A method for transferring an elevation reference of an over-long distance river-crossing tunnel

Abstract

This invention discloses a method for measuring the elevation benchmark transfer of ultra-long-distance cross-river tunnels, relating to the field of ultra-long-distance cross-river leveling technology. The method involves setting up measurement points on both banks of the water area to be measured. A first measurement method is used to determine the elevation difference between adjacent measurement points on the same bank, and the first elevation data for each measurement point is obtained by combining this with a known elevation starting point. Simultaneously, a first measurement device is used to measure the first measured values ​​between adjacent measurement points on the same bank and the second measured values ​​between corresponding measurement points across the river to verify the first elevation data. A second measurement method is used to obtain the second elevation data for each measurement point. Based on the accepted first and second elevation data, a set of elevation change parameters along the survey line is calculated, and a consistency check is performed. If the check passes, the second measured value is accepted. This invention, through a dual verification mechanism, achieves the first-order leveling accuracy requirement for ultra-long-distance cross-river leveling and is suitable for projects crossing wide waterways.

Description

Technical Field

[0001] This invention generally relates to the field of ultra-long-distance cross-river leveling technology, and specifically to a method for measuring the elevation benchmark of ultra-long-distance cross-river tunnels. Background Technology

[0002] Cross-river leveling is a core component of the construction of large-scale projects such as high-speed railways and bridges. Its purpose is to accurately determine the elevation difference between control points on both sides of the river and ensure that the elevation benchmarks on both sides are consistent.

[0003] Currently, ultra-long-distance cross-river leveling mainly employs GNSS-based cross-river leveling methods. The basic principle is as follows: GNSS control points are established on both banks of the river. Geodetic heights at each point are obtained through static GNSS observations. Simultaneously, normal heights of some control points are obtained through precise leveling within the land area, allowing for the calculation of elevation anomalies at each point. Then, mathematical models (such as straight-line fitting or surface fitting) are constructed using the known elevation anomaly data to estimate the elevation anomalies at the cross-river points. Finally, the GNSS geodetic heights of the cross-river points are substituted into the model to convert them into normal heights, thus obtaining the cross-river leveling difference.

[0004] However, the core of existing methods lies in fitting the spatial distribution of geoid undulations using mathematical models. Geoid undulations are influenced by various factors such as underground material density and topography, inevitably leading to discrepancies between the model and the actual distribution in actual measurements. Moreover, when the river crossing distance exceeds 10 kilometers, this model deviation is drastically amplified, making it difficult to meet the accuracy requirements of first-order leveling. Therefore, a new method for measuring the elevation benchmark transfer of ultra-long-distance river-crossing tunnels is urgently needed to solve these problems. Summary of the Invention

[0005] In view of the above-mentioned defects or deficiencies in the existing technology, it is desirable to provide a method for measuring the elevation benchmark transfer of ultra-long-distance river-crossing tunnels.

[0006] This invention provides a method for measuring the elevation benchmark transfer of ultra-long-distance river-crossing tunnels, including: Multiple measurement points are set up on both banks of the water area to be measured. The elevation difference between adjacent measurement points on the same bank is determined using a first measurement method to obtain a first known elevation difference dataset. Based on the first known elevation difference dataset, the first elevation data of each measurement point is obtained. The multiple measurement points include known elevation starting points. Using a second measurement method, the first elevation difference between adjacent measurement points on the same bank and the second elevation difference between corresponding measurement points across the river are measured simultaneously under the same environmental conditions. The first elevation difference between adjacent measurement points constitutes the first elevation difference measurement value dataset. Based on the first known elevation difference dataset and the first elevation difference measurement dataset, the first elevation difference measurement value between the same adjacent measurement points is compared with the elevation difference to obtain multiple sets of measurement deviations; When all the measurement deviations are less than or equal to the first preset deviation, the second elevation data of each measurement point is obtained by the third measurement method. Based on the first elevation data of the measurement points and the second elevation data of each measurement point, the first elevation change parameter set and the second elevation change parameter set corresponding to the two banks are calculated. A consistency check is performed based on the first set of elevation change parameters and the second set of elevation change parameters. When the consistency check result is passed, the second elevation difference measurement value is used as the elevation difference between the corresponding measurement points across the river.

[0007] According to the technical solution provided by the present invention, the multiple measurement points on the same bank include multiple sets of measurement point pairs; each set of measurement point pairs is arranged along a preset cross-river construction path; and two measurement points in each set of measurement point pairs are arranged along the flow direction of the river. One of the measurement points in all the measurement point pairs on both sides of the strait is located on the same straight line, and the other measurement point in all the measurement point pairs on both sides of the strait is located on the same straight line, and the two straight lines are parallel to each other.

[0008] According to the technical solution provided by the present invention, two adjacent sets of measurement point pairs form a closed loop, and two adjacent closed loops share the same set of measurement point pairs; each measurement segment of the closed loop includes a first measurement segment, a second measurement segment, a third measurement segment, and a fourth measurement segment connected sequentially with each measurement point as an endpoint; The method of determining the elevation difference between adjacent measurement points on the same bank using a first measurement method to obtain a first known elevation difference dataset includes: The first measurement method is used to perform forward and backward measurements on each section of each closed loop to obtain the forward and backward elevation differences for each section. The average of the forward and backward elevation differences is taken as the initial elevation difference between the two measurement points of the section. For a closed loop, the loop closure error is calculated based on the initial elevation differences corresponding to the first, second, third, and fourth measurement segments in the closed loop. When the loop closure error is less than or equal to the loop closure error limit, the initial elevation difference is used as the elevation difference between adjacent measurement points to obtain the first known elevation difference dataset.

[0009] According to the technical solution provided by the present invention, the method of simultaneously measuring the first elevation difference between adjacent measurement points on the same bank and the second elevation difference between corresponding measurement points across the river under the same environmental conditions using a second measurement method includes: Under the same environmental conditions, the second measurement method is used to simultaneously measure the first elevation difference between adjacent measurement points on the same bank and the second elevation difference between corresponding measurement points across the river; the first elevation difference is the elevation difference between adjacent measurement points on the same bank, and the second elevation difference is the elevation difference between corresponding measurement points across the river.

[0010] According to the technical solution provided by the present invention, the method of simultaneously measuring the first elevation difference between adjacent measurement points on the same bank and the second elevation difference between corresponding measurement points across the river using the second measurement method specifically includes: For each section of the closed loop, forward and backward observations are performed to obtain the forward and backward elevation difference measurements for each section. The average of the forward and backward elevation difference measurements is taken as the first and second elevation difference measurements between the two measurement points in that section.

[0011] According to the technical solution provided by the present invention, the step of calculating the first set of elevation change parameters and the second set of elevation change parameters corresponding to both banks based on the first elevation data of the measurement points and the second elevation data of each measurement point includes: For each of the measurement points, the elevation anomaly value of the measurement point is calculated based on the second elevation data and the first elevation data of that measurement point. The elevation anomalies of two adjacent measurement points on the same bank along the survey line direction and the horizontal distance between the two measurement points are selected. Multiple elevation change parameters of the left bank and the right bank along the survey line direction are calculated to form the first set of elevation change parameters corresponding to the left bank and the second set of elevation change parameters corresponding to the right bank. The survey line direction is set based on a preset cross-river construction path.

[0012] According to the technical solution provided by the present invention, the step of performing a consistency check based on the first set of elevation change parameters and the second set of elevation change parameters, and taking the second elevation difference measurement value as the elevation difference between corresponding measurement points across the river when the consistency check result is passed, includes: Based on the set of parameters for the first elevation change, the deviations of multiple sets of parameters corresponding to the left bank are calculated. Based on the set of second elevation change parameters, the deviations of multiple sets of same-bank parameters corresponding to the right bank are calculated; Based on the first set of elevation change parameters and the second set of elevation change parameters, the elevation change parameters of each measurement segment on the left bank are compared with the elevation change parameters of the corresponding numbered measurement segments on the right bank one by one, and the difference between the corresponding measurement segments on both banks is calculated to obtain multiple sets of cross-bank parameter deviations. Each of the same-bank parameter deviations is compared with the second preset deviation, and each of the cross-bank parameter deviations is compared with the third preset deviation; when all the same-bank parameter deviations are less than or equal to the second preset deviation, and all the cross-bank parameter deviations are less than or equal to the third preset deviation, the consistency check result is passed, and the second elevation difference measurement value is taken as the elevation difference between the corresponding measurement points across the river.

[0013] According to the technical solution provided by the present invention, the first measurement method is precise leveling, and the first elevation data is the normal height of each measurement point; the second measurement method is measurement using radar equipment; the third measurement method is GNSS static observation, and the second elevation data is the geodetic height of each measurement point.

[0014] In summary, this technical solution specifically discloses a method for measuring the elevation benchmark transfer of ultra-long-distance river-crossing tunnels, including: setting up multiple measurement points on both banks of the water area to be measured; using a first measurement method to determine the elevation difference between adjacent measurement points on the same bank to obtain a first known elevation difference dataset; and based on the first known elevation difference dataset, obtaining the first elevation data of each measurement point; the multiple measurement points include known elevation starting points; using a second measurement method under the same environmental conditions to simultaneously measure the first elevation difference between adjacent measurement points on the same bank and the second elevation difference between corresponding measurement points across the river; the first elevation difference between adjacent measurement points constitutes a first elevation difference measurement value dataset. Based on the first known elevation difference dataset and the first elevation difference measurement dataset, the first elevation difference measurement values ​​and elevation differences between adjacent measurement points are compared to obtain multiple sets of measurement deviations. When all measurement deviations are less than or equal to the first preset deviation, the second elevation data of each measurement point is obtained using the third measurement method. Based on the first elevation data and the second elevation data of each measurement point, the first elevation change parameter set and the second elevation change parameter set corresponding to both banks are calculated. A consistency check is performed based on the first elevation change parameter set and the second elevation change parameter set. When the consistency check result is passed, the second elevation difference measurement value is used as the elevation difference between the corresponding measurement points across the river.

[0015] Beneficial effects: This invention first performs deviation verification on the same-bank observation data of the second measurement method, filtering out unqualified observation data; then, it uses GNSS observation data to calculate the set of elevation change parameters on both banks, completing a dual consistency check for both same-bank and cross-bank measurements. After passing both levels of verification, the cross-river elevation difference measurement value is accepted. This invention abandons the dependence of traditional GNSS cross-river leveling on elevation anomaly fitting models, avoiding the accuracy loss caused by model fitting distortion at ultra-long distances. Combined with the closed-loop measurement point layout to constrain the quality of land area measurements, it effectively improves the accuracy and reliability of ultra-long-distance cross-river leveling results, adapting to the unified operation requirements of cross-river elevation benchmarks in large-scale engineering projects. Attached Figure Description

[0016] Other features, objects, and advantages of the invention will become more apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings: Figure 1 This is a schematic diagram of the working conditions for a method of measuring the elevation benchmark transfer of ultra-long-distance river-crossing tunnels.

[0017] Figure 2 This is a schematic diagram illustrating the layout principle of a method for measuring the elevation benchmark transfer in ultra-long-distance river-crossing tunnels.

[0018] Figure 3 This is a flowchart illustrating a method for measuring the elevation benchmark transfer in ultra-long-distance river-crossing tunnels.

[0019] Figure 4 This is a schematic diagram of the unfolding process of step S100 in a method for measuring the elevation benchmark transfer of ultra-long-distance river-crossing tunnels.

[0020] Figure 5 This is a schematic diagram of the unfolding process of step S400 in a method for measuring the elevation benchmark transfer of ultra-long-distance river-crossing tunnels.

[0021] Figure 6 This is a schematic diagram of the unfolding process of step S500 in a method for measuring the elevation benchmark transfer of ultra-long-distance river-crossing tunnels. Detailed Implementation

[0022] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and not intended to limit it. Furthermore, it should be noted that, for ease of description, only the parts relevant to the invention are shown in the accompanying drawings.

[0023] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other. The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0024] Example 1 To make the technical solutions of the embodiments of the present invention clearer and easier to understand, the application background of the embodiments of the present invention will be introduced below.

[0025] Cross-river leveling is a core surveying and mapping component in the construction of large-scale projects such as high-speed railways, large cross-river and cross-sea bridges, and water conservancy projects. Its purpose is to accurately determine the elevation difference between control points on both sides of the river, achieve a unified elevation benchmark on both sides, and provide a reliable elevation starting point for engineering surveying, construction, and deformation monitoring.

[0026] Currently, ultra-long-distance cross-river leveling mainly employs the GNSS cross-river leveling method. Its basic principle is as follows: GNSS control points are established on both banks of the river, and the geodetic height of each control point is obtained through static GNSS observations; simultaneously, the orthonormal height of some control points is obtained using precise leveling within the land area, and the elevation anomaly of each control point is obtained by calculating the geodetic height and orthonormal height; then, mathematical models such as linear fitting and surface fitting are constructed based on the known elevation anomalies of the control points to estimate the elevation anomaly at the cross-river point to be measured; finally, the geodetic height obtained from GNSS observations at the cross-river point is substituted into the fitting model to convert it into the orthonormal height, and the cross-river leveling difference is calculated.

[0027] Existing GNSS leveling across rivers relies heavily on geoid fitting models. However, geoids are influenced by multiple factors, including the distribution of underground material density, local topography, and variations in the gravity field. Inevitably, there are model biases between the fitted model and the actual spatial distribution of geoids. This is especially true in ultra-long-distance scenarios exceeding 10km across the river, where the waterways between the two banks and the lack of intermediate land constraint points amplify model bias dramatically, significantly increasing the risk of fitting distortion and often failing to meet the accuracy requirements of first-order and higher leveling measurements.

[0028] In addition, existing technologies also include cross-river measurement methods that utilize radar for long-distance, non-contact elevation difference observation. Although radar can achieve long-distance, non-contact observation across rivers, disturbances such as water vapor, atmospheric refraction, and water surface reflection in the river area can introduce equipment drift and observation noise. Existing solutions lack effective verification and discrimination methods, making it difficult to distinguish between equipment environmental errors and actual elevation gradient changes in the observation results. Consequently, it is impossible to reliably determine whether the radar cross-river observation results are valid, and direct use of them can easily introduce gross errors.

[0029] Therefore, there is an urgent need for a cross-river leveling measurement method suitable for ultra-long-distance scenarios, which can perform multi-level validity checks on the results of long-distance cross-river observations, reduce measurement errors caused by model fitting distortion and environmental disturbances, and ensure the measurement accuracy and reliability of ultra-long-distance cross-river leveling results.

[0030] See Figure 1 This embodiment uses a 10.2km ultra-long-distance cross-river leveling project as the application scenario. In this scenario, traditional GNSS fitting methods can no longer meet the accuracy requirements of first-order leveling. Therefore, the method provided by this invention is adopted to ensure measurement accuracy, stability, and feasibility. Specifically, as... Figure 1As shown, measurement points are set up on the left and right banks of the river. In this embodiment of the invention, the measurement points can be divided into main measurement points (marked with red and green dots) and auxiliary measurement points (marked with yellow dots), with the auxiliary measurement points serving as densification points. Multiple measurement points on the same bank include multiple pairs of measurement points, each pair arranged along a pre-set cross-river construction path (i.e., the direction of the high-speed railway line to be built); the two main measurement points or auxiliary measurement points in each pair are arranged along the river's flow direction. Specifically, three pairs of measurement points are set up on the left bank, denoted as YJ01-YJ02, YJ03-YJ04, and YJ05-YJ06; correspondingly, three pairs of measurement points are set up on the right bank, denoted as YJ07-YJ08, YJ09-YJ10, and YJ11-YJ12. It should be noted that the two main measurement points in each pair are arranged along the river's flow direction; for example, YJ01 is upstream and YJ02 is downstream.

[0031] For example, a pair of measurement points consisting of auxiliary measurement points is set up between YJ01-YJ02 and YJ03-YJ04 on the left bank, including two auxiliary measurement points BM11 and BM12. BM11 is located on the same cross section as YJ01 and YJ03, and BM12 is located on the same cross section as YJ02 and YJ04. In this embodiment of the invention, the measurement point pair set between YJ03-YJ04 and YJ05-YJ06 includes auxiliary measurement points BM13 and BM14; the measurement point pair set between YJ07-YJ08 and YJ09-YJ10 includes auxiliary measurement points BM15 and BM16; and the measurement point pair set between YJ09-YJ10 and YJ11-YJ12 includes auxiliary measurement points BM17 and BM18. Further details are omitted here; please refer to [link to relevant documentation]. Figure 1 The diagram shows the layout. It should be noted that there are no measurement point pairs between YJ05-YJ06 and YJ07-YJ08. These two sets of measurement point pairs are cross-river measurement point pairs, located on the riverside of the left and right banks respectively. The measurement section between them spans the entire river surface, used to achieve cross-river transfer of elevation benchmarks between the two banks. In this embodiment of the invention, YJ05-YJ06 on the left bank serves as the end point of the cross-river section, and YJ07-YJ08 on the right bank serves as the starting point of the cross-river section. YJ05 corresponds to YJ07, and YJ06 corresponds to YJ08.

[0032] It should be noted that the above-mentioned point numbering and layout quantity are only illustrative examples. In actual engineering, the number and spacing of measurement point pairs and leveling point pairs can be adaptively adjusted according to the river width, terrain conditions and accuracy requirements, all of which fall within the protection scope of this invention.

[0033] Further, see Figure 1In a surveying network, one of the measurement points in each pair of measurement points on both banks lies on the same straight line, and the other measurement point in each pair lies on the same straight line. These two lines are parallel to each other, and this straight line can be used as the surveying line direction. For example, YJ01, BM11, YJ03, BM13, YJ05 on the left bank and YJ07, BM15, YJ09, BM17, YJ11 on the right bank; and YJ02, BM12, YJ04, BM14, YJ06 on the left bank and YJ08, BM16, YJ10, BM18, YJ12 on the right bank. This ensures the symmetry of the network and the consistency of observations. The surveying line direction here can be understood as the surveying baseline determined by connecting the corresponding measurement points on both banks, along the pre-set cross-river construction path. For details, please refer to [link to relevant documentation]. Figure 1 The yellow river-crossing marker line is shown in the image. In this embodiment, the measurement section is the basic operational unit for both the first and second measurement methods. In practical applications, the main measurement points (numbered YJ series) serve as the primary control points for river-crossing leveling measurements. The distance between adjacent main measurement points is approximately 1 km. Auxiliary measurement points (numbered BM series) are laid out on the line connecting two adjacent pairs of measurement points formed by the main measurement points. These auxiliary points are used to divide the long measurement section into short sections that meet the stadia requirements for precise leveling measurements (the stadia distance at a single station generally does not exceed 50 m), ensuring that precise leveling measurements can be implemented station by station.

[0034] Based on the above explanation, please refer to Figure 3 The flowchart shown in this embodiment illustrates a method for measuring the elevation benchmark transfer of ultra-long-distance river-crossing tunnels, including: S100. Multiple measurement points are set up on both banks of the water area to be measured. The elevation difference between adjacent measurement points on the same bank is determined by the first measurement method to obtain the first known elevation difference dataset. Based on the first known elevation difference dataset, the first elevation data of each measurement point is obtained. The measurement point pairs include the known elevation starting point.

[0035] Specifically, the purpose of this step is to establish a global elevation benchmark, providing a standard answer for subsequent calibration and verification. The first measurement method in this embodiment is precision leveling, one of the most accurate elevation measurement methods in the prior art, capable of obtaining the accurate normal elevation of each measurement point relative to the national elevation benchmark. The first elevation data here refers to the normal elevation (altitude) of each measurement point, obtained by observing and adjusting station by station along a closed leveling route using a precision leveling instrument. The first known elevation difference dataset is a set of elevation differences between adjacent measurement points on the same bank, calculated based on the normal elevation of each measurement point. Examples include the elevation difference between YJ01 and YJ02 on the left bank, and the elevation difference between YJ01 and BM11. These elevation differences serve as a benchmark for subsequent verification of the accuracy of radar measurement data.

[0036] See Figure 4 Step S100, "determining the elevation difference between adjacent measurement points on the same bank using the first measurement method to obtain the first known elevation difference dataset," specifically includes the following steps: S101. Using the first measurement method, perform forward and backward measurements on each section of each closed loop to obtain the forward and backward elevation differences for each section. Take the average of the forward and backward elevation differences as the initial elevation difference between the two measurement points of that section.

[0037] S102. For a closed loop, based on the initial elevation differences corresponding to the first, second, third, and fourth measurement segments in the closed loop, calculate the loop closure error of the closed loop. When the loop closure error is less than or equal to the loop closure error limit, use the initial elevation difference as the elevation difference between adjacent measurement points to obtain the first known elevation difference dataset.

[0038] It should be noted that, in combination Figure 2Two adjacent sets of measurement points form a closed loop, and two adjacent closed loops share the same set of measurement points. Each segment of the closed loop includes the first segment, the second segment, the third segment, and the fourth segment, which are connected sequentially with each measurement point as an endpoint. Here, a segment can be understood as the measurement path unit defined between two main measurement points, between two auxiliary measurement points, and between two main measurement points and each auxiliary measurement point in two adjacent measurement point pairs, i.e., each edge of the closed loop. Taking the left bank as an example: Closed loop 1 is formed by measurement point pairs YJ01-YJ02 and BM11-BM12, with its four sides as follows: YJ01→YJ02 (as the first measurement segment of closed loop 1, composed of two main measurement points), BM11→BM12 (as the second measurement segment of closed loop 1, composed of two auxiliary measurement points), YJ01→BM11 (as the third measurement segment of closed loop 1, with the main and auxiliary measurement points connected sequentially), and YJ02→BM12 (as the fourth measurement segment of closed loop 1, with the main and auxiliary measurement points connected sequentially); Closed loop 2 is formed by measurement point pairs YJ03-YJ04 and BM11-BM12, sharing BM11-BM12 with closed loop 1 (i.e., sharing the measurement segment BM11→BM12); Closed loop 3 is formed by measurement point pairs YJ03-YJ04 and B... The system consists of M13-BM14, sharing the YJ03-YJ04 measurement section with closed loop 2; closed loop 4 consists of measurement point pairs YJ05-YJ06 and BM13-BM14, sharing the BM13-BM14 measurement section with closed loop 2; similarly, on the right bank, closed loop 5 is formed by measurement point pairs YJ07-YJ08 and leveling point pairs BM15-BM16, closed loop 6 is formed by measurement point pairs YJ09-YJ10 and BM15-BM16 (sharing BM15-BM16 with closed loop 5), closed loop 7 is formed by measurement point pairs YJ09-YJ10 and BM17-BM18 (sharing YJ09-YJ10 with closed loop 6), and closed loop 8 is formed by measurement point pairs YJ11-YJ12 and BM17-BM18 (sharing BM17-BM18 with closed loop 7).

[0039] Since all sections on the same bank are located on land, the precision leveling instrument can be used to conduct measurements station by station along the pre-set route without any obstruction of view across the river. For example, according to the first-order leveling measurement specifications, forward and backward measurements are performed on the four sections of closed loop 1 (YJ01→YJ02, BM11→BM12, YJ01→BM11, YJ02→BM12). Taking section YJ01→BM11 as an example: during the forward measurement, the leveling instrument is placed at an appropriate position between YJ01 and BM11, and the scale readings of YJ01 (back scale) and BM11 (front scale) are read respectively. The difference between the readings is the forward elevation difference of this section. Subsequently, a re-measurement was conducted, that is, a new observation was performed from BM11 towards YJ01 to obtain the re-measured height difference. Finally, the average of the two values ​​is taken as the initial elevation difference for this section. Similarly, the forward and backward measurements of the other three sections of closed loop 1 (YJ01→YJ02, BM11→BM12, YJ02→BM12) are completed in sequence to obtain the initial elevation difference of each section. The measurement of other closed loops will not be described in detail here.

[0040] To ensure the accuracy of the initial elevation differences, these initial elevation differences need to be verified. For each closed loop, the initial elevation differences of the four sides of the closed loop are summed to calculate the loop closure error. Theoretically, the loop closure error should be 0 (because the starting and ending points are the same point). However, in actual measurements, due to errors, it is not 0. Therefore, the magnitude of the loop closure error directly reflects the internal accuracy of the precision leveling measurement. According to the technical requirements for first-order leveling in the "National First and Second Order Leveling Measurement Specifications" (GB / T12897-2006), the accidental mean square error per kilometer of leveling measurement should not exceed ±0.45mm, and the total mean square error should not exceed ±1.0mm. In this embodiment of the invention, it is assumed that the loop length of closed loop 1 is approximately 2.5km, so the loop closure error limit is set to ±4.7mm. This value can be adjusted according to the actual situation. If, in actual measurement, the measured value of the loop closure error of closed loop 1 is +2.3 mm, which is less than the tolerance limit of ±4.7 mm, the observation data of closed loop 1 is deemed qualified. Then, the initial elevation differences of the four measurement segments are used as the elevation differences between adjacent measurement points and included in the first known elevation difference dataset. If the measured value of the loop closure error of a certain closed loop (e.g., closed loop 3) is +8.6 mm, which is greater than the tolerance limit corresponding to its loop length (e.g., ±5.2 mm), the observation data of that closed loop is deemed unqualified. In this case, each of the four measurement segments contained in the closed loop needs to be checked one by one. For example, check the original observation records, whether the instrument i-angle exceeds the limit, whether the scale is vertical, and whether the observation conditions (weather, temperature gradient) are abnormal. After identifying the problematic measurement segment, re-measure back and forth until the loop closure error of the closed loop is less than or equal to the loop closure error limit. Based on the above explanation, closed loops 2 to 8 are measured back and forth, loop closure error calculated, and qualification determined in the same manner to obtain the final verified first known elevation difference dataset.

[0041] After obtaining the first known elevation difference dataset, the first elevation data for each measurement point can be calculated based on the first known elevation difference dataset and the known elevation starting point. Specifically, the known elevation starting point is a known leveling point in the national elevation control network (such as YJ01 in this embodiment), which has a known accurate normal height value and is used to extrapolate the relative elevation difference to the absolute normal height of each measurement point, i.e., the first elevation data. For example, the normal height of BM11: ; The first elevation data for auxiliary measurement point BM11, The accurate normal height value of the known elevation starting point; The elevation difference between the main measurement point YJ01 and the auxiliary measurement point BM11 can be used to obtain the final first elevation data for all other measurement points on the same bank. Similarly, the known elevation starting point on the right bank is YJ07, which, like YJ01 on the left bank, belongs to the national elevation system and has a known accurate normal height value. (Determined by the National Elevation Control Network), thus determining the first elevation data of all measurement points on both the left and right banks. It should be noted that the sign of the elevation difference in the above calculation formula is determined by the actual observed values ​​from the precise leveling survey; when substituting into the formula, simply use the algebraic quantities for accumulation. This embodiment only uses YJ01 and YJ07 as starting points on both banks for illustrative purposes. In actual engineering projects, multiple nationally known leveling points are typically laid out along the leveling route for verification or joint adjustment. Those skilled in the art can adaptively adjust the number and distribution of starting points according to engineering needs, all of which fall within the scope of protection of this invention.

[0042] S200. Using the second measurement method, simultaneously measure the first elevation difference between adjacent measurement points on the same bank and the second elevation difference between corresponding measurement points across the river under the same environmental conditions. The first elevation difference between adjacent measurement points constitutes the first elevation difference measurement value dataset. After completing the point layout and benchmark elevation acquisition in step S100, the second measurement method is used to simultaneously measure the first elevation difference between adjacent measurement points on the same bank and the second elevation difference between corresponding measurement points across the river under the same environmental conditions. The first elevation difference measurements between adjacent measurement points constitute the first elevation difference measurement dataset. This step aims to acquire measurement data for all sections at once using the second measurement method, providing radar measurement values ​​for the subsequent first verification, and acquiring the original measurement data (second elevation difference measurements) of the cross-river section as candidate values ​​for the final cross-river elevation difference.

[0043] In one specific embodiment, step S200 specifically includes: under the same environmental conditions, simultaneously measuring the first elevation difference between adjacent measurement points on the same bank and the second elevation difference between corresponding measurement points across the river using a second measurement method; the first elevation difference measurement value is the elevation difference between adjacent measurement points on the same bank, and the second elevation difference measurement value is the elevation difference between corresponding measurement points across the river.

[0044] Specifically, the second measurement method involves radar equipment, such as microwave ranging radar or millimeter-wave radar. Its working principle is to determine the spatial distance between two points by emitting electromagnetic waves and receiving reflected signals. Combined with the horizontal angle between the measurement points, the elevation difference between the two points is calculated using trigonometric functions. Radar measurement uses electromagnetic waves as the carrier wave and is not limited by line-of-sight conditions or weather conditions, making it suitable for ultra-long-distance (≥10km) river-crossing measurement scenarios. "Same environmental conditions" means that the same-bank measurement and the river-crossing measurement are completed within the same time window, under the same meteorological conditions (temperature, air pressure, humidity), and under the same atmospheric refraction conditions. If the same-bank measurement and the river-crossing measurement are conducted at different times and under different environmental conditions, it is impossible to guarantee that the environmental influences on the two measurements are consistent.

[0045] Furthermore, the second measurement method is used to simultaneously measure the first elevation difference between adjacent measurement points on the same bank and the second elevation difference between corresponding measurement points across the river, specifically including: The radar equipment is set up sequentially at each measurement point, and forward and backward observations are performed on each measurement segment of each closed loop to obtain the forward and backward elevation difference measurements for each measurement segment. The average of the forward and backward elevation difference measurements is taken as the first and second elevation difference measurements between the two measurement points of that measurement segment.

[0046] Specifically, the radar equipment is installed as follows: For same-bank sections, the radar main unit is installed at the starting point of the section, and the reflecting prism or reflector is installed at the ending point of the section. Electromagnetic waves are emitted and reflected signals are received. The slant distance between the two points is measured, and the elevation difference of the section is calculated by combining the vertical angle. For cross-river sections (YJ05→YJ07, YJ06→YJ08), the radar main unit is installed at the cross-river end on the left bank (e.g., YJ06), and the reflecting prism is installed at the corresponding cross-river end on the right bank (e.g., YJ08). The slant distance across the river is directly measured and converted into the elevation difference.

[0047] The first elevation difference measurement value is the elevation difference between adjacent measurement points on the same bank as measured by radar equipment. This includes the elevation difference between main measurement points (e.g., YJ01→YJ02, YJ03→YJ04), between auxiliary measurement points (e.g., BM11→BM12, BM13→BM14), and between main and auxiliary measurement points (e.g., YJ01→BM11, BM12→YJ03) across all land sections. The first elevation difference measurement values ​​of all sections on the same bank are summarized to form the first elevation difference measurement value dataset. The second elevation difference measurement value is the elevation difference between corresponding measurement points across the river as measured by radar equipment. Specifically, it is the elevation difference between the left bank river crossing endpoint pair (YJ05-YJ06) and the right bank river crossing starting point pair (YJ07-YJ08), spanning the entire river surface. This includes the elevation difference between the two parallel river crossing measurement lines YJ05→YJ07 and YJ06→YJ08. The second elevation difference measurements of all cross-river sections are compiled to form the second elevation difference measurement dataset, which serves as a candidate for the final cross-river leveling difference results.

[0048] In practical applications, measurements for each section are completed sequentially within the same time period (such as the same time period on a single morning) to ensure that all measurements are taken under the same environmental conditions. For both non-river-crossing and river-crossing sections, each section undergoes an independent cyclic observation to obtain forward and reverse elevation differences. Finally, the average of the forward and reverse elevation differences is taken as either the first or second elevation difference between the two measurement points in that section.

[0049] It should be noted that the model, operating frequency, and range of the radar equipment can be selected according to the actual river crossing distance and accuracy requirements. For example, for a 10.2km river crossing measurement, a millimeter-wave radar equipment with a range of not less than 15km can be selected. Those skilled in the art can adapt the specific selection of the radar equipment according to engineering needs, and all such adjustments fall within the scope of protection of this invention.

[0050] S300: Based on the first known elevation difference dataset and the first elevation difference measurement dataset, compare the first elevation difference measurement value and the elevation difference between the same adjacent measurement points to obtain multiple sets of measurement deviations; This step aims to complete the on-site calibration and verification of the radar equipment by comparing the radar's measurement results of known sections on the same bank with the true reference values ​​of precise leveling measurements segment by segment. Since both the first elevation difference measurement dataset and the first known elevation difference dataset contain the elevation differences between adjacent measurement points on the same bank, the two sets of data can be compared segment by segment.

[0051] Specifically, for each section along the same bank, the difference between the radar measurement and the precise leveling measurement is calculated as the measurement deviation for that section. The calculation formula is: ,in, For the number The measured value of the first elevation difference of the section being measured; For the number The elevation difference of the measured section.

[0052] Measurement deviations of all sections on the same bank After each calculation is completed, the measurement deviations are compared with a first preset deviation, which is a pre-set allowable deviation threshold. The value of this threshold is determined based on engineering accuracy requirements; for example, it can be set to 3mm in this embodiment. This limit reflects the maximum allowable deviation range for radar measurements in ultra-long-distance river-crossing scenarios. If the deviation falls within this range, it indicates that the radar measurement accuracy meets engineering requirements; if it exceeds this range, it indicates a significant error in the radar measurement. If the measurement deviations of all sections on the same bank... If all values ​​are less than or equal to the first preset deviation, the first verification is deemed to have passed, proving that the radar equipment has reliable measurement accuracy under the current environmental conditions (current temperature, air pressure, and atmospheric refraction state) and that the measurement results are credible. Therefore, the first elevation data of each measurement point is accepted.

[0053] S400. When all measurement deviations are less than or equal to the first preset deviation, the second elevation data of each measurement point is obtained by using the third measurement method. Based on the first elevation data of the measurement points and the second elevation data of each measurement point, the first elevation change parameter set and the second elevation change parameter set corresponding to the two banks are calculated. This step aims to acquire independent elevation data for each measurement point using GNSS measurement methods, which are completely different from radar measurement principles, and then calculate the elevation anomaly rate of change for each survey line direction. Since GNSS and radar employ completely different physical measurement principles—GNSS is based on satellite radio signal positioning, while radar is based on electromagnetic wave ranging—their error sources are independent of each other. If the calculation results obtained from these two independent methods can corroborate each other, the reliability of the final cross-river results will be significantly improved.

[0054] Specifically, the third measurement method is GNSS static observation, and the second elevation data is the geodetic height of each measurement point. Geodetic height is the distance from a ground point along the normal direction to the reference ellipsoid; it is the elevation value directly output by GNSS positioning. Unlike normal height (based on the quasi-geoid), geodetic height is based on the reference ellipsoid, and the difference between the two is called geoid undulation. .

[0055] The specific implementation method of GNSS static observation is as follows: Dual-frequency or tri-frequency GNSS receivers are synchronously set up at each measurement point for long-term continuous static observation. The observation duration is no less than 23 hours, with no less than 3 observation periods, a sampling interval of no more than 30 seconds, and a cutoff elevation angle of no more than 15°. Precise ephemeris is used for baseline calculation, with a fixed solution success rate of no less than 95%. Through the above observation and calculation, high-precision geodetic height (i.e., second elevation data) is obtained for each measurement point. In the GNSS control network composed of multiple synchronous observation baselines, the geodetic height of all measurement points is uniformly calculated using the network adjustment method to ensure that the relative accuracy between points meets the requirements. An observation duration of no less than 23 hours can cover the geometric distribution period of different satellite constellations, effectively reducing the influence of errors from the ionosphere and troposphere; no less than 3 observation periods can avoid the decrease in calculation accuracy caused by poor satellite geometry in a single period, thereby ensuring the calculation accuracy and reliability of the geodetic height of each measurement point.

[0056] See Figure 5 Step S400, "based on the first elevation data of the measurement points and the second elevation data of each measurement point, calculate the set of first elevation change parameters and the set of second elevation change parameters corresponding to both banks," specifically includes the following steps: S401. For each measurement point, the elevation anomaly value of the measurement point is calculated based on the second elevation data and the first elevation data of the measurement point. No. Elevation anomalies at each measurement point The calculation process is as follows: ; in, For the first The first elevation data of the measurement points has been accepted; For the first Second elevation data for each measurement point; elevation outliers This reflects the degree of separation between the quasi-geoid and the reference ellipsoid at that point. In the land section, The changes in values ​​usually exhibit a certain degree of spatial continuity and regularity, but are influenced by the distribution of underground material density, resulting in variations at different locations. Values ​​may vary.

[0057] S402. Select the elevation anomaly values ​​of two adjacent measurement points on the same bank along the survey line direction and the horizontal distance between the two measurement points. Calculate multiple elevation change parameters for the left and right banks along the survey line direction to form a first set of elevation change parameters corresponding to the left bank and a second set of elevation change parameters corresponding to the right bank. The survey line direction is set based on a preset cross-river construction path.

[0058] Along the survey line, the elevation anomaly rate of change for the survey section is calculated based on the elevation anomaly values ​​of two adjacent survey points on the same bank and the horizontal distance between those two points. ; No. Elevation anomaly rate at each measurement point The calculation process is as follows: ; in, For the first Elevation anomalies at individual measurement points; For the first Elevation anomalies at individual measurement points; For the first The measurement point to the first The horizontal distance between the measurement points. To further clarify, the measurement points along the survey line direction refer to the measurement points arranged sequentially along the pre-designed cross-river construction path.

[0059] In this embodiment, taking the left bank as an example, the measurement points along the survey line are sequentially: YJ01→BM11→YJ03→BM13→YJ05, YJ02→BM12→YJ04→BM14→YJ06. The horizontal distances between these measurement points are determined by on-site measurements. Further details about the right bank are omitted here, as the principle is essentially the same. Based on this, the elevation anomaly change rates corresponding to each measurement segment on the left and right banks along the survey line can be obtained, thus forming the first set of elevation change parameters (including the elevation anomaly change rates between YJ01→BM11, BM11→YJ03, YJ03→BM13, and BM13→YJ05) and the second set of elevation change parameters (including the elevation anomaly change rates between YJ02→BM12, BM12→YJ04, YJ04→BM14, and BM14→YJ06).

[0060] S500. Based on the first set of elevation change parameters and the second set of elevation change parameters, a consistency check is performed. If the consistency check result is passed, the measured value of the second elevation difference is used as the elevation difference between the corresponding measurement points across the river.

[0061] This step aims to verify the mathematical consistency and absence of gross errors between GNSS and precise leveling data by comparing the deviations in the elevation anomaly rates of change across different sections. Since the elevation anomaly rate of change calculated in step S400 is derived from the joint calculation of GNSS geodetic height and precise leveling orthographic height, its accuracy and reliability depend on the quality of both types of data. If gross errors exist in the GNSS geodetic height of a particular section, the elevation anomaly rate of change for that section and adjacent sections will exhibit anomalous jumps. These anomalies can be identified and eliminated through consistency checks.

[0062] Specifically, see Figure 6Step S500 specifically includes the following steps: S501. Based on the first set of elevation change parameters, calculate the deviations of multiple sets of same-bank parameters corresponding to the left bank. S502. Based on the set of second elevation change parameters, calculate the deviation of multiple sets of same-bank parameters corresponding to the right bank; S503. Based on the first set of elevation change parameters and the second set of elevation change parameters, compare the elevation change parameters of each measurement segment on the left bank with the elevation change parameters of the corresponding numbered measurement segments on the right bank one by one, and calculate the difference between the corresponding measurement segments on both banks to obtain multiple sets of cross-bank parameter deviations. S504. Compare the deviations of each parameter on the same bank with the second preset deviation, and compare the deviations of each parameter across the river with the third preset deviation. When all deviations of the parameters on the same bank are less than or equal to the second preset deviation, and all deviations of the parameters across the river are less than or equal to the third preset deviation, the consistency check result is passed, and the second elevation difference measurement value is taken as the elevation difference between the corresponding measurement points across the river.

[0063] Specifically, the consistency check includes the following process: (a) Checking for deviations in parameters from the same shore Same-bank parameter deviation check is used to verify the deviation of adjacent measurement sections on the same side of the bank. Whether the values ​​are smooth and continuous. Since the geological conditions and topographic relief on the same bank usually change continuously along the survey line, adjacent survey sections... The values ​​should be close and should not show drastic jumps. Specifically, based on the first set of elevation change parameters on the left bank and the second set of elevation change parameters on the right bank, two sets of same-bank parameter deviations are calculated, namely, multiple sets of same-bank parameter deviations corresponding to the left bank and multiple sets of same-bank parameter deviations corresponding to the right bank.

[0064] Taking the left bank as an example, the two adjacent measurement sections on the left bank... Subtracting the values ​​and taking the absolute value yields the same-bank parameter deviation; specifically, this corresponds to multiple sets of same-bank parameter deviations on the left bank. The calculation process is as follows: ; in, and This represents the elevation anomaly rate of change between two adjacent survey sections along the survey line on the left bank; the same applies to the right bank, so it will not be elaborated further here.

[0065] (ii) Cross-shore parameter deviation check Cross-bank parameter deviation checks are used to verify whether the trends of elevation anomalies at corresponding locations on both banks are systematically consistent. Although the geological conditions on both banks may differ (e.g., the left bank is bedrock, while the right bank is alluvial), this is not always the case. The values ​​themselves may differ, but the trends of change across different measurement sections should be spatially consistent. Specifically, the deviations of multiple sets of cross-shore parameters... The calculation process is as follows: ; in, , The left bank The elevation change parameters of each section and the right bank The rate of change of elevation anomalies in each measurement section.

[0066] Meanwhile, the cross-bank parameter deviation here only applies to the corresponding sections on the left and right banks; for example, YJ01→BM11 and YJ11→BM17 on the left bank constitute a corresponding cross-bank section; YJ03→BM13 and YJ09→BM15 on the left bank constitute a corresponding cross-bank section; other corresponding sections will not be elaborated on here.

[0067] (III) Limit Comparison and Judgment Each deviation of the same-bank parameters was compared with the second preset deviation, and each set of cross-bank parameter deviations was compared with the third preset deviation. The second preset deviation is the deviation of adjacent measurement sections on the same bank. The maximum allowable deviation between them is used to control the same side of the shore. The smoothness of the values; in this embodiment, the second preset deviation can be set to 0.2 mm / km. The third preset deviation is the corresponding measurement segment on both banks. The maximum allowable deviation between the values ​​is used to control the corresponding positions on both sides. To ensure consistency of values, since there may be systematic differences in geological conditions on both sides of the strait, the third preset deviation is usually slightly larger than the second preset deviation. In this embodiment, the third preset deviation can be set to 0.4 mm / km.

[0068] Finally, when all deviations of parameters on the same bank are less than or equal to the second preset deviation, and all deviations of parameters across the river are less than or equal to the third preset deviation, the consistency check result is passed, which is equivalent to passing the second verification. Since the first verification (step S300 radar calibration verification) has been passed in step S300, and both verifications have been passed, the second elevation difference measurement value between the corresponding measurement points across the river (i.e., the elevation difference between YJ05→YJ07 and YJ06→YJ08) measured by the radar in step S200 is finally adopted as the final measurement result of the cross-river leveling elevation difference. Here, the specific values ​​of the second preset deviation (0.2mm / km) and the third preset deviation (0.4mm / km) are exemplary descriptions of this embodiment. In actual engineering, they can be adaptively adjusted according to the accuracy requirements of cross-river leveling and the geological conditions of the survey area, all of which fall within the protection scope of this invention. It should be noted that the specific values ​​of the first, second, and third preset deviations mentioned above can be found in the section on same bank in the "National First and Second Order Leveling Surveying Standards" (GB / T 12897-2006). Poor value, different shore The limits for the difference in values ​​and the mean square error of the elevation difference across the river are determined and adjusted in combination with the accuracy requirements of the high-speed railway cross-river leveling measurement and the actual cross-river distance. The above values ​​are only examples for illustration.

[0069] It should be noted that if either the same-shore parameter deviation or the cross-shore parameter deviation exceeds the limit, the consistency check will fail. In this case, the result calculated in step S400... If the values ​​are abnormal, it may be due to gross errors in the GNSS geodetic height at a certain measurement point, errors in the normal height of the precision leveling measurement, or unexpected differences in geological conditions between the two banks of the river. Therefore, it is necessary to investigate the measurement points corresponding to the out-of-limit section, remove the gross error data, recalculate or re-perform GNSS static observations until the consistency check is passed.

[0070] In summary, this invention discloses a method for measuring the elevation benchmark transfer of ultra-long-distance river-crossing tunnels, the beneficial effects of which include: (1) Both traditional optical and GNSS cross-river leveling methods adopt a "measure first, calculate later, and verify afterward" approach. That is, after completing all field measurements and office calculations, the accuracy is evaluated using statistical indicators such as the closure error of the closed loop. Under this approach, if the closure error exceeds the limit, all measurement work must be restarted; and during the measurement process, operators cannot judge the reliability of the cross-river data in real time. This invention utilizes known elevation benchmarks set up on the same bank to obtain standard answers through precise leveling measurements. First, radar measures the known sections on the same bank. Only when the measurement results of all sections on the same bank meet the accuracy requirements are the radar measurement data of the unknown cross-river sections accepted. This "verifying the unknown with the known" on-site pre-verification mechanism enables real-time on-site judgment of the reliability of measurement data without waiting for post-calculation, effectively reducing the risk of rework.

[0071] (2) A dual independent verification mechanism is established to ensure the reliability of the cross-river results. The first verification is radar calibration verification, which compares the radar's on-bank measurements with the true value of the precision leveling benchmark segment by segment to confirm the measurement accuracy of the radar equipment under the current environmental conditions from a physical perspective. The second verification is GNSS consistency check, which uses GNSS to obtain geodetic height data that is completely independent of the radar principle, calculates the elevation anomaly change rate of each section, and performs on-bank and cross-bank consistency checks. The two verifications use different technical methods and have independent error sources. Only when both verifications pass will the cross-river results be accepted, thus providing a fundamental guarantee for the reliability of the final cross-river leveling height difference results.

[0072] (3) Achieve simultaneous acquisition of all measurement data with a single network setup. Data from precise leveling, radar synchronous measurement, and GNSS static observation are all acquired simultaneously after a single network setup, eliminating the need to establish separate control points for different measurement methods. The main and auxiliary measurement points simultaneously serve the triple purpose of establishing a precise leveling benchmark, verifying radar calibration, and calculating GNSS elevation anomalies. Compared to the existing technology that requires separate establishment of GNSS control points and leveling points, this invention significantly reduces the workload in the field and improves operational efficiency.

[0073] (4) Applicable to ultra-long distance measurements, unaffected by line-of-sight conditions and weather. Both radar and GNSS use electromagnetic waves as carrier waves for measurement, unaffected by line-of-sight conditions, weather, day and night, etc., and can operate in all weather conditions. Traditional optical cross-river leveling methods are limited by line-of-sight distance (optical micrometer method not exceeding 500m, distance trigonometric leveling method not exceeding 3.5km). This invention effectively solves the engineering problem of ultra-long distance cross-river leveling measurements of more than 10km, and can be widely applied in the construction of large-scale infrastructure such as high-speed railways, highway bridges, water conservancy projects, urban rail transit, and power projects. It meets the reliability requirements of cross-river elevation transfer for major projects such as high-speed railways and has important engineering application value.

[0074] The above description is merely a preferred embodiment of the present invention and an explanation of the technical principles employed. Those skilled in the art should understand that the scope of the invention is not limited to the specific combination of the above-described technical features, but also includes other technical solutions formed by arbitrary combinations of the above-described technical features or their equivalents without departing from the inventive concept. For example, technical solutions formed by substituting the above-described features with (but not limited to) technical features with similar functions disclosed in this invention.

Claims

1. A method for measuring the elevation benchmark transfer of ultra-long-distance river-crossing tunnels, characterized in that, include: Multiple measurement points are set up on both banks of the water area to be measured. The elevation difference between adjacent measurement points on the same bank is determined using a first measurement method to obtain a first known elevation difference dataset. Based on the first known elevation difference dataset, the first elevation data of each measurement point is obtained. The multiple measurement points include known elevation starting points. Using a second measurement method, the first elevation difference between adjacent measurement points on the same bank and the second elevation difference between corresponding measurement points across the river are measured simultaneously under the same environmental conditions. The first elevation difference between adjacent measurement points constitutes the first elevation difference measurement value dataset. Based on the first known elevation difference dataset and the first elevation difference measurement dataset, the first elevation difference measurement value between the same adjacent measurement points is compared with the elevation difference to obtain multiple sets of measurement deviations; When all the measurement deviations are less than or equal to the first preset deviation, the second elevation data of each measurement point is obtained by the third measurement method. Based on the first elevation data of the measurement points and the second elevation data of each measurement point, the first elevation change parameter set and the second elevation change parameter set corresponding to the two banks are calculated. A consistency check is performed based on the first set of elevation change parameters and the second set of elevation change parameters. When the consistency check result is passed, the second elevation difference measurement value is used as the elevation difference between the corresponding measurement points across the river.

2. The method for measuring the elevation benchmark of an ultra-long-distance river-crossing tunnel according to claim 1, characterized in that, The multiple measurement points on the same bank include multiple sets of measurement point pairs; each set of measurement point pairs is arranged along a pre-set cross-river construction path; two of the measurement points in each set of measurement point pairs are arranged along the flow direction of the river. One of the measurement points in all the measurement point pairs on both sides of the strait is located on the same straight line, and the other measurement point in all the measurement point pairs on both sides of the strait is located on the same straight line, and the two straight lines are parallel to each other.

3. The method for measuring the elevation benchmark of an ultra-long-distance river-crossing tunnel according to claim 2, characterized in that, Two adjacent sets of measurement point pairs form a closed loop, and two adjacent closed loops share the same set of measurement point pairs; each measurement segment of the closed loop includes a first measurement segment, a second measurement segment, a third measurement segment, and a fourth measurement segment connected sequentially with each measurement point as an endpoint; The method of determining the elevation difference between adjacent measurement points on the same bank using a first measurement method to obtain a first known elevation difference dataset includes: The first measurement method is used to perform forward and backward measurements on each section of each closed loop to obtain the forward and backward elevation differences for each section. The average of the forward and backward elevation differences is taken as the initial elevation difference between the two measurement points of the section. For a closed loop, the loop closure error is calculated based on the initial elevation differences corresponding to the first, second, third, and fourth measurement segments in the closed loop. When the loop closure error is less than or equal to the loop closure error limit, the initial elevation difference is used as the elevation difference between adjacent measurement points to obtain the first known elevation difference dataset.

4. The method for measuring the elevation benchmark of an ultra-long-distance river-crossing tunnel according to claim 3, characterized in that, The method of simultaneously measuring the first elevation difference between adjacent measurement points on the same bank and the second elevation difference between corresponding measurement points across the river under the same environmental conditions using the second measurement method includes: Under the same environmental conditions, the second measurement method is used to simultaneously measure the first elevation difference between adjacent measurement points on the same bank and the second elevation difference between corresponding measurement points across the river; the first elevation difference is the elevation difference between adjacent measurement points on the same bank, and the second elevation difference is the elevation difference between corresponding measurement points across the river.

5. The method for measuring the elevation benchmark of an ultra-long-distance river-crossing tunnel according to claim 4, characterized in that, The method of simultaneously measuring the first elevation difference between adjacent measurement points on the same bank and the second elevation difference between corresponding measurement points across the river using the second measurement method specifically includes: For each section of the closed loop, forward and backward observations are performed to obtain the forward and backward elevation difference measurements for each section. The average of the forward and backward elevation difference measurements is taken as the first and second elevation difference measurements between the two measurement points in that section.

6. The method for measuring the elevation benchmark of an ultra-long-distance river-crossing tunnel according to claim 3, characterized in that, Based on the first elevation data of the measurement points and the second elevation data of each measurement point, the set of first elevation change parameters and the set of second elevation change parameters corresponding to both banks are calculated, including: For each of the measurement points, the elevation anomaly value of the measurement point is calculated based on the second elevation data and the first elevation data of that measurement point. The elevation anomalies of two adjacent measurement points on the same bank along the survey line direction and the horizontal distance between the two measurement points are selected. Multiple elevation change parameters of the left bank and the right bank along the survey line direction are calculated to form the first set of elevation change parameters corresponding to the left bank and the second set of elevation change parameters corresponding to the right bank. The survey line direction is set based on a preset cross-river construction path.

7. The method for measuring the elevation benchmark of an ultra-long-distance river-crossing tunnel according to claim 6, characterized in that, The step of performing a consistency check based on the first set of elevation change parameters and the second set of elevation change parameters, and when the consistency check result is passed, using the second elevation difference measurement value as the elevation difference between the corresponding measurement points across the river, includes: Based on the set of parameters for the first elevation change, the deviations of multiple sets of parameters corresponding to the left bank are calculated. Based on the set of second elevation change parameters, the deviations of multiple sets of same-bank parameters corresponding to the right bank are calculated; Based on the first set of elevation change parameters and the second set of elevation change parameters, the elevation change parameters of each measurement segment on the left bank are compared with the elevation change parameters of the corresponding numbered measurement segments on the right bank one by one, and the difference between the corresponding measurement segments on both banks is calculated to obtain multiple sets of cross-bank parameter deviations. Each of the same-bank parameter deviations is compared with the second preset deviation, and each of the cross-bank parameter deviations is compared with the third preset deviation; when all the same-bank parameter deviations are less than or equal to the second preset deviation, and all the cross-bank parameter deviations are less than or equal to the third preset deviation, the consistency check result is passed, and the second elevation difference measurement value is taken as the elevation difference between the corresponding measurement points across the river.

8. The method for measuring the elevation benchmark of an ultra-long-distance river-crossing tunnel according to claim 1, characterized in that, The first measurement method is precise leveling, and the first elevation data is the normal height of each measurement point; the second measurement method is measurement using radar equipment; the third measurement method is GNSS static observation, and the second elevation data is the geodetic height of each measurement point.

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