Method for monitoring layered deformation of frozen soil roadbed and driving device

Abstract

The present application relates to the technical field of frozen soil subgrade engineering monitoring, and particularly relates to a frozen soil subgrade layered deformation monitoring method and a driving device, the method comprising: drilling and coring at a subgrade to-be-measured position, obtaining undisturbed soil sample cores and numbering and storing; driving reflective sheets into the soil body of the drill hole side wall in turn, so that the projections of the reflective sheets of each layer on the horizontal plane do not overlap each other; backfilling the undisturbed soil sample cores into the drill hole and compacting, so that the reflective sheets are attached to the backfilled soil body; arranging a geological radar on the road surface, periodically scanning the drill hole position in a monitoring period, and receiving the reflected electromagnetic wave signals of the reflective sheets of each layer; then inverting to obtain the three-dimensional space coordinates of the reflective sheets of each layer at different monitoring times, and calculating the layered deformation according to the coordinate change amount. The present application has small construction disturbance, the reflective sheets are tightly coupled with the soil body, and long-term, nondestructive and high-precision fine monitoring of the layered deformation at each depth inside the frozen soil subgrade can be achieved.

Description

Technical Field

[0001] This invention relates to the field of monitoring technology for frozen soil subgrade engineering, and in particular to a monitoring method and device for monitoring the layered deformation of frozen soil subgrade. Background Technology

[0002] Frozen soil subgrades are highly susceptible to deformation phenomena such as frost heave and thaw settlement under the long-term effects of seasonal freeze-thaw cycles, perennial permafrost degradation, and vehicle loads. Due to differences in internal temperature and stress states, the deformation of frozen soil subgrades exhibits significant stratification characteristics, meaning that the degree and pattern of deformation differ markedly at different soil depths. If subgrade deformation cannot be monitored in a timely and accurate manner, it will lead to uneven settlement, cracking, and even thaw settlement failure of the subgrade, seriously threatening the safety and stability of road traffic.

[0003] Currently, existing technologies for monitoring the deformation of permafrost subgrade mainly include settlement bar monitoring, total station monitoring, fiber optic sensing monitoring, and some deep displacement gauge monitoring. However, these existing technologies generally have the following shortcomings in practical applications: (1) It is difficult to achieve refined identification of the layered deformation of deep soil layers. Most monitoring methods can only reflect the settlement of the subgrade surface or the overall situation, and cannot accurately capture the layered displacement information of soil layers at different depths inside the subgrade. (2) Construction and installation cause great disturbance. The installation of deep sensors usually requires large-diameter drilling or large-area excavation. The construction process damages the original structure of the subgrade, which can easily lead to distortion of monitoring data. (3) The long-term stability of sensors is poor. The freeze-thaw cycle environment is complex and harsh. Traditional mechanical sensors or electronic components are prone to failure under long-term stress, low temperature and water erosion, resulting in high maintenance costs and making it difficult to meet the long-term monitoring needs of permafrost areas.

[0004] Although ground-penetrating radar (GPR), as a non-destructive testing technology, boasts advantages such as high resolution and rapid scanning, current research primarily utilizes it for qualitative detection of roadbed defects, with insufficient exploration of its potential for quantitative monitoring of internal roadbed displacement. Furthermore, when using GPR in conjunction with embedded markers for roadbed deformation monitoring, the placement of these markers is crucial. However, current techniques typically involve simple borehole insertion without considering the gaps between the marker and the surrounding soil, resulting in markers being either suspended or detached. This can easily lead to significant discrepancies between measured marker displacement and actual soil deformation, or even marker detachment and failure. Moreover, conventional borehole installation often requires manual excavation of large holes or the use of heavy hammers, which not only causes significant disturbance to the roadbed structure but also makes it difficult to ensure accurate placement of markers at different depths and adequate backfill compaction.

[0005] Therefore, there is an urgent need for a device and method that minimizes construction disturbance, has a simple structure, can operate stably for a long time, and can achieve refined monitoring of soil deformation at different depths in frozen soil subgrades. Summary of the Invention

[0006] The purpose of this invention is to overcome the technical problems of existing monitoring markers (sensors, reflectors, etc.) having poor deformation coupling effect with the soil when buried in the roadbed, which makes it impossible to accurately identify the deformation of soil layers at different depths inside the frozen soil roadbed, and also has the problems of large construction disturbance and high monitoring cost. The invention provides a monitoring method and driving device for the layered deformation of frozen soil roadbed.

[0007] In a first aspect, the present invention provides a method for monitoring the layered deformation of frozen soil subgrade, comprising:

[0008] S1: Drill holes at the locations to be measured in the roadbed, and obtain undisturbed soil cores arranged along the depth direction during the drilling process. Number and save the undisturbed soil cores according to the core depth order. S2: Several reflective sheets are driven into the soil on the sidewall of the borehole in sequence along the depth direction of the borehole, so that the projections of the reflective sheets at each layer on the horizontal plane do not overlap. S3: The original soil core samples saved in S1 are backfilled into the borehole in the order of their original depths, and the backfill soil is compacted in layers to make the reflective sheet of each layer fit into the backfill soil. S4: Deploy ground-penetrating radar on the roadbed and pavement, periodically scan the borehole location within a preset monitoring period, emit electromagnetic waves and receive electromagnetic wave signals reflected by the reflectors at each layer; based on the propagation time and phase change of the electromagnetic waves, invert and obtain the three-dimensional spatial coordinates of the reflectors at each layer at different monitoring times, and calculate the layered deformation of the frozen soil roadbed at the corresponding depth based on the change of the three-dimensional spatial coordinates.

[0009] This invention effectively overcomes many problems existing in the prior art through its core construction process of "core sampling and preservation—radial installation of reflective plates—in-situ backfilling and compaction of undisturbed soil cores." First, by employing core sampling, numbering and preservation, and then in-situ backfilling, it avoids the severe damage to the roadbed structure caused by traditional large-scale excavation or large-diameter drilling, minimizing construction disturbance. Second, by embedding reflective plates into the sidewall soil of the borehole and backfilling with undisturbed soil cores with high density, it ensures close contact between the reflective plates and the backfill soil and surrounding roadbed soil, solving the technical problems of pre-embedded markers being prone to suspension and poor coupling with soil deformation. Finally, by layering reflective plates within the borehole and controlling the non-overlapping projections, combined with subsequent non-contact periodic scanning and coordinate inversion by ground-penetrating radar, it achieves long-term, high-precision, and high-efficiency refined monitoring of layered deformation at different depths within the frozen soil roadbed without damaging the roadbed. This method not only improves the reliability of layered deformation monitoring but also provides reliable data support for subsequent safety assessment and maintenance of frozen soil roadbeds.

[0010] Preferably, in step S2, the reflective sheet is driven into the soil using a driving device, and the driving step of the reflective sheet includes: S21: Place the center rod vertically in the borehole, so that the bracket is supported on the ground around the borehole opening; place the pull rope displacement sensor on the ground on one side of the borehole opening, and connect the pull rope of the pull rope displacement sensor to the top of the conveying mechanism; S22: Adjust the insertion depth of the central rod in the borehole according to the height parameter measured by the pull rope displacement sensor, so as to control the actuator to align with the preset driving position of the reflector; S23: The reflective sheet is placed into the inlet at the top of the conveying mechanism, so that the reflective sheet moves down the conveying mechanism and is placed on the placement platform in front of the execution end of the actuator; S24: Activate the actuator to push the reflector into the soil, and reset the actuator after the reflector is inserted into the soil. S25: Repeat S22~S24, readjust the height of the actuator, and rotate the center rod at a preset angle to complete the insertion of all reflective sheets in sequence, and ensure that the projections of several reflective sheets on the horizontal plane do not overlap.

[0011] This scheme further defines the specific steps for inserting the reflectors. By utilizing the linkage between the pull-rope displacement sensor and the depth control center rod, the actuator can be precisely controlled to align with the preset insertion position of each reflector layer, avoiding layer errors caused by inaccurate depth positioning. Through the orderly delivery of reflectors by the conveying mechanism, and in conjunction with the pushing and resetting of the actuator, as well as the rotation of the center rod to adjust the orientation, not only is the insertion action automated and highly efficient, but it also effectively ensures that the reflectors at each layer do not overlap on the horizontal plane. This provides reliable spatial conditions for subsequent ground-penetrating radar to accurately identify the independent reflection signals of each layer, eliminating the problem of mutual interference of radar signals caused by overlapping reflectors.

[0012] Preferably, in S2, the reflective sheet is a circular reflective sheet, and insulating sheets are attached to both sides of the reflective sheet. The insulating sheets are used to isolate the roadbed soil from the reflective sheet. After the reflective sheet is driven into the soil of the borehole sidewall, the gap between the reflective sheet and the borehole sidewall is less than or equal to 2 mm.

[0013] This scheme optimizes the specific structure and installation gap of the reflector. A circular reflector is used in conjunction with a double-sided insulating sheet. On one hand, the insulating sheet effectively isolates moisture and salt in the subgrade soil, preventing corrosion and failure of the copper reflector and extending the service life of the monitoring device. On the other hand, the insulating sheet eliminates stray reflections at the interface between the reflector and the soil, ensuring the stability and clarity of the radar reflected signal. The gap between the reflector and the borehole sidewall is controlled within 2mm, ensuring close contact between the reflector and the soil, minimizing loosening or delayed displacement of the reflector due to installation gaps, and significantly improving the dynamic response accuracy of layered deformation measurement.

[0014] Preferably, in S3, the undisturbed soil sample core is backfilled by layered filling and compaction, with each layer having a thickness of less than or equal to 20cm and a compaction degree of greater than or equal to 95%. After backfilling, the soil is left to stand for 24 to 48 hours.

[0015] This scheme precisely defines the backfill compaction process. Employing a layered filling and compaction method with each layer ≤20cm thick and a compaction degree ≥95% ensures that the backfill soil has a highly consistent density and mechanical properties with the undisturbed soil. This effectively avoids additional compressive settlement of the backfill soil under subsequent freeze-thaw cycles or loads, preventing false monitoring data caused by deformation of the backfill section itself. After backfilling, allowing it to stand for 24-48 hours allows the internal stress of the backfill soil to fully dissipate and consolidate, ensuring that the mechanical boundary conditions of the soil remain consistent with the surrounding undisturbed roadbed during long-term monitoring, further improving the accuracy of deformation monitoring.

[0016] Preferably, in S4, the ground-penetrating radar is arranged at multiple measuring points on the roadbed and pavement to perform periodic scanning. The multiple measuring points correspond to different borehole locations on the same cross section of the roadbed. The reflected electromagnetic wave data of each layer of reflectors are acquired, the propagation time of the electromagnetic waves in the roadbed soil is recorded, and the propagation speed of the electromagnetic waves in the roadbed soil is determined by combining the relative permittivity of the roadbed soil. Then, the initial depth of each layer of reflectors is calculated.

[0017] This scheme clarifies the multi-point scanning layout of ground-penetrating radar at different borehole locations on the same cross section of the roadbed. This allows the method to not only acquire longitudinal deformation information of the roadbed, but also effectively monitor differential settlement and uneven deformation in the transverse direction (such as the center of the road, left shoulder, and right shoulder), providing more comprehensive spatial deformation data for the overall stability evaluation of the roadbed. Simultaneously, by combining the actual relative permittivity of the roadbed soil to calculate the electromagnetic wave propagation velocity, the deviation in electromagnetic wave velocity caused by factors such as the uneven composition of the frozen soil subgrade medium and changes in moisture content is eliminated, effectively improving the benchmark accuracy of initial depth calculation and subsequent three-dimensional coordinate inversion.

[0018] Preferably, in step S4, the step of inverting and obtaining the three-dimensional spatial coordinates of the reflective sheet at each layer at different monitoring times includes: S41: Determine the current three-dimensional spatial coordinates of each layer of reflector in the current monitoring cycle based on the propagation time difference and phase difference of electromagnetic waves in the medium; S42: Calculate the difference between the current three-dimensional spatial coordinates and the three-dimensional spatial coordinates of the previous monitoring cycle to obtain the three-dimensional displacement of each layer of reflector. S43: The three-dimensional displacement is used as the layered deformation of the subgrade soil at the corresponding depth, and the layered deformation rate at the corresponding depth is calculated based on the layered deformation and the monitoring time interval of the current monitoring cycle.

[0019] This scheme refines the specific logic for obtaining three-dimensional coordinates through inversion and calculating deformation. By combining the propagation time difference and phase difference of electromagnetic waves in the medium, it fully leverages the high-resolution advantage of high-frequency ground-penetrating radar, significantly improving the sub-millimeter-level positioning accuracy of reflective targets (reflectors). By calculating the difference between the three-dimensional coordinates in different monitoring periods, it achieves precise quantification of the layered deformation of the roadbed from "point" to "quantity". Furthermore, by dividing the deformation by the time interval to calculate the layered deformation rate of each layer, it can intuitively reflect the dynamic deformation rate of the frozen soil roadbed in different seasons (such as the frost heave period and thaw settlement period), providing a key rate indicator for roadbed early warning and treatment.

[0020] In a second aspect, the present invention provides a device for inserting a reflective sheet, comprising a central rod, a bracket, an actuator, a conveying mechanism, and a pull-cord displacement sensor. The central rod is inserted into a buckle of the bracket. The actuator is fixedly connected to the central rod. The conveying mechanism is fixedly connected to one side of the central rod and is located above the actuator when the central rod is vertical. The outlet of the conveying mechanism is aligned with the actuator end of the actuator. The pull-cord displacement sensor is connected to the top of the conveying mechanism via a pull cord.

[0021] The driving device of this invention, through the cooperation of the bracket and the central rod, can quickly establish a stable vertical working reference above the borehole; the actuator is fixed to the central rod, ensuring that the height of the actuator can be adjusted through the central rod; the design of the conveying mechanism allows the reflector to be accurately and reliably conveyed to the actuator by gravity without the need for manual drilling; in particular, the cooperation between the pull rope displacement sensor and the top of the conveying mechanism solves the technical problem that traditional devices cannot accurately know the real-time depth of the actuator in deep hole operations, realizes closed-loop feedback control of the driving depth, significantly reduces the construction operation difficulty of deep hole layer driving, and improves the driving positioning accuracy.

[0022] Preferably, the actuator includes a controller, a motor, a gear set, a screw, a precessing rod, and a fixed sleeve. The precessing rod is sleeved on the screw and connected to the screw via a threaded connection. The precessing rod passes through the fixed sleeve and is circumferentially fixed to the fixed sleeve. The controller is connected to the motor via a wire. The motor is connected to the screw via the gear set. The screw can rotate around its own axis under the drive of the motor and drive the precessing rod to extend and retract via a threaded connection. The actuating end of the precessing rod is provided with a placement platform for placing the reflector.

[0023] This solution defines the specific power transmission structure of the actuator. The controller, motor, and gear set provide a stable and controllable power source. Through the threaded engagement of the screw and the advance rod, the rotational motion of the motor can be smoothly and efficiently converted into the high-precision linear extension and retraction motion of the advance rod. Combined with the circumferential limiting of the advance rod by the fixed sleeve, it avoids the advance rod from rotating with the screw and being unable to achieve extension and retraction using the threaded engagement, and also ensures the linearity and accuracy of the thrust during the driving process. The setting of the placement platform ensures that the reflector remains in the accurate position before driving, preventing directional deviation, thereby ensuring that the reflector cuts into the frozen soil subgrade vertically with an ideal posture.

[0024] Preferably, the conveying mechanism includes a guide plate and a plurality of guide impellers, the shafts of the guide impellers are connected to the guide plate, the plurality of guide impellers are arranged vertically on the guide plate, and the side of the guide plate is connected to the central rod through a connecting rod.

[0025] This solution optimizes the conveying path of the reflector sheet within the borehole. By setting several vertically arranged guide impellers on the guide plate, the reflector sheet can slide smoothly along a fixed track under its own gravity, effectively preventing the reflector sheet from getting stuck, flipping, or tilting during the descent. This ensures that each reflector sheet lands accurately on the placement platform of the actuator in a flat position, guaranteeing the smoothness and reliability of the equipment during continuous multi-sheet installation operations and avoiding construction interruptions caused by material jamming.

[0026] Preferably, the top of the conveying mechanism is provided with an upwardly extending bend, and the pull rope of the pull rope displacement sensor can be vertically connected to the bend.

[0027] This design optimizes the connection between the top of the conveying mechanism and the rope displacement sensor. By incorporating an upward-extending bend at the top of the conveying mechanism, the rope of the rope displacement sensor is connected to this bend in a completely vertical direction, eliminating measurement errors caused by the rope's tilt or bending. This further ensures the real-time feedback accuracy of the rope displacement sensor regarding the depth of the actuator, improving the adaptability and measurement accuracy of the device in harsh frozen soil construction environments.

[0028] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention provides a method and device for monitoring the layered deformation of frozen soil subgrade. Through the core construction process of "core sampling and preservation—radial installation of reflective pads—in-situ backfilling and compaction of undisturbed soil cores," it effectively overcomes many problems existing in the prior art. First, by using core sampling and numbering for preservation, followed by in-situ backfilling, the severe damage to the subgrade structure caused by traditional large-scale excavation or large-diameter drilling is avoided, resulting in minimal construction disturbance. Second, by driving reflective pads into the sidewall soil of the borehole and backfilling with undisturbed soil cores with high density, the close fit between the reflective pads and the backfill soil and surrounding subgrade soil is ensured, solving the technical problems of pre-embedded markers being easily suspended and having poor coupling effect with soil deformation. Finally, by layering the reflective pads within the borehole and controlling the non-overlapping projections, combined with subsequent non-contact periodic scanning and coordinate inversion by ground-penetrating radar, long-term, high-precision, and highly efficient fine-grained monitoring of layered deformation at different depths within the frozen soil subgrade is achieved without damaging the subgrade. This method not only improves the accuracy and reliability of layered deformation monitoring, but also provides reliable data support for the subsequent safety assessment and maintenance of frozen soil subgrades. Attached Figure Description

[0029] Figure 1 This is a schematic diagram of ground-penetrating radar monitoring.

[0030] Figure 2 This diagram illustrates the drilling, sampling, reflector insertion, and backfilling processes.

[0031] Figure 3 This is a schematic diagram of the injection device.

[0032] Figure 4 This is a schematic diagram showing the connection between the rope displacement sensor and the bent section above the guide plate.

[0033] Figure 5 This is a schematic diagram of the cross-section of the screw, the advance rod, and the fixed sleeve.

[0034] Figure 6 This is a schematic diagram of the cross-sectional structure of the reflector.

[0035] Figure 7 This is a schematic diagram of the planar layout of the boreholes.

[0036] Figure 8 This is a schematic diagram of the horizontal projection of the reflector surrounding a single borehole.

[0037] Figure 9 This is a flowchart illustrating the monitoring method.

[0038] Figure 10 This is a horizontal projection diagram of the central rod, the part of the actuator located inside the borehole, and the conveying mechanism.

[0039] Marked in the image: 1. Ground penetrating radar; 2. Reflector; 3. Road surface structure; 4. Subgrade structure; 5. Foundation structure; 6. Drill hole; 7. Sample core; 8. Environmental chamber; 9. Clip; 10. Center rod; 11. Controller; 12. Guide plate; 13. Guide impeller; 14. Pull rope displacement sensor; 15. Bracket; 16. Motor; 17. Gear set; 18. Screw; 19. Advance rod; 20. Fixing sleeve; 21. Placement platform; 22. Insulating sheet; 23. Copper sheet; 24. Driving device; 25. Connecting rod; 26. Pull rope; 27. Bending part; 28. Key. Detailed Implementation

[0040] The present invention will now be described in further detail with reference to specific embodiments. However, this should not be construed as limiting the scope of the present invention to the following embodiments; all technologies implemented based on the content of the present invention fall within the scope of the present invention.

[0041] Unless otherwise specified, the use of terms such as "upper," "lower," "left," "right," "center," "inner," and "outer" to indicate orientation or positional relationships in the description of specific embodiments of the present invention is based on the orientation or positional relationships shown in the accompanying drawings, or the orientation or positional relationship in which the product / equipment / device is typically placed during use. These terms are merely for the purpose of facilitating the description of the present invention or simplifying the description in specific embodiments, enabling those skilled in the art to quickly understand the solution, and do not indicate or imply that a particular device / component / element must have a specific orientation, or be constructed and operated in a specific positional relationship. Therefore, they should not be construed as limitations on the present invention.

[0042] Furthermore, the use of terms such as "horizontal," "vertical," "suspended," and "parallel" does not imply that the corresponding device / component / element must be absolutely horizontal, vertical, suspended, or parallel, but rather that it can be slightly tilted or have a deviation. For example, "horizontal" merely means that its direction is more horizontal relative to "vertical," not that the structure must be completely horizontal, but that it can be slightly tilted. Alternatively, it can be simplified to mean that the corresponding device / component / element, when set in a "horizontal," "vertical," "suspended," or "parallel" direction, can have an error / deviation of ±10% relative to the corresponding direction, more preferably within ±8%, more preferably within ±6%, more preferably within ±5%, and more preferably within ±4%. As long as the corresponding device / component / element is within the error / deviation range, it can still achieve its function in the present invention.

[0043] Furthermore, the use of terms such as "first," "second," and "third" in terminology is merely for distinguishing descriptions of identical or similar components and should not be interpreted as emphasizing or implying the relative importance of a particular component.

[0044] Furthermore, in the description of the embodiments of the present invention, "several", "more than", and "a number of" represent at least two. The number can be any number, such as two, three, four, five, six, seven, eight, nine, or even more than nine.

[0045] Furthermore, in the description of the technical solution of this invention, unless otherwise explicitly specified / limited / restricted, the terms "set up," "install," "connect," "link," "provided with," "laid out," and "arranged" should be interpreted broadly. For example, they can refer to fixed connections, detachable connections, or integral connections; they can refer to common connection methods in the art, such as welding, riveting, bolting, and threaded connections. Such connections can be mechanical, electrical, or communication connections; they can be direct connections or indirect connections through an intermediate medium; and they can refer to the internal communication between two components.

[0046] Example 1 like Figures 1 to 10 As shown, this embodiment provides a method for monitoring the layered deformation of frozen soil subgrade. It mainly achieves long-term, high-precision monitoring of the layered deformation at different depths inside the frozen soil subgrade by core sampling through borehole 6, precise installation of reflector 2, backfilling and compaction of undisturbed soil cores, and periodic monitoring and inversion by ground-penetrating radar 1. The frozen soil subgrade includes pavement structure 3, subgrade structure 4 and foundation structure 5 from top to bottom. Borehole 6 usually needs to pass through pavement structure 3 and subgrade structure 4 to enter the lowest layer of foundation structure 5.

[0047] S1: Core drilling and core preservation First, drilling is conducted at the locations to be measured on the roadbed. Before drilling, measuring points are marked at the center, left shoulder, and right shoulder of the roadbed according to the cross-sectional structure of the roadbed. An engineering geological drilling rig is used with diamond or carbide drill bits to drill borehole 6. The diameter of borehole 6 can be selected based on actual monitoring needs and the size of the reflector 2, typically 5 cm, 7 cm, or 15 cm. The depth of borehole 6 needs to be determined based on the total thickness of the roadbed and the depth of each monitored soil layer.

[0048] During drilling, as the drill bit descends, continuously arranged cylindrical undisturbed soil cores 7 are obtained along the depth direction. Each extracted undisturbed soil core 7 is immediately numbered according to its corresponding core depth, and the sampling location and depth information are recorded. To ensure that the physical and mechanical properties of the undisturbed soil cores 7 do not change, the numbered undisturbed soil cores 7 are placed in sealed plastic wrap or a waterproof bag, and then sealed and stored in a temperature-controlled environmental chamber 8 with temperature and humidity control until the subsequent backfilling step.

[0049] S2: Reflector installation and spatial layout After drilling is completed, a number of reflective plates 2 are driven into the soil on the sidewall of the borehole 6 in sequence along the depth direction of the borehole 6 using a special driving device 24.

[0050] The reflector 2 is preferably made of circular copper sheet 23 because copper has extremely high electromagnetic wave reflectivity and excellent electrical conductivity. The thickness of the reflector 2 can be selected from 2 to 5 mm, and the diameter can be determined according to the diameter of the borehole 6 and the required layout density. To prevent corrosion of the copper sheet 23 by groundwater and salt, and to eliminate stray reflections at the interface between the reflector 2 and the soil, a layer of polytetrafluoroethylene (PTFE) insulating sheet 22 is attached to both the upper and lower surfaces of the copper sheet 23. The relative permittivity of the insulating sheet 22 is between 2.0 and 2.2, and its thickness is controlled within 1 mm to ensure that its influence on the penetration and propagation of electromagnetic waves is within a controllable range and will not interfere with the recognition accuracy of the reflected signal.

[0051] During the installation of the reflector 2, the installation depth is precisely controlled using the installation device 24. The installation device 24 includes a central rod 10, a support 15, an actuator, a conveying mechanism, and a pull rope displacement sensor 14. First, the support 15 is stably supported on the ground around the borehole 6. The central rod 10 is then vertically inserted into the borehole 6 through the buckle 9 of the support 15. The pull rope displacement sensor 14 is placed on the ground to one side of the borehole, and the pull rope 26 of the pull rope displacement sensor 14 is connected to the top bend 27 of the conveying mechanism to ensure that the pull rope 26 is always in an absolutely vertical state, eliminating measurement errors. Based on the height parameters fed back by the pull rope displacement sensor 14, the operator adjusts the insertion depth of the central rod 10 up and down, thereby controlling the actuator to align with the preset installation position of the reflector 2 at the current layer.

[0052] Next, a single reflector 2 is placed at the entrance of the top of the conveying mechanism. Relying on its own weight, the reflector 2 slides down the guide plate 12 and each guide impeller 13 inside the conveying mechanism, finally landing smoothly and upright on the placement platform 21 in front of the actuator's execution end. The actuator is then started; the internal motor 16 decelerates through the gear set 17 and drives the screw 18 to rotate. The screw 18, through a threaded engagement, drives the advance rod 19 to move horizontally outward, forcibly pushing the reflector 2 placed on the placement platform 21 into the frozen soil or roadbed soil on the side wall of the borehole 6. When the advance rod 19 has traveled to the preset stroke and the reflector 2 is fully inserted into the soil, the motor 16 is started in reverse, causing the advance rod 19 to move backward and reset.

[0053] Specifically, the gear set 17 contains 3 gears. In addition to transmitting the rotation effect of the motor, the gear set 17 also plays the role of slowing down the device and increasing the torque. The gears can be made of medium carbon steel or nylon (the middle gear is made of nylon, mainly to reduce noise and unnecessary wear).

[0054] After installing one reflector 2, adjust the vertical height of the center rod 10 according to design requirements to correspond to the next layer, and rotate the center rod 10 circumferentially at a preset angle. Repeat the above conveying and driving operation to drive the next reflector 2 into the sidewall of the borehole 6 at a different circumferential orientation. Because there is an angular deviation in the circumferential direction between the reflectors 2, the projections of the reflectors 2 on the horizontal plane do not overlap. Specifically, the centers of all reflectors 2 are usually arranged around the vertices of a regular polygon surrounding the central axis of the borehole 6. If the diameter of the borehole 6 is A, the diameter of the reflector 2 is a, and the side length of the regular polygon is a, then the geometric relationship between the size of a single reflector 2 and the diameter of the borehole 6 can be determined using the following formula:

[0055] Where n is the number of single-layer reflective sheets 2 or the number of layers installed.

[0056] After the reflectors 2 at each layer are installed, it is necessary to ensure that the gap between the outer edge of the reflector 2 and the side wall of the borehole 6 is less than or equal to 2 mm, so as to ensure that there is rigid contact between the reflector 2 and the soil and avoid subsequent settlement deformation from being delayed.

[0057] In some more specific implementations, the spacing m between adjacent reflectors 2 (at different layers) is set to 5 cm, 10 cm, or 15 cm. The deployment depth and density can be determined based on the total roadbed thickness L and monitoring requirements. For example, the number n of reflectors 2 to be deployed can be calculated using the following formula:

[0058] It should be noted that, Figure 1 The relative positions of the reflective sheets 2 shown are only approximate; in reality, the reflective sheets 2 do not overlap vertically.

[0059] S3: In-situ backfilling and compaction of undisturbed soil core After all reflectors 2 were installed, in-situ backfilling was carried out. The undisturbed soil cores 7, numbered and stored in S1, were backfilled into borehole 6 segment by segment according to their original depth, strictly following the order of their numbers from deep to shallow. During backfilling, a layered compaction method was adopted, strictly controlling the thickness of each layer (usually no more than 20 cm). Immediately after each layer of undisturbed soil was laid, compaction was carried out using a small compaction hammer or vibratory tamping plate to ensure that the compaction degree of the backfill soil was greater than or equal to 95% (compaction degree calculation formula is...). Where ρ is the actual dry density of the backfill soil. (This refers to the maximum dry density of the backfill soil). Since the backfill soil is undisturbed, after high-density compaction, it can completely match the mechanical properties of the original soil, thus ensuring a tight deformation coupling between the reflector and the backfill soil, as well as between the backfill soil and the surrounding undisturbed soil.

[0060] After backfilling is completed, the soil needs to be left to stand for 24 to 48 hours to ensure that the stress within the soil is completely dissipated. After the soil has settled, the road surface is restored to a smooth surface, and the construction process is complete.

[0061] S4: Periodic monitoring and inversion of ground-penetrating radar The core of the monitoring method lies in using ground-penetrating radar 1 for non-destructive periodic scanning. Ground-penetrating radar 1 is deployed on the roadbed surface, and multiple corresponding measuring points are set on the ground according to the locations of the multiple boreholes 6 drilled in S1. Typically, the measuring points of ground-penetrating radar 1 correspond one-to-one with the positions of the center, left shoulder, and right shoulder of the roadbed cross-section to obtain deformation data for the entire cross-section.

[0062] Ground-penetrating radar 1 emits high-frequency electromagnetic waves into the roadbed. To achieve sub-millimeter level reflection resolution, the radar antenna's transmission frequency can be set to a wide bandwidth of 1 GHz to 10 GHz. When the radar waves propagate through the roadbed soil, they encounter highly reflective reflective sheets 2 (an insulating sheet 22-wrapped structure), resulting in significant strong reflection signals. The receiving antenna of ground-penetrating radar 1 records the electromagnetic wave signals reflected back from the reflective sheets 2 at each layer and the corresponding electromagnetic wave propagation time.

[0063] Due to the relative permittivity of frozen soil subgrade r and relative permeability μ r The relative permittivity and relative permeability of the subgrade soil vary with moisture content, temperature, and density. To accurately calculate the depth, it is necessary to conduct sampling tests or use an in-situ dielectric constant measuring instrument to determine the actual relative permittivity and relative permeability of the subgrade soil beforehand, and then apply the electromagnetic wave propagation velocity formula. Calculate the actual propagation speed of electromagnetic waves in the roadbed medium. v (in c Let be the speed of light in a vacuum, and take 3 × 10⁻⁶. 8 m / s). Based on the measured electromagnetic wave propagation time t Substitute into the formula z = v × t The initial depth of each layer of reflector 2 can be calculated by dividing by 2.

[0064] S5: Calculation and Output of Deformation Parameters To obtain the deformation of the roadbed under freeze-thaw cycles or vehicle loads, the S4 radar scanning process needs to be repeated within a preset monitoring period. The monitoring period can be set to 15 days, 30 days, or 90 days, etc., according to actual engineering requirements.

[0065] After each scan, the electromagnetic wave data is inverted. First, a Cartesian coordinate system for the roadbed is established, typically with a fixed marker on the road surface as the origin, the horizontal X and Y axes as the horizontal axes, and the vertical Z axis downwards, thus determining the initial coordinate system. Based on the electromagnetic wave data from each scan, combined with the electromagnetic wave propagation time difference and phase change, the three-dimensional spatial coordinates of each layer of reflectors at the current monitoring time are inverted and obtained. x t , y t , z t The phase change correction formula is Δ. =2 π Δ r / λ , where Δ For the phase difference, Δ r Due to the poor propagation path of electromagnetic waves, λ The wavelength of an electromagnetic wave in a medium ( λ = v / f , f (Radar transmission frequency).

[0066] The three-dimensional spatial coordinates of the current monitoring period ( x n , y n , z n ) and the three-dimensional spatial coordinates of the previous monitoring period ( x n 1, y n 1, z n 1) By performing difference calculations, the three-dimensional displacement Δ of each layer of reflector can be obtained. s The calculation formula is Δ s =( x n x n 1) 2 +( y n y n 1) 2 +( z n z n 1) 2 This three-dimensional displacement corresponds to the stratified deformation of the frozen soil subgrade at that depth.

[0067] In addition, to analyze the deformation trend of the frozen soil subgrade, the time interval Δ between the two monitoring sessions was considered. t Calculate the delamination rate at each depth. v i The formula is v i =Δ s i / Δ t i (where Δ) s i For the first i Deformation of a layer during a certain monitoring period, Δ t i (This corresponds to a time interval). By calculating the layered deformation rate, the dynamic deformation rate of the roadbed in different seasons or under different load stages can be intuitively reflected, thus providing a scientific basis for the early warning, maintenance, and upkeep of the roadbed.

[0068] Example 2 Based on the monitoring method of Embodiment 1 above, this embodiment further provides a device 24 for inserting a reflective sheet 2.

[0069] The reflector 2 insertion device 24 has an overall vertical column structure, including a central rod 10, a bracket 15, an actuator, a conveying mechanism, and a rope displacement sensor 14.

[0070] The center rod 10 serves as the main load-bearing frame of the entire device and is made of high-strength alloy steel. The center rod 10 passes through the inner hole of the buckle 9 of the bracket 15. By tightening the fasteners of the buckle 9, the vertical position of the center rod 10 can be fixed at any time, ensuring that the center rod 10 remains absolutely vertical.

[0071] The actuator is fixedly connected to the center rod 10 at a certain height. Specifically, the actuator consists of a controller 11, a DC brushed motor 16, a gear set 17, a screw 18, a feed rod 19, and a fixed sleeve 20. The fixed sleeve 20 is fixed to the center rod 10, the feed rod 19 passes through the inner cavity of the fixed sleeve 20, and a key 28 (such as...) is provided on the surface of the feed rod 19. Figure 5As shown in the diagram, the keyway fit structure allows the advance rod 19 to move linearly along its axis within the fixed sleeve 20, preventing circumferential rotation (i.e., circumferential fixation is maintained through the keyway fit). The screw 18 is installed in the inner hole of the advance rod 19 and connected to it via a threaded connection. The DC brushed motor 16 is electrically connected to the controller 11 via wires. When the controller 11 issues a drive command, the DC brushed motor 16 rotates, and through the gear set 17, it reduces speed and increases torque, driving the screw 18 to rotate around its own axis. Due to the threaded connection between the screw 18 and the advance rod 19, and because the advance rod 19 is limited by the fixed sleeve 20 and cannot rotate, the rotation of the screw 18 forces the advance rod 19 to extend and retract axially. A placement platform 21 is located below the advance rod 19, adjacent to the bottom of the advance rod 19 and fixedly connected to the fixed sleeve 20. The placement platform 21 is used to receive and position a single reflector 2. In this embodiment, the thrust of the advance rod 19 is designed to be between 0.5 MPa and 1.5 MPa (determined based on the tensile strength of the frozen soil), the speed of the motor 16 is controlled at around 1000 rpm, and the longitudinal cross-sectional area of ​​the reflector 2 of the advance rod 19 is about 30 square millimeters. Therefore, it can ensure sufficient breaking force to press the reflector 2 into the frozen soil, while not damaging the frozen soil skeleton structure due to excessive pressure.

[0072] The conveying mechanism is fixedly connected to one side of the central rod 10. When the central rod 10 is vertically positioned, the conveying mechanism is located directly above the execution end of the actuator. Specifically, the lower end of the guide plate 12 is directly above the placement platform 21, meaning the guide plate 12 is vertically aligned with the placement platform 21. The conveying mechanism includes the guide plate 12 and several guide impellers 13. The guide plate 12 is a vertically elongated strip. The shafts of the guide impellers 13 are vertically connected to the guide plate 12, and the guide impellers 13 are arranged vertically at intervals on the guide plate 12. The side of the guide plate 12 is fixedly welded to the central rod 10 via connecting rods 25. The top of the conveying mechanism has an upwardly extending, angled bend 27. The pull-rope displacement sensor 14 is installed on the ground near the borehole 6. Its pull rope 26 is pulled vertically upward and fixedly connected to the bend 27 at the top of the conveying mechanism. This absolutely vertical pull method can minimize the depth measurement error caused by the tilt of the pull rope 26 due to direct connection with the guide plate 12. Here, the structure of the conveying mechanism can also be a hollow cylindrical structure. The inner diameter of the cylinder can be slightly larger than the outer diameter of the reflector 2. After the reflector 2 is inserted into the cylinder, it can fall directly along the axis of the cylinder onto the placement platform 21.

[0073] The method of inserting the reflector 2 is carried out using the inserting device 24: When using this device, first move the entire device above the borehole 6, and place the bottom of the support 15 stably on the flat ground around the opening of the borehole 6, so that the central rod 10 and the actuator are placed inside the borehole 6 (the controller 11 is placed on the ground outside the borehole 6 and connected to the motor 16 via a wire). The operator can accurately determine the current depth of the advance rod 19 by observing the reading of the pull rope displacement sensor 14, and select whether to adjust the insertion depth of the central rod 10, thereby adjusting the height of the advance rod 19 to be in the preset insertion position. After the height is adjusted, place a single reflector 2 with an insulating layer into the entrance at the top of the conveying mechanism. Under its own gravity, the reflector 2 slides down along the guide plate 12, and after being guided and limited by each guide impeller 13, it finally lands smoothly on the placement platform 21 in front of the advance rod 19.

[0074] Next, the controller 11 is activated, causing the DC brushed motor 16 to rotate, which in turn drives the gear set 17 and the screw 18 to rotate. The advance rod 19 extends outward, pushing the reflector 2 on the placement platform 21 into the roadbed soil in a horizontal position. When the reflector 2 is fully embedded and reaches the preset depth, the controller 11 controls the motor 16 to reverse, and the advance rod 19 retracts and resets.

[0075] Subsequently, the operator loosens the fasteners on the clip 9, moves the center rod 10 up or down, adjusts the height of the actuator to align with the next layer, and simultaneously rotates the center rod 10 around its own axis by a preset angle (for example, if N reflectors 2 need to be installed, rotate 360° / N each time) to ensure that the projections of the reflectors 2 at different layers on the horizontal plane do not overlap. The rotation angle of the center rod 10 can be measured using a dedicated angle measuring tool to ensure that the rotation angle is as accurate as possible. The next reflector 2 is then placed in, and the above operation is repeated to achieve high-efficiency and high-precision installation of multiple layers and multiple orientations of reflectors 2.

[0076] In summary, this invention provides a method and device for monitoring the layered deformation of frozen soil subgrades. Through the core construction process of "core sampling and preservation—radial installation of reflective pads—in-situ backfilling and compaction of undisturbed soil cores," it effectively overcomes many problems existing in the prior art. First, by using core sampling and numbering for preservation, followed by in-situ backfilling, the severe damage to the subgrade structure caused by traditional large-scale excavation or large-diameter drilling is avoided, resulting in minimal construction disturbance. Second, by driving reflective pads into the sidewall soil of the borehole and backfilling with undisturbed soil cores with high density, the close fit between the reflective pads and the backfill soil and surrounding subgrade soil is ensured, solving the technical problems of pre-embedded markers being easily suspended and having poor coupling effect with soil deformation. Finally, by layering the reflective pads within the borehole and controlling the non-overlapping projections, combined with subsequent non-contact periodic scanning and coordinate inversion by ground-penetrating radar, long-term, high-precision, and high-efficiency refined monitoring of layered deformation at different depths within the frozen soil subgrade is achieved without damaging the subgrade. This method not only improves the accuracy and reliability of layered deformation monitoring, but also provides reliable data support for the subsequent safety assessment and maintenance of frozen soil subgrades.

[0077] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for monitoring the layered deformation of frozen soil subgrade, characterized in that, include: S1: Drill holes (6) at the locations to be tested in the roadbed, and obtain undisturbed soil cores (7) arranged along the depth direction during the drilling process. Number and save the undisturbed soil cores (7) according to the core depth order. S2: Several reflective sheets (2) are driven into the soil on the side wall of the borehole (6) along the depth direction of the borehole (6) so that the projections of the reflective sheets (2) at each layer on the horizontal plane do not overlap. S3: The original soil core (7) saved in S1 is backfilled into the borehole (6) in the order of its original depth, and the backfill soil is compacted in layers so that the reflective sheet (2) of each layer is in contact with the backfill soil. S4: Arrange the ground-penetrating radar (1) on the roadbed and pavement, and periodically scan the location of the borehole (6) within the preset monitoring period. Emits electromagnetic waves and receives electromagnetic wave signals reflected by the reflectors (2) at each layer. Based on the propagation time and phase change of the electromagnetic waves, inverts and obtains the three-dimensional spatial coordinates of the reflectors (2) at each layer at different monitoring times. Calculates the layered deformation of the frozen soil roadbed at the corresponding depth based on the change in the three-dimensional spatial coordinates.

2. The method for monitoring layered deformation of frozen soil subgrade according to claim 1, characterized in that, In S2, the reflective sheet (2) is driven into the soil using a driving device (24). The driving step of the reflective sheet (2) includes: S21: Place the center rod (10) vertically in the drill hole (6) so that the bracket (15) is supported on the ground around the hole opening; set the pull rope displacement sensor (14) on the ground on one side of the hole opening and connect the pull rope (26) of the pull rope displacement sensor (14) to the top of the conveying mechanism; S22: Adjust the insertion depth of the center rod (10) in the borehole (6) according to the height parameter measured by the pull rope displacement sensor (14) to control the actuator to align with the preset driving position of the reflector (2); S23: The reflector (2) is placed into the inlet at the top of the conveying mechanism, so that the reflector (2) moves down the conveying mechanism and is placed on the placement platform (21) in front of the execution end of the actuator; S24: Activate the actuator to push the reflector (2) into the soil, and reset the actuator after the reflector (2) is inserted into place; S25: Repeat S22~S24, readjust the height of the actuator, and rotate the center rod (10) at a preset angle to complete the insertion of all reflective sheets (2) in sequence, and ensure that the projections of several reflective sheets (2) on the horizontal plane do not overlap.

3. The method for monitoring layered deformation of frozen soil subgrade according to claim 1, characterized in that, In S2, the reflective sheet (2) is a circular reflective sheet (2), and an insulating sheet (22) is attached to both sides of the reflective sheet (2). The insulating sheet (22) is used to isolate the roadbed soil from the reflective sheet (2). After the reflective sheet (2) is driven into the soil of the side wall of the borehole (6), the gap between the reflective sheet (2) and the side wall of the borehole (6) is less than or equal to 2 mm.

4. The method for monitoring layered deformation of frozen soil subgrade according to claim 1, characterized in that, In S3, the original soil sample core (7) is backfilled by layered filling and compaction. The thickness of each backfill layer is less than or equal to 20cm, and the compaction degree of the backfill soil is greater than or equal to 95%. After the backfill is completed, it is left to stand for 24 to 48 hours.

5. The method for monitoring layered deformation of frozen soil subgrade according to claim 1, characterized in that, In S4, the ground-penetrating radar (1) is arranged at multiple measuring points on the roadbed and pavement to perform periodic scanning. The multiple measuring points correspond to different borehole (6) positions on the same cross section of the roadbed. The reflected electromagnetic wave data of each layer reflector (2) is obtained, the propagation time of the electromagnetic wave in the roadbed soil is recorded, and the propagation speed of the electromagnetic wave in the roadbed soil is determined by combining the relative permittivity of the roadbed soil. Then, the initial depth of each layer reflector (2) is calculated.

6. The method for monitoring layered deformation of frozen soil subgrade according to claim 1, characterized in that, In S4, the steps for inverting and obtaining the three-dimensional spatial coordinates of the reflective sheet (2) at each layer at different monitoring times include: S41: Determine the current three-dimensional spatial coordinates of each layer of reflector (2) in the current monitoring cycle based on the time difference and phase difference of electromagnetic wave propagation in the medium; S42: Calculate the difference between the current three-dimensional spatial coordinates and the three-dimensional spatial coordinates of the previous monitoring cycle to obtain the three-dimensional displacement of each layer of reflector (2); S43: The three-dimensional displacement is used as the layered deformation of the subgrade soil at the corresponding depth, and the layered deformation rate at the corresponding depth is calculated based on the layered deformation and the monitoring time interval of the current monitoring cycle.

7. A device for inserting a reflective sheet, characterized in that, The device includes a central rod (10), a bracket (15), an actuator, a conveying mechanism, and a pull rope displacement sensor (14). The central rod (10) is inserted into the buckle (9) of the bracket (15). The actuator is fixedly connected to the central rod (10). The conveying mechanism is fixedly connected to one side of the central rod (10) and is located above the actuator when the central rod (10) is vertical. The outlet of the conveying mechanism is aligned with the actuator end of the actuator. The pull rope displacement sensor (14) is connected to the top of the conveying mechanism via a pull rope (26). The conveying mechanism includes a guide plate (12) and a plurality of guide impellers (13). The shaft of the guide impellers (13) is connected to the guide plate (12). The plurality of guide impellers (13) are arranged vertically at intervals on the guide plate (12). The side of the guide plate (12) is connected to the center rod (10) through a connecting rod (25).

8. The device for inserting the reflective sheet according to claim 7, characterized in that, The actuator includes a controller (11), a motor (16), a gear set (17), a screw (18), a precessing rod (19), and a fixed sleeve (20). The precessing rod (19) is sleeved on the screw (18) and connected to the screw (18) by a threaded engagement. The precessing rod (19) passes through the fixed sleeve (20) and is circumferentially fixed to the fixed sleeve (20). The controller (11) is connected to the motor (16) by a wire. The motor (16) is connected to the screw (18) by a transmission through the gear set (17). The screw (18) can rotate around its own axis under the drive of the motor (16) and drive the precessing rod (19) to extend and retract through a threaded engagement. The actuating end of the precessing rod (19) is provided with a placement platform (21) for placing the reflector (2).

9. The device for inserting the reflective sheet according to claim 7, characterized in that, The top of the conveying mechanism is provided with an upwardly extending bend (27), and the pull rope (26) of the pull rope displacement sensor (14) can be vertically connected to the bend (27).

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