The Northern Pacific (NP) Railway began laying track eastward from Kalama, Washington, in March, 1871, and westward from near Duluth, Minnesota, in July, 1871. The eastern segment of the track reached the Missouri River at Bismarck, North Dakota, in June, 1873. However, no bridge spanned the Missouri, and thus the NP faced a major obstacle to the transportation of railroad construction materials westward. Boxcars loaded with equipment and supplies had to be ferried across the river, causing delays of many hours, if not days. During a few, exceptionally cold months, perilous crossings of the Missouri could be made by trains following tracks laid across ice on the frozen river. Efficient and safe crossing of the river became imperative to the very survival of the company.

View, facing to the east, of the pier construction. East pier is visible in right foreground. In upper-left, workers can be seen laying masonry on one of the middle pier caissons (February, 1882).

Construction of piers for a bridge at Bismarck began in 1881. The eastern pier was placed on a twenty-foot-thick concrete foundation which bottomed in bedrock claystones at a depth of 40 feet below the surface. The two middle piers were located in the river and, therefore, posed more difficult construction problems. The excavations for these two piers were made possible by the use of pneumatic caissons, much like giant diving bells, which enabled the men to work below the water line.

If any fatalities or injuries occurred during construction of the bridge, they are not reported in the engineer's report. On October 21, 1882, the soundness of the bridge was tested by slowly transferring eight locomotives onto the three spans and measuring the deflection of each span under the accumulated weight. The successful completion of the test was marked by sounds of whistles from the eight locomotives, the whistles of steamboats below the bridge, and the cheers of the thousands of on-lookers who had gathered to watch.

In 1882, just after completion of the bridge, the east pier began shifting toward the Missouri River. The pier moved an average of 3 to 3.6 inches per year from 1883-1887. A number of corrective measures were attempted, but all were futile. In 1898, the pier was successfully moved back by sliding the massive feature along rails onto an enlarged and deepened foundation.

East pier being slid back into position approximately 23 inches along steel rails (May 29, 1898).

By 1902, however, the pier had again shifted back 4 inches. Many of the railroad engineers blamed the leakage from the recently-constructed city water reservoirs, located on the hill above the east pier. Speculation was that the reservoirs were leaking 50,000 to 60,000 gallons of water daily. To intercept groundwater flow from the reservoirs, NP crews hand dug a 4-foot by 6-foot tunnel at a slight upward grade for 483 feet towards the reservoirs. Twenty-nine perforated pipes were later driven down from the surface to feed water into the tunnel system.

Still, the east slope and pier continued to move. In 1918, a cofferdam consisting of a large pit braced with thick timbers and excavated down to the base of the foundation, was constructed around the pier. The cofferdam succeeded in slowing the movement of the pier under the pressure of the sliding hillside, but it itself had to undergo majors repairs in 1923 and 1940 due to damage caused by pressures by the landslide.

Cofferdam constructed around east pier to protect pier from pressures of landsliding. The cofferdam periodically filled with water and was a favorite swimming hole for area youth.

In 1951, the hillslope above the bridge was trimmed and the base of the slope recontoured. The slide continued to move, albeit at a much reduced rate. In 1963, the year that the NP discontinued keeping records on the site, the slide was moving at a rate of approximately 1/3 of an inch per year. No estimates are available of the cost to the NP to repair and maintain the east pier, but it likely involved hundreds of thousands of dollars.

East pier of the Bismarck railroad bridge, 1991.

With its dark spans, tall masonry piers, and sleek ice breakers, the railroad bridge today is arguably the most majestic of the four bridges that now span the Missouri River at Bismarck. The bridge stands as a tribute to the engineers and crews who built and have maintained it.

Bismarck railroad bridge in 1991, with east pier visible in left foreground.

A more complete description of the construction and engineering problems associated with the Bismarck railroad bridge can be found in North Dakota History, Spring, 1995, Vol. 62(2), pp. 2-19.

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This web site is maintained in public service through a cooperative effort of the North Dakota Geological Survey and by the Department of Geosciences at North Dakota State University.

LINKS TO OTHER RELEVANT SITES:

• North Dakota Geological Survey Home Page

• Geology in North Dakota

• Department of Geosciences, North Dakota State University

• Toils Induced by Weak Soils: a Photo-Essay on NP's Stockwood Fill