Abstract:
Bank stabilization structures are used to prevent the loss of valuable land within
the urban environment and the decision for the type of structure used depends on the
properties of the stream. In the urban areas of Southern Ontario there is a preference for
the use of armourstone blocks as bank stabilization. The armourstone revetment is a free
standing stone structure with large blocks of stone layered vertically and offset from one
another. During fieldwork at Forty Mile Creek in Grimsby, Ontario armourstone failure
was identified by the removal of two stones within one column from the wall. Since the
footer stones were still in place, toe scour was eliminated as a cause of failure.
Through theoretical, field, and experimental work the process of suction has been
identified as a mode of failure for the armourstone wall and the process of suction works
similarly to quarrying large blocks of rock off bedrock streambeds. The theory of lateral
suction has previously not been taken into consideration for the design of these walls.
The physical and hydraulic evidence found in the field and studied during experimental
work indicate that the armourstone wall is vulnerable to the process of suction.
The forces exerted by the flow and the resistance of the block determine the
stability of the armourstone block within the wall. The design of the armourstone wall,
high surface velocities, and short pulses of faster flowing water within the profile could
contribute to armourstone failure by providing the forces needed for suction to occur,
therefore adjustments to the design of the wall should be made in order to limit the effect.
