GEOSYSTEM FAILURES FROM A 1000-YR FLOOD EVENT: PIPE CULVERTS

South Carolina recently experienced a 1000-year rainfall event that caused catastrophic flooding and crippled the transportation infrastructure. Initially, almost 400 roadways were closed due to flooding, a majority of which were closed from roadway washouts. Initial SCDOT reports indicated that many of these roadway washouts resulted from failure of the pipe culvert soil system beneath the roadway. Pipe culverts are used primarily to channel water beneath roadways from uphill drainage or roadside ditches. In South Carolina, they are made from reinforced concrete, aluminum or high-density polyethylene and are installed in either trench or embankment configurations.

During an extreme flood event, failure of the pipe culvert may be accelerated by a) instability of the local ground caused by rapid increase of ground water table, b) erosion of the structural fill supporting the pipe culvert, reducing the overall strength of soil-pipe system, and c) increasing of hydrostatic pressure which applies additional water loads to the pipe and structural fill and can cause buckling of the pipe. Furthermore, as pipe culverts age with time, the pipe material deteriorates due to abrasion and other environmental stresses. The culvert infrastructure is critical to not only preventing flooding during normal and extreme conditions but is integral to proper road and highway maintenance.

Results from a post-flood reconnaissance study aimed to collect perishable data from sites where pipe culverts failed and roadways were washed out will be presented. The study included collection of extensive photographic evidence and documentation of descriptive information related to the failure; collection of soil samples, and field and laboratory geotechnical tests. These data form valuable sets of well-documented case histories that can be used in the future to support large-scale research for advancing our fundamental understanding of complex failure mechanisms in extreme scenarios.