Monitoring and Maintenance of Stabilization Works
Selection of the correct approach, or an effective compromise, is a matter of
engineering judgement focused on the question "Why did the work fail?".
If the need for maintenance is due to conditions not expected to recur, in which
neither the type of protection nor the basic design criteria were at fault, then the original
material may be adequate for repair. For example, bare areas on the bank slope caused by
differential slope settlement can be rearmored with the original material of the same size and
thickness, if the subgrade has stabilized.
If the type of protection is still deemed suitable, but the original design criteria were
apparently not conservative enough, then the same method can be used, but with more
conservative design criteria. For example, stone armor displaced by hydraulic forces can be
replaced with stone of a greater size and layer thickness.
However, if the method itself appears at fault because of unforeseen circumstances,
consider the use of a different technique or material for repairs. For example, if toe scour
adjacent to a rigid armor or flexible mattress revetment exceeds the capacity of those
materials to accommodate the scour, then consideration should be given to using stone for
repair of the toe protection.
The great variation in protection methods and stream characteristics makes it
infeasible to further discuss details of maintenance techniques. However, there are two
materials which, between them, are useful over such a wide range of conditions that they
merit special mention: stone and vegetation.
Stone is often the material of choice because it can be used in almost any
maintenance situation. In particular, damaged work is often characterized by
irregular contours and the possibility of further scour or settlement. Stone's
self-adjustment ability is well adapted to this situation.
Vegetation is well suited for marginal situations where bank erodibility is low,
and no emergency exists, but where taking no remedial action would lead to
eventual failure. Vegetation is often inexpensive yet effective where it is
supported by adjacent structural protection. Planting can be done at the
optimum season, since no emergency exists.