Abstract: When a largespan tunnel passes through mudstone with sandstone strata, diseases can be easily caused by unsymmetrical pressure. To study the unsymmetrical pressure characteristics and influencing factors of bedding tunnels in mudstone and sandstone strata, the influence of the bedding dip angle of sandstone, spacing, and groundwater on the mechanical characteristics of the largespan bedding tunnel of the ZhengzhouWanzhou highspeed railway is studied using field measurements and the numerical simulation method. The results show the following. (1) Compared with the homogeneous mudstone stratum, the displacement and plastic zone of the surrounding rocks around the tunnel are asymmetric after excavating the bedding of the largespan tunnel in the mudstone and sandstone strata, and the displacement of the surrounding rocks in the normal bedding direction is greater than that in the tangential direction. (2) The most unfavorable dip angle of the bedding tunnel is 45°, and the influence of bedding on the mechanical characteristics of the tunnel gradually decreases when the bedding spacing of the sandstone exceeds 3 m. (3) The displacement of the surrounding rocks, range of the mudstone plastic zone, and range of the sandstone bedding plastic zone increase in the mudstone and sandstone strata containing groundwater. Stability of the surrounding rock decreases, and the groundwater aggravates the degree of the unsymmetrical pressure of the bedding tunnel.

Key words: highspeed railway tunnel, mudstone with sandstone, bedding tunnel, mechanical characteristics, groundwater, numerical simulation, field monitoring