Friday, June 30, 2017

Building Dams in Earthquake Regions, Part II

As Californians, we live with the possibility of earthquakes.  Here at the Calaveras Dam Replacement Project we are in the middle of constructing a new dam that will be strengthened to resist seismic forces and withstand a 7.25 magnitude earthquake.  Dam technology has evolved since we built the original dam in 1925. 

If you missed our first blog about the technology used in construction of the original dam, see it here. The methods used in constructing the new Replacement Calaveras Dam are very different. Here’s why.

New Construction Methods

We are using state of the art dam technology and engineering to enhance the safety of this large civil structure.

A Sound Foundation

Our director Dan Wade says that building an earth and rock fill dam is a lot like painting a house. You need to strip all the old paint off the walls to get to good wood. You need to prime the surface so it will hold the new paint. The very last thing you do is paint.  We have been doing the preparation for the building of our dam for 6 years. We have moved more than 7 million cubic yards of soil to reach competent rock as a solid foundation of the new dam. 

A cross section of the replacement dam showing the different zones. Green is upstream (the reservoir side), light yellow is downstream, the clay core is in the center, and the narrow yellow strips are the drains and filters.


Controlling Water Seepage

We have drilled the grout curtains (see our previous blog about curtains and blankets) extending more than 100 feet below the dam’s foundation to control water seepage. We have done even more work to treat the foundation of the core of the dam, which is made of impervious clay. Remember the drain blanket? That also is constructed on the downstream face (the dry side away from the reservoir) to control water. The new dam will have various filter zones and drain zones on both sides of the dam to control the movement of water so it does not compromise the structural integrity of the dam.

Resisting Seismic Forces

A wide core will help the new dam be robust. In addition, the materials placed in this dam will be compacted using heavy machinery.

Here's the dam being constructed as it looks now. The different zones are clearly visible.

The complete removal of unstable rock and soil to form a solid foundation, careful design and placement of filters and drains within the dam to control water, extensive grouting and sealing of the foundation of the dam, a robust core and heavy compaction of all materials enable the replacement Calaveras Dam to withstand seismic forces and serve our customers for generations to come.

Monitor our progress at building the dam here at sfwater.org/sunolvalley.


See you around the Valley! 

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