Michigan County Engineers Conference

2-23-11by

Ken SkorsethSDLTAP – Program Manager

Gravel Road Maintenance

Critical Issues

Roadway ShapeSurface Gravel SelectionModern Traffic DemandsPreservation

Crown

One of the biggest challenges in gravel road maintenance.

Some roads have too little crown, some have too much.

Imagine a cattle trailer on this road.

The road has 13 inches of crown on a 20′ top

Crown should be near ½ inch per ft (or 4%)

Example: 24 ft roadway should have approx. 6 inches of crown.

This Device is Helpful

The Next Challenge – High Shoulders!

Outstanding example!

Excellent example in a confined R-O-W

Shouldering Operations

•The issue of good surface gravel (aggregate) cannot be emphasized enough!!

•Good aggregate surfacing differs from base and other construction aggregates.

•When it’s right, problems diminish!

Surface Gravel

•Many state DOTs do not have a surface aggregate spec.

•Many specifications that do exist are quite loose and do not allow close enough control of gradation.

•Many states going away from plasticity index testing requirement.

Problems With Specifications

•The need for more plastic fines to serve as binder for surfacing.

•Smaller top-sized stone that will remain embedded in the surface.

Two Fundamental Differences in Surface and Base Aggregates

Similar ADT, Similar roadway shape, but different surface materials!

Dramatic Contrast

“Where it is planned that the soil aggregate surface course is to be maintained for several years without bituminous surface treatment-----, the engineer should specify a minimum of 8% passing the----No. 200 sieve-----, and should specify a maximum liquid limit of 35 and plasticity index range of 4 to 9 in lieu of the limits given in Section 2.2.2.

AASHTO’s Materials Manual – 2001 edition, Designation M-147 has these recommendations:

Sample specifications comparison:

Deep Layer Needed to Carry Heavy Loads

14.5 inches of gravel needed to carry 25 to 50 trucks per

day over weak subgrade!

From SDDOT Rural Road Design, Maint, & Rehab Guide

Road Failure in Brown County – Township Road

Road Failure on a Brown County Road

Traffic has changed on local roads/streets!

Largest Deere tractor in 1953!

Today!

Option: Geotextile Separation

Six years of performance

Another Issue – Gravel Preservation

A Chloride Stabilized Road Since 1998!

Portland Cement Railcar Offloading Facility

Seven-axle portlandcement hauler being loaded.

Time in: 2:05PM

Time out: 2:12PM

The road carries up to 80 of these rigs per day.

Less than 200 tons of gravel replaced in 12 yrs!

•Ordinary Twp road reshaped in 1998.•Approximately two to three inches of gravel in place.•Eight inches good quality surface gravel added.•Liquid MgCl treatment applied after reshape each year.

Without Adequate Funds for Base Improvement and Paving – Stabilized Gravel is an Alternative.

Maitland Rd – Lawrence Co, SD

Heavy Residential Traffic & Continued Development

A Model of Successful Gravel Stabilization for 21 Years

•Eight inches of gravel originally placed after aggressive reshape in 1989. •Liquid MgCl2 treatment applied annually thereafter.•Four inches of gravel replaced after 12 years.

One Section of Maitland Rd With Asphalt Surface

Get ready to face the challenges of maintaining gravel roads in the future!

Thanks!