Increasing the Clearances
Typical view of undercutter lowering the track under a bridge.
As has been previously reported, Conrail is being split up between CSX Corporation and Norfolk Southern. The latter carrier has concluded an agreement with CP Rail which will allow Norfolk Southern to interchange directly with Guilford Rail at the CPDH yard at Mohawk, New York, formerly a facility of the Delaware and Hudson Railroad. This agreement will permit Norfolk Southern to compete for traffic to and from New England and the Maritime Provinces.
Grinding tool on location inside the Hoosac Tunnel.
The shift from boxcar to container freight has become a major consideration as Guilford Rail looks to the future. One limitation has been the overhead clearance measuring 18 feet 3 inches from Ayer, MA westward to the New York connections. The current practice of doublestacking of containers has focused attention on the need to increase this clearance if the Norfolk Southern route is to be viable. Accordingly, the Engineering Department intensively studied the West End of the railroad to see what could be done, anticipating that the Hoosac Tunnel would be the major obstacle to increasing the clear height over the tracks. It was developed that a clearance of 19 feet 6 inches could be obtained by applying several unique methods in the Hoosac Tunnel and at 23 other locations. These methods resulted in either removal of the obstruction or lowering of the track below an obstruction, by various means described following.
The obstructions removed from the Hoosac Tunnel thus far were eliminated by a grinding arm mounted on an excavator-type machine which rides on the track. The operator moves the grinding tool against the rock and, using a clearance frame as a guide, grinds each protruding area until the desired profile is obtained. It was calculated by laser survey techniques (20 million survey points were examined) that 1,000 cubic yards of rock have been ground from the tunnel bore in the unlined portions. In the next phase, the track will be lowered in about 3,000 feet of the metal-lined portion by removing ballast under the track and installing shallow ties where ledge or drainage lines prevent undercutting. This work is expected to be finished in 1998.
Geogrid at Cole Avenue, Williamstown, MA.
An undercutting machine, complete with its operating crew and support tools, was employed to lower the track at 13 locations. This machine actually digs the ballast out from under the track to a depth of 8 inches, and the track is lowered in the process. If ledge is struck, however, the digging tool, a set of scoop-like cutters on a continuous chain, may break or stall, and the ledge may have to be broken out by air hammer. At Williamstown, Massachusetts the undercutting revealed a track support system based on wooden piling and support beams made necessary by an underground lake of clay which would not hold the track. After the undercutting operation, the restored track continued to settle into the clay and it finally became necessary to construct a “geogrid” foundation, a special plastic fabric of cells which are filled with ballast stone - this acts as a platform to support the track while allowing adequate drainage. Sheet piling was also required to support an embankment and a large quantity of drainage collection piping was installed to move water away from the track. Hardly a routine project!
Undercutter at work.
At Fitchburg, Massachusetts, the undercutting ran into a number of large boulders under the track as well as ledge. Three city water mains had to be lowered, as did a communications duct containing utility cable lines. Another utility conduit, which is actually a small tunnel under the track, had to be lowered by breaking and lowering its roof. Clearance on two bridges in Fitchburg will be improved by installing special low profile steel ties welded to steel deck plates.
Lowering the track at Orange, MA.
At other locations, track has been realigned to clear a bridge obstruction, bridge design has been altered at 2 bridges, 4 bridges have been raised and 2 unused bridges have been removed. This project, while not yet complete, has allowed some imaginative and innovative techniques for problem-solving to get fully tested. The end result will provide Guilford Rail System with greatly enhanced competitive capability across the West End of the railroad.
The business part of the undercutter. (Note the clearence under ties at left center)
South Maine Street overpass, Orange MA after undercutting.
Thanks to Bill Furey, Phil Brake, Steve Nevero and Roger Pritchard for photographs.