Minnesota TR-3. Culvert OUTLET Protection for Outlets at Grade

v.2-2009

Project: Designed By: Date:

Location: Checked By: Date:

INPUTS

Is this a cantilevered outlet (y/n) enter Y or N

Q cfs (culvert capacity/design discharge)

Tw ft (from waterway calculations, see definition below)

do ft (diameter of circular culvert)

Alternative or depth for C factor FT (depth of scour hole - alternative 2)

C 0.0082 (constant for alternative 1, 2, or 3 of MN TR-3)

OUTPUTS

D50 #VALUE! in (Riprap)

Riprap Thickness in (min.12 inches)

L1 OR 2 N/A ft for ALT. 1 Length of protection

W1 OR 2 N/A ft for ALT. 1 Width of protection

Depth 0.0 ft for ALT. 2 Depth of scour hole selected

L N/A ft for ALT. 3 Length of protection

####### to #VALUE! 100

####### to #VALUE! 85

####### to #VALUE! 50

####### to #VALUE! 15

Alternatives:

2 - Preformed scour hole, Fig 3-2

3 - Lined channel expansion for defined downstream channel, Fig 3-3

Equations

D50 median stone size (ft)

D50 = C Q 4/3

C constant used for alternatives

Tw do Q design discharge (cfs)

do pipe diameter (ft)

S depth of scour hole (ft) (0.5*do - 1.0*do)

D50s mean particle diameter of the soil (ft)

Tw tailwater depth above the invert

of the culvert (ft)

Rock Gradation

1 - Horizontal blanket for no defined channel below outlet, Fig 3-1

Percent of total weight smaller

than the given sizeSize of Stone, inches

Refer to Figures 3-1, 3-2, and 3-3 for the geometry for Alternatives 1, 2, and 3.

Minnesota TR-3. Culvert INLET Protection

v.2-2009

Project: Designed By:

Location: Checked By: Date:

0.04Q do 1/5

do1.5

D50S

R = radius of scour hole, feet

do = Pipe diameter, feet

D50S = Mean particle diameter of the existing soil at the inlet, feet

Q = Design discharge, cfs

Q= cfs (culvert capacity)

D50S= ft (mean particle diamter of the existing soil / rock at the inlet)

do= ft (diameter of circular culvert)

R= feet, radius of scour hole to be lined (based on D50s)

0.05Q

do1.5

D50 = Minimum mean stone diameter of riprap at inlet, feet

D50 = feet

Riprap Thickness= inches (min. 9 to 12 inches)

to 100

to 85

to 50

to 15

Spreadsheet created by Mike O'Shea and based on "Loose Riprap Protection" Minnesota Technical Release 3, July 1989

Rock Gradation

Size of Stone, inches

Percent of total weight

smaller than the given size

R = 0.15do +

D50 = 1.3 - 0.075do Note1

Note 1: factor of 1.3 is only required within one pipe diameter of inlet, but for simplicity, the entire gradation at the inlet can be 1.3xD50

Flow

Culvert Inlet

R

Minnesota TR-3. Culvert OUTLET Protection for Outlets at Grade

v.2-2009

Project: Designed By:

Location: Checked By: Date:

Area

(sq ft)

Perimeter

(feet)

Hydraulic

Radius

(feet)

0.000 0.000

0.000 0.000

0.000

Eq. 3-8

feet = inchesEquivalent Single Culvert Diameter for Same DI =

Use an equivalent culvert diameter of feet to calculate the rock size for inlet and

outlet protection

inches

inches

cfs (sum of the culvert capacities/design discharge)

Diameter of 1st Culvert =

Diameter of 2nd Culvert =

Note: This procedure calculates the equivalent diameter of one round culvert with the same Discharge Intensity of

2 culverts. This spreadsheet is made for 2 conduits, but this procedure can be used for more than 2 conduits

adjacent to each other with the same orientation.

Horizontal blanket for no defined channel

below outlet (Figure 3-1). The blanket shall

have zero grade. The end of the blanket

shall be flush with existing channel or

ground surface

L1 = 3do x [Q/(do)5/2]

L2 = 1.8do x [Q/(do)

5/

Preformed scour hole

(Figure 3-2)

Lined channel expansion for defined

downstream channel (Figure 3-3)

Use this column

Texture < Sieve SizeSize (mm) Size (inches) Size (feet)

Cobble 12.0" 304.8 12.0 1.0

Cobble 6.0 " 152.4 6.0 0.5

Gravel 3.0 " 76.2 3.0 0.3

Gravel 2.0 " 50.8 2.0 0.2

Gravel 1- 1/2 " 38.1 1.5 0.1

Gravel 1.0 " 25.4 1.0 0.1

Gravel 3/4 " 19.05 0.750 0.063

Gravel 1/2 " 12.7 0.500 0.042

Gravel 3/8 " 9.525 0.375 0.031

Sand # 4 4.76 0.187 0.016

Sand # 10 2 0.079 0.007

Sand # 20 0.84 0.033 0.003

Sand # 40 0.42 0.017 0.001

Sand # 60 0.25 0.010 0.001

Sand # 140 0.105 0.004 0.000

Fines # 200 0.074 0.003 0.000

HELP!

This page is for use in figuring the D50 of the existing soils at the inlet or outlet (D50s).

The TR-3 provides information on loose riprap protection including design and failure of riprap, design

considerations, protection of inlets and outlets, streambank protection and field evaluation tips.

Rock chute and lined channels steeper than 5-6%, and side inlet channels should NOT use these

guidelines.

Protection at conduit inlet and outlets

Without protection scour holes at the inlet can develop and reach a maximum size for a given

discharge which can be predicted with Blaisdell's equations. Control of scour hole development

can be obtained by using concrete or riprap.

When stilling basins are not able to be built at the outlet of conduit, 3 alternatives are discussed:

1) Horizontal blanket, with no slope, can be used if there in not a defined channel below the outlet.

2) A preformed scour hole shallower than a stilling basin, lined with riprap.

3) a lined channel expansion if the channel continues beyond the outlet of the culvert.

Multiple Outlets require attention to make sure there is enough outlet protection for all conduits.

The Discharge Intensity must be calculated for each conduit separately and added together to obtain

a total DI value if the conduits are laid along the same orientation. If the conduits discharge at the

same point from different orientations, the equations should be applied separately to each conduit,

the,n on the plan view, the separate dimensions calculated for each conduit should be plotted,

scaled off, and the "worst case" should be identified and selected for design.

General Spreadsheet Project Information

CLIENT: Enter your client's name here.

DSN BY: Enter your name or initials.

COMMENTS: Enter any pertinent job information.

COUNTY: Enter the county where the project is located.

CHK BY:______ To be filled in manually by the person checking your design.

DATE: Enters today's date.

DATE:______ To be filled in manually when your design is checked.

Outlet Protection

This spreadsheet is NOT desinged to be used for cantilevered outlets. If the outlet is cantilevered

design note 6 should be used.

Inputs Units Description

Q cfs Culvert capacity/design discharge

Tw ft Tailwater depth above the invert of the culvert, feet

do ft Diameter of circular culvert

ft depth of scour hole if choosing Alt. 2.

Alt. 1 or Alt. 3 are choices from the pull down menu too.

C Calculated constant for type of protection 1, 2, or 3 of MN TR-3

Minnesota Technical Release 3 (July 1989) SCS

Loose Riprap Protection

Outputs Units Description

D50 in Median stone size

Riprap Thickness in Min.12 inches

L1 OR 2 ft for ALT. 1. Length of protenction

W1 OR 2 ft for ALT. 1. Width of protenction

L ft for ALT. 3. Length of protenction

Equations Used

D50 = C Q 4/3

Tw do

Intlet Protection

Inputs Units Description

Q cfs Design discharge

D50S ft Mean particle diameter of the existing soil at the inlet

do ft Diameter of circular culvert

Outputs Units Description

R ft Radius of scour hole

D50 ft Minimum mean stone diameter of riprap at inlet

Riprap Thickness in min. 9 to 12 inches

Equations Used

0.04Q do 1/5

0.05Q

do1.5

D50S do1.5

Multiple Conduits

This spreadsheet is designed to be used with 2 conduits, but can be used for more than 2 conduits

R = 0.15do + D50 = 1.3 - 0.075do Note1

Flow

Culvert Inlet

R

Note 1: factor of 1.3 is only required within one pipe diameter of inlet, but for simplicity, the entire gradation at the inlet can be 1.3xD50

adjacent to each other with the same orientation.

Inputs Units

Diameter of 1st Culvert in

Diameter of 2nd Culvert in

Sum of the culvert capacities/design discharge cfs

Outputs Units

Equivalent single culvert diameter ft/in

Design Culvert Diameter to use in Design ft

After a designed culvert diameter is computer, return to either the inlet or outlet spreadsheet

to finish the design.