Abstract: At present, the frequently used methods for cross-river elevation measurement include leveling, ranging trigonometric elevation, and GNSS cross-river elevation measurement. Conventional leveling has a relatively short sight distance, and ranging trigonometric elevation measurement requires very high site conditions, requiring mutual visibility and synchronous alignment observation between measurement points. The measurement accuracy is greatly affected by wind, atmospheric refraction, and distance. As the measurement distance increases, the influence of vertical deviation also increases, and the accuracy of trigonometric leveling has decreased. When the span exceeds 3500m, there is no relevant standard specification to follow, which is a considerable challenge for cross-river elevation transfer measurement with a span of more than 10km. This paper studies the use of measurement method for elevation measurement of ultra-long-distance cross-river projects. The basic principle of BeiDou cross-river leveling method is firstly introduced in the paper, taking the elevation transmission of Chongming-Taicang river-crossing tunnel of Shanghai-Chongqing-Chengdu high-speed railway as an example, the layout scheme of leveling control network, field measurement quality control, data processing, and accuracy analysis are elaborated during the implementation of cross-river leveling measurement. The practical results show that: In the survey area with relatively flat terrain and relatively gentle change rate of elevation anomaly, the control network is optimized by laying compulsory observation pier, and the two-line cross-river leveling method is adopted. All the accuracy indexes attached inside and outside meet the requirements of second-order leveling. The 10.2km ultra-long-distance cross-river leveling technology has been successfully applied to the second-class level transmission in Chongming-Taicang cross-river tunnel of Shanghai-Chongqing-Chengdu high-speed railway, which has very good reference significance for similar engineering projects.

Key words: ultra long distance, cross-river leveling, abnormal change rate of elevation, second-order leveling