Study On Creep Characteristics Of Anthracite Under Pore Water Pressure

Studies have shown that the pore pressure in rock mass has a certain influence on creep characteristics.At present,the creep constitutive model proposed in the creep test of water-bearing coal and rock can accurately describe the creep characteristics of water-bearing coal and rock,which lays a theoretical foundation for the research on the creep characteristics of coal and rock under the action of pore pressure.However,the early achievements are often focused on the creep properties of coal under the influence of temperature,axial pressure and confining pressure,while the research on the influence of coal porosity on the creep characteristics under the action of pore pressure is neglected.Therefore,this paper takes anthracite coal of shenghua coal industry as the research object,Uses CT scanner to explore its porosity,and classifies it according to the porosity interval.Uniaxial creep tests of coal and rock with different porosity interval,creep tests of coal samples with the same porosity interval under different pore pressure,creep tests of coal samples with different porosity interval under the same pore pressure,creep curves of coal samples with different porosity interval under the same pore pressure were obtained.The creep characteristic curves of coal samples under graded loading are studied and their creep properties are analyzed.On this basis,the nonlinear viscous element and plastic element are combined and connected in series with the traditional Burges model to establish a creep model that can describe the nonlinear viscoelastic plastic characteristics of coal under the action of pore pressure of coal and rock with different porosity,and the relevant parameters in the equation are fitted.The results are as follows:(1)The porosity of anthracite specimens was analyzed by CT scanning technology,and the specimens were divided into three categories according to the porosity ranges of 5%?10%,10%?15% and 15%?20%.Through the strength test of specimens in each classification interval,it is found that the strength of specimens decreases gradually with the increase of porosity.The influence of porosity on the strength of specimens is obvious.When the porosity of specimens changes from 5%?10% to 10%?15% and 15%?20%,the uniaxial compressive strength decreases by 9.6% and 22.3%.(2)Uniaxial creep test shows that the instantaneous strain variable of specimens with different porosity ranges increases with the increase of porosity.It indicates that at the early stage of stress loading,the pores are gradually compressed,and the larger the porosity,the more obvious the deformation,and with the increase of loading classification,this compaction phenomenon gradually disappears.(3)The study shows that the changes of pore pressure and porosity under low stress loading will affect the instantaneous creep of creep,resulting in different initial strain values of the creep curve.(4)With the increase of porosity and pore pressure,the time for specimens to enter the accelerated creep stage from stress loading at the failure stage is gradually shortened,and the time to enter the accelerated creep stage from the deceleration creep stage is also gradually shortened.(5)The classical Newton body was improved,new mechanical elements were introduced to describe the accelerated creep stage,and a creep constitutive model was established to fully describe the creep characteristics of coal samples with different porosity under different pore pressure.The creep model parameters were regressive analyzed and identified with software Origin2018,and the creep parameters of the new constitutive model were obtained.The applicability of the model is verified and it is concluded that the model can well reflect the creep characteristics of specimens with different porosity ranges under the action of pore pressure.