174
11 Detecting Fingerprints of Gravity Erosion Drivers …
duration, and slope gradient and height. The sensitivity analysis focuses on g n and
g v . The increase ratios of R g (%) are obtained as follows:
R g = (g 2 − g 1 )/g 1
(11.1)
where g 1 is the total volume of all failures, g n , or the individual volume each event,
g v, for an experiment before the triggering element was changed, cm
3 ; g 2 is that after
the triggering element was changed, cm
3 . An increased ratio of the above output in
percent is calculated with the growth rate of a parameter, while other parameters are
fixed in an experiment:
S = R g /R t
(11.2)
R t = (t 2 − t 1 )/t 1
(11.3)
where S is the sensitivity parameter to analyze the sensitivity of the triggering elements on the failure number and volume of each scar morphology; t is one of the
triggering elements, e.g., slope height, slope gradient, rainfall duration, and rainfall
intensity; R t is the increased ratio of the triggering element, %; t 1 is the value before
being changed in an experimental group; t 2 is that after being changed. This approach
allows for a qualitative investigation of the effect of conditioning factors.
11.3 Results and Discussion
11.3.1 Characteristics of Failure Scars
The classification of failure-scar morphology is valuable because it can reflect the
stability of slope scar, the triggering method of the mass failure, and the frequency and
size of the gravity erosion. We observed the scar morphologies of all gravity erosions
in ten sets of gully bank collapse experiments (Table 11.1). Then, we classified the
scars into the following six types based on the shapes of the intersection lines:
(1) Translational face (Tf). The scar morphology, which is an inclined plane with
an intersection line consisting of a straight line, is termed the translational face
(Fig. 11.1a). This implies that the soil block fails along an almost planar failure
surface.
(2) Polygonal side (Ps). The scar morphology is called a polygonal-side when the
intersection line is a broken line. This kind of scar has at least two intersecting
planes, one of which is the low-angle incline plane, and another which is a
relatively steep surface. As shown in Fig. 11.1b, the Ps scar closely resembles
the shape of a stair-step.
11 Detecting Fingerprints of Gravity Erosion Drivers …
duration, and slope gradient and height. The sensitivity analysis focuses on g n and
g v . The increase ratios of R g (%) are obtained as follows:
R g = (g 2 − g 1 )/g 1
(11.1)
where g 1 is the total volume of all failures, g n , or the individual volume each event,
g v, for an experiment before the triggering element was changed, cm
3 ; g 2 is that after
the triggering element was changed, cm
3 . An increased ratio of the above output in
percent is calculated with the growth rate of a parameter, while other parameters are
fixed in an experiment:
S = R g /R t
(11.2)
R t = (t 2 − t 1 )/t 1
(11.3)
where S is the sensitivity parameter to analyze the sensitivity of the triggering elements on the failure number and volume of each scar morphology; t is one of the
triggering elements, e.g., slope height, slope gradient, rainfall duration, and rainfall
intensity; R t is the increased ratio of the triggering element, %; t 1 is the value before
being changed in an experimental group; t 2 is that after being changed. This approach
allows for a qualitative investigation of the effect of conditioning factors.
11.3 Results and Discussion
11.3.1 Characteristics of Failure Scars
The classification of failure-scar morphology is valuable because it can reflect the
stability of slope scar, the triggering method of the mass failure, and the frequency and
size of the gravity erosion. We observed the scar morphologies of all gravity erosions
in ten sets of gully bank collapse experiments (Table 11.1). Then, we classified the
scars into the following six types based on the shapes of the intersection lines:
(1) Translational face (Tf). The scar morphology, which is an inclined plane with
an intersection line consisting of a straight line, is termed the translational face
(Fig. 11.1a). This implies that the soil block fails along an almost planar failure
surface.
(2) Polygonal side (Ps). The scar morphology is called a polygonal-side when the
intersection line is a broken line. This kind of scar has at least two intersecting
planes, one of which is the low-angle incline plane, and another which is a
relatively steep surface. As shown in Fig. 11.1b, the Ps scar closely resembles
the shape of a stair-step.