## 3 Dynamic Compressive Mechanical Properties of Sandstone after Corrosion by Strong Alkali Solution
### Dynamic Compressive Strength and Dynamic Peak Strain Variation  
Under the condition of impact air pressure 0.60 MPa, the deterioration of dynamic compressive strength with corrosion time of the sandstone specimens corroded by strong alkali solution at different times is shown in Figure 6.  
It can be seen from Figure 6 that the dynamic compressive strength of the standard sandstone specimens without corrosion reached 204.11 MPa, while the dynamic compressive strength of the specimens decreased by 7.27%, 18.36%, 34.06%, 49.14%, and 53.53% after corrosion for five different times, respectively, compared with the non-corroded specimens. It shows that the dynamic compressive strength of the sandstone specimens corroded by strong alkali solution was obviously lower than that of non-corroded specimens, that is, it deteriorated more greatly; the dynamic compressive strength of the sandstone specimens corroded by different times with the extension of corrosion time showed a sharp decline in the early stage and a steady and slow decline in the later stage, and the dynamic compressive strength of the specimens corroded at 28 d was the smallest. We compared our results with those in [1,22] and found that compared with the sandstone specimens in our study, the dynamic compressive strength of the limestone specimens decreased less with the extension of corrosion time after corrosion by a strong alkali solution. The reason for this analysis is that the main component of the limestone is calcite, which is not easily dissolved in a strong alkali solution, and only a small amount of hydrolysis reaction exists, while the main component of sandstone is quartz, which easily reacts with OH\({}^{-}\) ions in strong alkali, and with the prolongation of corrosion time, the internal microfracture pores of the sandstone increased, leading to its structural deterioration and causing an obvious decrease in dynamic compressive strength, and the dynamic compressive strength of the specimens decreased in a quadratic function relationship with corrosion time, as shown in Equation (2). \[\sigma_{d}=0.2445t^{2}-10.571t+199.93\ (R^{2}=0.9942) \tag{2}\]  
where \(\sigma_{d}\) is the dynamic compressive strength of the specimen after corrosion at different times, MPa. The dynamic peak strain curve of the specimen after corrosion by the strong alkali solution for different times is shown in Figure 7.  
As can be seen from Figure 7, the dynamic peak strain of the sandstone specimen increases as a quadratic polynomial function with the extension of corrosion time, and the curve is fitted as shown in Equation (3). \[\varepsilon_{d}=-0.006t^{2}+0.3248t+14.042\ (R^{2}=0.9983) \tag{3}\]  
where \(\varepsilon_{d}\) is the dynamic peak strain of the sandstone after different times of corrosion by the strong alkali solution, \(10^{-3}\). Figure 6: Variation curve of dynamic compressive strength with the solution corrosion time. The dynamic peak strain of each sandstone specimen after different times of corrosion by a strong alkali solution is greater than that without corrosion, which shows that the strain-softening effect of sandstone specimens after corrosion placed in a strong alkali solution is significant, and the softening effect of the specimens will be enhanced with the increase in corrosion time. The \(\varepsilon_{d}\) value of sandstone specimens corroded for 1 d increased by 2.60% compared with that of non-corroded specimens. Compared with 1 d, the \(\varepsilon_{d}\) value increased by 2.73% at 3 d. The \(\varepsilon_{d}\) value after 7 d of corrosion increased by 8.13% compared with that after 3 d of corrosion.