Study On Acoustic Thermal Response Characteristics And Damage Evolution Law Of Freeze-Thaw Sandstone During Uniaxial Compression

Unstable failure of frozen rock is the fundamental cause of engineering disasters in tunnels,oil and gas pipelines and other infrastructures in cold regions.Accouate and effective prediction of freeze-thaw rock instability process can provide reliable precursor information for structu ral failure of rock engineering under low temperature environment,which has important theoretical value and practical significance for damage early warn ing and damage evolution law of rock engineering in cold regions.In this paper,the Cretaceous Luohe Formation sandstone in Binchang mining area is taken as the research object.The uniaxial compression acoustic emission-thermal infrared real-time monitoring test of sandtone under different freeze-thaw cycles was carried out and the acoustic emission and thermal infrared information during the failure process of freeze-thaw sandstone are obtained.The damage mechanics theory is applied to study the acoustic-thermal precursor information and damage evolution process of freeze-thaw sandstone under uniaxial compression load,which provides a scientific basis for predicting the damage of sandstone under freeze-thaw action.The main work and conclusions are as follows:(1)The acoustic emission-thermal infrared real-time monitoring test of sandstone under uniaxial compression after 0,5,10,20 and 30 freeze-thaw cycles was completed.The variation of the acoustic emission parameters,thermal infrared radiation response characteristics and mechanical properties of the frozen-thawed sandstone were obtained.(2)The freeze-thaw cycle leads to the deterioration of mechanical properties of sandstone,and the decrease rate of mechanical parameters increases with the increase of freeze-thaw cycles.Freeze-thaw action changed the failure mode of rock samples.Under the action of freeze-thaw cycles,the failure mode of rock samples gradually changed from the shear failure without freeze-thaw to the mixed failure of splitting shear.After 30 freeze-thaw cycles,the rock samples showed X-shaped conjugate inclined plane shear failure mode.(3)Acoustic emission ringing count and acoustic emission energy are produced near the peak stress in rock samples with less freeze-thaw cycles.With the increase of freeze-thaw cycles,the time of AE ring count and AE energy appear in advance.The change of acoustic emission ringing count and energy can reflect the failure characteristics of freeze-thaw sandstone under uniaxial compression.The synchronous increase of ringing count and acoustic emission energy can be regarded as a precursor of rock failure.Before the peak strength,the sudden drop of r value and b value shows that the large-scale cracks in the rock sample are connected,which is the precursor of rock sample failure and can be used as an early warning of rock sample failure.The change rule of RA-AF value shows that the acoustic emission signal of freeze-thaw sandstone failure is tensile-shear composite signal,and the shear signal is dominant.The change rule of RA-AF value provides a basis for the identification of freeze-thaw sandstone failure mode.(4)Thermal infrared temperature and infrared thermography have good response to each failure stage of frozen-thawed sandstone.Before the destruction of frozen-thawed sandstone,thermal infrared temperature increases sharply,and infrared thermography shows obvious anomalies before the destruction.With the increase of freeze-thaw cycles,the thermal infrared temperature fluctuation frequency of rock samples before destruction is high,and the thermal image has obvious changes.The temperature distribution histogram and three-dimensional thermal image evolution map of the important time nodes in the loading process realize the evaluation of the temperature anomaly area and high temperature range of the rock surface.The thermal infrared warning index k value based on rock element distribution is proposed.The change rule of k value in the process of freeze-thaw sandstone failure is the same as that of rock sample temperature,and it is advanced.With the increase of freeze-thaw times,the time gap between k value and temperature increases sharply.(5)According to the acoustic-thermal precursor information coupling characteristics of sandstone under different freeze-thaw cycles,the order of acoustic-thermal abnormal signals is:thermal infrared temperature→acoustic emission ringing count→acoustic emission energy→infrared thermal image.The freeze-thaw cycle enhances the sensitivity of acoustic-thermal precursor information.(6)Based on the energy principle,the variation trends of strain energy,thermal infrared radiation energy and acoustic emission energy in the process of rock fracture are calculated and analyzed.The variation trends of the three energies are consistent.The damage evolution pattern of freeze-thaw sandstone based on acoustic-thermal energy is proposed.The failure of freeze-thaw sandstone is the result of multiple energy coupling.(7)Based on the damage mechanics theory,the constitutive model of freeze-thaw sandstone is constructed with the acoustic-thermal parameters in the failure process of rock samples as the benchmark,which well reflects the failure process of freeze-thaw sandstone.Compared with the test,it is found that the error of the thermal infrared parameter damage constitutive model is smaller than that of the acoustic emission parameter constitutive model,and the error is smaller and smaller with the increase of the number of freeze-thaw cycles.