# Effect of Water Content and Cementation on the Shear Characteristics of Remolded Fault Gouge
## 5 Conclusions  
Through direct shear tests conducted on remolded fault gouge samples with varying water contents (10-30%) and cementation degrees (0%, 1%, 3%), key shear strength parameters--including shear strength, cohesion, and internal friction angle--are systematically analyzed. Coupled with correlation analysis and model development, the following conclusions are drawn:  
(1) Shear Strength:  
Higher water content reduces the shear strength of fault gouge, whereas a greater degree of cementation enhances it. When cementation becomes strong, the material's failure mode shifts from ductile sliding to brittle, cliff-type rupture. Because these two factors act in opposition, their coupling produces a nonlinear response: at low cementation, water simply weakens the gouge, but at high cementation, a small amount of moisture can first mobilize additional bonding and raise the peak strength before further wetting lubricates the shear plane and triggering a sharp strength drop. Thus, cementation not only counteracts the softening imposed by water but also governs whether the gouge behaves like a ductile soil or a brittle, weakly cemented rock. (2) Cohesion:  
Cohesion exhibits a peak at intermediate water contents. As cementation degree increases, cohesion consistently rises, regardless of water content. The presence of cementing agents strengthens the bonding between particles, enhancing the material's overall resistance to shear. (3) Internal Friction Angle:  
A clear inverse relationship exists between internal friction angle and water content. This decline is more significant in samples with low cementation. Under high cementation conditions, the internal friction angle shows minimal variation across different water contents, indicating that the added cementing materials stabilize the grain structure and reduce the water sensitivity of interparticle friction. (4) Regulatory Role of Clay Content:  
Clay content does not alter the overall trend of how shear strength parameters respond to changes in water content and cementation degree, but it significantly influences the magnitude of these responses. As clay content increases, the water content corresponding to peak cohesion and shear strength shifts to higher values, and the internal friction angle becomes more sensitive to moisture, showing a steeper decline. This indicates that fault gouge with a higher clay content tends to have higher plastic limits and exhibits stronger hydro-mechanical sensitivity. (5) Development and Validation of Predictive Models:  
A semi-empirical model is developed to quantify the shear strength of fault gouge as a function of water content and cementation degree by incorporating experimentally observed nonlinear and coupled effects into an extended Mohr-Coulomb framework. The proposed model accurately predicts both cohesion and internal friction angle and demonstrates strong agreement with experimental results (with \(R^{2}\) = 0.8309 for training and \(R^{2}\) = 0.8172 for testing). The model provides a practical and physically meaningful tool for estimating the shear strength behavior of fault gouge under variable hydro-mechanical conditions, offering valuable insights for fault stability assessment in geotechnical and geological engineering. Conceptualization, W.W., H.L., H.P. and S.B. ; Methodology, W.W.; Validation, H.L. ; Formal analysis, W.W.; Investigation, W.W. and S.B. ; Resources, H.L. ; Data curation, W.W.; Writing--original draft, W.W.; Writing--review & editing, W.W. and H.L. ; Supervision, H.L. ; Project administration, H.L. ; Funding acquisition, H.L. All authors have read and agreed to the published version of the manuscript. **Funding:** This research was funded by the National Natural Science Foundation (U22A20166), Excellent Young Scientists Fund Program of National Natural Science Foundation of China (No. 52122403), and Natural Science Foundation of Wuhan (No. 2024040701010062). **Institutional Review Board Statement:** Not applicable. **Informed Consent Statement:** Not applicable.