When the train bridge valley was cut, the earth was levelled perfectly to allow the train track a smooth transition. Winter after winter, rainstorm after rainstorm, the steep walls of the valley began to erode and it wasn't until a train derailment (and a full crash investigation was lanched) that I noticed the the bridges had sunk an inch and there was half a foot of track dangling in the open air appoaching and departing the bridge.
Using pictures of retaining wall cribbing, old cedar fence boards were cut into 3/4 x 3/4 x 12" strips. Creating a 4 x 4 grid, the strips were nailed with 3" nails which were staggered changing positions each course to ensure overlap of connection. The resulting cribbing stacks for the plactic arch bridge became 16" high. With a square shovel the dirt was removed at the bridge abutments locations and stored in a plastic bin. A long 2X4 was rested on the rail ballast on either side of the valley and the cribbing was adjusted to the correct height. With the plastic arch bridge being so delicate a wood frame replica representing it's length and height was created so it could be inserted and removed from the abutment gap to check spacing. The removed dirt was placed back into the cris-cross of the cribbing and was packed with the end of a small post every couple of inches.
With the bridges levelled, supported and secured the old troll under the bridge shouldn't be disturbed again for a long long time.
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