185 Application of GPS in Horizontal Control Survey of Very Long Tunnel

When a tunnel is very long, it is difficult to establish a tunnel construction control network by triangulation method. Therefore, in recent years, GPS positioning technology is used for tunnel horizontal control survey. In the layout of middle-distance tunnel control network, the datum of the control network must be designed and the side length should be projected onto the mean ground plane of the survey. Moreover, initial data must be processed. To avoid the demnification of internal coincidence accuracy of GPS network, “one point and one azimuth” is used as initial data of control network. This paper, taking the implementation of the construction control network of the general canal tunnel of Piloting Water from Da to Huang Project in Qinghai Province as an example, introduces the experience that GPS technique is utilized to realize the holing through control survey for very long tunnel in the case of no specification for tunnel transfixion survey exceeding 8 kilometers at home. In addition, the basic theory and course of data processing in tunnel GPS network are also expounded and the method of “one point and one azimuth” used for adjustment of trilateration network is discussed in the paper. The results of this research have a fairly great value of reference in scheming of very long tunnel holing through control survey.

Generally triangulation or precise traversing is adopted in tunnel construction. However, lots of transferring points need layout. This leads to large number of work and serious error cumulative accumulation. Triangulation and precise traversing needs high observation conditions and inter-visibility, and the environment around the tunnel increases the difficulty of the general surveying method. As a new high-tech positioning method, GPS provides the insurance for engineering control survey with high efficiency and internal coincidence accuracy of the net, and no need of large number of tie-points and working all day. The “Technical Specifications for Hydraulic and Hydroelectric Engineering” only provides technical standard for tunnel holing through less than 8 kilometers long, so it has important significance on hydraulic and hydroelectric engineering, highroad and railway project that how to realize the super-long tunnel control survey using GPS technique.