A Longitudinal Trail Research Program on Soil Stabilizers

July 1, 1999

National Center on Accessibility
National Center on Accessibility, Indiana University-Bloomington

This study was originally conducted by the National Center on Accessibility at Bradford Woods between 1997 and 1999.


The purpose of this project is to compare the effectiveness of surface treatments for creating a trail accessible to people with mobility impairments. Specifically, this study is examining the longitudinal effects of surface treatments on surface firmness and stability, the costs of applying the treatments, and their relative maintenance demands.

What is being tested

The trail base contains compacted soil indigenous to central Indiana. The types of surfaces used were Quarter Minus Limestone, #11 limestone (refers to stone size), and indigenous soil. Quarter Minus Limestone is a by-product of crushed limestone in which the limestone fines are no larger than a quarter inch and most fines are dust particles.

A Longitudinal Trail Research Program on Soil Stabilizers

All surface materials were applied in 3-inch depths. The stabilization products used with the surfaces were Mountain Grout*, Road Oyl Resin Modified Emulsion, and Stabilizer. Mountain Grout* is a single component hybrid polyurethane system designed to stabilize and solidify soils. (*Mountain Grout has since been changed and renamed). Stabilizer is a concentrated organic (ground seed hulls) soil additive powder. Road Oyl Resin Modified Emulsion is a pine resin emulsion and is not petroleum based.

Test Procedures

To evaluate the surface, a device called a Rotational Penetrometer that measures the firmness and stability was used. This tool evaluates the surface by measuring how deep an eight inch pneumonic wheel that has a constant pressure of forty pounds will penetrate the surface when rotated 90 degrees.Each one of the test plots is evaluated on a monthly basis, with readings being taken in random locations on each evaluation. Five different measurements are taken of each surface every month.The same location is never measured twice in one month.The test surface has received a large amount of foot traffic over the last two years. The plots are on the main path at Bradford Woods that connects the dining facility to the rest of the camp. This trail has an average of seventy-five users per day.The test surfaces of the trail were lined with 2″ x 6″ boards to designate the sides of the trail and separate each surface application plot.

Note: The Rotational Penetrometer is used as a standard measurement device in the ANSI/RESNA Standard for Ground and Floor Surfaces

After Two Years of Use

1. Quarter Minus Limestone with Stabilizer
This test plot has shown considerable wear and is breaking down at the sides. The results of this test so far have indicated that this surface has had an average of .36 -.59 inch penetrations.

2. Quarter Minus Limestone with Road Oyl Resin Modified Emulsion
This plot has shown little wear and is holding up well under all the trail use. There is an average penetration of .05 -.08 inches on this surface. This surface has proven to be very usable by people with mobility impairments.

3. Quarter Minus Limestone with Mountain Grout Soil Stabilizer
This plot has shown the least wear of all test plots, the average penetration on this plot was .009 -.03 inches.

4. Quarter Minus Limestone
This test plot has had an average penetration of .10 – .90 inches. This plot has shown instability when wet and under adverse temperature changes. This surface has degraded and broken down much faster than other surfaces where stabilizers have been applied.

5. 50% #11 Limestone and 50% soil
This surface has an average penetration of .45 – 1.2 inches, it has been the second worst surface in terms of decay.

6. Soil
This surface has had the poorest results over the last two years; the average penetration is .35 -1.80 inches. When wet, people with mobility impairments have deemed this surface inaccessible and the surface has shown a substantial amount of decay.

7. Soil and Mountain Grout
This surface has an average penetration of .21 – .87 inches with signs of decay on the edges of this test plot and in the middle.

Quarter Minus Limestone with
Mountain Grout Soil Stabilizer
.009-.03 inches
Quarter Minus Limestone with
Road Oyl Resin Modified Emulsion
 .05-.08 inches
Quarter Minus Limestone .10-.90 inches
Soil and Mountain Grout Soil Stabilizer.21-.87 inches
Quarter Minus Limestone with Stabilizer.36-.59 inches
50% #11 Limestone and 50% soil.45-1.2 inches
Soil.35-1.80 inches

ANSI/RESNA Standards for Firmness and Stability

Very Firm/StableModerately Firm/StableNot Firm/Stable
Firmness0.3 inch or less >0.3 & <0.5 inch >0.5 inch
Stability0.5 inch or less>0.5 & <1.0 inch>1.0 inch