Overview:

Because the logging trucks that haul their lumber usually exceed legal highway load limits, Weyerhaeuser have developed private haul roads, which they have to build and maintain themselves. Truck traffic is high with about eighty, to one hundred trucks per day hauling logs one way and traveling empty the other way. The roads are covered with a 10 to 15cm layer of gravel and the company operates three graders, which permanently re-grade the roads and keep them in shape.

The roads fail due to weak areas in the road base, which develop into so-called "holes". These roads consist largely of silty clays (A-6 and A-7-6). Where the base has a large inclusion of clay, it develops a very soft area and the road fails. These "holes" cause the trucks to slow right down to a crawl and this wastes their trip time and reduces cycle times. The holes are caused by clay being forced further and further towards the surface layer of gravel, and due to the typical kneading action of the clay, these holes grow until they cover the whole width of the road, some being 20 meters long. The bit of gravel on top is dusty and powder dry, but the clay beneath it is completely soaked to above OMC.

Figure 1: "Holes" surface view.	Figure 2: Section view of clay cone.

The roads are traditionally graded by three graders, which are permanently deployed to keep the gravel surface trimmed. They merely push more gravel onto these holes to try to keep the trucks moving over them at a reasonable pace.

In winter the roads obviously freeze and so provide a good haul road with no maintenance, and while hauling was being done only during the winter months, there were few problems. However, due to economic pressures, the trucks now operate year round, also hauling in summer when the roads are not frozen, and this results in a maintenance nightmare.

Due to the high center of gravity of the loaded logging trucks, Weyerhaeuser has the policy to flatten out the crown of the road in winter to reduce the chance of trucks slipping sideways into the ditch. This means that they lower the center of the road by about four inches in the winter.

When considering how to rehabilitate the roads using CBR PLUS, this reduction in height of the crown in winter would mean that in the middle of the road, only about 5cm or less of treated layer would remain if one would only treat the upper 15cm. For this reason it was decided to treat to a depth of 30cm.

1998 PROJECT

1200 meters of the road, 11 meters wide, (from KM 18.0 to 19,2) were treated in the typical fashion by using two graders, windrowing the top layers and after mixing the lower layer, packing it in 7,5cm lifts. Application rates were 0.011 l/m2/CBR PLUS SUPER per 15 cm layer i.e. 0.022 l/m2. Good results were obtained and after the first twelve months the road proved to be solid and required significantly less grading. A hard dustless surface had formed over most of the section and generally the results were satisfactory. A fair amount of surface abrasion caused by the heavily loaded tires occurred, and periodic maintenance had to be undertaken.

At the same time, as a trial, we also treated the top 30cm of the holes by applying CBR PLUS and mixing in some gravel with the clay. These trials however, did not prove successful, as the problem really developed much further down under the surface, and the 30cm layer was just not sufficiently strong to bridge the poor soggy clay underneath.

In 2000 this section was surfaced with a DL10 Special spec crude to further reduce dust and maintenance with little prep work and it has since proved to be a good solution.

1999 PROJECT:

Based on the above section's performance, Weyerhaeuser decided to treat a further 1.5km the following year (from KM 13.0 to 14.5). The late Tom Lange supervised construction of this section, which was completed with some delays due to rain and poor weather. A part of the section was soaked by rain during construction and took quite some effort to dry out.

Figure 3: Ripping soil.	Figure 4: Mixing & drying 30 cm layer.

The proper construction of a 30cm layer proved to be quite difficult. The conclusion is that in the future, construction time of such "double" layers has to take three times as long as single 15cm layers, particularly where layers have to be dried out, due to excessive moisture conditions caused by rain.

The results were satisfactory, but again the layers took a long time to cure and really harden up. Construction was completed by mid July 1999 and the roads froze in the fall as usual at the beginning of November 1999. The thaw usually occurs in May.

Figure 5: Road 6 Weeks after Completion.	Figure 6: End of Summer with Light Gravel Application.

During a site visit in late May 2000, we again undertook DCP readings and found the results to be very encouraging. (See Schedule 1) When averaged out, the DCP Results of the road section in question showed the following encouraging results.

Figure 7: Road soft after heavy rain May 2000.	Figure 8: Road after Application of Gravel.

These results indicate a significant improvement on the whole treated section of the road, but the "holes" in this section remained a problem. Even though we had recommended that the soil in these soft areas be dug out and removed, between Tom and the client, they decided to again only treat the top 30cm. Although there was an improvement for the "holes" it is not anticipated that they will last indefinitely.

In 2001 the client decided to seal the surface with DL10 special Spec Crude and the resultant treated road has proved satisfactory.

Figure 9: Road with DL 10 spec crude surface.

From the previous year's projects, it had become evident that the surface treatment alone of the soil over the "soft spots" did not provide a sufficiently strong layer to bridge the soft poor soils in these soft spots. As a result, these holes or patches of soft soil reappear after a while and then continue to grow as the area around them is weakened and broken out by the trucks passing over them.

For this reason, and after discussion with the Contractor, it was recommended to repair these holes prior to treating the base and sub-base layers over the top.

There were approximately 12 holes in the project section to be treated and the first step was to remove the base and sub-base layers and windrow this soil to the side. The holes were then opened up with a shovel and the poor clay soil was removed. A geo-textile sheet was placed over the open base in the hole to provide a barrier and also drainage to a smaller extent, and the hole was then re-filled and compacted with pit run gravel type material and compacted

The base and sub-base material was then replaced over the compacted pit run and shaped and compacted.

Base and Sub-base Stabilization:

• A light shower plus a safety orientation delayed our start until noon.
• The CBR PLUS was introduced through MPH 100 mixer with 5,100 liters of solution added / pass (CBR PLUS was diluted @ 50:1 because of the high field moisture content of the soil).
• 15 cm x 4.5 meters of the S.B. section (~2/5 of road width) was ripped and windrowed onto the N.B. section. The bottom 15 cm was then treated in 2 passes with the MPH 100. After compaction the top 15 cm was moved back and treated in a similar fashion.
• 400 liters of CBR PLUS from ser #'s 3705, 3706, 3707 and 3708 was used. Work concluded at 10 pm.
• Work commenced at 7 am Saturday with the top 15 cm x 6.5 mm of the N.B. section (~3/5 of road width) being ripped and windrowed onto the S.B. section. The bottom 15 cm was then treated in 3 passes with the MPH 100. After compaction the top 15 cm was moved back and treated in a similar fashion.
• 575 liters of CBR PLUS from ser #'s 3704, 3709, 3710, 3711, 3712, and 3713 was used. Work concluded at 10 pm.
• Work commenced at 7 am on Sunday. The graders shaped the road to a 3.5 % crown and the 815's packed for 4 hours.
• The grid drum and wobblies were then used for 4 hours.
• 15 Liters of CBR PLUS (from ser # 3713) in 16,000 liters of water was top sprayed over the entire surface during final completion.
• 1.5" crushed aggregate was then applied at a rate of 200 T / km as a surface treatment.
• The surface was hard and tight, except in the areas in which Wapiti had repaired with excavation, geo-grid and gravel. It appeared that these spots had not been sufficiently dried and compacted prior to our treatment. It is doubtful if the CBR PLUS will tighten up these sections, as there were few fines present to treat (top 30 cm was 1.5" crush).

DCP Test Results:

We attach copies of DCP Results obtained on May 9, 2000 (Before) and August 2, 2000 and September 26, 2000. None of the DCP results were corrected for the in situ moisture contents at the time of recording. While there is no specific trend discernable from these results at this stage, it is felt that, after the ground has thawed and time is allowed for the layer to dry out this year, there could be more representative results, when new readings are taken.

Observations:

1. The Bomag road milling machine made a significant difference to the speed and efficiency with which the 12inch layer (Base and Sub base) was mixed and blended with the CBR PLUS water mixture. This is particularly appropriate when one considers the problematic way one would normally try to achieve this with graders.

2. Good compaction was achieved first with a drum type compactor and then with wobblies. The gravel surface provided good trafficability and an easily maintainable surface.

3. Throughout the construction, the soft spots remained somewhat weaker than the rest of the treated section, and did not show significant improvement throughout the season.

4. The gravel had embedded well into the surface and the resultant road surface appeared to provide a durable and smooth riding surface.

Project Photos

Bomag Road Milling Machine	Homogenous Well Mixed Soil Layer
View of the Road at KM20.0	View of Road after Gravel Application
Soil Surface before Gravel Application	Road Surface after Gravel Application