From: "Richard Eade"
To:

This entire revelation about the previously unknown ground conditions influencing the length of the tunnel but not its cost is a bit incredible so I thought I'd take a look at it in more detail.

GROUND CONDITIONS:

The length of the tunnel was to be determined by the choice of one of three east portals; the first just south of Laurier, the second just north of the Campus Station, and the third midway between Mann and the 417. Council
directed Staff to plan for the southerly most portal, south of Mann. The Consultants and staff were then looking at Cut & Cover for the section (at least) from the Campus Station (including the station) to the east portal.
They were also candidly saying that it was likely that Cut & Cover would be used for part of the section between the Campus Station and Laurier because of the depth of the bedrock.

If the bedrock was deep enough before to warrant Cut & Cover, would finding it to be deeper really have any affect at all?

And how much is the difference between what Staff was expecting and what was found by the drilling?

Figure 1: Rideau - Plan vs. Geotech results

In the figure, the dashed black lines were from the original plan, with the upper one showing the approximate start of the bedrock and the lower one showing the limit of weathered rock. The dashed red line is the new estimate
of the start of competent bedrock, based on the geotech study.

Not much difference in the region of the Rideau Centre; there is still a deep valley in the bedrock. Notice that Staff has positioned the station to the west of the valley to minimize the problems. Since the tunnel is to be lined (according to the approved recommended plan's document - TBM Launch Site, page 47 of ACS2009-ICS-PGM-0214 - Document 1.pdf) the TBM can proceed through the valley, pushing on the tunnel lining. This section will likely need some special treatment to help the TBM but it is not too difficult.

There are really no differences in what the boring found to what was expected until right at the 'kink' in the Transitway a hundred and fifty metres south of Laurier.

Figure 2: Laurier - Plan vs. Geotech results

Notice that the geotech study found a second, broader valley right at the 'kink'. It should be realized that there has been only a single bore (T-17) between the two bores which found pretty much what was previously expected; the red dashed line is only a guess as to how the bedrock dips to the depth found in T-17. This dip could have been handled in the same manner as the valley under Rideau Street, but since Staff was already planning to use Cut & Cover from the Campus Station, it would be sensible to extend that Cut & Cover a hundred and fifty metres further north and simply pull the TBM out at the 'kink'. Unfortunately, this will be a fairly deep Cut & Cover, which will mean higher cost; however, this cut will need to be made just to recover the TBM and get the tunnel up to the surface for a shortened tunnel.

Since the Campus Station was already planned to be built using Cut & Cover, any changes in the bedrock depth under the station is almost irrelevant; in fact, slightly lower is slightly better because there could be less blasting needed. Once the tunnel is south of the station, the bedrock was already predicted to be mostly below the tunnel.

Figure 3: Mann - Plan vs. Geotech results

Notice that south of the station the predicted and actual are both too deep for the TBM; which is why Cut & Cover as planned originally.

Something to note is that these bore-holes were west of where the tunnel was to run and therefore would be lightly down-hill from the tunnel's path; it is no wonder that the bedrock is being measured a couple of metres lower than what is expected along the tunnel.

TUNNEL LENGTH:

So, the only section which was different from what was expected is right around the 'kink'. There is reason to make a change in this section, but not in the rest of the tunnel to south of Mann. It should be noted that Staff is recommending shortening the tunnel by 600 to 900 metres. From the planned east portal, a 600 metre shortening would cut the tunnel back to the south end of the Campus Station, while 900 metres would go back to the 'kink'.
Going back 900 metres offers little benefit since the TBM recovery pit and its Cut & Cover construction would likely be back at Laurier which is an area that the TBM could be cutting through. If the Cut & Cover began at the start of where the bedrock dips, then the TBM could be used for the maximum distance before a Cut & Cover ramp brought the tunnel up to a surface Campus Station. This ramp would have a grade of about 5% and, thus, like other grade changes in the plan, preclude any vehicles other than LR vehicles; i.e. there is no simple upgrade path to a heavy-rail subway. This change would represent a reduction of about 800 metres on the length of the tunnel, almost all of which was planned to be Cut & Cover, and result in no reclamation of the Transitway land beside the University.

COST:

Based on the projected costs from the approved plan (Cost Estimates on page 54 of ACS2009-ICS-PGM-0214 - Document 1.pdf) the tunneling costs, including the stations and all rail infrastructures was to be $735M for the 3.2 Km
distance. If we subtract out the $90M for each of the three downtown stations and $65M for the Campus Station, the tunneling and fitting of the tunnel was about $125M per Km. So we should be subtracting approximately $65M for the station and $75M for 600m of tunneling, so a saving of roughly $140M. However, there are now conversion costs for the surface line; which run an average of about $60M per Km, including stations. Thus, we need to add in the cost of about 800m, so almost $50M, leaving a total saving of only $90M. Since $90M represents only about 4% of the $2.1B project cost, the saving would be insignificant and would likely be eaten up by a small cost increase elsewhere.

CONCLUSION:

Staff could have easily overcome the change in ground condition at the 'kink' if they had wanted to, using part of the $100M Director's Contingency if needed. It is more likely that Staff is trying to find possible ways of reducing the tunnel cost to overcome increases they have found elsewhere. Notice that one of the first parts of the plan to be sacrificed is a change which Council directed because it thought that reclaiming the Transitway land would make a more inviting environment beside the university. Council should ask for a complete, updated cost estimate of each piece of the project; with comparisons to the previous ($2.1B) estimate so that Council can see where the costs are going up and where things should be adjusted. I do not believe it would be wise for Council to make a decision on such a change in isolation of the rest of the picture.

Richard Eade

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