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Thursday, December 12, 2013

What’s Going On Next to the Highway 92 Crossing?

Alexis Pope, the sole female diver on the project, 
rigs a water pump for washing out the culvert. 
The divers work on the barge 
as well as underwater.
If you cross the Crystal Springs Reservoir on Highway 92, you’ll pass a construction barge yet no construction is visible. The real action is 60 feet underwater, where divers with the Water System Improvement Program work on a seismic upgrade of the Upper Crystal Springs Dam lower culvert. The culvert has been weakened by past earthquakes where it crosses the San Andreas Fault.
To strengthen and provide flexibility to the 370’ long tunnel, the contractor has placed a 42” wide high density polyethylene pipe (HDPE) inside the 60” wide brick lined tunnel in a process called “sliplining”. Flexible grout and slurry delivered by a materials barge are pumped in-between the old pipe and new slipline to provide additional cushioning against future earthquakes. 
In addition, a vertical portal will be installed outside the area where the culvert crosses the fault as a fail-safe. It will maintain water flow from Upper Crystal Springs to the Lower Crystal Springs Reservoir if a major seismic event damages the lower culvert where it is bisected by the fault. 
Divers wear video cameras, communication lines and lights
on their helmets, and a warm water hose for comfort,
all connected to the barge via lengthy cables. 
Project Schedule
Dredging for vertical portal: December 2013
Expected completion: February 2014
This project, together with all of the other improvements to the regional distribution system, will allow the SFPUC to meet its goal of delivering potable water within 24 hours after a major earthquake.
A crane and temporary buildings are staged 
on the barge to support underwater construction work.
Photos by Robin Scheswohl, SFPUC

For more information on construction diving in the Crystal Springs - San Andreas Reservoir system, please see our article from April 2013.

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