11.1 A Retrospective Study on the Failure Scar on the Slope
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slope stability analysis such as the Swedish slice method, Bishop method, and Janbu
method, based on the conceptual arc-shaped scar to study the mass failure, also
present some limitations. As addressed by Xu and Low (2006), analysis based solely
upon circular slip surfaces may significantly overestimate the safety of the slope.
In many cases, the failure scar may deviate significantly from a circle or a plane
(Morgenstern and Price 1965). Therefore, the limitations simplifying the landform
hampered attempts to apply the classical methods forecasting mass failures (Deng
et al. 2011). In fact, the natural slip scars encompass a wide variety of surfaces that can
satisfy any failure mechanism, such as the scar with differing shear strength properties
or with complex pore-pressure distributions. Hence, to improve the accuracy and
practicability of the model prediction, future projections should avoid too simplified
conceptual scars and be based on a suitably complete mass-failure theory.
Sensitivity analysis plays an important role in exploring the triggering mechanisms of gravity erosion. The method helps to identify the most influential factors,
including geology, geomorphology, and climate. The eigenvalues of erosive precipitation, such as rainfall amount, intensity, and duration, are the primary driving forces
of gravity erosion on the Loess Plateau (Zhou et al. 2016; Zhou and Wang 1992), and
the soil water content, infiltration depth, specific weight, cohesiveness, and friction
angle change along with time during the rainfall infiltration period (Chang et al. 2013;
Stark et al. 2005). Meanwhile, a slope failure is generally located along the slope of
the stress concentration, while the geometry of the slope, such as slope shape, height,
gradient, etc., is a critical factor affecting the stress distribution of the slope (Zhang
and Fan 2015; Lu and Godt 2013). Global warming is expected to lead a more vigorous hydrological cycle, including more total rainfall and more frequent high-intensity
rainfall events (Nearing et al. 2004). Thus, the above-mentioned factors are complex
on the Loess Plateau, and are frequently affected by the rainfall-induced mass failures
with different occurrences and sizes. Hence, identifying the most influential factor
corresponding to the scar pattern may improve the accuracy and practicability of the
prediction model of gravity erosion. Xu et al. (2015a) proposed an increase-rateanalysis method to recognize the effect of each causal factor and of the combination
of factors on the susceptibility to gravity erosion. An advantage of the method is
that the influences caused by the randomness of the gravity erosion can be readily
overcome. Moreover, the method is easy to understand, simple to calculate, and its
result is easy to read. Nevertheless, the average number of mass failures in an event
of rainfall is not a suitable factor with which to analyze the sensitivity on the number
of gravity erosion. Here, we improved the method using the total value (i.e., the total
volume and number of mass failures in an event of rainfall) to evaluate the variations
in the gravity erosion concerning the changes in various causal factors.
The objective of this study is to evaluate the natural factors affecting the distribution of scar morphology on the gully bank. To that end, we conducted a series of
steep slope collapse experiments, and we used a topography meter designed by us
to observe the patterns of failure scars in the process of mass failure. Moreover, the
increase-rate-analysis method was used to analyze the sensitivity of gravity erosion
corresponding to different scar morphologies.
171
slope stability analysis such as the Swedish slice method, Bishop method, and Janbu
method, based on the conceptual arc-shaped scar to study the mass failure, also
present some limitations. As addressed by Xu and Low (2006), analysis based solely
upon circular slip surfaces may significantly overestimate the safety of the slope.
In many cases, the failure scar may deviate significantly from a circle or a plane
(Morgenstern and Price 1965). Therefore, the limitations simplifying the landform
hampered attempts to apply the classical methods forecasting mass failures (Deng
et al. 2011). In fact, the natural slip scars encompass a wide variety of surfaces that can
satisfy any failure mechanism, such as the scar with differing shear strength properties
or with complex pore-pressure distributions. Hence, to improve the accuracy and
practicability of the model prediction, future projections should avoid too simplified
conceptual scars and be based on a suitably complete mass-failure theory.
Sensitivity analysis plays an important role in exploring the triggering mechanisms of gravity erosion. The method helps to identify the most influential factors,
including geology, geomorphology, and climate. The eigenvalues of erosive precipitation, such as rainfall amount, intensity, and duration, are the primary driving forces
of gravity erosion on the Loess Plateau (Zhou et al. 2016; Zhou and Wang 1992), and
the soil water content, infiltration depth, specific weight, cohesiveness, and friction
angle change along with time during the rainfall infiltration period (Chang et al. 2013;
Stark et al. 2005). Meanwhile, a slope failure is generally located along the slope of
the stress concentration, while the geometry of the slope, such as slope shape, height,
gradient, etc., is a critical factor affecting the stress distribution of the slope (Zhang
and Fan 2015; Lu and Godt 2013). Global warming is expected to lead a more vigorous hydrological cycle, including more total rainfall and more frequent high-intensity
rainfall events (Nearing et al. 2004). Thus, the above-mentioned factors are complex
on the Loess Plateau, and are frequently affected by the rainfall-induced mass failures
with different occurrences and sizes. Hence, identifying the most influential factor
corresponding to the scar pattern may improve the accuracy and practicability of the
prediction model of gravity erosion. Xu et al. (2015a) proposed an increase-rateanalysis method to recognize the effect of each causal factor and of the combination
of factors on the susceptibility to gravity erosion. An advantage of the method is
that the influences caused by the randomness of the gravity erosion can be readily
overcome. Moreover, the method is easy to understand, simple to calculate, and its
result is easy to read. Nevertheless, the average number of mass failures in an event
of rainfall is not a suitable factor with which to analyze the sensitivity on the number
of gravity erosion. Here, we improved the method using the total value (i.e., the total
volume and number of mass failures in an event of rainfall) to evaluate the variations
in the gravity erosion concerning the changes in various causal factors.
The objective of this study is to evaluate the natural factors affecting the distribution of scar morphology on the gully bank. To that end, we conducted a series of
steep slope collapse experiments, and we used a topography meter designed by us
to observe the patterns of failure scars in the process of mass failure. Moreover, the
increase-rate-analysis method was used to analyze the sensitivity of gravity erosion
corresponding to different scar morphologies.