# Effect of Water Content and Cementation on the Shear Characteristics of Remolded Fault Gouge
## 1 Introduction  
Fault sealing performance is critical for preventing fluid leakage and maintaining structural integrity in underground gas storage [1], CO\({}_{2}\) geological sequestration [2], and oil and gas development [3, 4]. Effective fluid-sealing fault zones commonly feature a zoned structure, generally comprising a damage zone, a fractured zone, and the host rocks, progressing outward from the fault core [5, 6]. The characteristics of these zones depend significantly on the in situ stress conditions, rock properties, and regional tectonic activity [7]. Within the fault structure, fault gouge--a fine-grained, clay-rich material primarily found in the damage zone--greatly influences fault sealing and stability [8, 9, 10]. In brittle rock formations, damage and fractured zones are typically well-developed [11, 12, 13]. Conversely, in plastic rock formations, fracture zones are less developed, with clay-rich materials filling fractures through plastic deformation, enhancing fault sealing properties [14; 15]. Additionally, fluids within the fractured zone can become supersaturated and precipitate cements, such as quartz and carbonates, which seal the fractures and thereby enhance the sealing capacity of the fractured zone as well [16; 17]. Due to inherent structural complexities and weaknesses, faults are often susceptible to reactivation along pre-existing fault planes during subsequent tectonic movements. Moreover, fault sealing performance may vary significantly across different periods or different segments owing to variations in internal structural characteristics and interactions among various zones [18; 19; 20]. Such reactivations and ruptures are significantly influenced by the mechanical properties of fault gouge, characterized by low cementation strength and high frictional coefficients [21; 22; 23]. Therefore, comprehensive knowledge of fault gouge's mechanical behavior is essential for predicting fault stability and ensuring geological storage safety. Previous studies have extensively investigated both natural and remolded fault gouge. [PERSON] et al. [24] systematically sampled fault gouge from five typical faults in China and measured key mechanical parameters, such as clay content, water content, and shear strength. [PERSON] et al. [25] conducted double direct shear tests under a normal stress of 25 MPa on fault gouge composed of 50% montmorillonite and 50% quartz particles, demonstrating that porosity evolution controls the mechanical properties of fault gouge. Specifically, higher porosity corresponds to lower peak shear strength. [PERSON] et al. [26], as well as [PERSON] and [PERSON] et al. [27], found that the frictional strength of fault gouge decreases as clay content increases through shear tests. [PERSON] et al. [28] and [PERSON] et al. [29] investigated the relationship between the strength parameters of remolded fault gouge, water content, and cementation degree. [PERSON] et al. [30] performed triaxial shear tests on 15 types of fault gouge to explore the relationship between frictional strength and water content. [PERSON] et al. [31] conducted shear experiments on three types of remolded fault gouge with different fabrics, indicating that as water content increases, the softening characteristics of fault gouge initially strengthen and then weaken. Collectively, these studies underline structural characteristics, cementation, and water content as primary influencing factors on fault gouge strength [32; 33; 34]. Although previous studies investigated various factors influencing the strength of fault gouge, most of these studies focused on the effect of a single factor on the fault gouge's mechanical properties. Furthermore, some studies, such as those by [PERSON] et al. [28] and [PERSON] et al. [30], used natural fault gouge samples or natural fault gouge powders for their experiments. However, due to the inherent heterogeneity of natural rocks and the variability of sampling locations, these samples often suffer from limited reproducibility and consistency.