May Dinner Meeting: Uplift Pressures Below Spillway Chute Slabs
In addition to our presentation, the ASCE society President-Elect Kancheepuram "Guna" N. Gunalan will also be in attendance, so this event will be a great opportunity to meet him. We will also celebrate our dedicated life members, so come out show your support.
Hydraulic jacking has led to notable failures of spillway chutes, including Bureau of Reclamation facilities at Dickinson Dam (1967) and Big Sandy Dam (1984), and the service spillway chute at Oroville Dam (2017), operated by the California Dept. of Water Resources.
The Bureau of Reclamation has performed two laboratory studies aimed at determining the uplift pressures that can be generated at open joints or cracks in spillway chute slabs: 1) open-channel flume testing at relatively low velocities (15 ft/s max) in about 1976; and 2) pressurized water tunnel testing at higher velocities (48 ft/s max) in about 2007.
Reclamation has recently initiated a new research program on this topic, and the first task has been a reanalysis of data from both previous studies using a dimensionless approach and making adjustments for effects of the water tunnel configuration that distorted the measured uplift pressures compared to an open-channel situation. This reanalysis has successfully united these data sets so that uplift pressures can be estimated as a function of the velocity head of the spillway flow and the geometry of the joint or crack expressed as the ratio of the crack width and offset height. The next phase of the research will evaluate boundary layer effects, since neither of the previous test facilities included a significant boundary layer.
Tony L. Wahl, P.E., has worked 29 years in the Bureau of Reclamation Hydraulics Laboratory after earning B.S. and M.S. degrees at Colorado State University. Tony has done a wide variety of hydraulic structures-related work in his career and has specialized in providing useful software tools to the profession. In the early 1990s he wrote the widely used WinADV program to post-process velocity data collected from the first ADVs, and a few years later he led the development of WinFlume, a program used to calibrate and design long throated flumes, the modern choice for critical-flow measurement structures.
Mr. Wahl conducted the first lab tests of Coanda-effect screens—high-efficiency, self-cleaning screens used at irrigation, hydropower, and water supply intakes. His 2001 journal paper and computer program are widely cited and he is now studying effects of surface tension on Coanda-effect screen capacity.
Mr. Wahl has been active for many years in embankment breach modeling, including lab studies and development of procedures for estimating canal breach outflow hydrographs based on canal hydraulic characteristics, embankment geometry, and soil erodibility. He has worked extensively with Dr. Greg Hanson’s submerged jet erosion test for measuring erodibility of cohesive soils, comparing it to the Hole Erosion Test and leading Reclamation’s use of both tests for dam safety applications.
Recently, Mr. Wahl has been studying hydraulic jacking due to uplift pressures at open joints in high-velocity spillway chutes. A new paper analyzes previous Reclamation testing, and new lab work is planned to evaluate boundary layer effects. Another notable project is SpillwayPro, a spreadsheet application developed recently with Dr. Henry Falvey to upgrade Reclamation’s tools for modeling cavitation potential and aerator improvements for spillway chutes.
Mr. Wahl frequently contributes to ASCE conferences and journals and has received Best Discussion and Outstanding Reviewer awards. He was the 2005 Bureau of Reclamation Federal Engineer of the Year.
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1475 S. Colorado Boulevard
Denver, CO 80222