Tunneling and Bridging to Success:
Forest Road Design on B.C.’s West Coast

Landslides associated with old logging roads have made us recognize all too well the mistakes of the past…

and encouraged us to try and do things differently.

The story of the CW300 road is an example of how this challenge was met.

It is a story of
steep terrain…..

Avalanches, debris flows and rockfall…

An Adit

A Bridge

Difficult terrain and…

A dedicated team!

The project is located near Phillips Arm,
about 65 km north of Campbell River.

The story began years ago when the volume and value of timber in the Shore Creek valley was noted.

The first attempt to access the Shore Creek valley was via a direct line from the Clearwater Valley.

The route crossed a very steep sidehill that required a considerable amount of endhauling.

Construction ended abruptly when a cutslope failure buried the road heading.

Water from slopes above had overwhelmed material in the cutslope, causing it to fail.

Slide 17

To do this, the following strategy was devised:

After much effort and reconnaissance, a second route was proposed.

The second route involved using a switchback located at the top of an incised alluvial fan.

There were two problems, however: the switchback was in an avalanche slidepath and…

there wasn’t a lot of room to build the switchback.

The route was feasible, though, and so the decision was made to assess it in detail.

To this end, a detailed terrain stability field assessment of the proposed route was completed.

This assessment identified hazards and provided specific recommendations for benching and endhauling.

The same information was presented on maps so that complex technical data could be readily understood by the design and construction teams.

The detailed map showed terrain, benching, and endhauling requirements, and hazards.

This detailed information helped ensure that all issues were identified and dealt with.

When all the information was compiled, a number of problems were identified.

It was found that the switchback, although feasible, would require a large area and fill.

To reduce the area needed, a railroad switchback was proposed for this location.

A railroad switchback would also require much less fill and cause less site degradation.

To turn, a logging truck coming down the hill would drive into the first leg of the switchback,

back up into a natural slot in the rock,

and then continue on down the road.

Several additional things had now been learned about modern road construction:

However, the detailed geotechnical analysis found one particularly difficult issue.

Although most of the terrain through which the road would pass was either stable,

or at least could be managed for hazard….

one area presented a major problem.

Unstable rock!

At this location, faulting had broken the rock into vertical slabs that were unstable.

Although it was possible to remove one or two slabs, there was no assurance that others would not be present.

Blasting and scaling experts were brought in to help plan a course of action.

They determined that the unstable rock could be removed, but that it would be costly and

leave a lot of unsightly rock covering growing sites and wildlife habitat.

Most worrisome was the uncertainty factor: would scaling actually remove the hazard…

and allow the road to be safely built and used.

And then, of course, there was still the matter of the snow avalanches and debris flows.

These problems were severe enough to warrant another review of the road location.

Fortunately, the earlier work had been detailed enough to allow all options to be re-considered.

This included an option that involved crossing Shore Creek from a deactivated road.

It would then involve using the railroad switchback concept at another location.

Most critical was to determine whether the railroad switchback was viable at this location.

The design team was again sent out and were able to confirm that such a switchback was possible.

This third route avoided most of the avalanche, debris flow, and rockfall hazards.

It was also located in an area of more stable rock, although partially in an old rockslide deposit.

But the slide deposit represents a single event, unlikely to re-occur, and was deemed not to be a threat to the road.

To use this route, an old deactivated road first had to be assessed, and then re-built.

Again, a detailed plan was prepared that accurately established the amount of fillslope pullback and endhauling required.

The next problem was how to cross Shore Creek at the base of a waterfall.

Crossing the creek was one challenge, dealing with the possibility that the bridge could be damaged by cascading ice was another.

Again, the design team was dispatched to the field to try and solve yet another problem.

The team used tree damage to determine how ice cascades down the waterfall.

The tree evidence made it possible to clearly define the path of the cascading ice.

Allowing troughs of less hazard to be identified

The bridge was then located in one of the troughs.

Finally, a log crib and placed rock fill were used to complete the bridge crossing.

Once past the bridge, the road up to the switchback was still a challenge.

There were steep slopes, rock, and two remaining avalanche and debris flow gullies.

Again, a metre by metre geotechnical analysis and a detailed site plan were used to design the road.

The site maps provided the necessary detail to allow accurate planning to be carried out.

The biggest hurdle was the switchback itself- it still needed more room.

Unlike the alluvial fan switchback, there was no slot into which a truck could back into.

So a slot was made and the adit was born!

It would provide the additional room for trucks to actually turn around.

Trucks coming down the hill move forward,

back into the adit,

and then continue down the road.

To minimize site degradation, the road was kept narrow, and a minimal ditch and numerous cross-drain culverts were installed.

Retrieved fill from the deactivated road, and excess material from the new road, were endhauled to safe spoil sites.

After 7 years of planning and construction, the road was finally finished!

Now the business of harvesting wood could finally begin!

Summary: what made this project successful?