LOCATION:

Treatment Objectives:

• Increase the strength or bearing capacity of the base layer
• Reduce moisture content in the base layer
• Observe any potential failure due to freeze thaw action in the soil
• Observe improved workability of soil during construction.

Construction Method:

One lane of the asphalt seal layer was ripped and moved to the middle of the road using a grader. The base was then ripped with a grader and broken into fine pieces using a Pulvimixer and pieces larger than 150 mm were removed or broken up.

As the soil was very wet, at optimum moisture content there was concern that the water tanker and other equipment would get stuck or slip off the road and it was decided to add as little water as possible in applying the CBR PLUS. The CBR PLUS was mixed into the water tanker at the rate of 100 parts water to one part CBR PLUS. The dosage rate of CBR PLUS was 0.03 liters per square meter. The mixture was then applied during four equal runs of the water tanker onto the top of the loosened soil and this was immediately followed with the Pulvimixer to thoroughly mix the top 150 mm. The soil was then mixed further by grader.

Once the correct shape had been achieved, the layer was compacted using the sheep's foot compactor. After the third run, the sheep's foot compacter started to climb out of the soil, indicating that desired compaction was being achieved. The soil was then further compacted with a rubber wheel compactor and after final shaping with the grader, the road was opened to traffic. After 3 days the road was again sealed with a cold asphalt seal. The same procedure was then applied to the other lane of the road which was seal coated within a day of construction being completed.

Comments:

1. With the soil being very wet and the need to add water in applying the CBR PLUS there was concern that the soil workability and slipperiness may result in vehicles getting stuck or slipping off the road. After the operators had applied half the CBR PLUS, a significant change was observed. This change resulted in reduced slipperiness and improved traction of the tanker.
2. It is normal practice with this type of soil to place it in maximum lifts of 75 mm, and compacting each lift before placing the next lift. Compaction typically takes 6-8 passes with the sheep's foot compactor. After the application of the CBR PLUS, it was possible to place the soil in a 150 mm lift and compaction was achieved with 3-4 passes.
3. The soil workability changed and improved grading characteristics
4. Despite the wet soil, compaction was sufficient to allow traffic on the newly constructed section.
5. The improvement in soil workability results in reduced construction time.

Result :

In-situ CBR calibration readings taken with a dynamic core penetrometer, showed an increase in CBR of approximately 2.5 times in the soil treated with CBR PLUS over untreated soil and a decrease in moisture content of 20 to 35 percent.

There was no indication of any adverse effects resulting from the freeze and thaw cycles of the treated sections over one complete winter season.

Although the treated CBR values may still be low for the traffic on the road, the amount of visible rutting after the first year was reduced significantly.

It is also anticipated that CBR values could have been further improved, had the section been allowed to remain open to traffic to dry out and compact further, and only sealed after a period of three weeks.