| Our tidal observation instruments simultaneously is measuring atmospheric pressure, and the characteristics of atmospheric pressure daily changes are obvious, which changes approximately 1～2hPa. The observation quality of similar tide instruments is different in the same environment. Generally the quality of observation instruments on the central platform is better than on the edge.On atmospheric effect issues of geophysical observations, domestic and foreign experts mainly study atmospheric correction methods of surface displacement, gravity, tilt and strain earth tide observations. Actual observation model is established and the atmospheric pressure corrections are carried through by the regression analysis from the residuals and pressure data of tidal observations. Furthermore, the atmospheric correction error model is established for calculating the atmospheric effects from global and regional of weather data. However, the above studies hardly describe and solve Cavern Effect. It is necessary to study and estimate the impact of the pressure load on the tidal platform in the cave.Based on the finite element software ANSYS,the observation platform finite element models including the platform and cave models are constructed. To take the atmospheric pressure as a load, simulations are conducted for observation platforms. The main conclusions are as follows:1. For the platform model, the displacement and deformation of observation platform was of asymmetrical symmetry distribution. Near the edge,the maximum displacements are separately about 4.0×10-7m,4.0×10-7m,6.0×10-7m in the directions of x, y and z.2. For cave model, the displacement and deformation are asymmetric because of the asymmetric structure of the model in x direction along cave, the maximum displacements of two ends are separately 4.5×10-7m and 1.5×10-7m,while it is about 2.0×10-7m in y direction.3. In the middle region 0.5m and 0.3m away from the ends of platform, the horizontal and vertical changes equably, the changes difference are in the order of about 10-7m～10-8m. At the point where the thin marble meets, displacement mutation generally less than 10-8m, the maximum displacement changes are 10-7m.4. When the platform is increased by the thickness of 1m(equivalent to the usual equipment pier height), the characteristics of displacement and deformation on the surface of observation platforms are as above, and the maximum displacement reaches 10-6m.5. The displacement and deformation of the joints are the same as the load cycle. The maximum linear strain between two joints is up to 10-9.
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