Citation

Weeks FC, Trueblood TB, Krause A, Wyllie DC. Transp. Res. Rec. 1987; 1119: 115-118.

Copyright

(Copyright © 1987, Transportation Research Board, National Research Council, National Academy of Sciences USA, Publisher SAGE Publishing)

DOI

unavailable

PMID

unavailable

Abstract

In June 1984 routine scaling of loose rock from above the north portal of the 175-ft-long Tunnel 5 on the Alaska Railroad's Seward-Anchorage line revealed some large cracks and very unstable rock. Before stabilization work could be started, a 10-ft length of the tunnel collapsed, burying the track. Traffic was stopped for 48 hrs while the track was cleared and an assessment was made of stability conditions. In this paper are described the emergency procedures that were undertaken during the next month to correct the hazardous rock stability conditions in this area. The stabilization procedure consisted of blasting to daylight the 150-ft-long tunnel, thus forming a steep rock cut as much as 120 ft high. Because of the very unstable condition of the rock, it was necessary to remove the tunnel in a single blast consisting of about 600 holes. Most of the holes, with lengths of up to 80 ft, were drilled on the slope above the tunnel on a 6-ft-square pattern. Exceptions were the shear line holes, which were drilled on 2-ft centers, and two rows of holes drilled from the tunnel into the outside rib pillar. The holes were laid out in rows at 45 degrees to the track centerline and were detonated at 25-msec intervals using an electronic sequencer. The rib holes were detonated last in the sequence. The blast produced a stable face that required no stabilization and the total track closure time for loading and mucking was 50 hours.

Record URL:
http://onlinepubs.trb.org/Onlinepubs/trr/1987/1119/1119-014.pdf


TRT Terms: Collapse; Disasters and emergency operations; Failure; Presplitting (Blasting); Rocks; Tunnels
Identifier Terms: Alaska Railroad
Uncontrolled Terms: Emergency procedures
Geographic Terms: Alaska
Old TRIS Terms: Tunnel failures
Subject Areas: Bridges and other structures; Construction; Design; Geotechnology; Highways; Public Transportation; I25: Design of Tunnels; I43: Rock Mechanics; I54: Construction of Tunnels;

Language: en

Keywords

RAILROAD PLANT AND STRUCTURES - Track; TUNNELS AND TUNNELING; ROADS AND STREETS - Slope Stability