The orthotropic anisotropy of sedimentary rocks has a significant impact on the force and deformation behavior of the project. In this paper, radial pressurization tests were carried out in the borehole in a typical northern karst area to obtain the deformation properties and orthotropic anisotropy of the rock masses. The test results showed that the deformation modulus and elastic modulus of the limestone rocks in the dam site area obeyed normal distribution. The deformation modulus was basically larger than the proposed deformation modulus of Class II rocks (10 GPa). The deformation behavior and anisotropy degree of the limestone showed a weak correlation with the elevation, but a strong correlation with the development density of the rock joints. The larger development density of the rock in the right bank test section leads to a larger degree of orthotropic anisotropy and frequency of occurrence.

The accurate judgment of topographic bias tunnels is directly related to reasonable tunnel design and construction safety. In this study, numerical simulations were carried out to determine the unsymmetrical coefficient of topographic unsymmetrical-loaded tunnels, according to the critical thickness of the cover layer of the topographic bias tunnel proposed in the Chinese Code. The unsymmetrical coefficient was analyzed via control variable method and orthogonal test method. The results showed that it is appropriate to take 1.2 as the criterion for all types of topographic unsymmetrical-loaded tunnel in practical application. The influence of different topographic factors, mechanical properties of the surrounding rock, rock quality, construction methods and tunnel spans on the unsymmetrical coefficient were summarized by the control variable method. The results of multifactor analysis under an orthogonal design revealed that the influence of Uc is in the following order: slope angle, overburden thickness, construction method, surrounding rock quality, and height-to-span ratio. Article Highlights The Chinese code for topographic unsymmetrical-loaded tunnels presents a the determination of the corrected unsymmetry coefficient. Single-factor analysis determines the change pattern of the corrected unsymmetry coefficient under the influencing factors. Polar analysis based on orthogonal tests determines the strength of the factors influencing the corrected unsymmetry coefficient.