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.