Study On Creep Mechanical Characteristics Of Artificially Frozen Soft Sandstone In Cretaceous Stratum

In order to study the rheological damage caused by the freezing method in the Cretaceous water-rich soft sandstone strata in the western region,several important factors affecting the rheological properties of the frozen soft sandstone are:freezing temperature,water condition of the rock formation,freezing the wellbore or Confining pressure of roadway,etc.,relying on the National Natural Science Foundation of China(51774231)to carry out conventional mechanical tests and creep mechanics tests and other basic physical parameters of typical Cretaceous red sandstones in the background of Shaanxi Binchang Mengcun and Gansu Xinzhuang freezing shaft project.Experiments were conducted to investigate the freezing creep mechanical properties of the Cretaceous soft sandstone,and to establish a creep constitutive model using the Cretaceous frozen soft sandstone to provide guidance for the construction of the mine in the Northwest.After research and analysis,the following main conclusions are drawn:(1)By X-ray diffraction mineral composition analysis,it is concluded that the red sandstone is mainly quartz and feldspar minerals,accompanied by a small part of clay minerals,and magnified by electron microscopy,it is seen that the red sandstone is a large particle cemented and filled with clay minerals.And the interior contains small cracks,large pores and loose structure.(2)The peak intensity of red sandstone decreases exponentially with the increase of saturation,most of the strength loss is below 40%saturation,and the peak axial stra in of sandstone increases with the increase of saturation,and at 80%saturation.Increase the strain by the most.The long-term strength of red sandstone increases exponenti ally with saturation,and the long-term strength ultimate strength is about 60%-70%;the red sandstone creep variable increases linearly with saturation,and the red sandstone softens with water.(3)The strength of the Cretaceous soft sandstone increases with the decrease of te mperature,and the Poisson's ratio and elastic modulus increase with the decrease of temperature;the peak intensity increases with the increase of confining pressure,and the peak point strain increases with The increase of confining pressure increases linearly;soft sandstone obviously has pore encryption stage at normal temperature,and skipst his stage directly at low temperature.(4)The long-term strength of red sandstone increases with the decrease of temperature,and the stress level corresponding to long-term strength also increases.The stress level of long-term strength of red sandstone at 20? under 6 MPa confining pressure is 20%higher than that at room temperature.Red sandstone The amount of deformation decreases as the temperature decreases.(5)The stress level corresponding to the long-term strength of red sandstone incre ases with the increase of confining pressure,and the change of confining pressure from OMPa to 2MPa is the most obvious;the deformation of red sandstone decreases with the increase of confining pressure,indicating the lateral constraint of confining pressure.The deformation of the rock has a constraining effect;after the failure,the shear angle of the red sandstone increases as the confining pressure increases.(6)Through the summary of soft rock rheological theory,the influencing factors of soft rock creep characteristics mainly include:stress level,confining pressure,temperature,water content,freeze-thaw action,chemical corrosion,dry-wet cycle,seepage The damage constitutive model of the modified Kyle body is established by combining the experimental data analysis.The fitting data of the constitutive model can be optimized for the creep curve of the accelerated creep stage.