## 5 Conclusions  
This study involved mechanical testing of weakly cemented sandstone under both saturated and unsaturated conditions. It utilized experimentally derived mechanical parameters to establish a numerical simulation model, which was employed to analyze changes in the physical and mechanical properties of weakly cemented sandstone when exposed to water. Additionally, numerical simulations were used to fit and the compare permeability curves with indoor permeability experiments. The study aimed to analyze the reasons for changes in permeability under different stress conditions and explore the associated flow characteristics. The main conclusions are as follows:  
1. After being saturated with water, weakly cemented sandstone experiences a significant reduction in uniaxial compressive strength, accompanied by a transition from brittle to plastic failure. The stress-strain curves from numerical simulations closely matched the experimental results. The use of the Hoek--Brown method for estimating rock deformation parameters ensured the accuracy of subsequent permeability simulations. 2. Indoor permeability experiments revealed a distinctive pattern in the permeability curve of weakly cemented sandstone, which differed from conventional sandstone. The permeability curve exhibited a trend resembling a \"\(\sqrt{\cdot}\)\" characterized by an initial gradual reduction, followed by an increase, and eventual stabilization. The stress-strain curve did not exhibit a stress-drop phase after reaching peak strength. The numerical simulation results showed excellent agreement with the experimental outcomes. Subsequently, simulations of permeability curves under varying confining pressures were conducted, revealing a trend of initial reduction followed by an increase, providing a foundational basis for the development and analysis of numerical models related to weakly cemented strata. 3. An analysis of the causes of changes in permeability from a pore perspective indicated that confining pressure restricted the expansion of micro-cracks in the rock. Pore pressure prompted the development of fractures, starting in high-pressure areas and extending to low-pressure areas. Permeability gradually increased with rising pore pressure, while increased confining pressure led to a decrease and subsequent increase in permeability for weakly cemented sandstone. Axial compression initially reduced permeability before gradually increasing it. In numerical simulations, the value of normal stiffness showed a negative correlation with permeability before stabilizing. 4. Using programming to monitor the quantity of fissures during the compression numerical simulation, a damage parameter 'D' was introduced, refining the expression of the damage parameter. It was observed that, with increasing confining pressure, the damage parameter initially decreased and then rapidly increased. Additionally,  
Figure 18: Changes of rock damage variable D under pore- pressure difference. the magnitude of the hydraulic pressure differential exhibited a direct proportional correlation with the damage parameter. This comprehensive exploration provides valuable insights into the complex interplay between hydraulic pressure, mechanical properties, and the dynamics of permeability in weakly cemented sandstone. In the end, we have deepened our understanding of the hydraulic characteristics under varying stress conditions..  
Conceptualization, W.Z., H.L. and M.C. ; methodology, W.Z., H.L. and M.C. ; software, W.Z. and H.L. ; validation, W.Z., X.L. and Z.C. ; investigation, W.Z., W.C. and Z.C. ; data curation, W.Z. and H.L. ; writing--original draft preparation, W.Z. and H.L. ; writing--review and editing, W.Z., H.L. and Z.C. All authors have read and agreed to the published version of the manuscript.