Keywords: GPS settlement deformation monitoring expressway
China Library Classification Number: TB22 Document Identification Number: Part A Number:1672-3791(2012) 05 (a)-0073-02.
1 project overview
The whole expressway is constructed according to the standard of two-way four-lane fully enclosed expressway, and the design speed standard is100 ~120km/h. In the GPS settlement and deformation monitoring project, 10km will be selected. This section of highway is characterized by plains and hills, and the designed subgrade width is 26 m. This route is designed as four lanes. According to the literature, there are 1 1 plane control points of each system in this section, but only 5 of the 10 plane control points were found after field search.
Of the five control points, two are first-class points of the State Bureau of Surveying and Mapping, 1 is second-class point, and two are urban surveying system points. Because these control points belong to different measurement systems, their levels are also different. In September of 20 1 1 year, the author measured the 10km section. Based on GPS technology, the elevation measurement is compared with the elevation data of second-class leveling, and the elevation of GPS is consciously checked during the measurement.
2 Project implementation process
(1) five AshtechZ-X dual-frequency GPS receivers are selected as the main instruments for this observation, and NAZ+ GPM3 level is selected as the second level. On this basis, the difference between the two measurement results is analyzed, and the accuracy of GPS point coordinates is tested based on the total station.
(2) Static GPS network is adopted, and the form of GPS network is edge-connected. Number of satellites during observation >; 5. Tolerance control range: horizontal plus or minus 5mm, vertical plus or minus10 mm; Carry out leveling with reference to the accuracy index of second-class leveling. (3) There are 14 deformation monitoring points and 7 GPS reference points within l0km of the survey area. Each deformation monitoring point is planned to monitor 1h ~ 2h.
3 accuracy analysis
3. 1 Accuracy analysis of GPS settlement deformation monitoring network in survey area
Based on the deformation monitoring network of this expressway 10km section, the accuracy of GPS reference network and monitoring network is analyzed. The settlement deformation monitoring network of this bid section consists of 7 datum points and 14 monitoring points, among which the datum points include JZ03, JZ06, JZ08, JZ09, JZ 10 and JZ65438. The monitoring points are BJ0 1, BJ02, BJ04, BJ05, BJ07, bj1,BJ 12, BJ 13, BJ 14 and bj/kloc. Through long-term precise leveling observation and benchmark analysis, the stability of JGO4 point is determined. Based on JZO4, the whole GPS network is solved, and the GPS settlement deformation monitoring network is arranged in the form of edge connection.
See table 1 for the median error of the calculated side length of GPS reference network baseline. As can be seen from the table, the baseline calculation accuracy of GPS reference network is high, reaching millimeter level. The maximum error of baseline side length is only 5.7mm, and the minimum error of baseline side length is 0.1mm. The GPS reference network is adjusted in WGS-84 coordinate system as a whole. In the adjustment process, the JG04 point with accurate WGS-84 coordinates is fixed, thus effectively improving the position accuracy of the whole datum network. After adjustment, the spatial rectangular coordinates, Gaussian plane rectangular coordinates and geodetic coordinates (WGS-84 coordinate system) and related accuracy information of other datum points can be obtained. Similarly, the WGS-84 coordinate system is selected for the adjustment of the monitoring network. After adjustment, the spatial rectangular coordinates, geodetic coordinates (WGS-84 coordinate system) and related accuracy information of the monitoring points are obtained; On this basis, the point and direction of JGO4 are fixed and averaged, and the adjustment is selected in the Gaussian plane of WGS-84 coordinate system. After adjustment, the Gaussian plane rectangular coordinates of deformation monitoring points, the plane side length between monitoring points and their related information can be obtained.
As can be seen from the table 1, the accuracy of the north-south and east-west components is better than that of the elevation component, and the accuracy of the elevation component is less than 6mm. Some points are affected by surrounding observation conditions (especially multipath effect), and some points are affected by urban observation environment, so the accuracy is slightly lower, and the error of most points is about 4mm, which meets the accuracy requirements of settlement deformation monitoring. In order to get higher accuracy, more measures can be taken in the observation process: (1) Before data acquisition, the phase center position of each antenna should be accurately checked, especially the vertical difference; (2) The observation period has increased to more than 10h, and there are more synchronous observation stations (Table 2).
3.2 Settlement monitoring and consistency analysis with precision leveling.
Comparing the measurement results of GPS and total station, it can be seen that the maximum difference of the same coordinate measured by the two methods is △ xmax = 4.0 mm and △ ymax = 5.0 mm respectively. Therefore, the result of GPS measurement is accurate and reliable. According to the consistency test results of positioning accuracy, the point accuracy measured by GPS technology can reach millimeter level, which is in good agreement with the results measured by total station and can better meet the accuracy requirements of highway deformation monitoring. Using GPS to measure the elevation of deformation monitoring points, and then comparing GPS elevation with leveling elevation, the comparison results have high reference value.
After calculation, the maximum difference between GPS elevation and leveling elevation is less than 5 mm, and GPS elevation can meet the accuracy requirements of highway deformation monitoring. The data processing results of GPS show that the monitoring accuracy can reach millimeter level in the horizontal direction and millimeter level in the vertical direction. It completely meets the accuracy requirements of highway settlement deformation monitoring. The data in the following table are representative highway GPS settlement deformation monitoring points extracted from engineering examples. Take this data as an example for data analysis.
Table 3 only lists the data of five observation periods for analysis, from which it can be seen that the data of different periods have changed, the elevation between adjacent observation periods has not changed much, and the monitoring period has not changed much, and tends to be stable. In other words, when the expressway has just entered the operation stage, it is most prone to settlement and deformation. Therefore, the early maintenance and maintenance of the expressway that has just been put into use is quite critical.
On this basis, the author selects some deformation monitoring points in the process of highway use for analysis, and first draws the trend map of elevation change. Because the deformation monitoring points are randomly selected, the overall change of 10km section can be represented by graphics. As can be seen from the graph results, the monitoring points at the initial stage of highway use show an obvious sinking trend with the passage of time. Through the scientific maintenance of the expressway, we can see that in the later period of settlement monitoring, the pavement structure of the expressway is relatively stable with high strength, and then in the later period of actual operation, the elevation changes little, and the height difference between two adjacent observation periods tends to zero. In other words, the results of engineering practice show that the expressway is stable.
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