11.3 Results and Discussion
185
In comparison, the frequency and size of the mass failure with different scar
patterns were more susceptible to the change of slope gradient than they were to
height (Fig. 11.5). Zhu and Hong (2011) also discovered that the slope gradient was
more sensitive to the slope stability than to slope height. Slope gradient determines
the state and distribution of stresses in the slope mass, and controls the stability and
mode of instability of the slope (Dai et al. 2017; Zhang and Liu 2010). In addition,
slopes with lower gradients required more cumulative precipitation before a mass
failure occurred (Wu et al. 2017). For the rainfall characteristics, rainfall intensity and
duration were equally important in influencing the frequency of mass failure with the
scar Uc, while the rainfall duration significantly affected its size (Fig. 11.5a, b). This
could explain why shallow landslides are typically induced by intense rainfall, while
deep-seated landslides require rainfall with a longer duration (Zhang et al. 2016).
It is the increased rainfall duration that increases the water content and pore-water
pressure and thus reduces the soil shear strength, eventually resulting in mass failure
(Xu et al. 2013). Meanwhile, the rainfall intensity affects the rainfall kinetic energy,
which shortens the pathway for water to approach deeper soil strata, thus increasing
the possibility of mass failure (Lin and Chen 2012).
11.3.6 Hazard Risks Suggested from the Scars
The damage caused by a mass failure largely depends on its velocity and volume, but
the velocity is extremely difficult to evaluate systematically. Hence, some researchers
assessed the hazard of mass failure using the landslide type, volume, and scar (e.g.,
Jaiswal et al. 2011). In this study, the mass volume and scar morphology were applied
to assess the damage caused by gravity erosion. The result of the study is that the
damage caused by the translational-shaped failure may be much more serious than
that caused by the other shaped failures. Particularly, the large-scale rapid mass
failures corresponding to the Tf scar occurred on the steep slope, and it was often
accompanied by a crack at the top of the slope (Fig. 11.8). Due to the crack occurrence
on the top of the slope, the mass failure with the Tf scar will widen the channel. In
other words, once gullies develop, they increase the connectivity in the landscape,
hence raising the risk of flooding and reservoir sedimentation in a catchment (Ionita
et al. 2015; Poesen et al. 2003). Derbyshire (2001) also pointed out that the mass
failure with the scar Tf has the characteristics of rapid disintegration and high sliding
velocities, and this kind of failure is abundant in the loess region of North China.
As we know, rapid landslides pose lethal threats, whereas slow movements damage
properties but seldom cause fatalities (Iverson et al. 2000). Thus, the mass failure
with the scar Tf, which moves quite rapidly downhill, is the most violent gravity
erosion and might cause great harm to buildings and lives.
Although the slope gradients of the initial landform were 70° or 80° in the experiments, multiple mass failures occurred in one region, resulting in a decrease of
the slope gradient. Therefore, the arc-shaped scars, including Uc, Dc, and Co, also
occurred in the experiments. In the experiments L1, L3, and L6, the scar morphology
185
In comparison, the frequency and size of the mass failure with different scar
patterns were more susceptible to the change of slope gradient than they were to
height (Fig. 11.5). Zhu and Hong (2011) also discovered that the slope gradient was
more sensitive to the slope stability than to slope height. Slope gradient determines
the state and distribution of stresses in the slope mass, and controls the stability and
mode of instability of the slope (Dai et al. 2017; Zhang and Liu 2010). In addition,
slopes with lower gradients required more cumulative precipitation before a mass
failure occurred (Wu et al. 2017). For the rainfall characteristics, rainfall intensity and
duration were equally important in influencing the frequency of mass failure with the
scar Uc, while the rainfall duration significantly affected its size (Fig. 11.5a, b). This
could explain why shallow landslides are typically induced by intense rainfall, while
deep-seated landslides require rainfall with a longer duration (Zhang et al. 2016).
It is the increased rainfall duration that increases the water content and pore-water
pressure and thus reduces the soil shear strength, eventually resulting in mass failure
(Xu et al. 2013). Meanwhile, the rainfall intensity affects the rainfall kinetic energy,
which shortens the pathway for water to approach deeper soil strata, thus increasing
the possibility of mass failure (Lin and Chen 2012).
11.3.6 Hazard Risks Suggested from the Scars
The damage caused by a mass failure largely depends on its velocity and volume, but
the velocity is extremely difficult to evaluate systematically. Hence, some researchers
assessed the hazard of mass failure using the landslide type, volume, and scar (e.g.,
Jaiswal et al. 2011). In this study, the mass volume and scar morphology were applied
to assess the damage caused by gravity erosion. The result of the study is that the
damage caused by the translational-shaped failure may be much more serious than
that caused by the other shaped failures. Particularly, the large-scale rapid mass
failures corresponding to the Tf scar occurred on the steep slope, and it was often
accompanied by a crack at the top of the slope (Fig. 11.8). Due to the crack occurrence
on the top of the slope, the mass failure with the Tf scar will widen the channel. In
other words, once gullies develop, they increase the connectivity in the landscape,
hence raising the risk of flooding and reservoir sedimentation in a catchment (Ionita
et al. 2015; Poesen et al. 2003). Derbyshire (2001) also pointed out that the mass
failure with the scar Tf has the characteristics of rapid disintegration and high sliding
velocities, and this kind of failure is abundant in the loess region of North China.
As we know, rapid landslides pose lethal threats, whereas slow movements damage
properties but seldom cause fatalities (Iverson et al. 2000). Thus, the mass failure
with the scar Tf, which moves quite rapidly downhill, is the most violent gravity
erosion and might cause great harm to buildings and lives.
Although the slope gradients of the initial landform were 70° or 80° in the experiments, multiple mass failures occurred in one region, resulting in a decrease of
the slope gradient. Therefore, the arc-shaped scars, including Uc, Dc, and Co, also
occurred in the experiments. In the experiments L1, L3, and L6, the scar morphology