Geotechnical Engineering Circular No. 9 Design, Analysis, and Testing of Laterally Loaded Deep Foundations that Support Transportation Facilities
Download 6.03 Mb. View original pdf
|
Soldier Rev B
- Navigate this page:
- Figure 6-14: Illustration of scour conditions including degradation and general scour and local scour (after Brown et al. 2010).
| 6.7.5 Scour Scour is a primary design consideration for bridges over waterways other transportation structures may also have foundations in or near waterways that may need to be assessed for scour conditions as well. The evaluation of scour should be a multidisciplinary task that includes hydraulic engineers, structural engineers, geotechnical engineers, and construction specialists. Evaluation of scour should be performed in accordance with Publication No. FHWA-HIF-12-003, Evaluating Scour at Bridges, by Arneson et al. (2012), also referred to as HEC-18. Bridge foundations are to be designed for the worst conditions that may result from scour for the year flood event, or from a lesser event with deeper scour potential. This is considered the design flood and is not an extreme event condition. Bridge foundations are also to be checked to ensure they will not fail for an extreme flood event, such as the year flood. This is considered the check flood and is considered an extreme event. Scour includes general scour from the flood (degradation of the riverbed, as well as contraction scour due to the presence of the structure in the waterway, and local scour around the foundation elements themselves. Scour components for bridge foundations are illustrated in Figure 6-14. 91 Figure 6-14: Illustration of scour conditions including degradation and general scour and local scour (after Brown et al. 2010). The effects of scour will lower the surface elevation in the vicinity of the deep foundation elements. In some cases, entire soil layers maybe removed due to scour. The lateral analysis for the scour condition must account for these changes in the subsurface profile (i.e., Block 5 in Chapter 5). Consideration should be given as to whether additional lateral loads are applicable to the scour condition, such as vessel impact loads, wave loads, loads due to water pressure, debris loads, larger moments or axial forces due to unsupported foundation lengths, etc. Multidisciplinary coordination is required to ensure that all proper loads have been considered and accounted for. The result of scour is that the lateral resistance of the deep foundation will be decreased (due to removal of materials) and the loads on the foundation element maybe increased. Although actual scour conditions maybe variable, for analysis of laterally loaded deep foundations, the entire soil depth within the scour zone should be considered to be removed by scour. Additional considerations for design of drilled shafts and driven piles for scour conditions, including considerations for design of axial capacity and considerations for construction and installation, can be found in Brown et al. (2010) and Hannigan et al. (2016). Download 6.03 Mb. Share with your friends:
|