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原文传递 Developing Bridge-Scour Equations for Colorado Mountain Streams.

题名：	Developing Bridge-Scour Equations for Colorado Mountain Streams.
作者：	Molinas, A.; Mommandi, A.; Khan, A.; Sollenberger, B.
关键词：	Hydraulic conditions, Plan of Action (POA), Bridge sites, Scour (Erosion), Colorado Mountain Streams, Sediments (Geology), Bridge-scour
摘要：	CDOT currently uses FHWA’s HEC-18 methods to estimate bridge-pier scour values. Velocities, depths, and energy slopes for a bridge site are first computed in applying the FHWA methods. By applying these computed hydraulic parameters to pier-scour equations given in FHWA’s HEC-18 design manual, scour values are computed for the bridge under consideration. The laboratory and field data used in developing the FHWA equations was based largely on streams with uniform sediments, subcritical-flow conditions, and flatter gradients. In western states where many bridges cross steep mountain channels, bridge-scour equations are applied beyond the range of conditions for which they were derived. Traditional equations overestimate bridge scour for hydraulic conditions encountered in steep mountain streams. In this research study, a new bridge pier-scour equation has been developed suitable for streams flowing through mountainous regions of Colorado. This equation utilizes a dimensionless excess-velocity concept, and relates this flow parameter to pier scour. Dimensionless excess velocity, by including critical and scour-initiating velocities in its definition, accommodates the presence of cobbles and boulders through the critical-velocity term, as well as finer sand-gravel size material through the scour-initiating velocity term. The general form of the equation leads to calibration coefficients relating critical and scour-initiation velocities to representative fine material (D35 of parent-sediment material found on the river bed), and to average coarse material that exists in abundance along mountain streams. This report presents the development of the new scour equation, and applies this equation to compute pier scour at 16 different sites scattered across mountainous parts of CDOT Regions 3 and 5. Sources of data used in the analysis are derived from 16 bridges through a culmination of bridge-scour studies conducted for CDOT by Hydrau-Tech, Inc. for a Plan of Action (POA) for Scour-Critical Bridges study. Additional coarse-material data collected for this project is described, along with methodologies employed to determine pier-scour estimates. As shown in the report, measured and computed pier-scour values for the 38 piers included in the study show very good agreement through the entire range of observed scour values, which vary from 0 to 14 ft. Considering that the coarse material in the streams varied from 2 to 24 in, the computed velocities ranged from 2 to 15 ft/sec, and that the range of parent materials varied from sand and gravel to boulder sizes, it can be concluded that the equation was tested through a wide range of flow and environment conditions, and has been shown to be an excellent predictor.
报告类型：	科技报告