# Effect of Water Content and Cementation on the Shear Characteristics of Remolded Fault Gouge
## 2 Methods and Materials
### Experimental Procedure  
Figure 3 illustrates the shear testing procedure for the fault gouge samples. Prior to the experiments, all mineral samples used to prepare the fault gouge are placed in an oven at 70 \({}^{\circ}\)C and dried for 24 h to ensure complete dryness. After drying, the mineral samples are weighed together with Portland cement powder according to the predetermined mass ratios and degrees of cementation, followed by thorough mixing for at least 10 min to ensure uniform distribution of the dry components. The total mass of the dry components is calculated based on the fixed volume of the ring cutter mold (6.18 cm in diameter and 2 cm in height) to ensure a consistent dry density of 1.5 g/cm\({}^{3}\) across all specimens.  
Distilled water is then added to the mixture to achieve the specified water content levels, followed by further mixing using the same procedure to ensure consistent water distribution. The amount of added water is calculated so that the wet density matches the expected value based on the combined mass of solids and water. After uniform stirring,  
\begin{table}
\begin{tabular}{c c c c} \hline
**Sample** & **Cementation Degree (\%)** & **Water Content (\%)** & **Normal Pressure (kPa)** \\ \hline C0W10 & & 10 & 100/200/300/400 \\ C0W15 & & 15 & 100/200/300/400 \\ C0W20 & 0 & 20 & 100/200/300/400 \\ C0W25 & & 25 & 100/200/300/400 \\ C  
the mixture is molded into ring cutter samples. The total mass of each molded specimen is then measured to confirm that the actual wet density meets the target value.  
The prepared ring cutter samples are placed in a consolidation apparatus and consolidated under a pressure of 400 kPa for 2 h to ensure the stability and consistency of the samples. Following consolidation, the samples undergo geotechnical direct shear tests using a ZJ-4 direct shear apparatus (Guodian Nanjing Automation Co., Ltd., Nanjing, China) under four normal pressures: 100, 200, 300, and 400 kPa. The horizontal shear displacement rate is set at 0.8 mm/min throughout the test. Each shear test is terminated once the horizontal displacement reaches 8 mm, which ensures full development of post-peak shear behavior.  
Under these experimental conditions, shear stress-shear displacement curves are obtained for the fault gouge samples at each water content and degree of cementation. Shear strength parameters--cohesion (\(c\)) and internal friction angle (\(\varphi\))--are determined based on the Mohr-Coulomb failure criterion. Specifically, the peak shear stress under each normal stress level (100, 200, 300, and 400 kPa) is plotted as the vertical axis against the corresponding normal stress as the horizontal axis. A linear regression is then performed on the peak points. The intercept of the best-fit line corresponds to the cohesion \(c\), while the slope of the line determines the internal friction angle \(\varphi\), calculated as \(\varphi\) = arctan (slope).  
These experimental procedures are designed to systematically investigate the shear characteristics of fault gouge under varying physical conditions, providing experimental data and theoretical support for further exploration of the mechanical behavior and deformation mechanisms of fault gouge. The findings are expected to offer valuable insights for assessing fault stability, particularly in applications related to underground gas storage and geological sequestration.