Abstract

Surface movement is suspected in the pier foundation of the Neveille H. Colson Bridge based on historical aerial photography, past movement of the foundation, and recent geomorphic evidence. Aerial photography dating back to the 1940's suggest this earthslide has formed as a result of the Brazos River meandering. The earthslide is located on a cutbank of the river and aerial photography indicates the presence of a landslide scarp prior to bridge construction. Initial construction was completed by the Texas Department of Highways and Public Transportation (TDHPT) in 1954. Since this time the TDHPT has performed numerous bridge pier adjustments to the structure including a complete pier replacement in 1979 as a result of pier rotation. Various mitigation procedures have been recommended by a local engineering consultant, one which was carried out included the excavation of soil at the head of the earthslide. Surveys since the excavation show that the earthslide has stabilized in the area of the replaced pier.

Geomorphic features in other areas of the earthslide, however, suggest active surface movement and include the following: three well developed movement scarps, surface tension cracks, irregular topography, sag ponds and rotated trees. Subsurface geology indicates that this earthslide may have a rotational failure plane in Brazos River alluvium changing to a translational failure plane at depth within the underlying Oakville Formation.

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