Degradation Mechanism Study Of Mechanical Properties Of Sandstone Under The Interaction Of Chemical Corrosion And Freeze-thaw Erosion

The rock experienced groundwater, chemical corrosion such as acid rain in the rock engineering in cold regions, the mechanical properties, the deformation characteristics and failure characteristics affected by freezing and thawing erosion and chemical etching dual function. The damage degree and change of pore fracture,destroy all closely related with freeze-thaw erosion, chemical corrosion and their coupling effect. For the study of stress-strain characteristics and pore change of rock under the coupled action of chemical erosion and freeze-thaw cycle, this paper set up a orthogonal test of different number of days and different chemical solution for comparison, on this basis set up a orthogonal test of different freeze-thaw cycles and different chemical solution, hereafter doing the rock uniaxial compression test,acoustic emission testing, ultrasonic testing and nuclear magnetic resonance(NMR)detection. Main research work includes:Place sandstone in three different pH value of chemical solution corroded then proceed to the freeze-thaw cycle test, on this basis, carry through ultrasonic testing,discusses the compressional wave velocity changes, and at the same time record parameters change and test pHenomenon. Sandstone after subjected to chemical corrosion and the freeze-thaw cycle effect, take nuclear magnetic resonance(NMR)detection, uniaxial compression test and acoustic emission monitoring, and discuss the relationship of porosity, T2 curve change and stress-strain curves under different corrosion environments, combined with macro mesoscopic angles were analyzed.Combining acoustic emission monitoring data and the stress-strain curve is analyzed,and discussed from the angle of energy and acoustic emission.Test results show that in the pure chemical corrosion and coupling effect of chemical erosion with freeze-thaw cycles, with the increase of soaking days and freeze-thaw cycles, the quality of the sandstone and ultrasonic longitudinal wave velocity had different degrees of reducing, acid-base property of solutions has a tendency to gradually change into neutral, sandstone in neutral salt solution afterfreezing and thawing appear to visible cracks; the peak strength and elastic modulus decrease, the failure mode is fracturing; porosity have different degree of increases,the second peak of T2 curve gradually developed, T2 spectrum area increased gradually; rate of acoustic emission events, the accumulative counts of acoustic emission events decrease gradually, the stress-strain stage corresponding to the biggest rate of acoustic emission events after corrosion in different chemical solution is different; the total input energy, elastic energy and dissipated energy all have a certain degree of decrease, dissipated energy experienced the process of a slow increase, remain unchanged and increases quickly with the stress increased. In a freezing and thawing cycle, when the solution gradually frozen, the chemical corrosion effect reduced little by little, and frost heaving force increases gradually;When the solution while melting, chemical corrosion effect gradually strengthen,frost heaving force gradually disappear, two kinds of erosion, mutual influence the mechanical properties of the sample.