Study On The Creep Behavior Of Sandstone Considering Initial Damage Effect

During the excavation process of underground engineering,the surrounding rock body will inevitably bear the cumulative effect of damage caused by disturbance,resulting in the existence of a mechanical properties of the surrounding rock body deterioration damage zone.At the same time,different degrees of damage within the damage zone will show significant rheological phenomena under the long-term effect of constant load,the mechanical properties of the damaged surrounding rock body was one of the important factors to determine the bearing capacity of the surrounding rock and the long-term stability of underground engineering.In view of this,taking sandstone as the research object,pre-damaged sandstone specimens with different degrees of initial damage were prepared by adding and unloading,and the influence of the degree of initial damage on the uniaxial compression mechanical properties of sandstone was analyzed,and creep tests were carried out on specimens with different degrees of initial damage to establish a creep damage model considering the effect of initial damage,and finally ANSYS was used to conduct a numerical simulation study of creep.The main research work and results were as follows:(1)Sandstone specimens with different degrees of initial damage were prepared by predamage with unloading,and the influence of unloading ratio on elastic modulus and longitudinal wave velocity was investigated,and the degree of initial damage was characterized by damage variables based on elastic modulus and longitudinal wave velocity.The basic mechanical parameters such as uniaxial compressive strength and elastic modulus were calculated,and the functional relationship between the mechanical parameters and the initial damage variables was established.(2)Creep tests considering the initial damage effect were carried out to study the basic creep properties and the effect of the initial damage degree on creep deformation,creep rate,damage stress and damage mode,and a long-term strength determination method based on the steady-state creep rate was proposed through the analysis of the long-term strength determination method of rocks.(3)Based on the creep curve characteristics,a nonlinear creep model that can describe accelerated creep was established based on the Nishihara model,and the Levenberg-Marquardt+general global optimization method was used to invert the creep parameters and discuss the influence of the initial damage degree on the model parameters;further considering the initial damage effect,damage variables related to stress level,initial damage degree and time were introduced,and the accelerated The resulting model can well describe the three stages of creep and can reflect the effect of initial damage on the creep process.(4)With the help of finite element analysis software ANSYS,finite element analysis of sandstone creep under test equivalent conditions was carried out to derive creep deformation curves of specimens with different initial damage degrees,analyze the influence of initial damage degree on creep characteristics from the perspective of numerical simulation,and analyze the creep deformation law at different locations in the axial direction of the specimens.This paper has 72 pictures,19 tables and 90 references.