Minnesota and International Railway Trestle at Blackduck
On the Blue Ox Trail (Voyager Trail) just East of the end of Cedar Avenue in Blackduck, MN
+47.72600, -94.5478547°43'34" N, 94°32'52" W
The M&I Railway Train Trestle at Blackduck is constructed of a timber superstructure and substructure accessed by gravel approaches on the northeast and southwest ends. The superstructure consists of the deck, floor system and railing. The deck portion of the superstructure forms the roadway and distributes the vehicle load. The Blackduck trestle deck is not original and was reconstructed with 12' timber beams arranged in a longitudinal orientation with a surface area of 8,412 square feet. Below the deck are the original 8" x 8" ties that are approximately 15 feet long resulting in a total of 672 linear feet. The floor system is comprised of 282 fifteen-foot-long 10" x 18" beams fastened together to form two sets of 30" x 18" longitudinal stringers resulting in a total of 4206 linear feet and is supported by 46 pile bents. The railing system completes the superstructure. The timber railings are not original and are constructed of vertical wood posts, symmetrically placed with a horizontal wood cap resulting in a total of 1402 linear feet. The railing on the east side is reinforced with struts.
The substructure transmits loads from the superstructure to the supporting soil or rock and consists of abutments that support the bridge ends and bents that provide intermediate support for the multi-span structure. Each bent is constructed of five 16" diameter timber piles with the end piles battered approximately 7°. Each bent is reinforced with 3" x 10" cross sway bracing and also with a horizontal return (photo # 15, 16, 18-22). The piles are secured by the cap which is formed by two 7 ~" x 14" beams fastened together and secured to each bent. The base of the trestle is reinforced with 6" x 10" longitudinal bracing fastened at the inside of the 2~ and 4~ piles. A single timber structural member is located at the bottom of each bent, near the ground. The timber pile abutment on the southwest end is comprised of a backwall and wingwalls. The backwall is comprised of four stacked horizontal 9" x 17" timbers with stepped ends and is reinforced with five timber piles. The wingwalls extend away from the trestle forming a right angle with the backwall. [NRHP Form]
- August 18, 2014: Added by Dave King