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14 2 Mueller Zhuravlyov Froehlich 1.5 ys/a 1 0.5 0 1 2 3 4 5 6 7 8 V1/Vc Figure 10. Normalized scour depth versus V1 /Vc. Local Scour Evolution Data and the remainder in the 5.0 to 5.5 mm range. The higher- velocity tests were conducted with the smaller sediment. Laboratory Data A limited number of laboratory experiments have been A relatively large number of laboratory-scale local scour performed with complex shaped piers (i.e., piers composed evolution rate experiments, with simple shaped structures, of a pile group, pile cap, and a column). Methods have been has been conducted and reported in the literature. A total of developed to estimate scour depths at complex piers using the 195 scour time series data sets was compiled for circular or equations developed for single cylindrical piers (Richardson square piles. A list of contributing researchers with their and Davis 2001 and Sheppard and Renna 2005). The effective number of reported clear-water and live-bed experiments is diameter of a complex pier is obtained using known pier, presented in Table 3. Figures 11 and 12 show the distribution of sediment, and flow values. The effective diameter is the diam- local scour evolution data collected in laboratory experiments. eter of a single circular pile that will experience the same local The matrices in these figures show the ranges and distribution of scour as the complex pier under the same flow and sediment variables covered by the scour evolution data. For example, the conditions. This approach seems to work well for equilibrium third row from the top in Figure 11 shows the values of velocity scour depths for the limited data that exist. However, this and three of the other variables for the data. The first plot from approach has not been tested for scour evolution rates. Also, the left shows that the data covers a wide range of velocities from it is not known how scour evolution rates for complex piers 1 ft/s up to 7 ft/s but that with few exceptions the water depths compare with those for their equivalent circular piers. are less than 1 ft. Also, there are no data for high-velocity flows and large depths. The second plot shows that most of the tests Field Data were performed with piers less than 1.5 ft in width. The third plot is a histogram showing the distribution of velocities for the tests, The only time-dependent local scour field data obtained in the majority being around 1 ft/s. The last plot in this row shows the information and data search portion of this study were velocities and sediment size for the tests. The sediment sizes are that reported by Walker (1995). In that study, the scour hole grouped into three ranges: 1 mm and smaller, 3.0 to 3.5 mm, at a 2.0 ft wide square pile on a bridge over a tidal inlet on the Northwest Florida Coast (East Pass near Destin, Florida) was filled with the surrounding sand and the redevelopment of the Table 3. Sources and number of scour evolution scour hole monitored for a period of approximately 10 days. data sets. The unsteady (tidal) flow at this site, which exceeded sediment critical velocities at peak flow, reversed direction approxi- Data Source Number of Data Sets Oliveto and Hager (2002) 80 mately every 14 h. After 10 days the scour depth was near the Rajasegaran (1997) 14 original value. Grimaldi (2005) 3 The laboratory and field equilibrium scour data compiled Melville and Chiew (1999) 21 Sheppard et al. (2004) 14 during this project are given in Appendix D (available on the Sheppard and Miller (2006) 24 NCHRP Report 682 summary web page: www.trb.org/Main/ Total 156 Blurbs/164161.aspx).
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15 6 4 y1 (ft) 2 0 3 2 a (ft) 1 0 6 V1 (ft/s) 4 2 D50 (mm) 4 2 0 0 2 4 6 0 1 2 3 2 4 6 0 2 4 y1 (ft) a (ft) V1 (ft/s) D50 (mm) Figure 11. Plots of the data for local scour evolution rates. 6 4 V1/Vc 2 10 y1/a 5 0 4 log(a/D50) 3 2 2 4 6 0 5 10 2 3 4 V1/Vc y1/a log(a/D50) Note: The dashed lines indicate the wide-pier boundary. Figure 12. Plots of normalized data for local scour evolution rates.