Upstream and Downstream on the Truckee River

Exciting Recent Project Work

MDA recently completed a soil nail wall design for the Tahoe Pyramid Bikeway 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 a 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.

MDA’s geotechnical report 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 us over a year ago with the soil exploration and laboratory testing (direct shear strength tests). In the current 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!

Ants from Space

While preparing for a soil exploration in the Spanish Springs Valley (north of Sparks in Washoe County), I noticed an unusual pattern in the Google Earth imagery.

As seen in the image below, roughly every 50 feet there is a clearing between the sage brush.

At many of these clearings, it appears a small lighter-colored dot may be located at the center of it.

Difficult Site Access 2014

MDA has made a specialty of working on hard-to-access Lake Tahoe project sites.

Many sites are inaccessible to site exploration in winter, both due to snow cover and Tahoe Regional Planning Agency restrictions on grading between October 15 and May 1 of each year.

For typical residential sites under these conditions, we may do preliminary evaluations based on ReMi shear-wave velocity surveys and dynamic cone penetrometer; some sites we have worked on defy conventional exploration even in the summer and have required the use of similar methods.

Ward Creek Stream Bank Restoraton in 2015-2016

The picture to the right is of a completed portion of a stream bank restoration project which Marvin Davis & Associates has been involved in, on and off, for several years.

The project is on Ward Creek, which discharges into Lake Tahoe. MDA developed the project (with geomorphology input from Cardno, landscaping (not yet installed) by High Desert Landscaping, and with the owner’s permitting consultant, Agan Consulting), prepared plans, and provided responses and revisions to meet the permitting agency requirements (Tahoe Regional Planning Agency, Lahontan Water Quality Review Board, Army Corps of Engineer, Placer County, Fish and Game). The project as shown is complete, but prior to replanting; the young cottonwood in the far bank was protected in place and rock placed around it. This portion of the creek regularly runs dry in late fall, as what water there is in the upstream reaches sinks into the permeable alluvial fan.

Meadowood Mall Pile Driving 2016

In the beginning of March, we observed pile driving for seismic foundations for a new Dick’s Store at Meadowood Mall. This was a project that Jonathan had brought along from his previous employer – to finish the foundation recommendations and consult on the pile driving operations.

The foundation soils under the site included intermittent areas of liquefiable sands, at about 20 to 27 feet below ground surface – possibly a buried stream channel – generally surrounded by less liquefiable clayier or denser soils. At the south corner of the proposed new store, liquefaction settlement were predicted in the range of 3 inches. There was less than 1 inch of liquefaction settlement predicted at most other locations. To accommodate this geological problem, rather than require mitigation of the entire store foundation, piles were put under the walls and columns in the south corner, for a total of 17 piles. Tie beams are planned between the pile supported column locations. The rest of the store is supported on conventional spread footings with minimal foundation ties except the normal strip foundation under the perimeter wall.

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