Bottomless Culvert

1
Bottomless Culvert Study
J. Sterling Jones FHWA TFHRC
Eastern/Southern Resource Center Hydraulic
Engineers Conference Orlando, FL
July 2000
2
(No Transcript)
3
(No Transcript)
4
(No Transcript)
5
(No Transcript)
6
(No Transcript)
7
(No Transcript)
8
(No Transcript)
9
(No Transcript)
10
DEFINITION SKETCH
11
Bottomless Culvert Analysis

• Scour at U. S. corners of bottomless culverts is
• analogous to bridge Abutment scour.
• Abutment scour is local contraction scour caused
• by flow concentration near the abutment with a
  
• multiplier to account vortices and other
  secondary
• currents.

12
Abutment Scour Analyses Based on Adjusting the
Local Equilibrium Contraction Scour Depth

• MD DOT Method By Chang
• GKY Method
• Terry Sturms Method

13
Basic Analysis

• Determine a local representative velocity, VR,
  near
• abutment prior to scour.
• Compute the representative unit discharge, qR,
  near
• the abutment
• qRvR ? y0
• Determine the critical incipient motion
  velocity, Vc, for
• the bed material in the culvert.

14
Basic Analysis

• Calculate the adjustment factor, KADJ, to
  account for
• vortices and secondary currents.
• ASSUME THE UNIT DISCHARGE REMAINS
• CONSTANT IN THE CONTROL VOLUME.
• Calculate the equilibrium contraction scour flow
• depth, y2.
• Calculate the max scour flow depth
• ymaxKADJ y2

15
Differences in Md DOT (Chang) Method GKY Method

• VR determination
• Vc
• Independent Variables used for KADJ
• regression

16
MD DOT (CHANG) Method for vR
17
GKY Method for vR
18
MD DOT (Chang) Method for vc
19
GKY Method for vc
20
Combined Methods for Depth10
21

• We mixed and matched but really did not make much
  difference R2gt0.94

BUT
Best combination was Shields, Manning, Blodgett
for Vc with GKY estimate for VR modified GKY
regression for KADJ.
22
(No Transcript)
23
ymax, measured - ymax, calculated
24
COMBINATION
25
COMBINATION
26
COMBINATION
27
COMBINATION
28
COMBINATION
29
COMBINATION
30
RIPRAP ANALYSIS (ISBASH METHOD)
31
RIPRAP ANALYSIS (CONTD)
32
RIPRAP ANALYSIS - RESULTS
33
KRIP f(Ab, y0)
34
D50,measured - D50,computed
35
SUMMARY
36
CONCLUSIONS

• Scour at the U.S. corners of bottomless culverts
  is
• analogous to bridge abutment scour.
• Best combination of abutment scour relationships
  was
• GKY approx. For VR and Shields, Manning,
  Blodgett
• for Vc.
• Analysis limited to clear water conditions.
• Culvert shape was not a significant parameter

37
CONCLUSIONS

• Additional Research
• Fixed Bed experiments with selective velocity
  measurements
• inside culvert.
• Live Bed scour logic.
• More data on riprap requirements.
• What if we have 2D model results for VR?

38
(No Transcript)