Rock Chute

Mike CoxState Conservation Engineer

Contractor Certification

Training

March 2008

Purpose: Stabilize the grade and control erosion in channels. Prevent the formation or advance of gullies.

Grade Stabilization Structure (410)

Rock Chutes are commonly used to

control grade in Indiana

Rock Chute-Advantages

• Most of the construction can be done with a backhoe or excavator

• Economical compared with poured concrete

Rock Chute - Disadvantages

• Rock can move during large storms• Hard to find larger rock sizes in certain areas• High overfalls require long chutes • Small rock size increases width and length of

chute

Rock Size vs Velocity

What is a d50?

• Expressed as D50 size (50% maximum passing by weight)

RIPRAP GRADATION

  d50 = 7 INCHES  

  SIZE % PASSING  

  14 100%  

  7 50%  

  2.3333 15%  

               

Example:p1 = 24”

p2 = 19.2”

D50 = (24” + 19.2”)/8

= 5.4 inches

Bedding

• Minimum Thickness = 6”• INDOT Sizes Specified

Geotextile

Riprap Thickness

• Minimum of 1’ thickness• Must be 2 times D50 size

Example:

If using D50 Size = 7” Riprap

Minimum Riprap Thickness = 2 * 7” = 14”

2xD50 min.

Installation Report

http://www.in.nrcs.usda.gov/technical/engineering/engineering.html

Landowner:Rock Chute Number or Location:TBM # and description:TBM Elev: TBM reading: HI:

I certify that I have constructed the Rock Chute in accordance with this report and the NRCS plans and specifications.Contractor: Signature: Date:

(print name)

ROCK CHUTE CONSTRUCTION CHECKOUT SHEET

Rock size:

SURVEY

Construction Tolerances-Rock Chute

Depth at Centerline: Grade to 0.1 foot below

Width: 10% wider not to exceed 1.0 foot

Top of Levee: Grade or above  

Side Slopes:     +0.1 ft./ft.  

Helping People Help the Land