Drilling Trinity River Bridge

Drilling Trinity River Bridge

Caltrans proposes to conduct drilling at the Trinity River Bridge (bridge number 05-0028). A planning study has been prepared that identifies constructing outrigger piers to mitigate for future scour. It is proposed that the structure be supported on pile foundations at the supports. The purpose of the drilling is to generate subsurface geotechnical data essential for the design of the proposed bridge retrofit. The borings will consist of 94-mm diameter, vertical mud rotary soil borings located in or around the vicinity of the proposed supports of the retrofit for the bridge. Phase 1 of the drilled four boreholes from the bridge deck. Phase 2 drilling-the boreholes will be drilled at the ground level under, in the channel, and under the bridge for the east outriggers at Pier 3 and Pier 4. Track, rubber tired, truck or trailer mounted drill rigs will be used to drill the boring. All of the borings are estimated to be 150 feet in depth. A tender truck carrying water and other drilling supplies will accompany the drill rig. Water will either be transported to the site or obtained onsite from the Trinity River. The drilling fluid is a mixture of either bentonite or polymer and water; the fluid is circulated through the boring via a closed system. Drilling fluid and cuttings will be stored in barrels and disposed of at an approved waste site when the investigations completed. Permits will be needed from the California Department of Fish and Game (Section 1602 Agreement), North Coast Regional Water Quality Control Board (401 Certification), and U.S. Army Corps of Engineers (NWP 6 Authorization). In addition, the USDA Forest Service, Shasta-Trinity National Forest has provided approval for the drilling and access on lands under their jurisdiction. The time duration of the Phase 2 fieldwork is estimated to be 2 to 4 week to complete the proposed borings.

Trinity