Geotechnical Engineering Online Library

The duration of a flood event in an ephemeral stream is finite, ranging from a few hours to a few days. However, for design of deep foundations, an assumption is typically made by geotechnical specialists that at the time of a flood event all stream bed geomaterials are saturated and fully-buoyant. This assumption leads to larger deep foundations because full-buoyancy can significantly reduce the geomaterial resistances to applied loads. Consequently, a large increase in foundation investigation and construction costs can occur. This paper presents a case study that included an evaluation of the infiltration of transient flood waters into unsaturated geomaterials within an ephemeral stream bed. Considerable cost reductions were realized as a result of this evaluation. The presented approach permits a rational geotechnical evaluation of deep foundations in ephemeral streams.

A 30-m long railroad embankment failure that occurred on May 25 2011 in the city of Ann Arbor, Michigan, is presented. Emphasis is given on the field observations of the failure, the characterization of the site conditions and the seepage and slope stability analyses, all of which represent important components of the training and practice of a geotechnical engineer. The failure occurred following a record wet season that resulted in ponding water against the embankment and high enough water pressures and exit gradients that resulted in instability of the railroad embankment. Detailed background material and the methodology for using the case history in geotechnical engineering education are presented.

Mangla Dam (Pakistan) is one of the largest Earth Core Rock fill Dam (ECRD) in the world in terms of volume of material used. The Sukian dyke of Mangla Dam Project is 5.33 km (17,500 ft.) in length and is founded on alternate beds of clay and weak (friable) sandstone. Raising of the dam subjected the project area including the dyke to an additional head of about 12.19m (40 ft.) in 2013. Before raising, the maximum seepage in the entire project was observed in the Sukian dyke area. An upstream blanket was selected to control seepage in this area after dam raising. FEM analyses were carried out to determine the efficiency of the upstream blanket in controlling seepage. After raising and impoundment, the FEM results were compared with instrumentation readings and seepage measurements and close agreement was observed.