Wilson Creek Restoration and SPGA Wall Project

The project proposes to stabilize the roadway from PM 12.69 to PM 12.95 with a modified alignment and construction of retaining walls. Approximately 1,400 feet of U.S. 101 would be realigned (immediately north of the Wilson Creek Bridge) by increasing the curve radius from 1,050 feet to 1,732 feet, shifting the alignment approximately 30 feet east. Two retaining walls would be constructed to stabilize the roadway beginning at the north end of the Wilson Creek Bridge: a 695-foot-long by 55-foot-high soldier pile ground anchor (SPGA) wall along the western shoulder below the highway, and a 595-foot-long by 19-foot-high soil nail wall (SNW) along the eastern shoulder. The northbound passing lane would be reduced in length from 1.57 miles to 1.22 miles by moving the southern limit north. The northbound passing lane currently begins south of the Wilson Creek Bridge and, upon completion of the project, would begin north of the SNW. The southbound passing lane would also be reduced in length from 0.72 miles to 0.50 miles, moving the southern terminus from south of the Wilson Creek Bridge to immediately north of the Wilson Creek Bridge. Reducing the length of the passing lanes allows for a smaller environmental footprint and improves safety with a larger curve radius, increased shoulder width, improved line of sight visibility, and more uniform traffic speeds. Currently, the lane configuration through the project area consists of four 12-foot-wide travel lanes, a northbound lane with a passing lane and a southbound lane with a passing lane. Existing shoulder widths throughout the project limits can be as little as 1-foot-wide to 6-feet-wide. The project would adjust the lane configuration on the Wilson Creek Bridge to have one 12-foot-wide northbound lane and one 12-foot-wide southbound lane with a 4-foot-wide median. Shoulder widths on the bridge would vary from 8.5 to 12-feet-wide on the northbound side, and from 11 to 20-feet-wide on the southbound side. North of Wilson Creek Bridge, the realigned roadway segment would be configured with one 12-foot-wide lane in each direction, one 12-foot-wide southbound passing lane, a 4-foot-wide median, and 10-foot-wide shoulders in both directions. Roadway excavation, including a 20-foot-wide access road, would total approximately 47,000 cubic yards (CY). Most of this excavated material would be used for construction of the SPGA wall and much of the material would be used to backfill or rebury the wall after it is constructed. After the SPGA wall is backfilled, an estimated 5 to 10 feet would remain above ground. Of the 47,000 CY of total material excavated, the estimated asphalt material to be hauled offsite permanently is approximately 14,000 CY. Material that is permanently hauled offsite would be disposed of at a commercial disposal site. The rest of the material would be either temporarily stockpiled on site within the roadway or existing pullouts, or temporarily stockpiled offsite. The offsite stockpiling location would be determined at a later phase of the project and would undergo applicable environmental compliance requirements. The project also includes the following work items: • drainage replacement and realignment • placing geosynthetic pavement interlayer (GPI) at joints • installing a centerline rumble strip and shoulder rumble strips where full shoulder is present • replacing rock slope protection (RSP) for an existing rocked drainage ditch near the northern bridge abutment and at culvert outlets • erosion control • traffic control • cold planing and hot mix asphalt overlay • replacing signs, replacing guardrail, delineators, and culvert markers in conflict with other work items (all guardrail systems being replaced would have minor concrete vegetation control placed underneath and standard galvanized steel posts and rails to be used instead of etched, stained, or otherwise treated posts and rails) • restriping • constructing a temporary access road • constructing a bioswale