Speakers: Christoph Goss, PhD, PE, and Morley Beckman, PE, Deere & Ault / Schnabel Engineering, Longmont, CO

Topic: Finding, Opening, and Stabilizing the Terry Tunnel

The Terry Tunnel served as the primary drainage and haulage tunnel for the Sunnyside Mine from 1907 until 1960 and secondary access until the mine closure in 1991. In 1994, the first bulkhead of the Sunnyside mine was installed in Terry Tunnel, and in 2000, the second bulkhead was installed. Subsequently, the portal was collapsed, backfilled, and revegetated. Prior to the completion of this project, mine water was still draining from the collapsed mine, and the exact location of the buried portal was unknown. Schnabel Engineering (formerly Deere & Ault Consultants) worked with Tetra Tech and the US EPA to perform a fluid hazard analysis for the site. By utilizing historical mine maps and converting them into the state plane coordinate system, Schnabel created planning documents to intercept and drain the mine water from behind the collapsed portal. Even with Schnabel’s coordination between geophysical subcontractors and land surveyors, it took three attempts to successfully intercept the Terry Tunnel.

Schnabel oversaw the borehole sonar and video survey, the downhole methods used to establish the conditions within the adit, the location of the portal and the location of the bulkhead. In the borehole, a temporary well and pump were installed to dewater the adit, collecting the mine water in a nearby retention pond. After dewatering was completed, Schnabel oversaw the excavation of the portal and developed plans and specifications to rehabilitate the 300 feet of adit to reach the bulkhead. Schnabel performed construction management during the rehabilitation, including new steel sets, portal structure, rock bolting, scaling and mucking within the adit. Schnabel performed a bulkhead inspection once the ground stabilization in the adit was completed.