dams with impervious membrane of asphalt concrete - Balwois

The body of a dam, as shown in the figure, consists of quarry run limestone, placed in layers and
compacted by vibrating rollers. It is divided into two zones, the grading and permeability of which
increases from upstream to downstream.
As for the watertight membrane on the upstream face, it extends to the walls and the bottom of the whole
reservoir. The membrane consists of a single layer (I) of dense-graded bituminous mix, 8 cm thick, which
is spread over a binding layer (BN) of semi-open graded bituminous mix, 10 cm thick. The binding layer
rests on a drainage layer (DR) of crushed stone. The system of pipes and drainage galleries makes it
possible to check and measure any seepage throughout the membrane.
The downstream face of the dam is lined with a layer of top soil, placed inside appropriate prefabricated
works.
As we can see from this example, opposite from the two types of the design that we mentioned earlier,
there are many other possibilities to arrange the layers. The Cesima Dam is just a case and not the only
one when layers are spread in a different way.
SPECIAL DESIGN CONSIDERATIONS
In order to improve the asphalt concrete dam’s safety, the following advices are:
• To control time after time the differential response to load along the membrane.
• To improve the ability of the system to yield or deform without cracking.
• To minimize the consequences of failures.
• Regular inspection of the system.
• To have an access for repairs and rehabilitation.
• To increase the durability of the outer impervious layer of the membrane.
Special attention must be paid to the critical connection details, at the interfaces of membrane-plinthcutoff,
in order to prevent or minimize seepage.
CONCLUSION
Earlier, as an disadvantage of a dam with impervious membrane of asphalt-concrete was mentioned their
height, nowadays this is no longer a problem. Since the height of those types of dams has started to rise,
we can suggest their use, especially in the cases as followed:
• Where the foundation for a dam consists of strong rock and where is an ample supply of strong
granular embankment construction material.
• Where no impervious soil for an earth core exists within an economical distance.
• Where severe wave action is expected in the reservoir and where rock for a rip rap blanket
involves an exceptionally long distance.
• If the cost of appurtenant structures is considerable, the most economical design for the whole
structure may be achieved with an upstream impervious membrane.
• In circumstances where long rainy seasons exist or where the construction period is limited.
Therefore, it can be concluded that earth and rock fill dams with asphalt concrete membrane are
concurrent with other types of dams, because they are easily and faster build and are more economical. If
the design and construction of those dams is based on the favorising circumstances, than dams with
impervious membrane of asphalt concrete are sustainable.
BALWOIS 2008 - Ohrid, Republic of Macedonia - 27, 31 May 2008 6