Calaveras Dam: Grouting in Numbers

What is grout? 

Most folks are likely familiar with using household grout for bathroom tiling work. Grout is a construction material commonly used to connect sections of concrete, fill voids, and seal joints. Grout is generally a mixture of water, cement, sand, and sometimes fine gravel.

How does it work for the dam?

The grouting operations are extremely important for the construction of the new replacement Calaveras Dam. Underneath the dam, we have designed a “grout curtain”. A grout curtain is a barrier that protects the foundation of a dam from water seepage and is used to strengthen the foundation of the dam. Essentially, the grout curtain fills cracks and fissures in the rock and works to control seepage and water flow. Our crews mix the grout onsite and inject the grout holes of the dam foundation. Holes are three inches in diameter and can reach up to a depth of 164 feet. Depending on the rock formation, the amount of injected grout used may differ.

Grouting Numbers Today

Over 589 holes have been grouted in the foundation. We have drilled almost 13 miles of grout holes. We have injected over 2.9 million pounds of cement grout into the foundation of the new dam.. How much grout is that? It is equivalent to approximately the same weight as 1,600 1967 model Volkswagen Beetles!

Grouting Operation taking place on the left abutment of the dam

Diagram of Grout Curtain – Calaveras Dam Replacement Project

Lined, Then Sealed, Then Delivered This Fall. The New Irvington Tunnel Reaches Another Milestone

Imagine an 8.5 foot in diameter steel pipe roughly the length of a tractor trailer. Now imagine gently placing it into a 14-foot tube the length of 1½ Golden Gate Bridges? Now weld each of them together from the inside of the installed pipe in less than two months.

Well, that is EXACTLY what we did. This week the New Irvington Tunnel contractor completed the installation of a total of 14,600 feet (2.7 miles) of the welded steel liner into the tunnel. The 50 foot segments were all installed from the Sunol Valley and transported with a customized pipe placer westward into the tunnel. This completes the steel lining for the entire 18,660 foot (3.5 miles) New Irvington Tunnel.

What’s next? More grouting! Our teams will mobilize in March to prepare the tunnel to place cellular grout into the space between the steel liner and the excavated tunnel. This will effectively backfill the space between the tunnel pipe and tunnel wall, sealing it off to prevent water from seeping into or out of the tunnel.

We plan to bring the New Irvington Tunnel into service this fall, when drinking water will officially be transmitted through the new tunnel. Final project completion of the New Irvington Tunnel Project – including above ground restoration - is expected in mid-2015.

The New Irvington Tunnel will provide a seismically designed connection for water supply for 2.6 million bay area customers. 

50 ft segments of steel liner being delivered
Photo credit: Robin Scheswohl

View of steel liner from inside of Alameda West Portal
Photo credit: Robin Scheswohl

Welding work taking place on steel liners
Photo credit: Robin Scheswohl

Filling the Void

Last week, crews digging the New Irvington Tunnel excavated an astounding 92 feet in just 3 days. This feat was all the more surprising given that the tunnel was passing through a fault zone where miners excavating the original Irvington Tunnel encountered an enormous amount of groundwater pouring into the tunnel. So much so that it was dangerous for the workers. What was different this time around? Grout.

Crews knew they had entered this zone when they probed 100 feet ahead of their tunnel face and found large amounts of groundwater. Before crews could do any mining forward, they had to inject 66,000 pounds of grout (think liquid cement) into the rock ahead of them to fill cracks and voids in the earth. That’s enough to fill up the water tank pictured below! Grouting fills these voids and keeps groundwater out of the tunnel. It keeps our miners safe and allows tunneling to continue.

Grout is taken by rail to tunnel heading and mixed inside of the tunnel. In November alone, approximately 423,000 lbs. of cement was injected into rock fractures, filling cracks ranging up to 1.5 inches in width.

As of December 4, 2012, over 13,100 feet has been mined. With 5,500 feet to go we expect tunnel expect tunnel excavation to be complete by mid-2014. For those that remember our Road Header Rendezvous Challenge we’ll have another one next year to celebrate NIT’s final hole-through!