The project includes construction of a Floating Screen Structure (FSS) that will be located adjacent to and hydraulically connected with the existing Water Temperature Control Tower (WTCT). For the FSS to fit next to the WTCT at low pool elevations, a complex excavation of rock (with the potential for rockfall hazard) and embankment fill will be required near the reservoir. The embankment fill excavation will be supported by retaining wall and the FSS will be moored to a newly-constructed mooring tower. Shannon & Wilson is providing geotechnical field explorations and laboratory testing for the excavation in embankment fill and intact rock for the United States Army Corps of Engineers (USACE), Portland District.

Our services include drilling and logging geotechnical borings for blast design, retaining wall design, mooring foundation design, and rock slope stability evaluation; completing televiewer surveys in bedrock encountered in all borings; packer testing in two of the borings (for mooring tower foundation design); laboratory testing on the rock core samples; structural and geologic mapping of rock slopes; evaluation of both local and global rock slope stability; design of permanent slope stabilization measures for the new rock cut slopes and existing rock slopes; and design of measures to mitigate the rockfall hazard to the FSS posed by the new rock cut and existing rock slopes.

After completing field explorations and analysis, our recommendations have included installing a draped mesh system to address the rockfall hazard, installing a pattern dowel and weep hole system along the existing slope, and installing untensioned grouted dowels.