SMALL DAMS PETITS BARRAGES

Thickness of
pervious layer
Thick
Design
method
Grout
Blanket
Full
surface
paving
Sketch Applications
It is effective in a pervious
bedrock layer.
It effectively prevents
piping. It is inexpensive.
It is extremely expensive.
It is only used to restrict
leakage to an extremely
small quantity.
During the execution of the upstream blanket especial care must be taken with
superficial cracks as a consequence of the drying clayed soils.
5.7.1.2 Blanket Grouting Method
This is a method that restricts seepage of reservoir water by controlling the vertical
seepage flow inside the reservoir, and by making the seepage route longer it lowers the
hydraulic gradient accordingly and it reduces the seepage quantity.
● Natural blanket
In the case where impervious soil is deposited as the surface layer of the pervious
ground to form a natural blanket, the effective seepage length xr created by the blanket is
obtained by equation (1)
xr =
t ・ d・
k
……………………………………………………………………(1)
k1
Bedrock→
Curtain grouting
Curtain grouting
Impervious blanket
Pervious bedrock layer
Pervious layer
Full surface paving
Pervious layer
Where:
t:blanket thickness(m)
d:pervious ground thickness(m)
k1:coefficient of permeability in the vertical direction of the blanket(m/s)
k:coefficient of permeability of the foundation ground(m/s)
And xr is, as shown in Figure 5.8, the horizontal distance of the blanket necessary to
create the head loss (Δhb). This means that the head loss caused by this blanket is equivalent
67