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Abstract In order to reveal the unloading creep failure mechanism of water-bearing mudstone，the rising axial pressure-reducing confining pressure creep tests，meso-structure tests and numerical simulation analysis were carried out for mudstone with different water contents. The results show that：(1) The water content has a significant effect on the creep deformation of mudstone，and the axial strain is significantly more affected by the water content than laterally at the same creep stress level. (2) SEM image analysis shows that the increase of moisture content leads to the increase of internal porosity of mudstone，and the mineral particles are dissolved and weakened，which is transformed from a dense and high strength to a loose porous and irregular accumulation structure with low strength. (3) Based on the real meso-structure characteristics of mudstone，a statistically equivalent meso-structure network is generated，and the corresponding GBM-PSC numerical model is established and verified. (4) The numerical simulation results show that the number of microcracks increases with the increase of moisture content，and the number of intragranular tensile cracks increases first and then stabilizes and then increases，while the number of intergranular shear cracks continues to increase with the increase of moisture content. The contact tangential force，angular deflection value and average porosity decrease first and then stabilize and then increase with the increase of unloading creep time，and the more the moisture content increases，the more significant the trend. (5) A three-stage unloading creep deterioration evolution model of dry and water-bearing mudstone is established，and the research results can provide a theoretical reference for the study of the creep deformation failure mechanism of excavation and unloading of soft rock engineering under the action of water.
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