2005/03/23 Council Agenda Packet

8 Task 05001 —Seismic Criteria URS will establish the seismic criteria to ensure post-seismic performance of the Portal 3 tower as follows: • Review and use the site-specific probabilistic seismic hazard evaluation completed by Dames&Moore (now URS) for the Lake Chaplain South Dam Seismic Upgrade Project. • Develop appropriate seismic criteria for the seismic upgrade design to ensure post- disaster services of the lifeline structures URS will use dual-performance-level seismic criteria,which will consider an Expected Earthquake (EE) and Maximum Considered Earthquake(MCE). Return periods of 150 and 2475 years will be used for the EE and MCE events.The dual criteria will ensure that the portal will: • Sustain no structural damage and be operational immediately after a seismic event less severe than EE. • Not fail by collapse or leak,but may crack under a seismic event less severe than MCE. Task 05002—Field Structural Audit URS will complete a field structural audit of the Portal 3 structure by completing the following: • Inspect the structural condition of the accessible interior and exterior parts of the portal. • Perform non-destructive tests using a Schmidt hammer to find the strength of concrete. • Inspect the conditions of the inflow gates. • Compare dimensions of the structure, where as-built drawings are available. • Obtain dimensions where no data is available. URS assumes that the water supply through Tunnel 2 will be temporarily shut down during the inspection to provide access to the interior of Portal 3. The inspection will be completed by Sri Rajah and Erich Lenz of URS. Advantage could also be taken of this shutdown to inspect the tunnel,which is not included in this scope. The Schmidt hammer evaluation will completed in accordance with ASTM C-805 guidelines. While Schmidt hammer measurements are not precise,URS has used this approach successfully in similar studies of intake/outlet towers by taking account of the instrument error. The manufacturer lists the instrument error to be plus or minus 15 %. URS has compared laboratory unconfined compressive strength test results on concrete cores with Schmidt hammer measurements taken near the core locations.The average laboratory test and Schmidt hammer strengths differed by less than 5 %. These comparisons confirmed that the Schmidt hammer gives reasonable strength estimates in the absence of as-built strength data. Task 05003—Review of Data URS will review all available data on the Portal 3 structure by completing the following: • Collect and review as-built drawings and reports on the portal • Compile and review data collected during the field structural audit. 29