围压对红砂岩应力波传播特性的影响

围压可以改变岩石内部微观结构，导致波阻抗发生变化，进而影响应力波在岩石中的透反射能力。为探索围压对岩石应力波传播特性的影响，通过一维应力波理论推导，得到了岩石应力波透射系数和反射系数随波阻抗值的变化关系。用红砂岩制备短试件和长试件，基于动静组合加载实验系统进行不同围压下的应力波传播试验，分析岩石的纵波波速、波阻抗、反射系数和透射系数与围压的关系。根据岩石波阻抗与围压的经验模型，结合理论分析所得的透射系数与波阻抗的关系，得到不同围压下透射系数的理论值，并与相应的试验值进行对比，证明理论分析结果的正确性。综合分析了岩石的纵波波速、波阻抗、透射系数和反射系数与围压的关系，得到围压对红砂岩应力波传播衰减特性的影响规律。结果表明，岩石短试件和长试件的纵波波速及波阻抗与围压之间均具有正向相关性。随着围压的增加，短试件反射系数的绝对值逐渐减小，透射系数逐渐增大，长试件的透射系数逐渐减小，透射系数和反射系数均与围压呈二次函数关系。纵波波速、波阻抗、透射系数及反射系数与围压的关系都表明，增大围压有利于应力波穿过岩石，减小其幅值的衰减。

Influence of confining pressure on stress wave propagation character istics in red sandstone

Confining pressure has a great effect on the internal microstructure of the rock,and results in a change in wave impedance,which affects the propagation attenuation laws of the stress wave in the porous rock subjected to high stress.In order to investigate the effect of confining pressure on the characteristics of stress wave propagation in rock,the relationships between both reflection coefficient and transmission coefficient with the wave impedance of rock were established based on one dimensional stress wave theory.Then the short and long rock specimens were made of red sandstone,and the experiments of stress wave propagation in specimens under different confining pressures were carried out based on the modified Split Hopkinson Pressure Bar (SHPB).Also,the experimental longitudinal wave velocities,wave impedances,reflection coefficients and transmission coefficients of rock under different confining pressures were analyzed.Based on the empirical relationship between wave impedance and confining pressure,and the theoretical relationship between wave impedance and transmission coefficient,the theoretical transmission coefficients under different confining pressures were obtained and compared with experimental values.The comparison shows that the differences between theoretical and experiment values were very small,and verifies the theoretical analysis of transmission and reflection coefficients are valid.The influence laws of confining pressure on the stress wave propagation along red sandstone were obtained by the comprehensive analysis of longitudinal wave velocity,wave impedance,transmitted and reflected coefficients of rock under different confining pressures.The results show that both the longitudinal wave velocity and wave impedance of rock specimen increase with the increase in confining pressure.With the increase of confining pressure,the transmission coefficient of short specimen increases,and the absolute value of reflection coefficient decreases,the transmission coefficient of long specimen,however,decreases gradually.The variation trends of both the reflection coefficient and trans mission coefficient with confining pressure can be fitted with quadratic function.All of the above variation tendencies show that the increase of confining pressure decreases the attenuation of its amplitude.