Demolition of the Milwaukee Railroad Trestle Pier, Lind, WA

摘要

Demolition blasting next to an active railroad can be very challenging because of track safety, blasting vibrations, potential track fouling by blast debris, and short work windows on a live track. Recently, in eastern Washington, one of the major railroad companies has been aggressively constructing a second main track to accommodate the expected increase in rail traffic of natural resource products. To accommodate construction of the second line, the railroad company used blasting demolition techniques to remove an old railroad trestle pier on the Milwaukee Road that was in the footprint of the new track bed. The trestle bridged the present rail line and flanked the track with two massive 550-ton (499 tonne) twin-columned steel reinforced concrete piers. The railroad contracted with a specialized contractor to remove the south pier using blasting demolition techniques. The blasting design presented the following challenges: blasting during live track conditions and short work windows; designing a V-notch blast pattern to ensure the pier fell away from the live track; drilling, loading, and timing of the shot; maintaining blasting vibrations at the track below 4 in./sec (102 mm/sec); maintaining ambient overpressure noise below 133 dB; control of fly rock and debris; and track protection and emergency debris removal plan. On March 15, 2014, the south columns were successfully blasted using a V-notch blast design and approximately 24 pounds (11 kg) of dynamite per column. The blast was designed to shoot a maximum of about 9 pounds (4 kg) of dynamite per delay with a 17 millisecond delay between detonation of the first and second columns. The pier fell cleanly as designed away from the track, and the blast vibrations at the rail were less than 1.0 in./sec (25 mm/sec); and blast overpressure was within limits.