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Accelerating creep before catastrophic failure commonly follows a power‐law velocity‐acceleration relationship, with the exponent typically near 2 but often evolving from 1 to 2 at a certain point, indicating a dynamic transition. The underlying mechanisms, however, remain unclear. Here we investigate this transition by monitoring the slip displacement of clayey soil during fluid‐injection creep experiments. This transition is discontinuous in the first run but becomes continuous in the initially pre‐sheared sample. Using a regularized rate‐and‐state friction model, we explicitly examine the relationship between the exponent and the frictional properties of the soil. This model describes the dynamic transition, with the exponent evolving from 1 to 2 across a broad range of frictional parameters. Furthermore, by incorporating idealized shear localization processes, the model qualitatively reproduces the shear‐history‐dependent transition. Our study demonstrates that a combination of structural evolutions and frictional properties may explain slow and fast slips observed in various shear systems. Plain Language Summary: Predicting when materials will fail or natural hazards will occur is complex because it involves various physical processes and parameters. An empirical power‐law velocity‐acceleration relationship has proven effective and reliable for forecasting creep failure and natural events like landslides and volcanic eruptions. Although its exponent is typically 2, it can evolve from 1 to 2 over time, indicating a dynamic transition between two distinct acceleration regimes. In our fluid‐injection experiments on clayey soil, we observe a slow‐to‐fast transition in slip displacement and a multi‐layered shear zone. This transition is initially discontinuous but becomes continuous when the sample is pre‐sheared. To elucidate the mechanism, we use a slider block to simplify landslide movement, with the friction of the slip surface governed by a regularized rate‐and‐state friction model. For a velocity‐weakening slip surface, this model predicts a shift from velocity‐independent to velocity‐weakening steady‐state friction, demonstrating a continuous slow‐to‐fast transition with the exponent evolving from 1 to 2. Furthermore, the combination of friction and shear localization processes qualitatively reproduces the discontinuous transition observed in experiments. These results indicate that slow and fast slips can be modulated by both frictional property and structural evolution, encouraging the consideration of their combined effects. Key Points: Fluid‐injection creep experiments on clayey soil show two distinct acceleration regimes, with a dynamic transition based on shear historyThe regularized rate‐and‐state friction model describes the power‐law velocity‐acceleration relationships and exponents for both regimesThe model, coupled with idealized shear localization in a multilayer structure, qualitatively reproduces the history‐dependent transitions [ABSTRACT FROM AUTHOR]

Grain comminution is commonly observed in numerous geological settings. To elucidate the role of grain comminution in dry granular friction, we sheared breakable halite (NaCl) grains using a ring‐shear configuration at a constant slip rate under various normal stresses. We observed transient frictional behaviors: a constant regime exhibiting a high friction coefficient at small slip displacements, and a weakening regime showing a substantial decay in friction at large slip displacements. The characteristic slip lengths for both regimes decreased with normal stress and were characterized by similar exponents. Micro‐X‐ray tomography revealed the evolution of microstructure from distributed grain comminution to progressive shear localization for these two regimes. We propose that the filling processes of comminuted fine particles, during which fine particles saturate and then overflow the shear zone, define transient frictional behaviors. This study may hold significant implications for natural shear systems, given the ubiquity of comminution and localization phenomena. Plain Language Summary: Grain comminution and structural evolution are common phenomena in natural settings, including earthquake faults and landslides. However, their role in granular friction remains unclear. To investigate this, we experimentally sheared breakable NaCl grains to simulate the processes within growing fault zones and visualized microstructural evolution using micro‐X‐ray computed tomography (CT). We observed two distinct frictional behaviors: a constant regime exhibiting a high friction coefficient at small slip displacements, and a weakening regime showing a substantial decay in friction at large slip displacements. The characteristic slip lengths for both regimes decreased with normal stress. Micro‐observations revealed drastic grain comminution and segregation processes in the constant regime, while the weakening regime showed progressive shear localization evolving from multiple discontinuous shear planes to one extremely localized shear plane. The higher constant friction appeared to result from large grain contacts, while the substantially lower steady‐state friction arose from comminuted fine particle contacts. We propose that grain comminution generates fine particles, gradually filling the pores within the shear zone in the constant regime, ultimately leading to frictional weakening by effectively reducing large grain contacts. The characteristic lengths defining transient behavior may be influenced by geometrical complexities and boundary conditions in various geological settings. Key Points: Sheared granular halite exhibits constant friction at small slip displacement and substantial weakening at large displacementCharacteristic slip lengths for constant friction and weakening decrease with normal stress and are characterized by similar exponentsThe production, saturation, and overflow of comminuted fines in the shear zone are key factors determining transient frictional behavior [ABSTRACT FROM AUTHOR]

This article presents the stress-strain characteristics of loess stabilized by SiO2 nanoparticles of different diameters. Atterberg limits, X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and specific surface area tests were also carried out. The phase characteristics, chemical composition, microstructure, and specific surface area of the stabilized loess were analyzed. The addition of SiO2 nanoparticles was found to improve the mechanical properties of loess soil effectively. [ABSTRACT FROM AUTHOR]