Experiment and Mechanism Investigation on Freezing-Thawing of Sandstone with Different Water Contents

Freezing-thawing cycles seriously affect the safety of underground engineering in cold regions. At present, most research studies focus on the effect of number and freezing temperature on freezing-thawing cycles. As another important factor, the mechanism of rock mass water content affecting freezing-thawing is less studied. This paper studied the influence of the water content on mechanical property, microstructure, and acoustic emission characteristics of sandstone. The results indicated that the uniaxial compressive strength (UCS) and elastic modulus (E) of sandstone after 20 freezing-thawing cycles decreased as the water content increased. However, the decreasing rate of UCS gradually decreased, while the decreasing rate of E gradually increased. Furthermore, the empirical formulas of UCS and E about water content were obtained. The porosity and plasticity of sandstone after 20 freezing-thawing cycles increased as the water content increased. The empirical formulas of UCS and E about water content were obtained. The porosity and plasticity of sandstone after 20 freezing-thawing cycles increased as the water content increased. The decreasing trend of UCS with porosity was the same as that of UCS with water content. The failure form of sandstone gradually changed from splitting failure to shear failure. The results of the acoustic emission test showed that the stress-strain curves combined with acoustic emission ring counting could reveal the damage evolution process of sandstone during loading.

Acoustic Emission Test of Changlongshan Pumped Storage Power Station Steel Bifurcation Pipe

The maximum test load of Changlongshan pumped storage power station steel bifurcation pipe is 10MPa. To ensure the safety of the water pressure test, acoustic emission is used to monitor the main welds of the crescent rib steel bifurcation and main cone. Taking NO.3 pipe’s data as an example, acoustic emission source location system was used to find the possible position of harmful defects, through the activity and intensity of the acoustic emission sources to confirm the defect significance. After analysis, the acoustic emission integrated level of the steel bifurcation pipe is in level II, the pipe’s data comply with the design requirements.