Method for monitoring hierarchical settlement by GNSS combined static level

Abstract

The present application relates to a kind of GNSS joint static level instrument monitoring layered settlement method, and different depth target soil layer is respectively drilled and buried settlement steel pipe, bottom is anchored in corresponding soil layer, top exposes surface;GNSS absolute reference point is set outside monitoring area, and the settlement steel pipe anchored in stable soil layer is selected as relative reference point in area, top installs GNSS receiver and liquid storage tank, the top of remaining steel pipe installs static level instrument, and connecting vessel system is constructed by liquid passage, air passage line.Its advantage is shown in: the present application will core monitoring equipment be all arranged in surface, fault can be directly surface maintenance, equipment can be completely recycled after monitoring, construction difficulty is low, and strong anti construction interference ability;By double reference system, each soil layer high-precision absolute settlement can be directly exported, adapt centimeter to meter level large settlement monitoring scene, can be applied to soft soil foundation treatment, foundation pit deformation, roadbed settlement and other types of engineering monitoring scene.

Description

Technical Field

[0001] This invention belongs to the field of geotechnical engineering monitoring technology, and relates to a method for monitoring stratified settlement using a GNSS combined with a static level. Background Technology

[0002] During engineering construction, especially in conditions such as soft soil foundation treatment and high embankment foundations, the stratified settlement of soil is a key indicator for assessing foundation stability and controlling construction progress and quality. Accurate and efficient monitoring of settlement at different soil depths is crucial for ensuring project safety and achieving information-based construction.

[0003] Layered settlement of soil is a geological phenomenon characterized by its insidious nature, slow development, and significant cumulative effects. Its formation is closely related to natural and anthropogenic factors such as increased overburden load, changes in groundwater level, and soil consolidation and drainage. In soft soil areas, when performing foundation treatment or large-area surcharges, the physical and mechanical properties of soil layers at different depths vary considerably, with different compression moduli and consolidation rates, leading to uneven settlement. If this uneven layered settlement is not effectively monitored, it can cause a series of engineering problems: in soft soil roadbeds, it can result in longitudinal cracking of the pavement, bridge approach slab settlement, and misalignment of pipeline interfaces; in severe cases, it can lead to foundation instability, slope slippage, and even threaten the safe use of adjacent buildings and structures. Therefore, meticulous, all-weather monitoring of layered settlement of soil has become an indispensable quality control component in major projects such as soft soil foundation treatment.

[0004] The core objective of layered settlement monitoring is to accurately obtain the compression amount, compression rate, and evolution over time of each soil layer under load, thereby assessing the effectiveness of foundation treatment, optimizing construction loading schemes, and predicting post-construction settlement. Real-time monitoring can promptly detect abnormal settlement trends (such as a sudden acceleration of compression in a soil layer), providing crucial data support for engineering early warning and emergency response. In surcharge preloading projects on soft soil foundations, layered settlement data can be used to determine the timing of unloading, avoiding premature unloading due to unstable settlement. In high embankment foundation construction, monitoring results can guide the adjustment of layer compaction thickness and compaction work to ensure the stability of the embankment itself. In deep foundation pit projects near existing tunnels or subways, accurate layered settlement monitoring can assess the disturbance impact of construction on the surrounding soil, ensuring the safety of operating lines.

[0005] For a long time, stratified settlement monitoring has relied on various traditional technologies. Common methods include stratified settlement markers combined with steel tape settlement meters and magnetostrictive stratified settlement meters. Stratified settlement markers require multiple settlement rings or magnetic rings to be buried underground, and sensors are lowered down to detect changes in the relative positions of each ring. However, these traditional technologies have many limitations in practical applications. First, core components such as sensors and cables, buried underground for extended periods, are easily damaged and difficult to repair or replace due to groundwater corrosion, soil compression, and construction disturbance. Second, most components are not recyclable, and material costs cannot be amortized after the project ends, resulting in high costs per monitoring point. Third, electronic equipment such as magnetostrictive sensors has limited range, making it difficult to adapt to large deformation conditions of several meters in soft soil areas. Fourth, the installation process is complex, requiring professionals to precisely deploy multiple sensing elements in boreholes, resulting in low construction efficiency and difficulty in ensuring quality. Therefore, there is an urgent need to develop a new stratified settlement monitoring method with equipment located above ground, recyclable and reusable, with a large range and easy installation.

[0006] Currently, a common approach for automated monitoring of soil stratified settlement is to use magnetostrictive stratified settlement observation devices. These devices require embedding settlement tubes and a series of magnetic rings that settle with the soil layers in a borehole. Magnetic sensors are placed inside the settlement tubes to detect changes in the position of each magnetic ring, thereby calculating the settlement of the corresponding soil layer. This method has the following problems and drawbacks: 1. Sensors are located underground, making maintenance difficult: Magnetic sensors and connecting cables are buried in boreholes. Once a fault occurs (such as cable breakage or sensor failure), it is difficult to repair or replace them, and may even lead to data interruption for the entire monitoring point.

[0007] 2. The equipment is not recyclable and has a high cost: Components such as magnetic rings and settling pipes are difficult to remove from the soil after the project is completed and cannot be reused, resulting in a large material cost for each monitoring point.

[0008] 3. Complex installation process: It requires precise control of the embedding depth and position of the magnetic ring, which places high demands on the technical skills of the construction personnel and results in relatively low installation efficiency.

[0009] 4. Susceptible to construction: Underground cables and sensors are at risk of being damaged during subsequent on-site construction (such as compaction or loading).

[0010] Therefore, there is an urgent need for a layered settlement monitoring method that is easier to install and maintain, recyclable, has good long-term stability, and is more cost-effective. Summary of the Invention

[0011] The purpose of this invention is to solve the above-mentioned problems existing in the prior art and to provide a method for monitoring stratified settlement using a GNSS combined with a hydrostatic level.

[0012] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A method for monitoring stratified settlement using GNSS combined with a hydrostatic level includes the following steps: Step 1: Drill holes at the monitoring points for different target soil layers, and bury independent settlement steel pipes in each hole. The bottom of each settlement steel pipe is fixed to the corresponding target soil layer, and the top is exposed above the ground. Step 2: Set up a GNSS absolute reference point in a stable area outside the monitoring area; Step 3: Within the monitoring area, select the settlement steel pipe located in the most stable soil layer as the relative reference point, and install the first GNSS receiver and the liquid storage tank on its top; Step 4: Install a hydrostatic level on the top of each of the other settlement steel pipes, except for the aforementioned relative reference point; Step 5: Connect the liquid chambers of all the hydrostatic levels to the storage tank through the liquid-conducting pipes to form a communicating vessel system, and balance the air pressure chambers of all the hydrostatic levels with the atmospheric pressure through the air-conducting pipes. Step 6: Establish a data processing and transmission system, connect and collect data from the first GNSS receiver and all hydrostatic level instruments, and remotely transmit the data to the data processing center; Step 7: Data Processing Steps Step (a): Based on the liquid level data of the hydrostatic level, calculate the relative settlement of the top of each settling steel pipe relative to the relative reference point; Step (b): Based on the data from the first GNSS receiver at the absolute GNSS reference point and the relative reference point, calculate the absolute elevation change of the relative reference point; Step (c): Add the relative settlement calculated in step (a) to the absolute elevation change obtained in step (b) to calculate the absolute settlement at the top of each settlement steel pipe. Step (d): Based on the difference in absolute settlement at the top of the steel pipe at different depths, obtain the stratified settlement of the corresponding target soil layer.

[0013] Preferably, the bottom of the settling steel pipe is provided with an extension structure to increase the contact resistance with the soil layer.

[0014] Preferably, in step 6, the data processing and transmission system is integrated on the top of the settlement steel pipe at the relative reference point, including a data acquisition unit and a power supply module.

[0015] Preferably, the power supply module is a solar power supply system.

[0016] Preferably, the method further includes an equipment recycling step, that is, after the monitoring is completed, the surface equipment on the top of each settlement steel pipe is disassembled to realize the recycling and reuse of the hydrostatic level, GNSS receiver and data acquisition device.

[0017] Preferably, both the liquid-conducting pipeline and the venting pipeline are made of corrosion-resistant materials.

[0018] Preferably, the data processing center performs real-time analysis and early warning of the collected data, and issues an alarm when the settlement exceeds a preset threshold.

[0019] Preferably, the hydrostatic level uses a high-precision capacitive or piezoresistive sensor.

[0020] Preferably, the GNSS absolute reference point uses a multi-satellite, multi-frequency GNSS receiver to improve positioning accuracy.

[0021] Another objective of this invention is to provide a GNSS-based hydrostatic leveling system for stratified settlement monitoring. A GNSS-based combined hydrostatic leveling instrument-based stratified settlement monitoring system includes: An external GNSS absolute reference point subsystem is used to provide a stable absolute coordinate reference; Multiple settlement steel pipes buried in different soil layers; A relative reference point subsystem includes a first GNSS receiver, a liquid storage tank, a data acquisition unit, and a power supply unit, all mounted on top of a selected settling steel pipe. Multiple hydrostatic levels are installed on top of the other settled steel pipes; A connected hydraulic pipeline system connects the liquid chambers of all hydrostatic levels to the storage tank; A connected piping system is used to keep the air chambers of all hydrostatic instruments pressure balanced; And a remote data transmission module.

[0022] Due to the adoption of the above technical solution, the beneficial effects obtained by the present invention include: 1. This invention breaks away from the traditional layout approach of burying core equipment underground in layered settlement monitoring technology. Instead, it places all core monitoring equipment, such as GNSS receivers, hydrostatic levels, liquid storage tanks, and data acquisition units, on top of the settlement steel pipe on the ground surface. This fundamentally solves the pain points of traditional technology, such as non-recyclable equipment and high maintenance difficulty. During the monitoring process, equipment failures can be repaired and replaced directly on the ground surface without destructive excavation. After the monitoring task is completed, all equipment can be completely disassembled and recycled for reuse in other monitoring projects, significantly reducing the total life cycle cost of the monitoring system. 2. This invention improves both construction adaptability and monitoring capabilities, requiring only two core processes: drilling and pipe laying, and surface equipment wiring. This avoids complex underground deployment, resulting in lower construction difficulty and a higher installation success rate. Furthermore, since there are no electronic devices or communication lines underground, they are not subject to damage from subsequent construction work, minimizing construction interference and enhancing adaptability. This technology also overcomes the range limitations of traditional layered settlement monitoring. By replacing sensors and adjusting the storage tank capacity, it can adapt to different monitoring needs, meeting ultra-large settlement monitoring requirements from centimeter to meter levels. Its application scope covers various engineering scenarios such as soft soil foundation treatment and foundation pit deformation monitoring. 3. This invention achieves direct output of high-precision absolute settlement data through a dual benchmark system design of "external stable GNSS benchmark point + regional relative benchmark point". By integrating GNSS absolute elevation data and relative settlement difference from hydrostatic level, the absolute settlement of each soil layer relative to the stable geodetic benchmark can be directly calculated. Compared with the traditional monitoring scheme that can only obtain relative displacement, the data accuracy and practical value are significantly improved. It can be directly used for engineering safety assessment and geological deformation analysis. The overall technical solution takes into account both performance and economic advantages, and is more practical. Attached Figure Description

[0023] Figure 1 This is a structural flowchart of an embodiment of the method for monitoring stratified settlement using a GNSS combined with a hydrostatic level instrument according to the present invention.

[0024] Figure 2 This is a schematic diagram of the overall installation of an embodiment of the method for monitoring stratified settlement using a GNSS combined with a hydrostatic level instrument according to the present invention.

[0025] The attached figures are labeled as follows: 1. Settling steel pipe; 2. GNSS receiver; 3. Liquid storage tank; 4. Data acquisition device; 6. Solar power supply system; 7. Liquid supply pipeline; 8. Gas supply pipeline; 9. Data and power cables. Detailed Implementation

[0026] Please participate Figure 1 , Figure 2 As shown, this invention mainly provides a method for monitoring stratified settlement using a GNSS combined with a hydrostatic level. It employs a combination of techniques including "drilling and burying settlement steel pipes + surface GNSS reference points + surface relative reference points (GNSS + liquid storage tank) + surface hydrostatic level array" to achieve automated and high-precision monitoring of stratified settlement at different soil depths. Specifically, it includes the following steps: Step 1: Drill holes at the monitoring points for different target soil layers, and bury an independent settlement steel pipe 1 in each hole. The bottom of each settlement steel pipe 1 is fixed to the corresponding target soil layer, and the top is exposed above the ground. Specifically: In the entire technical system of GNSS combined with hydrostatic level for monitoring stratified settlement, drilling and laying of settlement steel pipe 1 is the basic and key starting link, and its construction quality is directly related to the accuracy and reliability of subsequent monitoring data. Before formal construction, it is necessary to clarify the target soil layer stratification information, depth, and geotechnical mechanical properties of the area to be monitored based on the engineering survey report. In conjunction with the monitoring plan, the locations of monitoring points should be delineated, and settlement steel pipes, drilling equipment, fixing accessories, and measurement and calibration tools that meet the depth requirements should be prepared. Seamless carbon steel pipes should be preferred for the settlement steel pipes to ensure the strength and structural stability of the pipes, enabling them to move vertically in sync with the target soil layer.

[0027] Then, according to the monitoring point layout results, drilling is carried out: First, the surface attachments at the points are cleared, and the drilling rig is adjusted to a vertical position to ensure that the vertical deviation rate of the borehole is no more than 1%, so as to avoid the borehole deviation affecting the verticality of the subsequent settlement steel pipe; during the drilling process, drilling is carried out step by step, and the drilling depth and the target soil layer depth are checked in real time. When the drill bit reaches the designed burial depth of the corresponding target soil layer, drilling is stopped, the drill bit is removed, and debris in the hole is cleaned to complete the drilling operation. For multi-depth layered monitoring requirements, independent boreholes need to be constructed for different depth target soil layers in the same monitoring point area, and a horizontal distance of no less than 2m should be maintained between each borehole to avoid soil disturbance between boreholes affecting the monitoring results.

[0028] After drilling is completed, the settlement steel pipe 1 of the corresponding length is slowly lowered into the borehole to ensure that the bottom of the steel pipe is accurately positioned at the design location of the target soil layer. After adjusting the verticality of the steel pipe, the gap between the borehole wall and the outer wall of the steel pipe is backfilled and compacted with clean fine sand. This ensures that the steel pipe is in close contact with the surrounding soil layer and avoids additional consolidation resistance that restricts the synchronous displacement of the steel pipe with the soil layer. After the settlement steel pipe 1 is lowered and fixed, the top of the steel pipe is kept 0.5m-1.0m above the ground to ensure sufficient installation space for subsequent equipment such as static level and GNSS receiver. At the same time, temporary protection is provided for the top of the steel pipe to prevent debris from falling into the pipe or damaging the pipe opening during construction. The horizontal spacing between each settlement steel pipe is about 2m to ensure that they are independent of each other and do not come into contact with each other, so as to ensure that they can independently reflect the settlement of the corresponding soil layer.

[0029] Step 2: Set up a GNSS absolute reference point in a stable area outside the monitoring area; Specifically, outside the monitoring area, in a geologically stable region unaffected by construction disturbances (prioritizing areas with exposed bedrock, minimal or complete settlement deformation, avoiding areas affected by construction disturbances, underground mining areas, soft soil distribution areas, and areas prone to deformation; simultaneously, the location must have a wide field of view, with no tall buildings, mountains, or trees obstructing satellite signals within a 15° elevation angle above the location, and avoid strong electromagnetic radiation sources such as high-voltage lines, high-power transmitters, and microwave stations to reduce the impact of multipath effects and electromagnetic interference on GNSS signal reception), a GNSS observation benchmark point should be established. This benchmark point should be equipped with a GNSS receiver and communication module to provide the elevation benchmark for the entire monitoring system, and its coordinates should be obtained through long-term observation or in conjunction with national / local control points.

[0030] Step 3: Within the monitoring area, select the settlement steel pipe located in the most stable soil layer as the relative reference point, and install the first GNSS receiver 2 and the liquid storage tank 3 on its top; Specifically, among all the settlement steel pipes 1 that have been installed in the monitoring area, the settlement steel pipe with the largest installation depth and the bottom anchored to the stable bearing layer within the monitoring range is selected as the relative benchmark point for this monitoring area. The settlement steel pipe at this location is minimally affected by the deformation of the upper soil layer, and its own settlement deformation is much smaller than that of the soil layer to be monitored, so it can be used as a relative reference benchmark for settlement measurement of each layer in the monitoring area.

[0031] After selecting the settlement steel pipe 1 corresponding to the relative benchmark point, the top of the exposed steel pipe is first leveled: the pipe opening is machined into a horizontal installation base surface by horizontal milling or grinding, ensuring that the flatness deviation of the base surface is no more than 0.5mm. Debris and loose rust are cleaned from the pipe opening and surrounding area. If the pipe opening is deformed, it needs to be rounded to ensure the stability and horizontal accuracy of subsequent equipment installation. The first GNSS receiver 2, a liquid storage tank 3, a data acquisition device 4, and a solar power supply system 5 (including solar panels and batteries) are installed on top of this steel pipe. The settlement of this steel pipe will be monitored in real time by the GNSS. The liquid storage tank on top provides a uniform liquid level for all hydrostatic instruments at this monitoring point. A pressure reference surface is established. During the process, a customized adapter flange can be used to fix the first GNSS receiver 2 on the horizontal base surface at the top of the steel pipe. The adapter flange is fixed to the steel pipe by welding or bolting to ensure that the connection strength meets the requirements for wind resistance and disturbance resistance. The liquid storage tank 3 is fixedly installed next to the GNSS receiver at the top of the same settling steel pipe. The tank body is kept vertical and the tank opening is well sealed. The installation height of the liquid storage tank is consistent with the installation height of the static level instruments at other subsequent monitoring points to avoid exceeding the sensor measurement range due to excessive liquid level difference. After installation, a sealing test is performed on the liquid storage tank. After confirming that there is no leakage, the interface for the liquid inlet pipe and the air inlet pipe is reserved to facilitate subsequent connection with the static level instruments at each monitoring point.

[0032] In this embodiment, the bottom of the settlement steel pipe 1 is equipped with an extension structure to increase the contact resistance with the soil layer. The core function of this extension structure is to increase the contact area and anchoring resistance between the bottom of the settlement steel pipe and the target soil layer, preventing relative slippage between the steel pipe and the soil layer, ensuring that the settlement steel pipe can synchronously follow the vertical displacement of the target soil layer, and ensuring the accuracy of the stratified settlement monitoring results. Commonly used extension structures can be either circular steel plate trays or cross-shaped anchor plates, adapting to different soil conditions: circular steel plate trays with larger diameters are preferred for soft soil layers, while cross-shaped anchor plates can be used to enhance grip in sandy soil layers.

[0033] Step 4: Install a hydrostatic level on the top of each of the settlement steel pipes, except for the relative reference point; Specifically, each settlement steel pipe, except for the relative reference point, undergoes pretreatment of the installation base surface in sequence. The treatment requirements are consistent with those of the relative reference point: the top of the steel pipe exposed above the ground is ground and milled flat to ensure that the flatness deviation of the installation base surface of the pipe opening is no more than 0.5mm; the loose rust and debris at the pipe opening are cleaned, and the deformation of the pipe opening is corrected to ensure that the equipment remains horizontal and stable after installation, and to avoid measurement errors caused by the tilt of the base surface.

[0034] One static level is installed for each settling steel pipe. A custom-made adapter bracket is used to fix the static level on the horizontal base surface at the top of the steel pipe. The bracket and the settling steel pipe can be connected by expansion bolts or welding. After confirming that the bracket is horizontal, the static level is locked and fixed to the bracket through M4 screw holes. During the installation process, a level is used to check in real time to ensure that the horizontal deviation of the main body of the static level is no more than 1′, so as to avoid affecting the accuracy of liquid level measurement due to equipment tilt.

[0035] Step 5: Connect the liquid chambers of all hydrostatic levels to the storage tanks through the liquid inlet pipe 6 to form a communicating vessel system, and balance the air pressure chambers of all hydrostatic levels with the atmospheric pressure through the air outlet pipe 7. Specifically, the liquid passage 6 should preferably be made of hydrolysis-resistant, low-expansion transparent PU hose or PE rigid pipe to ensure good chemical and dimensional stability, and to prevent temperature changes from causing pipe deformation that could affect liquid level measurement. The venting passage 7 can be made of corrosion-resistant PVC or PE hose, ensuring smooth and unobstructed ventilation. The pipe length should be cut according to the actual distance between each monitoring point and the storage tank to avoid tension that could cause leakage at the joints. Starting from the outlet of the storage tank, all the liquid chambers of the hydrostatic level should be connected in series, with the connection order arranged from closest to furthest distance between the monitoring point and the storage tank. Each joint should be sealed with a hose clamp. After connection, check the pipe routing to avoid twisting, wrinkling, or local sagging that could form U-shaped bends and block the liquid flow channel, affecting the liquid level balance of the communicating vessel. After all the hydrostatic level instruments are connected, seal the end of the pipeline, open the vent valve of the storage tank and slowly inject degassed distilled water until the initial liquid level of all hydrostatic level instruments is in the middle of the sensor range. Let it stand for 2-4 hours until the liquid level stabilizes, and then check all interfaces to confirm that there is no leakage.

[0036] Connect the air pressure chambers of all hydrostatic levels to the air pressure balance end of the liquid storage tank or directly to the atmosphere via ventilation pipes to ensure that the air pressure chambers of all hydrostatic levels are consistent with the external atmospheric pressure, eliminating the interference of atmospheric pressure differences at different locations on liquid level measurement. After the ventilation pipes are connected, install a drying and breathable filter at the end of the pipes to prevent water vapor and dust from entering the air pressure chambers and affecting the operation of the sensors. At the same time, check the ventilation to ensure there are no pipe blockages or leaks.

[0037] Step 6: Establish a data processing and transmission system, connect and collect data from the first GNSS receiver and all hydrostatic level instruments, and remotely transmit the data to the data processing center; the data processing and transmission system is integrated on the top of the settlement steel pipe relative to the reference point, including a data acquisition unit and a power supply module.

[0038] Specifically, using data and power lines 8, each hydrostatic level is connected in series or parallel and then uniformly connected to a data acquisition unit located at the top of the steel pipe at the relative reference point. The data acquisition unit and power supply module are integrated and installed on the equipment platform at the top of the settlement steel pipe at the relative reference point, adjacent to the first GNSS receiver and the liquid storage tank. The data acquisition unit is fixed to the side wall of the steel pipe using a wall-mounted mounting bracket, positioned above the ground to prevent water from immersing the equipment during the rainy season. The solar power module is a solar power system. The photovoltaic panels in the system are fixed to the upper part of the steel pipe by brackets. The tilt angle is adjusted to adapt to the latitude of the project site to ensure the efficiency of photovoltaic power generation. The battery is installed in a protective box and integrated with the data acquisition device to ensure the stability of power supply.

[0039] The data acquisition unit is responsible for powering the hydrostatic level and collecting the liquid level height data of each hydrostatic level. Simultaneously, the data acquisition unit also connects to a GNSS receiver at a relative reference point to collect its positioning data. The data acquisition unit has a built-in or external 4G / 5G / NB-IoT / LoRa wireless communication module for remotely transmitting the aggregated data to a cloud server or monitoring center.

[0040] In this embodiment, the hydrostatic level uses a high-precision capacitive or piezoresistive sensor; during the process, the choice can be flexibly made according to the monitoring accuracy requirements, measurement range requirements and project budget: high-precision capacitive sensors are preferred for monitoring projects with small settlement and high precision requirements, while piezoresistive sensors are preferred for monitoring projects with large settlement and wide measurement range requirements.

[0041] In this embodiment, a multi-satellite, multi-frequency GNSS receiver is used as the GNSS absolute reference point to improve positioning accuracy.

[0042] Step 7: Data Processing Steps Step (a): Based on the liquid level data from the hydrostatic level, calculate the relative settlement of the top of each settling steel pipe relative to the relative reference point; Step (b): Based on the data from the first GNSS receiver at the GNSS absolute reference point and the relative reference point, calculate the absolute elevation change of the relative reference point; Step (c): Add the relative settlement calculated in step (a) to the absolute elevation change obtained in step (b) to calculate the absolute settlement at the top of each settlement steel pipe. Step (d): Based on the difference in absolute settlement at the top of the steel pipe at different depths, obtain the stratified settlement of the corresponding target soil layer.

[0043] Specifically, relative settlement calculation: All hydrostatic levels move vertically synchronously with the corresponding settled steel pipes. Based on the principle of communicating vessels, the change in liquid level is directly equal to the relative settlement difference. The data acquisition unit collects the liquid level readings of each hydrostatic level in real time, compares them with the initial liquid level to obtain the liquid level change value, and directly converts it into the real-time relative settlement of the top of the target monitoring steel pipe relative to the top of the relative reference point steel pipe in the area. The data acquisition unit calculates the real-time settlement difference (i.e., relative settlement) of the top of the corresponding settled steel pipe relative to the top of the relative reference point steel pipe based on the changes in the liquid level readings of each hydrostatic level. For example, if the liquid level of a certain hydrostatic level rises, it indicates that the settlement of the steel pipe it is located in is greater than that of the steel pipe at the relative reference point.

[0044] Absolute settlement calculation: Using a stable GNSS absolute reference point outside the monitoring area as the starting reference, differential calculation is performed on the observation data of the first GNSS receiver at the top of the relative reference point to obtain the absolute elevation change ΔH reference of the top of the steel pipe at the relative reference point from the initial time to the current time. Then, the absolute settlement of the top of the steel pipe at any target monitoring point can be directly calculated using the following formula: ΔH target = ΔH baseline + Δh relative Where Δh represents the relative settlement of the target steel pipe relative to the reference point. This method only requires the installation of a GNSS receiver at the reference point to convert the relative settlement of all monitoring points into absolute settlement, significantly reducing system costs.

[0045] (3) Stratified Settlement: Since the bottom of each settlement steel pipe is fixed to the target soil layer at different depths, the settlement steel pipe will move vertically synchronously with the corresponding soil layer. Therefore, the absolute settlement difference between the tops of the settlement steel pipes at adjacent depths is the stratified compression settlement of the corresponding soil layer between the two depths. The calculation formula is: Ssoil layern = ΔHsteel pipen - ΔHsteel pipen-1 Where ΔHn represents the absolute settlement at the top of the nth steel pipe with greater depth, and ΔHn-1 represents the absolute settlement at the top of the (n-1)th steel pipe with less depth. By calculating layer by layer, the stratified settlement of all target soil layers at all depths can be obtained, directly reflecting the deformation of each soil layer. (For example, the settlement of soil layer 3 = absolute settlement at the top of steel pipe 3 - absolute settlement at the top of steel pipe 2).

[0046] In this embodiment, the data processing center can also perform real-time analysis and early warning of the collected data, and issue an alarm when the settlement exceeds a preset threshold. Specifically, the data processing center deploys a monitoring cloud platform or local server system to receive GNSS elevation data and hydrostatic level data uploaded in real time from each monitoring point, automatically executes the aforementioned calculation process of relative settlement, absolute settlement, and stratified settlement, stores the calculation results in a time-series database, and generates a visualized settlement process curve and a stratified settlement statistics table, which supports online viewing, historical data export, and report generation. The system supports multi-level threshold early warning configuration, allowing users to set early warning thresholds and alarm thresholds separately according to engineering safety requirements. A rate warning is triggered when the daily settlement rate exceeds a preset value (usually a daily settlement ≥ 5 mm). The cumulative stratified settlement exceeds the maximum allowable design value, triggering a cumulative settlement warning. An abnormal jump in settlement data (exceeding the normal fluctuation range of the sensor) triggers a data anomaly warning.

[0047] Multi-level early warning can match the safety management requirements of different construction stages of a project, taking into account both monitoring sensitivity and early warning accuracy; When settlement data triggers preset early warning rules, the system automatically pushes alarm information through various means, including platform pop-up reminders, SMS push, mobile APP push, email notifications, etc., which can be pushed to multiple management personnel at the same time to ensure that the early warning information reaches them in a timely manner. The system also records information such as alarm trigger time, trigger index, and current settlement value, and retains a complete early warning log for subsequent source tracing and analysis.

[0048] In this embodiment, the method further includes an equipment recycling step, namely, after the monitoring is completed, the surface equipment on the top of each settlement steel pipe is disassembled to realize the recycling and reuse of the hydrostatic level, GNSS receiver and data acquisition device; Specifically, after the monitoring task is completed, the equipment will be dismantled and recycled in order from the outside in: 1. First disconnect each hydrostatic level from the liquid and air supply lines, drain the residual liquid in the lines, remove the hydrostatic level from the bracket at the top of the corresponding settling steel pipe, clean the sealing interface, and then seal and store it. 2. Disassemble the first GNSS receiver, liquid storage tank, data acquisition unit and solar power module at the top relative to the reference point in sequence, remove all exposed cables, clean the dirt and rust on the equipment surface, check the integrity of the equipment functions and then pack them in categories. 3. After all surface recyclable equipment is dismantled, the exposed portion of the settlement steel pipe is cut off, the drill holes are backfilled and compacted, and the original appearance of the surface in the monitoring area is restored, which will not affect the subsequent use of the site.

[0049] This invention also provides a GNSS combined with hydrostatic leveling instrument for stratified settlement monitoring, comprising: An external GNSS absolute reference point subsystem is deployed in a geologically stable area outside the monitoring area to provide a stable absolute coordinate reference for the entire monitoring system. Multiple settlement steel pipes are buried in the target soil layer at different depths at the monitoring points. The bottom of each settlement steel pipe is fixed to the corresponding target soil layer, and the top extends out of the ground. A relative reference point subsystem is deployed on the top of the selected settlement steel pipe as the relative reference. The relative reference point subsystem includes a first GNSS receiver, a liquid storage tank, a data acquisition unit, and a power supply unit. Multiple hydrostatic levels are installed one-to-one on the top of each of the settlement steel pipes, except for the relative reference point. A connecting hydraulic pipeline system is used to connect the liquid chambers of all the hydrostatic level instruments in series with the liquid storage tank to form a communicating vessel liquid level measurement system; A pressure balancing pipeline system is used to connect the pressure chambers of all the hydrostatic level instruments to each other and maintain a balance with atmospheric pressure. The remote data transmission module is electrically connected to the data acquisition unit and is used to remotely transmit the acquired GNSS data and hydrostatic level data to the data processing center.

[0050] The following describes the specific implementation of the present invention in detail using a soft soil subgrade treatment project for a highway as an example. This project requires monitoring the stratified settlement of soil layers at depths of 2m (soil layer 1), 5m (soil layer 2), 8m (soil layer 3), 12m (soil layer 4), and 15m (bearing layer).

[0051] Step 1: Drilling and laying of settlement steel pipes At the selected monitoring points, a drilling rig was used to drill holes with a diameter of 150 mm and a total depth of 31 m, penetrating all soil layers to be monitored and extending approximately 1 m below the bearing layer (soil layer 5).

[0052] Prepare seven galvanized settlement steel pipes with a diameter of 108mm, a wall thickness of 4mm, and individual lengths of 2m, 7m, 12m, 17m, 22m, 27m, and 32m respectively; weld a 140mm diameter annular base steel plate to the bottom of each steel pipe to increase the contact area with the soil and improve stability.

[0053] The longest (32m) settling steel pipe was lowered to the bottom of the borehole, with its base positioned at the bottom of the bearing layer at a depth of 31m. Slight pressure was applied to the top of the pipe to embed it into the bearing layer, and it was secured at the borehole opening with a temporary support, with the top of the pipe 1m above the ground.

[0054] Lower the sinking steel pipes in sequence with lengths of 27m, 22m, 17m, 12m, 7m, and 2m, ensuring that their bases are accurately positioned at the designed depths of 26m, 21m, 16m, 11m, 6m, and 1m, respectively. Maintain a gap of at least 2m between each steel pipe, and ensure that the drilling and sinking steel pipes are perpendicular during drilling and installation.

[0055] Backfill the borehole with medium-coarse sand until it reaches the ground level; compact the backfill during the process to ensure good coupling between the steel pipe and the surrounding soil. The top of each steel pipe should protrude 1m above the ground.

[0056] Step 2: Establish an external stable benchmark. On a stable bedrock about 500m away from the monitoring point, a concrete observation pier was poured, and a GNSS receiver and a 4G communication module were installed. After 72 hours of continuous observation, the high-precision geodetic height of the benchmark point was calculated and used as the system benchmark value.

[0057] Step 3: Select relative benchmarks for the monitoring area The settlement steel pipe with the largest burial depth (31m) was used as the relative benchmark point of the monitoring area.

[0058] Install a bracket on top of the steel pipe. Fix the following components to the bracket in sequence: a GNSS receiver (model same as the reference point), a 10-liter liquid storage tank, an 8-channel data acquisition unit, a 100W solar panel and its matching solar controller and battery (12V / 40Ah).

[0059] Connect the GNSS receiver to the RS485 interface of the data acquisition unit; connect the solar power system to the power input terminal of the data acquisition unit.

[0060] Step 4: Install a hydrostatic level on top of the remaining settlement steel pipes. At the top of the other six settling steel pipes (depths of 26m, 21m, 16m, 11m, 6m, and 1m), a capacitive grating hydrostatic level with a range of 1000mm and an accuracy of 0.1mm is installed.

[0061] Using an 8mm inner diameter PU tubing, lead the tubing from the bottom outlet of the storage tank at the top of the steel pipe relative to the reference point, and connect it in series to the liquid interfaces of each hydrostatic level, finally sealing the end interface. Ensure the tubing is free of bends and air bubbles; inject dedicated antifreeze hydrostatic leveling fluid into the system until the liquid level stabilizes in the middle of the measuring range of all levels.

[0062] Use a 6mm inner diameter PU vent tube to connect all the air pressure interfaces of the hydrostatic level in parallel, and finally connect them back to the air pressure balance port at the top of the storage tank.

[0063] Step 5: Lay out data and power lines A 4-core shielded cable is used as the data and power line, leading from the data acquisition unit and connected in parallel or series to the sensor interfaces of each hydrostatic level. Two cores of the cable are used for power supply (12V), and two cores are used for RS485 communication (A / B lines).

[0064] Configure the communication address of each hydrostatic level in the data acquisition unit and set the acquisition frequency to once per hour.

[0065] Step Six: Data Calculation and Settlement Analysis Data Acquisition and Transmission: The data acquisition unit starts up once an hour to sequentially read the liquid level values ​​(h1, h2, h3, h4, h5, h6) of 6 hydrostatic levels and the GNSS elevation values ​​(H reference_GNSS) relative to the reference point; all data are packaged and sent to the central server via 4G network.

[0066] Relative settlement calculation: After receiving the data, the server uses the initial liquid level values ​​(h01, h02, h03, h04, h05, h06) as a reference. At any given time, the relative settlement of the top of the steel pipe at a certain depth (e.g., 16m) (relative to the 32m reference steel pipe) is: Δhrelative = h0i - hi. If the value is positive, it indicates that the top of the steel pipe at that depth has settled more.

[0067] Absolute settlement calculation: The server simultaneously receives GNSS data (H-stable) from an external stable reference point. The absolute elevation change of the steel pipe relative to the reference point in the monitoring area is calculated as follows: ΔH_reference_absolute = H_reference_GNSS (current) - H_reference_GNSS (initial).

[0068] Therefore, the absolute settlement at the top of the steel pipe at any depth is: ΔH_target_absolute = ΔH_baseline_absolute + Δh_relative.

[0069] Compared with existing technologies, in this embodiment all core equipment is on the ground surface. After monitoring is completed, the GNSS, hydrostatic level, data logger, etc. can all be recovered, cleaned, and installed for the next monitoring project. The entire system has no theoretical monitoring limit and provides valuable absolute settlement data, which greatly improves the intelligence and precision of soft soil foundation monitoring.

[0070] It should be noted that this invention combines GNSS technology with a hydrostatic level to achieve high-precision measurement of the settlement of different soil layers. The hydrostatic level can accurately measure the relative settlement of the top of each settlement steel pipe relative to a relative reference point, with a measurement accuracy down to the millimeter level. The GNSS absolute reference point provides a stable absolute coordinate reference. By calculating the absolute elevation change of the relative reference point, the relative settlement is superimposed with the absolute elevation change to obtain the absolute settlement of the top of each settlement steel pipe, thereby accurately calculating the layered settlement of the corresponding target soil layer. This measurement method avoids the limitations of traditional single monitoring technologies and can more realistically reflect the settlement of underground soil layers. Meanwhile, the system employs a multi-satellite, multi-frequency GNSS receiver, capable of receiving signals from multiple satellite systems, thus improving positioning accuracy. The hydrostatic level uses high-precision capacitive or piezoresistive sensors to measure liquid level changes in real time, reducing measurement errors. Furthermore, the data processing center performs real-time analysis and processing of the collected data, further improving data accuracy through preprocessing steps such as data cleaning, format conversion, and outlier handling. When the settlement exceeds a preset threshold, the system promptly issues an alarm, providing reliable data support for engineering decisions. In addition, the system has real-time data acquisition and transmission capabilities. The data acquisition unit collects monitoring data from the GNSS receiver and hydrostatic level in real time, and transmits the data to the data processing center through the remote data transmission module. Data transmission utilizes wireless communication technologies such as GPRS, CDMA, and 4G to ensure timely and accurate data transmission. The data processing center performs real-time analysis and display of the monitoring data, allowing relevant personnel to view the dynamic changes in ground subsidence at any time via remote terminals and promptly grasp the subsidence trend. Furthermore, through real-time analysis of monitoring data, the system can promptly detect abnormal changes in ground subsidence. When the subsidence exceeds a preset threshold, the system automatically issues an alarm, reminding relevant personnel to take appropriate measures. This dynamic early warning mechanism can effectively prevent geological disasters caused by ground subsidence, ensuring the safety of engineering construction and people's lives and property. For example, in subway construction, the system can monitor the ground subsidence around the subway line in real time. When the subsidence exceeds a safety threshold, it will issue an alarm in a timely manner, allowing construction personnel to immediately adjust construction parameters and ensure the safe construction of the subway project. Compared to traditional underground monitoring equipment, all monitoring devices in this system are installed on top of settlement steel pipes above ground, avoiding the difficulties of maintaining underground equipment. Maintenance personnel can easily inspect, repair, and replace the equipment without extensive underground work, reducing maintenance costs and workload. For example, when the hydrostatic level malfunctions, maintenance personnel can replace the equipment on the surface without complex underground excavation. Meanwhile, the monitoring equipment in the system, such as GNSS receivers, hydrostatic levels, and data acquisition devices, can all be recycled and reused. After the monitoring project is completed, relevant personnel can disassemble the equipment, clean and maintain it, and use it for other monitoring projects. This recyclability not only reduces resource waste and lowers the long-term cost of monitoring, but also conforms to the concept of environmental protection and sustainable development.

[0071] The foregoing descriptions and embodiments are provided to enable those skilled in the art to understand and apply the present invention. It will be apparent to those skilled in the art that various modifications can be easily made to these contents, and the general principles described herein can be applied to other embodiments without creative effort. Therefore, the present invention is not limited to the foregoing descriptions and embodiments. Improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from its scope should be within the protection scope of the present invention.

Claims

1. A method for monitoring stratified settlement using GNSS combined with a hydrostatic level, characterized in that, Includes the following steps: ‌ Step 1: Drill holes at the monitoring points for different target soil layers, and bury independent settlement steel pipes in each hole. The bottom of each settlement steel pipe is fixed to the corresponding target soil layer, and the top is exposed above the ground. Step 2: Set up a GNSS absolute reference point in a stable area outside the monitoring area; Step 3: Within the monitoring area, select the settlement steel pipe located in the most stable soil layer as the relative reference point, and install the first GNSS receiver and the liquid storage tank on its top; Step 4: Install a hydrostatic level on the top of each of the other settlement steel pipes, except for the aforementioned relative reference point; Step 5: Connect the liquid chambers of all the hydrostatic levels to the storage tank through the liquid-conducting pipes to form a communicating vessel system, and balance the air pressure chambers of all the hydrostatic levels with the atmospheric pressure through the air-conducting pipes. Step 6: Establish a data processing and transmission system, connect and collect data from the first GNSS receiver and all hydrostatic level instruments, and remotely transmit the data to the data processing center; Step 7: Data Processing Steps Step (a): Based on the liquid level data of the hydrostatic level, calculate the relative settlement of the top of each settling steel pipe relative to the relative reference point; Step (b): Based on the data from the first GNSS receiver at the absolute GNSS reference point and the relative reference point, calculate the absolute elevation change of the relative reference point; Step (c): Add the relative settlement calculated in step (a) to the absolute elevation change obtained in step (b) to calculate the absolute settlement at the top of each settlement steel pipe. Step (d): Based on the difference in absolute settlement at the top of the steel pipe at different depths, obtain the stratified settlement of the corresponding target soil layer.

2. The method according to claim 1, characterized in that: The bottom of the settling steel pipe is equipped with an extension structure to increase the resistance to contact with the soil layer.

3. The method according to claim 1, characterized in that: In step 6, the data processing and transmission system is integrated on the top of the settlement steel pipe at the relative reference point, including a data acquisition unit and a power supply module.

4. The method according to claim 3, characterized in that: The power supply module is a solar power supply system.

5. The method according to claim 1, characterized in that: The method further includes an equipment recycling step, namely, after the monitoring is completed, the surface equipment on the top of each settled steel pipe is disassembled to realize the recycling and reuse of the hydrostatic level, GNSS receiver and data acquisition device.

6. The method according to claim 1, characterized in that: Both the liquid and gas pipelines are made of corrosion-resistant materials.

7. The method according to claim 1, characterized in that: The data processing center performs real-time analysis and early warning of the collected data, and issues an alarm when the settlement exceeds a preset threshold.

8. The method according to claim 1, characterized in that: The hydrostatic level uses a high-precision capacitive or piezoresistive sensor.

9. The method according to claim 1, characterized in that: The GNSS absolute reference point uses a multi-satellite, multi-frequency GNSS receiver to improve positioning accuracy.

10. A GNSS-based hydrostatic leveling system for stratified settlement monitoring based on the method of any one of claims 1 to 9, characterized in that, include: ‌ An external GNSS absolute reference point subsystem is used to provide a stable absolute coordinate reference; Multiple settlement steel pipes buried in different soil layers; A relative reference point subsystem includes a first GNSS receiver, a liquid storage tank, a data acquisition unit, and a power supply unit, all mounted on top of a selected settling steel pipe. Multiple hydrostatic levels are installed on top of the other settled steel pipes; A connected hydraulic pipeline system connects the liquid chambers of all hydrostatic levels to the storage tank; A connected piping system is used to keep the air chambers of all hydrostatic instruments pressure balanced; And a remote data transmission module.

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