Here at the Calaveras Dam Replacement Project we are
building what is called an earth and rock-fill dam. The replacement Calaveras Dam,
like all so-called embankment dams, is made of mostly compacted earth (see a cross section of the future dam below). An important aspect of this type of dam is the
management of water. All earthen dams leak, the important thing is to control
where the water flows to protect the integrity of your dam. In the case of the Calaveras Dam Replacement
project, we accomplish this with blankets and curtains.
No fooling! Here’s how it works. For years, the crews onsite have been
constructing an entire dam that extends more than 100 feet below the base of
the future dam. We call this a grout
curtain. Grout for those of you not in the construction industry is a special
mix of cement that can be injected or literally blown onto a surface to seal
it.
Grout Curtains
As you can see in the photo from 2015, crews drilled
countless small diameter holes into the bedrock a hundred feet down below the
future dam and injected the holes with pressurized grout. The grout effectively
seals up cracks and fractures within the rock underneath the new dam. We did this for years. Why is this grout
curtain so important? It prevents water from seeping underneath the new dam and
undermining it. In essence we drilled an
entire new dam underneath the future dam.
Drainage Blanket
If you thought grout curtains alone were enough to protect
the future Calaveras Dam, guess again! We need blankets, too. More specifically
a drainage blanket. The drainage blanket prevents water from exiting to, and
damaging, the down-stream face of the dam (the face of the dam away from the
reservoir). At the end of the drainage
blanket we are constructing a ‘mini dam’ made out of the same clay material as
the core to capture any water in the drainage blanket. You can see the drainage blanket being constructed here. This ‘mini dam’ is also
known as the seepage barrier. This
seepage water is then collected in an inspection well to monitor the condition
of the dam.
The Calaveras Dam Replacement Project, along with its
blankets and curtains, is more than 80% complete.
See you around the Valley!
