Abstract
Fault gouge has special mechanical properties and remarkable engineering effects. Using a ring shear test, the strength properties of the differently colored remolded fault gouges of the Shendaogou Fault in Yan’an were studied by changing moisture contents and normal stresses. Chlorite and illite are the main clay minerals in fault gouges; differences in mineral composition make fault gouges appear in different colors. Besides clay minerals, the dried fault gouges disintegration in water is also due to the transformation of gypsum. The gradation of green fault gouge and multicolor fault gouge is better than that of the red fault gouge, while the fault gouges’ strain softening properties become weaker as the coarse grain content increases. Affected by water content and normal stress, the shear planes can be divided into three failure modes: peeling failure, grooved failure, and sliding failure. With the increase of water content, there will be a significant weakening on cohesion and friction angle. A new parameter, the “Normal Stress Threshold (NST),” is introduced as a critical value for the emergence of the strain hardening phenomenon, and the NSTs of different fault gouges are significantly different. The functions obtained from the relation of residual strength, peak strength, and normal stress can be used to calculate shear strength parameters under any normal stresses. In addition, the residual strength of fault gouge is obviously different from clay and loess, which can be qualitatively explained by clay particle contents.
Highlights
As one of the most important weak zones in rock mass, fault zone is a basic condition that controls engineering safety in mountain areas [1,2,3]
In the 1980s, Geng et al [5] explored the physical and mechanical properties of 75 kinds of fault gouges in five fault zones and analyzed their mechanical parameters, such as volume modulus, elastic modulus, elastic wave velocity, compressive strength, shear strength, and residual volumetric strain. e strength of the San Andreas Fault gouge was measured within 200 MPa confining pressure, and the results showed that the fault gouge strength was reduced by the pseudopore pressure generated by loosely bound water in clays [6]
A Bromhead SRS-150 ring shear apparatus developed by GCTS Company was used to carry out the shear test, as shown in Figure 9. e shear device is mainly composed of sample box and loading board
Summary
As one of the most important weak zones in rock mass, fault zone is a basic condition that controls engineering safety in mountain areas [1,2,3]. E interface of the different color fault gouge was found to be the weak point of shear strength Zhang and He [11] researched the frictional sliding behavior of clay minerals and their influences on fault mechanical properties and found that the fault strength showed a negative correlation with clay content, and the difference in clay mineral. Wang et al [20] conducted direct shear tests to analyze the influence of water content and cementation on fault gouge strength. The slipping properties of fault gouges are analyzed during the ring shear test, and the strength parameters under different water contents are obtained, which can be helpful in judging the mechanical behavior of fault gouges and studying the engineering geological mechanical effects of fault zones
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