A Field Study of Spiling Reinforcement in Underground Openings

From measurements and observations of the physical model behavior in conjunction with calibrated numerical model results, the mechanisms by which prereinforcement displays its effectiveness was implied, but not verified. Further investigations were required to examine and substantiate the mechanisms by which prereinforcement and, in particular, spiling reinforcement work. A field instrumentation program was designed to monitor the spiling under actual tunneling conditions. This report describes the results of two such investigations. The first was carried out at the Burlington Northern Railroad pilot tunnel and main bore near North Bonneville, Washington, and the second at the Eisenhower Memorial Tunnel, South Bore. The results indicated that the reinforced arch thickness was strongly dependent on ground type, while arch capacity was largely a function of opening size, shape, and depth. At Bonneville, instrumented spiles used in conjunction with extensometers furnished information on the compatibility of the strains in spiles and that of rock mass in their immediate vicinity. At the Eisenhower Tunnel, the reinforcement/support system consisted of spiling, steel sets, and a two stage concrete liner. Support loads were calculated from instrumented steel sets. It revealed that the rock mass-reinforcement system was the primary factor in the permanent stabilization of the tunnel opening; whereas, the internal support system performed a secondary role in the control of local loosening. Report on Project Rational Design of Tunnel Supports. See also Rept. no. MRD-TR-2-75 dated Feb 75, AD-A012 816.