High energy waters erode undercut slopes and facilitate deposition of fine-grained sediments at slip-off slopes [53].
Preventive and remedial measures frequently have been taken to keep the channel open, and a program to stabilize its banks was designed to draw away rainfall that might otherwise undercut its slopes.
Lu et al. (1998) speculate that the pre-1952 landslide was a major contributing factor to the occurrence of the 1990 landslide, as it directed the stream into the opposite valley wall, causing undercutting of the slope.
Other significant interrelated failure processes of the dam models included wetting front propagation, downstream face saturation, exfiltration, hydraulic cracking, toe bifurcation, downstream slope undercutting, sloughing and late-stage overtopping.
Factors that showed the most significant correlation with the total depth of undercutting were found to be the vertical distance of the undercut unit from the slope crest, the relative position of the undercut unit from the slope crest, the total thickness of the undercut unit, joint spacing within the undercut unit, and the slake durability index of the undercutting unit.
The regression analysis resulted in an R2 value of 0.61, with the depth of undercutting correlating most strongly with a closer relative position of the undercut unit to the slope crest above it and to a closer spacing of orthogonal joints within the undercut unit.
Bench-and-slope landscape results from sequential removal (horizontal stripping) of layers via undercutting, wearing away, and slope retreat.
As described in the previous section, these landslides are attributed to the undercutting of the slopes associated with gullying.
The fabricated comb-drive actuator, with comb finger of +1° profile and 0.025 μm undercut, and folded beam of −1° slope and 0.075 μm undercut, is measured and compared with the models where both show consistent results.
This type of failure was primarily initiated by sapping erosion which occurred as a result of steady exfiltration of water from the downstream toe; which by extension, triggered gradual undercutting and debuttressing of the downstream slope as the mobilized mass 'flowed' downstream, thus lowering the dam height (Fig. 5a).
These knickpoints propagated upstream along trunk and tributary rivers, undercutting and destabilizing nearby slopes, of which the oldest is a paleosurface dated to ca. 150 kyr by cosmogenic nuclide dating.
