Effects of Inlet Geometry on Flow Capacity of Single and Multiple Barrel Box Culverts

Status: Complete

Contractual Process

The Federal Highway Administration (FHWA) will initiate a task order under the existing contract DTFH61-C-00050 to conduct a laboratory study described by the statement of work that follows. The process will be similar to the pooled fund process used routinely to transfer funds into FMIS for research administered by FHWA.

Bill Zaccagnino, FHWA's pooled fund coordinator, will set up an open ended pooled fund study for "Turner-Fairbank Highway Research Center (TFHRC) Hydraulics Lab Support" and assign a study number to be used to transfer SP&R or State funds to FMIS (accounting software). Dennis Judycki, Associate Administrator for Research and Technology (R&D), will send a memo approving 100 percent State Planning and Research (SP&R) funds to the Division Administrator for each state expressing an interest in initiating a lab study. States can then elect to use SP&R or State funds for the study. SP&R funds are transferred electronically via form PR-2; state funds are transferred via a check to the FHWA locked box in the FHWA Division office. After funds are transferred to FMIS, Sterling Jones ((contracting officer technical representative) for contract DTFH61-C-00050) will prepare a Procurement Request to allocate the funds to the task order initiated under the contract. The contractor invoices show costs by task orders. Unused funds at the end of a task order can be returned to the State.

Since this study is one of mutual interest to South Dakota Department of Transportation (SDDOT) and to FHWA, funds will be used to pay costs for the contractor personnel to conduct the study, but there will be no charges to the State for use of the lab or for oversight by FHWA's COTR.

A technical advisory panel including the FHWA COTR and designated members of the State providing funds will be set up to administer the contractors performance of the task order.

Problem Statement

As stated in the RFP: "Each year the SDDOT designs and builds many cast-in-place (CIP) and precast box culvert structures that allow drainage to pass under our roadways. The CIP boxes typically have 30-degree flared wing walls and the precast have straight wing walls with 4-inch bevel on the inside edges of the wing walls and top slab. Previous research, SD93-12, conducted on a limited number of single barrel box culverts, indicated that further research was necessary to determine the effects of multiple barrel structures, loss coefficients of unsubmerged inlets, and to determine the effect of 12 inch corner fillets versus 6 inch corner fillets. In order to optimize the design of both types of box culverts it is also necessary to determine the effects of span to rise ratio, skewed end condition, and optimum edge condition on typical box culvert installations.

The current analysis programs, used for sizing box culvert structures (HY-8 and others), do not analyze multiple barrel box culverts correctly. These programs model multiple barrel structures as though each barrel is a separate single box with its own wing walls, instead of as a multiple barreled section with one set of common wing walls (as is the actual condition for most CIP box culverts). In order for the department to assure optimized box culvert design, it is necessary to determine the effects of the various inlet conditions and box configurations that are used in South Dakota."

It is our opinion that extrapolating single barrel performance to multiple barrel culverts is not accurate. For example, with a wing wall configuration and a single barrel, the wing walls direct the flow directly into the barrel, reducing the contraction losses at the entrance. For the same configuration with multiple barrels, there is minimal contraction loss for interior barrels so losses are much lower. In other words, we expect that multiple barrels will perform better than a single barrel multiplied by the number of barrels. The research undertaken under this project to verify our hypothesis will be of value and FHWA is extremely interested in pursuing this.

We will optimize the wing wall bevels but do not expect this will have a significant impact on hydraulic performance. We do recognize that beveling improves performance, but the difference between an optimum bevel and the 45-degree bevel currently being used might be insignificant.

We do not expect that corner fillets significantly affect the design coefficients. These will affect hydraulic performance since they block flow area. As a result of the video conference, we have proposed two corner fillets for two culvert sizes using the optimum edge conditions in test matrix 3.1. We have included one benchmark test with current 45° edge conditions and the 6 inch corner fillet.

We have already compared the 30 degree flared wing wall to the straight wing wall in previous research for SDDOT and will review our previous work and incorporate results into the final report for this study.

From previous FHWA research on wide span culverts we know that higher span to rise ratio adversely affects hydraulic performance, but the smaller contraction ratios typically associated with wider spans improves hydraulic performance so the net affect is expected to be negligible. FHWA is interested in quantifying this impact and incorporating the findings into design guidance.

We expect that skewed end conditions will adversely affect hydraulic performance for multiple barrel systems since the flow will tend to go to the outside barrel. We will test this impact for single and multiple barrel configurations.

We will test various configurations for both inlet and outlet control and will need to test steeper barrel gradients than those specified in the RFP to ascertain inlet control. We will test slopes up to 3 percent, which is consistent with previous research we performed for SDDOT. The purpose of testing the steep-slope, 3 percent, is to ensure inlet control.

Background Summary

percent

FHWA has tested several inlet configurations for SDDOT and published findings in report number FHWA-RD-01-076. However, previous research does not illuminate precise hydraulic performance for the configuration issues specified in the RFP. We have also done special culvert inlet studies for Iowa, West Virginia, and FEMA. We have also performed studies of general interest, such as a study of widespan culverts.

Objectives

wing walls with top edges mitered to 2:1 Embankment slope
Culvert Rise = 6 ft, wall thickness= 8"
Headbox contraction ratio = 2.67:1
Corner Fillet = 6" and 12"
Model scale ratio = 1:12

Wingwall flare angle	Tailwater	Bevel	Corner Fillets	Culvert box type	Culvert slopes	Unsubmerged flow; target Q/AD^0.5	Submerged flow; target Q/AD^0.5
0°	High, Low	Optimum on wing walls and 6"-45^o on top slab as per drawing PC-A	6", 12"	6' x 6', 12' x 6'	0.03	0.5, 1.0, 2.0, 3.0, 3.5, 4.0	4.5, 5.0, 5.5, 6.0
0° on wingwall and 45°on top per sketch FC-S-0	High, Low	None on wingwalls and 45^o on top slab per sketch FC-S-0	6", 0"	6' x 6'	0.03	0.5, 1.0, 2.0, 3.0, 3.5, 4.0	4.5, 5.0, 5.5, 6.0

No. of test configurations = 6; no. of tests = 120 plus tests in mini flume to determine the optimized bevel edge.

We propose to use the 0.03 slope which will result in inlet control for low tailwater and outlet control for high tailwater conditions. The discharge intensity Q/AD^0.5= 4.0 may fall in either unsubmerged or submerged flow depending on the efficiency of the inlet.

3.2 Effects of multiple barrels

WW with beveled sides and top edges mitered to 2:1 Embankment slope

Culvert Rise = 6 ft, wall thickness= 8"

Model scale ratio = 1:12

Wingwall flare angle	No. barrels	Inner wall	Corner Fillet	Sketch Number	Edge conditions	Culvert box type	Culvert slopes	Unsubmerged flow; target Q/AD^0.5	Submerged flow; target Q/AD^0.5
0°	2 precast boxes	Non extended	12"	PC-D-1 or PC-D-3*	Optimum on wing walls and 6"-45^o on top slab as per drawing PC-A	2 x 6' x 6'	0.007, 0.03	0.5, 1.0, 2.0, 3.0, 3.5, 4.0	4.5, 5.0, 5.5, 6.0
0°	2 precast boxes	Extended	12"	PC-D-E	Optimum on wing walls and 6"-45^o on top slab as per drawing PC-A	2 x 6' x 6'	0.007, 0.03	0.5, 1.0, 2.0, 3.0, 3.5, 4.0	4.5, 5.0, 5.5, 6.0
0°, 30°	2 CIP boxes	Non extended	6"	FC-D-0 and FC-D-30	Square edge 45° top	2 x 6' x 6'	0.007, 0.03	0.5, 1.0, 2.0, 3.0, 3.5, 4.0	4.5, 5.0, 5.5, 6.0
0°, 30°	2 CIP boxes	Extended	6"	FC-D-0-E and FC-D-0-30-E	Square, 45° top	2 x 6' x 6'	0.007, 0.03	0.5, 1.0, 2.0, 3.0, 3.5, 4.0	4.5, 5.0, 5.5, 6.0
0°	3 precast boxes	Non extended	12"	PC-T	Optimum on wing walls and 6"-45^o on top slab as per drawing PC-A	3 x 6' x 6'	0.007, 0.03	0.5, 1.0, 2.0, 3.0, 3.5, 4.0	4.5, 5.0, 5.5, 6.0
0°	3 precast boxes	Extended	12"	PC-T-E	Optimum on wing walls and 6"-45^o on top slab as per drawing PC-A	3 x 6' x 6'	0.007, 0.03	0.5, 1.0, 2.0, 3.0, 3.5, 4.0	4.5, 5.0, 5.5, 6.0
0°, 30°	3 CIP boxes	Non extended	6"	FC-T-0 and FC-T-30	Square, 45° top	3 x 6' x 6'	0.007, 0.03	0.5, 1.0, 2.0, 3.0, 3.5, 4.0	4.5, 5.0, 5.5, 6.0
0°, 30°	3 CIP boxes	Extended	6"	FC-T-0-E and FC-T-30-E	Square, 45° top	3 x 6' x 6'	0.007, 0.03	0.5, 1.0, 2.0, 3.0, 3.5, 4.0	4.5, 5.0, 5.5, 6.0
0°	4 precast boxes	Non extended	12"	PC-Q	Optimum on wing walls and 6"-45^o on top slab as per drawing PC-A	4 x 6' x 6'	0.007, 0.03	0.5, 1.0, 2.0, 3.0, 3.5, 4.0	4.5, 5.0, 5.5, 6.0
0°	4 precast boxes	Extended	12"	PC-Q-E	Optimum on wing walls and 6"-45^o on top slab as per drawing PC-A	4 x 6' x 6'	0.007, 0.03	0.5, 1.0, 2.0, 3.0, 3.5, 4.0	4.5, 5.0, 5.5, 6.0
0°, 30°	4 CIP boxes	Non extended	6"	FC-Q-0 and FC-Q-30	Square, 45° top	4 x 6' x 6'	0.007, 0.03	0.5, 1.0, 2.0, 3.0, 3.5, 4.0	4.5, 5.0, 5.5, 6.0
0°, 30°	4 CIP boxes	Extended	6"	FC-Q-0-E and FC-Q-30-E	Square, 45° top	4 x 6' x 6'	0.007, 0.03	0.5, 1.0, 2.0, 3.0, 3.5, 4.0	4.5, 5.0, 5.5, 6.0

*Researcher will recommend model to test based on results of other tests

No. of set-up configurations= 36; No. tests=360

3.3 Effects of span to rise ratio

For this series of tests we will keep the contraction ratio constant while varying the span of the culvert from 1:1 to 6:1, which means we will vary the width of the headbox as we vary the span. The following conditions are proposed for these tests:

WW with beveled sides and top edges mitered to 2:1 Embankment slope

Culvert Rise = 6 ft, wall thickness= 8"

Headbox contraction ratio = 2.67:1

Corner Fillet = 0

Model scale ratio = 1:12

Wingwall flare angle	Span to Rise ratio	Culvert slopes	Unsubmerged flow; target Q/AD^0.5	Submerged flow; target Q/AD^0.5
0°, 30°	1:1, 4:1, 6:1	0.007, 0.03	0.5, 1.0, 2.0, 3.0, 3.5, 4.0	4.5, 5.0, 5.5, 6.0

No. of set-up configurations= 12; No. tests=120

3.4 Effects of Skew: 15⁰, 30⁰ and 45⁰

For this series of tests we will keep the contraction ratio constant, vary the skew angle for a triple barrel culvert and vary the number of barrels for one of the skew angles. Proposed test conditions are:

Flared WW and 45⁰top slab per sketch furnished by SDDOT top edges mitered to 2:1 embankment

Culvert Rise = 6 ft, wall thickness= 8"

Headbox contraction ratio = 4:1

Corner Fillet = 0

Model scale ratio = 1:12

No. barrels	Span to Rise ratio		Skew angle	Culvert slopes	Unsubmerged flow; target Q/AD^0.5	Submerged flow; target Q/AD^0.5
3	3:1		15⁰, 30⁰ and 45⁰	0.007, 0.03	0.5, 1.0, 2.0, 3.0, 3.5,4.0	4.5, 5.0, 5.5, 6.0
1	3:1		30⁰	0.007, 0.03	0.5, 1.0, 2.0, 3.0, 3.5, 4.0	4.5, 5.0, 5.5, 6.0

We will measure the EGL and the flow distribution in each barrel for the triple barrel test.

No. of test configurations = 8; no. of tests = 80

Task 4: Approval of Testing Matrix

We will modify the test matrix as appropriate following discussions and suggestions by the SDDOT technical review panel, but we will not proceed with testing until the matrix has been approved by SDDOT.

Task 5: Construct Detailed Models

FHWA will utilize the FHWA machine shop and Precision Plastics (a local plastics fabricator) to fabricate the models. The models will be available at the FHWA Lab for SDDOT review and digital photos will be furnished electronically for inspections as each model is completed before testing begins.

Task 6: Test Models as identified in the Approved Testing Matrix

The preliminary test matrix presented in Task 3 presents our initial estimate of the work to be accomplished. The cost for this task is directly related to the test matrix and any changes to the test matrix will change the costs associated with testing the models.

Task 7: Data Compilations and Recommendations for Implementation

For each configuration we will derive the following design coefficients as described in HDS-5:

Submerged outlet control entrance loss coefficient, k_e

Unsubmerged outlet control entrance loss coefficient, k_e

Submerged inlet control entrance loss coefficients, c & Y

Unsubmerged inlet control entrance loss coefficients, K&M

We will also develop nomographs and fifth order polynomials for inclusion in future updates to HDS-5.

Task 8: Preliminary Draft Report

We will prepare and deliver a preliminary draft report detailing our methodology, findings, conclusions, and recommendations.

Task 9: Final Report

We will review comments from the technical panel and incorporate all applicable when preparing the final report.The final report will be in accordance with FHWA requirements for a research report to be distributed electronically as a web document.

Task 10: Executive Presentation

We propose to establish a technical Advisory Panel (TAP) to include designated representatives from SDDOT and the FHWA COTR (Sterling Jones) to monitor progress of the task order. We propose to host two meetings of the TAP at the TFHRC and to send one engineer from the study team to brief SDDOT staff about the study prior to completion of the final report. In addition, the FHWA COTR will brief engineers from other DOT's at regional hydraulic conferences and technical sessions as opportunities are available.

Products

We will deliver the following:

Quarterly progress reports (1 copy)
Draft final report (10 copies)
Final report (including nomographs and fifth order polynomials for inclusion in future updates to HDS-5)
Executive summary
Excel Spreadsheet with all model test results
Digital photographs as requested

Implementation

We will make recommendations on how the results of this research can be implemented in the HY8 culvert design and analysis program to assist SDDOT hydraulic engineers design culverts.

Benefits

More accurate design coefficients will result in better culvert design and will result in the cost savings, increased safety, more reliable service, and improved design procedures.

Time Schedule

The time schedule is presented below. We will complete the project within the 15-month schedule specified in the RFP.

Chart showing project schedule

Facilities

The experimental setup includes three subsystems, culvert barrel, head and tailbox. The head and tailbox are currently under construction (Figure 1), both boxes will have Plexiglas walls, which are supported by a metal frame.

Figure 1 - Culvert headbox under construction

The headbox can be modified to vary the width of the approach flow. The height of the tailbox is adjustable to analyze different barrel slopes. The culvert barrel is made from a Plexiglas pipe. Up to 25 ceramic class pressure sensors (pressure range: 0 - 0.1 bar) will be mounted in the centerline on the bottom of the experimental set-up (Figure 2) to measure instantaneous hydraulic grade lines. Taking time averages will lead to more precise loss coefficient computation. The discharge will be provided by 5cfs computer controlled pump. Flow depths and mean velocities can be computed from pressure sensor measurements in the culvert barrel where flow is parallel to the invert. PIV and/or velocity probes will be used to augment these measurements in the highly turbulent region in the vicinity of the and in the headbox where the transverse flow distribution is extreme.

Figure 2 - Arrangement of the ceramic class pressure sensors

To measure instantaneous velocity flow fields the particle image velocimetry technique (PIV) is used. PIV utilizes a focused light source, a high-resolution digital camera, and sophisticated computer logic to trace particle movements. This technology makes it possible to accurately measure velocity in complex situations such as flow into culverts.

The experimental set-up of a PIV system typically consists of several subsystems (Figure 3). In most applications tracer particles have to be added to the flow. These particles have to be illuminated in a plane of the flow at least twice within a short time interval. The light scattered by the particles has to be recorded either on a single frame or on a sequence of frames. The displacement of the particle images between the light pulses has to be determined through evaluation of the PIV recordings.

Figure 3 - Experimental set up for Particle Image Velocimetry

SDDOT Involvement

SDDOT will be represented on the Technical Advisory Panel. SDDOT will review and approve the project scope and work plan (Task 2), approve the test matrix (Task 4), review the preliminary draft report (Task 8), and participate in meetings at TFHRC hosted by FHWA (Task 10). We have had preliminary discussions with Mark Clausen, South Dakota FHWA Division, to participate in data collection.