Calculation of Vertical Deviation and Tunnel Through Error Based on High-Precision Earth Gravity Field

Objectives: As a important traffic engineering under construction, the successful construction and operation of the major transportation hub project in west is of great significance to promoting the economic development of Tibet, enhancing national unity and even the development of the country. Ensuring the smooth through of dozens of long tunnels on the major transportation hub project in west is a difficult problem in the construction of the major transportation hub project in west. Due to the vertical deviation between the GNSS positioning results and the results of the traverse survey using the total station in the tunnel, it will affect the correctness of the pilot survey. Therefore, it is particularly important to calculate and analyze the vertical deviation of the planned stations of the major transportation hub project in west and key tunnel areas and the resulting tunnel through error. Method: In this paper, three sets of ultra-high-precision gravity field models (GECO model, EIGEN-6C4 model and SGG-UGM-2 model) with a maximum order of 2190 are used to calculate the vertical deviation of the area along the major transportation hub project in west, especially the planned stations. For the key tunnel area, the influence of the tunnel penetration error caused by the deviation of the vertical line is calculated and analyzed under the condition of different vertical angles of the control point outside the tunnel. Results: The research results show that: (1) The vertical deviation along the major transportation hub project in west has a larger meridian component, which is about 20", and the Prime Vertical component is below 1"; (2) Between the three gravity field models, the maximum difference of the vertical deviation between any two models is 0.04", the minimum is 0", the average difference is 0.005", the maximum difference of the meridional component is 0.6", the minimum is 0" and the average difference is 0.08"; (3) In the selected 6 key tunnel areas, when the vertical angle of the entrance is 45º, the horizontal penetration error caused by the vertical deviation of the important tunnel areas in the major transportation hub project in west planning is 170mm-190mm. When the vertical angle of the entrance outside the hole is 35º, the lateral penetration error value is 120mm-140mm. When the vertical angle of the entrance is 25º, the lateral penetration error value is 90-100mm. When the vertical angle of the entrance is 15º, the lateral penetration error value is 60-70mm. Conclusion: (1) The calculation results of GECO model, EIGEN-6C4 model and SGG-UGM-2 model are basically the same, and the difference is small, The slight difference is mainly caused by the different data sources and model solution methods of the three groups of models; (2) The vertical deviation of important tunnel areas in the major transportation hub project in west planning is very large, which will bring about the lateral through error of the tunnel far beyond the allowable value. The vertical angle of the control points outside the tunnel can directly determine the influence of the vertical deviation on the horizontal penetration error of the tunnel. In the actual construction process of major transportation hub project in west, it should be ensured that the control points outside the tunnel are buried on the contour surface as far as possible. If the vertical angle between the control points cannot be adjusted due to geological conditions, the vertical deviation must be corrected to weaken the influence of the penetration error, so as to ensure the smooth penetration of the tunnel.