Unexpected ground conditions and how to avoid them: case examples - Practical Engineering Geology - page 320

Figure 7.14 3D
model of postulated
failure mechanism,
Pos Selim.

Counter
scarp

Bulging

Foliation
dipping into
slope

Faults

detailed face mapping by geologists, review of displacement data and
examination of the various stages of failure, a model was derived that
can be used to explain the nature of the failure, the vectors of
movement and the fact that it has not yet failed catastrophically but is
bulging at one section of the toe (Figures 7.14 & 7.15) . Key aspects of
the geology are frequent joints that are oriented roughly orthogonal to
the schistosity, three persistent faults cutting across the failure and

a) c)

joint girdle

foliation

b)

rock
bridge

joint

Figure 7.15 (a) Digital model of Pos Selim landslide with movement vectors compiled by comparing
an orthophoto with an as-built CAD drawing (courtesy of Dr Andy Hansen). (b) Stereo plot with
concentration of poles near centre representing the foliation dipping back into the slope at about
14 degrees. Most joints form a girdle at about 90 degrees to the mean pole of the foliation. (c)
Explanation for main body of landslide - exploiting jointing and kicking out at the toe and upwards,

along foliation.