Mechanical deterioration effect and damage evolution characteristics of soft sandstone with different water-immersed heights under uniaxial compression

Soft sandstones are known to deteriorate with increasing water saturation. This study explores the effects of different immersion heights on the failure characteristics of soft sandstone obtained from the second member of the Paleogene Eocene Lushi Formation. Uniaxial compression strength (UCS) tests are performed on the rock samples with acoustic emission (AE) monitoring. The results show that water reduces the required stress level for initiating and expanding microcracks within the samples, severely affecting the damage characteristics. With an increase in immersion height, soft sandstone’s uniaxial compressive strength and elastic modulus linearly decrease. The P-wave propagation velocity also gradually decreases, and the number, activity, main peak frequency, energy, and amplitude peak of AE events decrease. There is a negative correlation between the main peak frequency of acoustic emission and the crack scale in the rock samples, and the AE characteristics better reflect the damage and failure characteristics of rock samples. In general, raising the immersion height increases the deterioration effect on the soft sandstone. Furthermore, the results of UCS and AE monitoring are then used to establish a simplified damage constitutive relationship of soft sandstone with different water immersion heights and the instantaneous and cumulative damage variables calculation method.