Like this:

I don’t like the proposed tunnel in Seattle.  I really don’t like it.  I’ve ranted and raved and complained about the tunnel on Twitter to the point that a few people even noticed that I don’t like it.  It suddenly occurred to me that I need more than 140 characters to explain why I really don’t like it, so here I go.

I don’t like the tunnel because it it is adding as much risk as it is taking away.   Why do I think that?  Well, based on the information provided by the  US Department of Transportation, Federal Highway Administration Technical Manual for Design and Construction of Road Tunnels, the  tunnel is a bad idea.  In fact, according to the manual, it faces the potential for catastrophic failure.  A significant section of the tunnel will be built in ground that studies show is likely to undergo liquefaction and ground failure.  According to the DOT manual:  “the greatest risk to tunnel structures is the potential for large ground movements as a result of unstable ground conditions (e.g., liquefaction and landslides) or fault displacements. In general, it is not feasible to design a tunnel structure to withstand large ground displacements.”

Large scale ground displacement?  That is exactly what is expected to occur in most of the soils the tunnel will be built through.  That is why we need to get rid of the Viaduct and seawall.  Remember this video?

Looking at geotechnical documents from the path of the tunnel (and we can, because there are available in an online database )  you see that most of the ground is exactly the type of ground is very clearly ground that readily liquefies in quakes.  This isn’t surprising, it is the type of ground one expects in an area that was once sand flats—sandy, watery—ready to liquefy when shaken.  (Don’t know what liquefaction is?  UW does a good job explaining).  What can ground that liquefies do? Here’s a video of ground in Japan liquefying during an earthquake:

When reading the WSDOT reports, there seems to be a contradiction between their emphasis of the role liquefaction will play in an earthquake for the viaduct and seawall (complete with video) and insisting that it won’t play any role on the tunnel. We had liquefaction in that area during Nisqually, we will have it on a much larger scale during larger earthquakes.

Ironically enough, the best report I’ve found confirming that over half of the proposed tunnel route is on ground prone to liquefaction is a WSDOT document evaluating the Alaskan Way Viaduct.

The report details past liquefaction and water main breaks along the tunnel route from the 1949 and 1964 earthquakes, they clarify that even though the worst problems will be where fill is located, there is also expected to be ground failure problems in areas without fill.

The conclusion of the report states:

• Widespread liquefaction is expected to occur in a design-level ground motion…Significant liquefaction is likely even if the motion is considerably less intense than the design-level earthquake motion.

• Liquefaction hazards extend throughout the waterfront fill. Major damage to Alaskan Way, the sea wall, piers, and lifelines along the Seattle waterfront could occur in a design-level ground motion.

and: “Widespread liquefaction is also expected to cause lateral movement of the waterfront fill toward Elliot Bay. The amount of movement will be strongly influenced by the seismic performance of the sea wall. Sea walls retaining similar liquefiable soils have failed with large lateral movements in past earthquakes. These lateral soil movements would occur in an irregular pattern and could induce large differential movements of the viaduct’s foundations. These lateral foundation movements could cause multiple sections of the viaduct to collapse.’

“The amount of lateral movement of the seawall is difficult to predict. Rough calculations for a particular section with a particular wall type indicate that lateral movements will be on the order of 3 to 4 feet.”

I suspect that the Federal Highway Administration would consider having a large part of the water front pushed 3 to 4 feet: “large ground displacement”

A local civic engineer said that liquefaction won’t be a problem, because the tunnel will be dug under areas most likely to liquefy in a quake–to be dug in soil that is highly compacted because of the weight of past glaciers.  That doesn’t fit though, since there is a  report by the Multi-disciplenary Center for Earthquake Engineering discussing how different soil types may cause damage to tunnels depending on the soil types. It is interesting because they in that report, they assume that the tunnel that face damage are  situations where they are built through rock with a layer of liquefiable soils on top. According to their findings, Tunnels through rock face a high risk of damage from ground displacement above the rock layer.

Our tunnel isn’t going to be built through rock with liquefiable soils above it.  In our area, we aren’t sitting on a layer of rock, we are, instead sitting in a large sediment filled basin .    If a tunnel built through rock faces damage if the soil above it liquefies, imagine how a tunnel though just compacted soil is going to do?  The key message of the report is that tunnels and soils that are prone to fail really shouldn’t be mixed:

“Ground failure can include different types of ground instability. These can include faulting, liquefaction, and tectonic uplift and subsidence. Faulting occurs when an increase in stress causes rocks to break. Liquefaction is a phenomenon in which the strength and stiffness of a soil is reduced by earthquake shaking or other rapid loading. … These phenomena have been responsible for tremendous amounts of damage in historical earthquakes around the world. Each of these hazards could possibly be detrimental to tunnel structures (Merritt, et al. 1985).”  http://mceer.buffalo.edu/education/reu/04Proceedings/01Adme.pdf

How does the location of the tunnel relate to that?  Well, we’ve pretty much got it all.  Liquefaction, and expected uplife and subsidence at that spot.  The heights of West Seattle is an example of previous uplift nearby.  I used Google Earth to overlay the locations of liquefaction mentioned in the report and the map of the liquefaction areas caused by Nisqually from PEER map The red dots are areas that experienced liquefaction, the yellow line at the bottom of the picture is one of the identified strands of the Seattle Fault.

There is a very good chance the tunnel will actually cross an active fault strand. The fault’s fracturing of the surface created an magnetic anomalies that created a pretty clear picture of its location. In areas with less development, it has been possible to do trenching and confirm strand locations, but in downtown Seattle there has been so much development for so many years it is almost impossible to hope to find an area where digging trenches will lead to exposing evidence of the fault. If you look at the image of the anomaly, you can see that it appears to go right over the proposed entrance of the tunnel (The image below is from here but I believe the original this report .)

Reading local media, the only real discussion of tunnels and earthquakes is a mention that during the last earthquake in San Francisco, the tunnels did OK. Yet, the literature on tunnels in earthquakes is clear, the fact is, there is a long history of tunnels being damaged in earthquakes, and the analysis is that the most likely conditions for severe damage is proximity to faults (0.97 miles from identified fault strand), ground displacement, and moving from different soil types (part of a tunnel being held securely by one type of ground, while another part of the tunnel is pulled and twisted)-all inevitable conditions of this tunnel.

And of course, if the liquefiable soils, and the proximity to an active crustal fault was not enough, the entrance of the tunnel is in the area where a tsunami has happened before.

Tsunami Inundation Map of Elliott Bay

So far I’ve read about the risks of cost overruns with this tunnel, but just about no talk about actual physical risk, ‘catastrophic risk’ as the DOT says.  When are we going to start talking about that?

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