Selection and Design of Channel Rehabilitation Methods
considered the benchmark against which other bank stabilization techniques are judged, not only because
it can be designed to solve almost any problem, but because it can be designed precisely, thus its
performance and cost can be predicted more reliably than for other methods. Other commonly used forms
of stone armor include: trenchfill revetment which is simply a standard stone armor blanket with a massive
stone toe constructed in an excavated trench behind the river bank, in anticipation that the river will
complete the work by eroding to the revetment, causing the stone toe to launch down and armor the
subaqueous bank slope; windrow revetment which is simply an extreme variation of a trenchfill revetment
consisting of rock placed on the floodplain surface landward from the existing bankline at a pre-determined
location, beyond which additional erosion is to be prevented; and longitudinal stone toe which is another
variation of the windrow revetment with the stone placed along the existing streambed rather than on top
bank.
Some armor materials other than stone which have the ability to adjust to scour, settlement, or
surface irregularities are: concrete blocks; sacks filled with earth, sand, and/or cement; and soil-cement
blocks. Armor materials which have been occasionally used in the past, but which have serious engineering
and environmental shortcomings are: rubble from demolition of pavement or other source; slag from steel
furnaces; and automobile bodies.
Advantages: Because its performance has been so thoroughly analyzed by research and practical
application in a wide range of conditions, stone armor can be designed with an especially high degree of
precision and confidence. The American Society of Civil Engineers' Task Committee on Channel
Stabilization Works stated in 1965 that:
Stone is the most commonly used material for upper bank paving for revetment
works, and in most cases has proved superior to other materials because of
durability and ability to conform to minor irregularities in the slope (ASCE, 1965).
Since that time, further development and application of manufactured proprietary armor materials, and
increasing emphasis on environmental considerations and the use of vegetation for erosion control, has
tempered that observation to some degree. However, the favorable attributes of stone armor are not
diminished by the increasing availability of alternative materials. Furthermore, well-graded stone can often
be placed without a separate underlayment material, because it provides permeability without exposing
bank material. This characteristic may be a crucial factor when comparing the economics of alternative
armor materials.
Disadvantages: Stone may be more costly than other materials, depending on its availability.
It requires heavy equipment for efficient placement on large projects. It may be considered unaesthetic for
some locations, and may not compare favorably with other materials in some environmental circumstances.
6.1.1.2 Rigid Armor
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