202
12 Effects of Gravity Erosion on Particle Size Distribution …
Table 12.3 PSDSS for various depths
Sampling depth
(cm)
Sample no. PSDSS (%)
d 50 (mm)
Clay
Silt
Sand
<0.002 mm 0.002–0.05 mm 0.05–2 mm
0–5
US1
1
31
68
0.105
US2
0
28
72
0.110
Mean
1
29
70
0.108
40–45
US3
1
39
60
0.072
US4
1
41
59
0.073
Mean
1
40
60
0.073
120–125
US5
1
45
54
0.055
US6
1
35
64
0.062
Mean
1
40
59
0.059
Fig. 12.5 The median
particle size of soil (d 50 )
versus soil depth
0
0.03
0.06
0.09
0.12
2.5
d
50 (mm)
Soil depth (cm)
42.5
122.5
of sand-sized particles in channel flows also showed a further decrease to a mean
value of 44% after mass failures in the comparison of 61% prior to mass failures.
Nevertheless, the deposited sediments on the channel bed had a sand content of 70%,
which was a clear indication of the selective deposition of coarse particles after mass
failures. Such selective accumulation of coarse materials on the channel beds can
form armouring surfaces in the field.
This study demonstrated the combined complex effects of source materials, erosion types, and selective detachment and deposition processes on PSDSS before and
after mass failures, though some of these individual factors have been investigated
by others (Asadi et al. 2011; Beuselinck et al. 2002; Collin et al. 1997; Gover 1985).
Our experimental results in PSDSS also compare well with the previous field studies