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To research the deformation regularity of loess tunnel in reserving core soil with annular excavation method compared with other construction methods, 3D Numerical Simulation is applied and the loess tunnel of highway is taken as an example. The research results show that[1]：The deformation of surrounding rock affected by the area of core soil is small.The stress regularity of different support structure influence on the area of core soil is different. This is mainly reflected that the maximum pressure stress of primary support increases with the area of core soil’s increasing, but the minimum bending moment of secondary lining is not appeared in the working condition which the minimum core soil area is.

In order to analysis the internal relation between the matric suction change and the tunnel disease, the paper combines the Dayoushan tunnel as an engineering example, uses the mathematical, field monitoring and model shear test and to analysis the the change rule of the martic suction and the influence of martic suction on the tunnle supporting force and plastic zone. The results show that when the water content is increasing, the unsaturated loess matric suction is reduction, the force of tunnel support is increasing and the radius of plastic zone is increasing. Due to the influence of surface water infiltration, the matric suction of the around soil in Dayoushan tunnel is reduction and cause the crown settlement, landslides and lining cracks. The disease treatment mainly lies in keeping the drainage system is smooth and secure for waterproof. For the similar unsaturated loess tunnel, the research results have reference significance.

Based on a certain loess tunnel in Kelan-Linxian Expressway in Shanxi province, the influence to primary support forces by different stress release is analyzed by the Ansys FE software in the step method excavation. The analysis results can reasonably reflect the actual case of primary support forces, and can offer related reference to the selection of reasonable design parameters for primary support.

The theoretical solution to the distribution of axial force in Mindlin displacement problem and the plastic radius of surrounding rock in the condition of elastoplastic homogeneous soil are deduced. Based on the results of field test, the problem of length optimization of systematic bolt in loess tunnel was discussed from the two perspectives of mechanical characteristic under the drawing force and the axial force at the location of neural point. The obtained results will offer the technical support for the length optimization of systematic bolt in loess tunnel, which has the guiding significance in the design and construction.

The 3D finite element simulation was adopted to study the globality stability of tunnel caused by the different excavation length of invert. Kelan-Linxian highway loess tunnels were taken as an example. The research results are shown as follows: The vertical displacement and horizontal convergence increased by the increasing of the excavation length of the invert. But the latter increase range is larger than the former. The horizontal convergence in sidewall is convergence value is greater than the level of the arch and the corner, the horizontal displacement primarily occurred in the side wall position. The surrounding rocks maximum plastic strain occurred in side wall and corner wall in 4 working conditions. The plastic zone occurred around from arch corner to wall side. In Tab. 4, the maximum plastic strain is increased by the excavation length of inverts increasing.

Based on the displacement solution of Mindlin problem, the elastic solution to the distribution of shear stress & axial force is deduced under the drawing load for mortar anchor in loess tunnel. The ultimate drawing load of systematic anchor in the sidewall is measured by means of field test based on a certain loess tunnel in Kelan-Linxian Expressway, and the forcing characteristic of the anchor is analyzed. The distribution forms of the shear stress & axial force are also discussed in different soil characteristics. The obtained results will offer the theoretical basis for the design &optimum of systematic bolt in loess tunnel, which has the guiding significance in the design and construction.

Based on selecting a tunnel collapse under typical conditions of the shallow-buried terrain under unsymmetrical pressure, analyzing the monitoring measurement date, using the software of finite element numerical simulation, the paper simulates the tunnel excavation in lengthwise, deduces the change laws of stress in primary support, the mechanical properties and the collapse mechanism.

Based on the Hejiazhuang tunnel on the Zhengzhou-Xi’an passenger dedicated railway,forcing cases of systematic anchor was studied in loess tunnel with large cross-section and forcing characteristics of systematic anchor at vault and sidewall parts were obtained; Causes that the forcing difference varies much were analyzed from the perspective of the law of radial displacement attenuation and distribution form of surrounding rock pressure，the related conclusions will offer reference value and guiding significance to the design and construction of such tunnels.