176
11 Detecting Fingerprints of Gravity Erosion Drivers …
(3) Convex (Co). If the intersection line is approximating an arc, and its corresponding center is in the inner slope, the scar morphology is known as a convex scar.
The Co scar, characterized by a gentle upper slope and steep lower slope, is
given in Fig. 11.1c.
(4) Upward concave (Uc). The Uc scar is defined as the intersection line that is close
to an upward concave arc. This means that the scar is an upward-arc surface
with a reverse foreside, gentle middle, and steep tail. The Uc scar is similar to
the crescent-shaped bed form, as shown in Fig. 11.1d.
(5) Downward concave (Dc). The Dc scar is a downward-arc surface. Morphologically speaking, a Dc scar is different from an Uc scar for the reason that the
center of the downward-arc is placed in the downside of the scar. Generally, a
Dc scar has lower stability compared with a Uc scar. Figure 11.1j shows a Dc
scar, which looks like a spoon-shaped cavity or parabolic cavity on the slope.
(6) Irregular appearance (Ia). A few irregular appearances also showed up in the
experiments; they were composed of at least two kinds of surfaces mentioned
in the previous paragraphs.
As shown in Table 11.1, ten sets of gully bank collapse experiments were conducted at the slope heights of 1 and 1.5 m, and slope gradients of 70° or 80° under
the rainfall intensities of 0.8 and 2 mm/min, respectively. Experimental results show
that the number of mass failures of the scars Tf, Dc, Uc, Ia, Ps, and Co were
134, 76, 69, 9, 7, and 3, respectively. That is, the number of mass failures in the
experiments corresponding to the scars Tf, Dc, Uc, Ia, Ps, and Co amounted to
45, 26, 23, 3, 2 and 1% of the total, respectively. Meanwhile, the total volume of
failures for six distinct morphological types, namely Tf, Uc, Dc, Ps, Ia, and Co were
1030.2 × 10
3 , 363.4 × 10
3 , 287.0 × 10
3 , 52.7 × 10
3 , 27.6 × 10
3 , and 10.8 × 10
3
cm
3 /m, and their volumes accounted for 58, 20, 16, 3, 2 and 1% of the total, respectively. This fact implies that Tf, Uc, and Dc were three types of major scars occurring
in the processes of gravity erosion on the steep loess slope, among which the Tf was
the most crucial.
The large-scale and frequent mass failures may harm both local buildings and
lives. In the experiments shown in Fig. 11.2, the peak volume of the individual
mass failures with the Tf, Uc, and Dc scars accounted for 78, 17, and 5% of the total
amount of whole peak events. Meanwhile, the frequencies of mass failure occurrences
corresponding to Tf, Uc, and Dc amounted respectively to 60, 30, and 10% of the total
number in all of the maximum-mass failures. Consequently, on the steep slope made
by hand with loess and under intense rainstorms, hazards caused by the translationalshaped failures may be much more serious and hazardous than those caused by the
other shaped failures.
11 Detecting Fingerprints of Gravity Erosion Drivers …
(3) Convex (Co). If the intersection line is approximating an arc, and its corresponding center is in the inner slope, the scar morphology is known as a convex scar.
The Co scar, characterized by a gentle upper slope and steep lower slope, is
given in Fig. 11.1c.
(4) Upward concave (Uc). The Uc scar is defined as the intersection line that is close
to an upward concave arc. This means that the scar is an upward-arc surface
with a reverse foreside, gentle middle, and steep tail. The Uc scar is similar to
the crescent-shaped bed form, as shown in Fig. 11.1d.
(5) Downward concave (Dc). The Dc scar is a downward-arc surface. Morphologically speaking, a Dc scar is different from an Uc scar for the reason that the
center of the downward-arc is placed in the downside of the scar. Generally, a
Dc scar has lower stability compared with a Uc scar. Figure 11.1j shows a Dc
scar, which looks like a spoon-shaped cavity or parabolic cavity on the slope.
(6) Irregular appearance (Ia). A few irregular appearances also showed up in the
experiments; they were composed of at least two kinds of surfaces mentioned
in the previous paragraphs.
As shown in Table 11.1, ten sets of gully bank collapse experiments were conducted at the slope heights of 1 and 1.5 m, and slope gradients of 70° or 80° under
the rainfall intensities of 0.8 and 2 mm/min, respectively. Experimental results show
that the number of mass failures of the scars Tf, Dc, Uc, Ia, Ps, and Co were
134, 76, 69, 9, 7, and 3, respectively. That is, the number of mass failures in the
experiments corresponding to the scars Tf, Dc, Uc, Ia, Ps, and Co amounted to
45, 26, 23, 3, 2 and 1% of the total, respectively. Meanwhile, the total volume of
failures for six distinct morphological types, namely Tf, Uc, Dc, Ps, Ia, and Co were
1030.2 × 10
3 , 363.4 × 10
3 , 287.0 × 10
3 , 52.7 × 10
3 , 27.6 × 10
3 , and 10.8 × 10
3
cm
3 /m, and their volumes accounted for 58, 20, 16, 3, 2 and 1% of the total, respectively. This fact implies that Tf, Uc, and Dc were three types of major scars occurring
in the processes of gravity erosion on the steep loess slope, among which the Tf was
the most crucial.
The large-scale and frequent mass failures may harm both local buildings and
lives. In the experiments shown in Fig. 11.2, the peak volume of the individual
mass failures with the Tf, Uc, and Dc scars accounted for 78, 17, and 5% of the total
amount of whole peak events. Meanwhile, the frequencies of mass failure occurrences
corresponding to Tf, Uc, and Dc amounted respectively to 60, 30, and 10% of the total
number in all of the maximum-mass failures. Consequently, on the steep slope made
by hand with loess and under intense rainstorms, hazards caused by the translationalshaped failures may be much more serious and hazardous than those caused by the
other shaped failures.