1. Introduction
A description of the interfacial friction behaviors of the geomaterials would be of considerable help in predicting catastrophic failure progress, typically landslides and earthquakes. However, the geomaterials possess porous randomness and multiphase heterogeneity. Consequently, there still is challenging to characterize the interfacial contact process and reveal the friction mechanism of the geomaterials. Now, the predictions of geological disasters mainly focus on empirical or semi-empirical methods deriving from the various real-time monitoring data on displacement and physical parameters of the geomaterials. However, the prediction of geological failure progresses based on physical mechanisms is still an urgent problem to be overcome.
Existing experimental studies focus on the relationship between the friction behavior and sliding velocity of the fault geomaterials (Dieterich, 1978; Marone, 1998; Tsutsumi and Shimamoto, 1997; Scholz and Engelder, 1976; Kilgore et al. , 1993), and widely consider the effects of temperature and saturation (Scholz, 2019; Blanpied et al. , 1995; Blanpiedet al. , 1998; Kubo and Katayama, 2015; Morrow et al. , 2000). Scholz and Engelder (1976) reported a logarithmic velocity dependence of friction coefficient in sliding experiments of granite. Then, Dieterich (1978) and Michael L. Blanpied et al. (1998) observed similar phenomena on Wsterly granite. They pointed out that granite had inherent velocity-dependent frictional weakening and temperature-dependent frictional strengthening at all velocities. Also, the velocity-dependent frictional weakening is very prevalent in rock avalanches (Hu et al., 2018; Wang et al., 2018; Hu et al., 2022) and glacier avalanches (Iversonet al. , 2017; Thøgersen et al. , 2019; Gräff and Walter, 2021), even some flow slides (Wanget al. , 2014; Pei et al. , 2017). In addition, velocity-dependent frictional strengthening has been observed in the clayed sliding zone of landslides (Wang et al. , 2010; Schulz and Wang, 2014; Miao and Wang, 2021). The velocity-dependent friction behavior controls the dynamics of faults and landslides on earth and other planets. These researches have provided new insights into the macro- or micro-mechanisms of the failure progress and velocity-dependent behaviors of geomaterials. Nevertheless, we know little about the underlying physics controlling the velocity-dependent friction behaviors of the geomaterials. Thus, it is urgent to establish a theoretical friction model based on the physical nature of the geomaterials.
Most experimental data-driven theoretical models are semi-empirical formulas lacking physical universality (Dieterich, 1979; Ruina, 1983; Scholz, 1998). Bowden and Tabor (B&T) considered the frictional strength of an interface as the product of an average velocity-dependent contact strength and the ratio of the actual contact area to the total contact area (Bowden and Tabor,1964; Berthoud et al. , 1999). The largely empirical rate-and-state (R/S) friction equations and Aging formulation (Dieterich, 1979; Dieterich, 1972) have been widely used to model time-varying friction phenomenology in rock (Marone, 1998; Dieterich, 1979; Beeler et al. , 1994) and a diverse set of industrial materials (Berthoud et al. , 1999; Prakash, 1998; Ronsin and Coeyrehourcq, 2001; Shroff et al. , 2014; Heslot et al. , 1994; Carlson and Batista, 1996). Einat Aharonov et al. (2018) developed a microphysics-based creep model, calculating the velocity and temperature dependence of contact stresses during sliding. Their model also focused on the thermal effects of shear heating. Recently, Casper Pranger et al. (2022) proposed transient viscous rheology that produces shear bands that closely mimic the rate- and state- dependent sliding behavior of equivalent fault interfaces.
The above theories successfully explain the effect of sliding on friction, especially in a high-velocity sliding state. Most models come from further developments of B&T theory or R/S theory. However, these models are not deep enough to reveal the physical nature of contact and friction behavior of geomaterials. Thus, some parameters of these models remain empirically fitted. The above models do not consider how the deformation of single contact asperities transitions to the entire contact surface because they ignore the stochastic processes of contact and friction. The shear and normal stress are the averages of a contact interface in the models. Moreover, some key influences, such as porosity and permeability, on the friction behavior of geomaterials are still not considered in these models. So, these empirically fitted models are challenging to predict interfacial friction behaviors for geomaterials accurately.
Thus, there has an urgent need to establish a physics-based interfacial friction model coupling micro-contact to macro-friction, which further discloses the effect mechanism of multi-physical factors on the friction behavior of geomaterials. Hence, we develop a multiscale friction model that can describe microscopic contact creep and macroscopic velocity-dependent friction. And we use the new model to examine the effects of slip velocity, temperature, porosity, and permeability on the frictional behavior of geomaterials. Finally, we discuss the physical mechanisms of these influences. Our model can elucidate the physics of interfacial friction for geomaterials and has the potential to predict geological disaster progresses.