If you are new to the world of dam construction, you might
wonder what types of materials are used in building one. Today’s blog will focus on what types of materials
we are using to construct the new Calaveras Dam. Calaveras Dam is an earth
embankment dam. Earth embankment dams
tend to be constructed of all types of geologic materials.
Calaveras Dam, July 2017
The picture above was taken recently; from it you can
visually see the different materials. Let’s start with the middle and the most
important material used in our dam, the core.
The Core of Calaveras Dam
Zone 1 & 1A—aka…the Core
The core is made up of clay.
Clay is very dense and less permeable than most materials. Our new dam will have a large core, which will help ensure that the dam withstands a 7.2 magnitude earthquake. The clay used in our dam has been ‘borrowed’
from the south end of Calaveras Reservoir.
The core is taking shape.
Zone 1A- Core’s foundation
At the bottom of the core, you will find Zone 1A material.
This clay is plastic, pliable clay, or another words, clay that has a Play-dohtm
like consistency. Zone 1A material is
placed on the foundation’s bedrock and acts as a seal against water flow
beneath the dam.
The core is the most important element of the dam and
therefore must be protected. We protect
our core by using filters in both the upstream (reservoir side) and the
downstream (dry side) of the dam to control the seepage of water and remove it
safely from the Dam.
Zone 2 and 2A- Sand
Upstream zones are made of sand (Zone 2A) and large gravel (Zone 5A)The
downstream filters or chimneys are made of sand (Zone 2) and pea gravel (Zone
3).
Zone 5-Rock Fill
Further protection for both the core and filters is provided
by rockfill shells. The upstream shell consists of hard durable rock because it
will be submerged in the reservoir, Zone 5 material. This material consists of metamorphic rock
known as blue schist.
The downstream shell (Zone 4) consists of onsite material
from a geologic formation known as Temblor Sandstone. While this is a sedimentary rock, it tends to
degrade into a gravelly, sandy soil and is best suited for drier conditions
than the upstream shell.
Zone 6- Rip Rap
Wave action in the reservoir due to wind can erode most
earthen materials. Large durable rocks
are placed on the slopes of the dam at the waterline to prevent this erosion. This
is Zone 6 also known as rip rap.
Image courtesy of www.fhwa.dot.gov
See you around the valley!
