optical fibers (1-1) are the same, and the grating sensing units (1-4) of the two ultra-weak grating optical fibers (1-1) are located in the same cross section, forming an inclinometer cross section (1-3); The midpoint of the center line of the two ultra-weak grating optical fibers (1-1) coincides with the center of the multi-core optical cable in the cross section of the multi-core optical cable, and the distance between the two ultra-weak grating optical fibers (1-1) is consistent in the composite multi-core optical cable; The distance between the two ultra-weak grating optical fibers (1-1) in the multi-core optical cable is not less than 10 mm, and the midpoint of the center line coincides with the multi-core optical cable; The gratings on the two ultra-weak grating optical fibers (1-1) appear in pairs in the same cross section of the multi-core optical cable, and the deviation is not greater than 1 mm; The failed inclinometer hole re-measurement method comprises the following steps: Step one: use a camera to check the inner wall of the inclinometer tube (4) of the failed inclinometer hole; Step two: expand the tube at the position where the inclinometer tube (4) has a small cross section and the inclinometer cable (1) cannot be lowered; press a drill rod (11) with a diameter slightly larger than the inclinometer cable (1) into the inclinometer tube (4), and install a conical tube expander (12) at the end of the drill rod to facilitate tube expansion; Step three: clean the scale inside the inclinometer tube (4); Step four: calibration of the inclinometer cable: the position of the grating on the two optical fibers, L is two optical fiber grating spacing; the other side of the grating is deformed transversely, and the transverse deformation S and the grating strain difference Δε proportional coefficient K are calculated; Step five: install the inclinometer cable; lower the inclinometer cable (1) made according to the hole depth into the inclinometer hole, fill the space around the inclinometer cable (1) in the inclinometer tube (4) with cement mortar, and measure the data after filling the cement mortar.

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