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Upstream and Downstream on the Truckee River
RTGA, formerly MDA, completed a soil nail wall design for the Tahoe Pyramid Bikeway (TPB) for a difficult section of trail above the Truckee River about 20 miles west of Reno at an area known as Iceland.
The TPB volunteer team has been extending the trail for the past five years as a labor of love. The new path section will travel below the freeway at this point and has to pass below a Caltrans retaining wall (shown below). This existing wall is 18 feet high and has tieback anchors 30 to 40 feet long under the freeway into bedrock. The team considered both trestle or soil nail wall options. A combination of near-active slope failures and expected heavy snow loading from plowing of the freeway nixed a trestle option.
The geotechnical report, as a part of the wall design, included data from two ReMi seismic lines and Dynamic Cone Penetrometer used to estimate depth of soil/ depth to bedrock. We also acknowledge a group of UNR engineering students who helped with the soil exploration and laboratory testing (direct shear strength tests). In the plan, the path will drop down the slope nearly to the base of the retaining wall shown below. The bikeway will traverse a fill bench approximately 10 feet wide supported by a soil nail wall with an exposed height of approximately 8 feet. The new wall will have a concrete face and soil nails 15 to 20 feet in length. We have proudly been able to be a part of this exciting project that will enhance the recreational enjoyment of our beautiful area. Plans were submitted by us and Robison Engineering to Caltrans and Nevada County, California.
By the way: Tahoe Pyramid Bikeway is always looking for interested volunteers to advance this undertaking. Check out their website at tpbikeway.org!
Downstream, we are ready to kick off our assistance on the first segment of the Truckee River Flood project at the mouth of the Truckee River downstream canyon near the east end of Sparks. RTGA/MDA was chosen to join the team with Atkins and Kleinfelder. Our role will include drilling the levee soil borings (with both private and public utility locates and contractor coordination) and providing independent technical review of the engineering analyses, reports, and recommendations. This important project will serve to enhance public safety and mitigate property damage from flood stage waters experienced in the lower Truckee River zone
Farther downstream, RTGA/MDA completed two projects at the Tahoe-Reno Industrial Center 15 miles east of Reno. We provided foundation recommendations for NV Energy for five dead-end or turning transmission line towers. Rather than drilling, we performed test pits and ReMi seismic surveys to identify the depth of soil and stiffness of bedrock. MDA also completed a geotechnical investigation and report for a proposed 12-acre commercial site shown below. This site is proposed to include a number of restaurant pads, small retail and larger commercial buildings.
Conventional wisdom and our experience for much of the TRIC site has been that some of the Tertiary volcanics are excavatable with large equipment – as performed at the Tesla factory, for example. However, the area shown here appeared to be a flow of much more competent, solid Pliocene lava which has high shear wave velocities (above 1,200 feet per second) and we did not believe it is readily excavatable without blasting. Alternate recommendations included that the developer place the buildings on fill so that utilities do not require significant excavation into bedrock. Development has not started at the commercial site yet, but we did hear from NV Energy that their contractor had to blast for the 15-foot depth drilled shafts foundations.