Seventeenth Statewide Conference on Local BridgesTuesday, October 25, 2011

Training Session: Culvert Design, Analysis - talk 2

Presented by: Peter Van Kampen, P.E. NYSDOT

Culvert Design An Overview of the NYS Highway Design

Manual Chapter 8

Peter Van Kampen, P.E. NYSDOT Design Services Bureau

Culvert Basics Outline

Culvert Basics Site Considerations Design Criteria Conventional Culvert Selection & Design Culvert Protection/Channel Linings Plans Culvert Failures Resources Questions

Types of Culverts - Shapes

* Source - HDS 5

Site Considerations Culvert Materials

Metal • Steel (CSP) • Structural plate, • Aluminum, (CAP) • Ductile iron (DIP)

Concrete – RCP (Class I – Class V) Plastic • Polyethylene – SICPP • Polyvinal chloride - PVC

Culvert – Chapter 8 HDM A culvert is usually a closed conduit (e.g., a pipe), but may be an open conduit (e.g., an arch), installed to convey runoff collected in roadside channels, and natural channels such as streams, underneath an embankment. Any single structure with a span greater than 20 ft (6.1 m) is a bridge. These structures require a different procedure for hydraulic analysis, and should be coordinated through the Regional Structures Group

What to Identify

Stream Width. Size/Location of Up/Down Stream

crossings. Stream Scour? Bed Material. Fish Bearing? Embankment Height.

Design Criteria

Or What do need to know before I select a culvert?

Photos to take

View from roadway upstream and down stream.

Inlet and outlet. Wingwalls and/or banks around

inlet/outlet. Interior if possible. Any scour or erosion noted. Scaled reference of bed material.

Design Storm Frequencies for Culverts and Channels

HDM Chapter 8 page 8-21 Table 8.2

Conventional Culvert Design Roughness Coefficients “n”

Reference HEC-22

Reference HDM, HEC-22, & HDS 5

Design Size Criteria Constraints

Design Storm Frequency (Per HDM) Design Headwater (HDM & ACOE/DEC)* Outlet Velocity (Natural Velocity - Scour)* Aquatic Organisms (ACOE/DEC/Fish

Wildlife) * Constraints defined/evaluated by designer

Culvert Terminology

EL Hd Headwater Elev.

Hw Headwater

Inlet Invert

Outlet Invert

H Head Loss Embankment

Roadway

Tw Tailwater

Tailwater Elev.

Cut-off wall

Cut-off wall

Calculate Q (flow)

TR-20 / TR-55 HydroCAD Regression Equations StreamStats in NY

http://water.usgs.gov/osw/streamstats/new_york.html

Check your answers with historical sources if able.

Culvert Design Process 1. Calculate “Q” for design storm. 2. Select pipe material and shape for site. 3. Calculate tailwater depth 4. Calculate maximum allowable headwater 5. Size culvert 6. Check outlet velocity 7. Design outlet protection

Conventional Culvert Design Culvert defined as structure with a span less

than or equal to 20 feet (6.1 m) Conventional culvert is a simple culvert placed

on grade with standard headwall, end section inlet (improved inlets not covered here)

Common shapes are box, circular, arch, and elliptical.

Common materials are concrete, plastic, steel and aluminum.

Calculate Tailwater Depth Use calculated flow rate from

hydrologic analysis and basic open channel flow calculation for downstream conditions and linings

Consider affect of major rivers &

streams downstream that could influence tailwater.

Determine if downstream

culvert/bridge size limitations exist Document non-conforming features.

Culvert Sizing Minimum Culvert Size Minimum culvert size is 2 ft.

Smaller diameters acceptable for shallow

depths and utility conflicts

1 ft. is acceptable for driveway pipes and field entrances.

Meets allowable Headwater criteria.

Maximum Allowable Headwater Determination (Hw) 2 ft. below lowest shoulder edge. No damage to upland properties. No increase to water surface elevation than that

allowed by floodplain regs (generally 1 ft). Headwater to pipe ratio:

Diameter or Rise Maximum Hw/D Ratio < 5 ft. 1.5 ≥ 5 ft. 1.0

Material Considerations

Design life/Service life (HDM Chapter 8.6.2.1) Stream conditions (Debris, Rocks, Ice movement) Chemical properties of project location

(alkalinity/acidic nature of the surrounding soils, see HDM chapter 8.6.2.2)

Height of fills Environmental considerations (fish passage,

mussels) Economics

Culvert Sizing Inlet vs Outlet Control

Inlet Control - Culvert is in inlet control when culvert is capable of delivering more flow than inlet will allow. Typically in supercritical flow.

Outlet Control – Culvert is in outlet control when the barrel losses are greater than the inlet loss. Typically in sub-critical flow.

Culvert Sizing Inlet Control Factors

Headwater depth – determines pressure flow • In general, we utilize calculations to determine

this depth given other criteria

Inlet Area – determined from the culvert size selected.

Inlet Shape – Determined from culvert chosen

Culvert Sizing Inlet – vs – Outlet Control

Culvert Sizing Determine Headwater Elevation

Headwater is controlled by Inlet or Outlet control of the culvert.

Inlet and outlet control influenced by several factors

Design must be checked for inlet & outlet

conditions to determine controlling feature.

Culvert Sizing Inlet Control Factors

Beveling the inlet headwall is a cheap and effective way to improve hydraulic flow through the culvert

Find Ke value for given end treatments.

0.9 0.5 square 0.2 beveled

0.5 or 0.2

0.7

Culvert Sizing Inlet Control Factors Inlet edge configuration - The major factor in culvert performance

Thin Edge Projecting (poor efficiency) Ke = 0.9

Thick walled inlet – acts similar to square edge headwall & typical end sections (typical installation) Ke = 0.5

Grooved end projecting/ box with bevel (highest efficiency) Ke = 0.2

•Bell end of projecting pipe upstream changes Ke from 0.7 to 0.2 •See Table 223 of HDS #5 for additonal Ke factor values

Sizing Culverts

HDS-5 http://www.fhwa.dot.gov/engineering/hydraulics/

library_arc.cfm?pub_number=7&id=13

HY-8 http://www.fhwa.dot.gov/engineering/hydraulics/

software/hy8/

Inlet or Outlet Control?

Inlet

Outlet

Culvert Sizing Outlet Control Factors

All inlet control factors apply. Headwater will be controlled by barrel properties. Barrel shape, length, area, slope and roughness

influence flow. Tailwater elevation – determined by open channel

flow calculations for downstream conditions.

Beveled Headwall

Flow Types (HDM Figure 8-6) Outlet Control

Outlet Velocity Calculations Inlet Control

• Determine normal depth and velocity of culvert barrel [Manning’s Equation V = (R.67S0.5)/n ] Culvert outlet velocity is assumed to be the same as the culvert barrel.

Outlet Control • Determine area of flow from the following (V=Q/A):

• TW < Dc Use Dc • D>TW<Dc Use TW • TW > D Use D

Outlet protection for stream and culvert

Check Velocity Design outlet protection (stone fill,

energy dissipater)

Flow Types (HDM Figure 8-5) Inlet Control

Outlet Velocity Calculations

Or use output from HY-8

Cut Off Walls for End Sections Standard Sheet 603-04

Outlet Protection & Linings

Prevents Scour Prevents Erosion

Outlet Velocity Calculations

Visual URBAN program https://mctrans.ce.ufl.edu/store/shopcart1.asp

Dumped stone Inlet Apron Apron sized by

diameter of culvert Design to minimum

stone blanket thickness or greater.

Extend height to

calculated headwater depth.

Dumped Stone Outlet Protection Design

Culvert Outlet Protection

Bank and Channel Linings -Geotechnical Procedure GDP-10

GDP-10 Provides guidance on the selection of protective linings for stream banks and channels

Geotechnical Procedure GDP-10 June 1995

STATE OF NEW YORK DEPARTMENT OF TRANSPORTATION

SECOND EDITION

Concrete and asphalt linings are not recommended.

GDP-10 Channel Lining Design Charts

Multiple Culvert Installation Standard Sheets 203-5 & 204-1

Standard Installation Std. Sheet 203-5 Installation with CLSM

Std. Sheet 204-1

Culvert Outlet & Lining Protection

DEC NYS Standards and Specifications for Erosion and Sediment Control. (AKA “The Blue Book”) also contains information for outlet and channel protection.

See Section 5, Pg. 5B.21

Culvert Outlet Protection

Safety Culvert End Safety Grates

STRUCTURAL LIMITATIONS

3 SIDED STRUCTURES • Need scour protection • Need piles driven to rock • Piles increase construction time • $$ Typically more expensive $$

STRUCTURAL LIMITATIONS Product Limitations Precast Concrete Span Rise* Structures Bottomless (3-sided) Min Max Min Max Conspan(arch) 12ft 48ft 3ft 13ft Hyspan (flat top) 6 ft 40 ft 2 ft 10 ft PC Arches (Bebo, 11 ft 60 ft 3.5 ft 22 ft Kistner, etc.) Box culvert (4-sided) 2 ft 20 ft 2 ft 10 ft

*Minimum rises are limited by NYSDOT practice that designs have span-to-rise ratios of 4 or less. A larger ratio (greater span in relation to rise) increases moments in the top slab and foundation loads to the point where they are impractical/uneconomical to build. Maximum rise is limited by shipping constraints for Conspan, Hyspan and Box Culverts. Listed above are some of the more common manufacturers of precast 3 sided structures.

Safety & Protection Culvert End Sections

NYSDOT end sections not hydraulically efficient

Ke=0.7

STRUCTURAL LIMITATIONS

Fill Height • Arched and round culverts handle large fills

better • As cover nears 10 ft and span approaches 20

ft, top slabs of box structures becomes excessively thick and impractical. • Arch types should be used for fills over 10 ft. • For other material fill limitations see HDM

chapter 8, Appendix A

PLAN SET Typical Sections (Culvert & Highway) Plan View Highway Profile (Existing & Proposed) Stream Profile Hydraulic Data Culvert and Wing Wall Elevations Staging Plan (if necessary) Guiderail Plans / Details

STRUCTURAL LIMITATIONS

Span to Rise Ratio • Longer span may increase rise • Raise the highway profile • Widen toe of slope • $$ Increase culvert length $$ • May also impact a greater amount of

stream bed and any adjacent wetlands

Culvert Failures

Seepage (Piping) Undermining Buoyancy Overtopping Blockage Materials

Culvert Failures Undermining - Caused by

scour at the outlet, removing material upstream.

Prevention: • Use cut-off wall at outlet • Proper outlet protection

Culvert Failures Seepage – Caused from flow of water on exterior of pipe.

Removes material, eventually leading to failure. Common on multiple pipe installations due to poor compaction between pipes.

Prevention: • Cut-off walls at inlet • Proper compaction of

material along barrel • Proper materials used

for backfill (not crushed stone)

• Anti-seep collars

Culvert Failures Overtopping – Caused by water going over feature,

eroding material from both upstream and downstream. Can be caused by inlet blockage.

Prevention: • Proper design of culvert for

storm event. • Review of watershed for

debris potential.

Culvert Failures Materials – Caused by soil conditions reacting with pipe

materials. Resulting in seepage and undermining.

Prevention: • Proper selection of culvert

materials for project site.

Culvert Failures Blockage – Primarily debris accumulation on inlet,

constricting flow and causing overtopping to occur. Can also be caused by end sections not being anchored.

Prevention: • Cut-off walls on end sections • Review of watershed for

debris potential • Use of debris deflectors

Culvert Failures Buoyancy – Caused by high water tables, with air being trapped in

barrel of culvert. Typically causes lifting of culvert resulting in seepage. Common with CSP and Plastic pipes.

Prevention: • Proper barrel material

selection. • Design of culvert to prevent

air entrapment in barrel

Questions?

Peter Van Kampen MO Design Albany, NY

e-mail: pvankampen@dot.state.ny.us

Resources

Highway Design Manual, Chapter 8 Open Channel Flow, FHWA Hydraulic

Design Series No. 3 (HDS-3) Open Channel Flow, FHWA Hydraulic

Engineering Circular 22 (HEC–22) Culvert Design, FHWA Hydraulic Design

Series No. 5 (HDS-5) Culvert Design, NHI Course 135056