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Collapse of the Fargo Grain Elevator One of the most dramatic bearing capacity failures was Fargo Grain Elevator collapse of 1955. This grain elevator was built near Fargo, North Dakota, in 1954. It was a reinforced concrete structure composed of twenty cylindrical bins and other appurtenant structures, all supported on a 15.8m (52ft) wide, 66.4 m (218ft) long, 0.71 m (2ft 4in) thick mat foundation. The average net bearing pressure, q’=q-’z0 = 76.1 kPa ((1590 lb/ft2), caused by the weight of the empty structure was 76.2 kPa. When the bins began to be filled with grain in April 1955, q’ began to rise, as shown in Fig. 2 below. In this type of structure, the live load (i.e. the grain) is much larger than the dead load; so by mid-June, the average net bearing pressure had tripled and reached 227 kPa (4,750 lb/ft2). Unfortunately, as the bearing pressure rose, the elevator began to settle at an accelerating rate, as shown in Fig. 3. Early in the morning of June 12, 1955, the elevator collapsed and was completely destroyed. This failure was accompanied by the formation of a 2 m bulge as shown in Fig. 4. Conduct a bearing capacity analysis on the Fargo Grain Elevator and back calculate the average undrained shear strength of the soil. The groundwater table is at a depth of 1.83m below the ground surface. Soil Strata A and B have unit weight of 17.3 kN/m3; stratum D has 14.9 kN/m3. The unit weight of stratum C is unknown. Assume that the load on the foundation acted through the centroid of the mat.

Fig. 1 Elevation views of the elevator.

Fig. 2 Rate of loading

Fig. 3 Settlement at centroid of mat.

Fig. 4 Cross section of collapsed elevator.