Energy dissipation in thirty-foot broken-back culverts using laboratory models.

Details

• Creators:
  Tyagi, Avdhesh ; Ali, Abdelfatah ; Hamilton, Matthew
• Corporate Creators:
  Oklahoma State University. School of Civil & Environmental Engineering
• Corporate Contributors:
  United States. Federal Highway Administration
• Subject/TRT Terms:
  • Culverts
  • Scour
  • Dissipation
  • Laboratory tests
  • Streamflow
  • Hydraulic jump
  • Froude number
• Publication/ Report Number:
  FHWA-OK-14-10
• Resource Type:
  Tech Report
• Geographical Coverage:
  Oklahoma
• Corporate Publisher:
  Oklahoma. Dept. of Transportation. Planning and Research Division
• Abstract:
  This research investigates the reduction in scour downstream of a broken-back culvert by forming a hydraulic jump ; inside the culvert. A broken-back culvert is used in areas of high relief and steep topography as it has one or more breaks in profile ; slope. A broken-back culvert in the laboratory represents a 1 (vertical) to 2 (horizontal) slope after the upstream inlet and then ; continuing 90 feet at a 1 percent slope in the flat part of the culvert to the downstream outlet. The prototypes for these experiments ; were either a two barrel 10-foot by 10-foot, or a two barrel 10-foot by 20-foot reinforced concrete culvert. The drop between inlet and ; outlet was selected as 30 feet. Three flow conditions were simulated, consisting of 0.8, 1.0 and 1.2 times the culvert depth. This report ; represents Phase V of broken-back culverts with a drop of 30 feet. The first phase of this research was performed with a drop of 24 ; feet, the second phase of this research was carried with for a drop of 6 feet, the third phase of this research, performed was a drop of ; 18 feet, and the fourth phase of this research was performed with a drop of 12 feet. ; The Froude number (Fr1) of the hydraulic jump created in the flat part of the culvert ranged between 2.53 and 5.66. This Fr1 classifies ; the jump as an oscillating to steady jump. The jump began nearly at the toe by placing sills and friction blocks of different sizes in the ; flat part. For new culvert construction, the best option to maximize energy dissipation under open channel flow conditions is to use one ; 5.83-foot sill located 33.33 feet from the outlet. The maximum length of the culvert can be reduced from 25 feet to 30 feet that was for ; middle sill. For existing and new culverts, the best option is to use one end sill with height of 6.67-foot. In pressure flow conditions, the ; optimal location was determined at a distance of 31.67 feet from the outlet for 4.17-foot sill. The length of the culvert can be reduced ; by 25 feet to 30 feet. Also, for new and existing culverts, the optimal end sill is to use one 4.17-foot sill height under pressure flow ; conditions. Such a scenario is important where right-of-way problems exist for culvert construction. Also examined was a slotted sill ; which has a cut in the middle for cleanup purposes. In open channel flow conditions, the best option to maximize energy dissipation is ; to use one 5.83-foot slotted sill located 33.33 feet from the outlet, and for end slotted sill is to use 7.5-foot height. In the pressure flow ; conditions, the optimal slotted sill was 5-foot at a distance of 41.67 feet from the outlet, and for end slotted sill is to use 4.17-foot ; height. The regular and slotted sills contain two small orifices at the bottom to allow the culvert to completely drain. The impact of ; friction blocks was found to be minimal. No friction blocks were used to further dissipate the energy.
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• Format:
  PDF
• Funding:
  ODOT SP&R Item Number 2254
• Download URL:
  https://rosap.ntl.bts.gov/view/dot/29397/dot_29397_DS1.pdf
• File Type:
  [PDF - 3.54 MB]
• Collection(s):
  US Transportation Collection
• Main Document Checksum:
  urn:sha256:2d3944ce837a877707935329b490577d2057f59882597d24d17d579fe3db5449