Mendocino Railway operates the popular Skunk Train along the historic California Western Railroad line. In the spring of 2013, a portion of the California Western Railroad Tunnel #1 collapsed, forcing Skunk Train excursion operations to cease.
The tunnel, originally completed in 1893, extends over 1,000 feet, from Pudding Creek to the Noyo River. Mendocino Railway retained LACO to perform a geotechnical evaluation, design a cost-effective emergency tunnel support system, prepare construction documents, and provide construction phase services, including construction observation and materials testing.
Our geotechnical team performed structural mapping and strength testing of rock exposed in the cavern following the collapse and provided design recommendations for a modern structural support system. The tunnel collapse occurred within a highly faulted and fractured Franciscan graywacke sandstone unit where the existing timber sets had experienced overloading. Our structural engineering team developed a model of the existing timber lining, designed temporary supports for stressed sections, and developed specifications for the repair. LACO’s construction services team prepared contract documents to support project bidding, reviewed contractor pay requests, answered RFIs, and observed placement of high-strength shotcrete and installation of over 100 rock bolts.
LACO developed prescriptive tunnel support recommendations using the Rock Mass Rating system, which allowed the design development to proceed quickly. A conceptual design was developed and bids were solicted from three pre-qualified contractors within in less than month. In order to allow the railroad begin excursion trips from the Willits Depot, we worked with the contractor, Caves Unlimited, to modify the temporary support design in a way that would allow “ghost” trains to traverse the tunnel before the final lining was completed.
