Based on the indoor triaxial compression test,the failure characteristics and mechanical properties evolution law of gypsum rock after dry-wet cycle are obtained.Combined with numerical simulation,the mechanical influence law of gypsum surrounding rock on the initial support structure of tunnel after dry-wet cycle is studied.The results show that with the increase of the number of dry-wet cycles,the shear surface decreases when the gypsum rock is destroyed,and a large area of rock spalling occurs on the surface of the rock sample;at the same time,with the increase of Poisson's ratio,the elastic modulus and peak deviatoric stress decrease,and the deterioration of elastic modulus is the most serious,which is about 49%lower than that of the same period.After 11 dry-wet cycles,the horizontal displacement of the side wall is the largest,about 1.5 times higher than that of the year-on-year,and the vertical displacement peak appears in the vault,which is 1.2 times higher than that of the year-on-year.The safety factor of each position of the initial support is reduced,and the vault,wall foot and side wall are greatly reduced,which are reduced by about 63%,36%and 53%respectively.The vault,wall foot and side wall of the primary support structure are weak points,which need to be strengthened and reinforced to ensure the safe operation of the tunnel.
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