For the replacement of a 1920s wood trestle railroad bridge, Nicholson installed 42, 7-inch micropiles. Pile installation was performed under the original, operational bridge, with up to 26 trains passing overhead each day. The substructure work for the new bridge was built between the existing timber bents, below the active tracks. New pile caps with abutment/pier were placed, and then the two active tracks were removed and replaced with pre-cast spans within a 10-hour window.
Micropile foundations were selected because the minimal disturbance during drilling operations enabled the tracks to remain operational. The compact drill rigs used on this project were able to operate in the low headroom areas below the existing bridge. To increase productivity, Nicholson used smaller diameter casing as the drill rods, leaving it in place as the core steel.
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