Tunnel in sandy soil

Hello everyone, in this post I am going to answer two other questions I got during the my tunnel lecture.

• How does the method of creating a tunnel change when tunneling through sand?

• Sand is a completely different material compared to hard rock. Building a tunnel through sandy ground could mean several things:
• Ground water and surface water could have a strong influence
• Collapse of tunnel face could impact the surface by building a deflection
• More direct load from above, especially when building shallow
• Positive attributes might be:
• Minimum gap between the outer tunnel lining and the soil surrounding the tunnel - positive interface interaction between tunnel and soil
• Grouting is easier and more successful in sandy ground - but, on the other hand, the grout might go anywhere or gets lost when the pores between the sand grains are large enough.
• The construction of a tunnel through a sandy ground can be done with a conventional excavation in several steps, like heading and bench method or NATM, with immediate support of the face and the tunnel walls. 
• Other options are possible. It all depends on the building site conditions and the contractor how they build tunnels in similar ground before and with what they are comfortable and professional at the same time.

• Cost effectiveness of crating a base tunnel compared to a raised tunnel, material removal, tunnel type (for trains, cars, utilities), aesthetic, ...?
• The effectiveness of a tunnel is strongly coupled with economics like an increase of train speed which results in less time traveled, which will give the people more time for meetings, work, etc.
• Further, the effectiveness is coupled to ecological considerations, like the environmental impact - a base tunnel might have less of a "surface"- impact than a train route partially above the mountain.
• Security during the service is a highly discussed subject as well - for instance, a base tunnel might have a higher risk of fire due to its length than a tunnel which lies higher in the mountain and is shorter for that matter. On the other hand, the road to get to the higher point at the mountain might be riskier, the train/car/truck has to slow down, possibly windy road...
• The older train routes above the mountains might be in very good condition and worth keeping, while others might be outdated and have to be replaced.
• The construction itself has its influences, e.g. the material transportation, concrete fabrication, dealing with excavation material, pollution during construction, and so on.. and a generalization cannot be made, it all depends on the specific project parameters.
• Since the tunneling industry advanced so rapidly in the past decades, I believe that more base tunnels are possible. This would reduce the noise emissions and environmental impact on the "surface" and creates a faster and maybe more secure option for the economy.
• To rap it up: it is hard to decide which one is more cost effective. Other factors might be as or even more important to the owner, the immediate population, and to politics. Large traffic projects, like tunnels are, have almost always political influences which could alter the cost effectiveness dramatically.

So, I hope I could answer - or not answer - the questions.

Please, correct, add, or otherwise comment on this. I am always eager to learn new things and to correct "old" views.

Thank you for reading.

Stephie

Summary of the 6th International Conference on Earthquake Geotechnical Engineering - 6ICEGE

What can I say about this outstanding conference?
The name alone speaks thousand words - Geotechnical Earthquake Engineering, and everybody who is internationally involved in this subject was there, attending the conference, participating in presentations, posters, and the exhibition. The program was so dense, the committee had to organize the conference in four parallel sessions each morning and afternoon over four days. And each session had their invited guest speaker of international importance. It was just an abundance in cutting edge knowledge presented.


But how can I summarize this vast amount of happenings?
Let me start with the conference city: Christchurch, New Zealand, where severe liquefaction took place during the Canterbury Earthquake Sequence in 2010/2011. 
The earthquake magnitudes reached up to Mw 7.1. The aftershocks were as devastating as the main events with magnitudes ranging from Mw 5.3 to 6.3. The city's central district simply collapsed and is under construction until today. This was the perfect venue for a conference of this order. 

Destroyed Church, Central District of Christchurch, NZ

The general public is informed after all what happened and even my taxi-airport driver naturally knew what lateral spreading is and asked me if I have had seen some of the affected places here in Christchurch, which I did by the way. The taxi drivers comment gave me a smile and reminded me of the speech the major of Christchurch gave at the beginning of the conference. She said that the work of an geotechnical eathquake engineer is very much important and supports all there is in a city! Thank you, major, for saying it out loud! This made us all feel acknowledged and supported in our work.

Back to the conference: I was particularly interested in this conference and the city where it took place because my own research interest in liquefaction. Other conference subjects, besides soil liquefaction, lateral spreading and their mitigation, were about specific case histories including Nepal, numerical modeling, soil-structure-foundation interaction, site effects, retaining structures and deep foundations, and many more.

I also enjoyed very much the possibility to meet new people, well known professors, like Misko Cubrinovski, who was the chairman of this conference and is a professor at the Canterbury University in Christchurch and one of the leading researchers in the field of liquefaction. I met other participants from the industry like Paul Somerville, one of the leading seismologist for subsurface ground-motions and shear-wave velocities, and I met other graduate students from well established universities around the world, e.g Christchurch, Vancuver BC, Perdue University, UC Berkeley, and others. Also, I was eager to learn about the Nepal Earthquake and took advantage of the complete Nepal session.

OSU Group at the 6ICEGE in Christchurch, New Zealand
From left to right: Scott Ashford, Michael Olsen, Stephanie Lange, 
Daniel Gillens, Ben Mason, Armin Stuedlein, and Kengo Kato

After the conference, the organizer offered Technical Tours. I attended a Technical Tour with the subject of slope instability and remediation on the Port Hills in Christchurch, which were hit hard by rock fall. The tour showed clearly that the temporary security measures - mainly shipping containers along roads and rock faces - were successful. Even the central district of Christchurch uses modified shipping containers for its shopping mall, which is a tourist attraction nowadays.
Four years after the last earthquake event, the city is still building itself up. The conference center downtown is not finished yet, so the conference took place at the Airforce museum - that is why there is an airplane in the background of our Oregon State University - OSU group picture.

In short, I can say that the conference was a total success in terms of learning new things and in terms of social networking.

After the conference was over, most participants took some days off to see some of New Zealand's beauty. I did my New Zealand travel before the conference. And here are some of my impressions.

Personal Impressions of New Zealand, October 2015

New Zealand is a nature's paradise with small windy roads, gentile green hills, harsh mountainous regions, and calm fjord-lands. And anybody how loves nature, birds, and volcanic activities, has to have New Zealand on his or her must-see list.

Why re-reading articles makes so much sense...

Hello there,

if you are like me - busy with so many to-do tasks - and having to start over to read some journal articles, because the last time you started to read this particular article, you stopped for some reason and forgot what it was about, then I have a solution for you, at least this solution works well for me:

For me, having to start over this 40-pages long article about sinking/ floatation of pipelines for the fifth time felt very much demotivating. But I know that this paper is going to be influential for my research. So, I really want to know what it says!

So, what needed to change?

Well, I sat down and thought about what I want to accomplish with my research and what part could this particular author contribute to. After I had done this, I started to read this paper with a different aim: I am taking additional notes on a totally different subject - what to look out for for the setup of physical experiments - as well as the main content.

And this gave me a moment of realization yesterday.
Journal articles are so dense in their content, due to the limited number of pages, that reading it a second time with a different point of view might open up new possibilities, new directions, and might contribute to your work in a totally different way.

I am so excited now to read further in this wonderful article - a pleasurable "candy reading"!

Thank you for listening!
Yours, Stephie.

Tunnel and earthquakes?

Hello everyone, as I mentioned in my last post I am going to use my blog here to answer questions I got during my tunnel lecture I gave last fall.

• What are types of tunnel earthquake reinforcement?

• To reinforce an inner tunnel lining the "normal" structural reinforcement bars are used. I put "normal" in quotation marks because the tunnel reinforcement has specific connection types, main bars in cross section are curved, and often tunnel linings are build segments of about 10 m or 30 ft in length so each edge has terminal bars.
• To get to the question against earthquakes: it depends. Building a tunnel in the ground goes along with a positive behavior against earthquakes - the ground shakes and it is assumed that the tunnel goes with the same movement.
• Challenges are at points of transitioning from a softer soil to, let's say, a hard rock. These points should receive the attention. A similar but more severe subject is the crossing of a fault line, e.g. the water mains in southern California cross the San Andreas Fault.
• Well, how do you build a tunnel at these difficult points? That is a difficult question to answer in just one blog article. It is less about reinforcement and more about the whole design of the tunnel. In March last year (2014), I attended parts of the Tunneling Class with Prof. Sitar at UC Berkeley as a guest listener and a representative from Jacobs Associates presented on the Claremont Tunnel with a diameter of 2.7 m or 9 ft crossing the Hayward Fault line near San Francisco. They constructed a pipe inside a tunnel that can withstand a lateral offset of 2.6 m or 8.5 ft. The whole project of seismic improvement costed $38 Million! Not every water department has such an amount for a seismic upgrade, but a loss of the main freshwater line would cost more after an event. For a more detailed description, the following two pictures have links below them.

Claremont Tunnel Design - Fault Crossing

Claremont Tunnel - Jacobs Associates

The subject of building tunnels across faults is very present and each solution is unique and innovative. And at some places, like L.A. and the San Andreas Fault with an estimated maximal offset of 7 m or 20 ft, solutions do not exist yet.

Thanks for "tuning in". If you have questions or comments, please contact me.

Stephie

Why do I care about tunneling?

Tunnels have a long history of being mysterious secrets, which are hidden away for hundreds or thousands of years as water supply systems or secret connections under existing cities. Studying tunnels requires me to go beyond the visible structure. Darkness and hard labor, together with engineering strategy and new machinery give me a mix of adventure and know-how. It is fascinating to create a tunnel in the ground, no one ever sees behind it, most parts of a tunnel are invisible to the normal eye. And yet, building a tunnel takes so much.

This passion of me is something I want to give on. So it came that I was able to give a lecture about tunneling at Oregon State University (OSU), where I study right now for my doctorate in geotechnical engineering.

I am going to use my blog here to answer the questions I got during the lecture. Some are going to be answered now, some in later posts.

• How long is a tunnel boring machine (TBM)?

• The TBM itself can be around 25 m (80 ft) long; however, the backup system to manage all the logistics for the tunnel excavation and support installation can be up to 150 m (500 ft) or more.

• How do you deal with extreme seasonal whether changes (-30°F to +80°F and icing issues in the portals)?

• The problem of extreme whether changes requires good construction materials and workmanship. Temperature changes must be considered during the design phase.

• Old tunnels can show icing at the walls close to the portals which could mean cracks somewhere in the wall so the water from the rock or surrounding ground can travel through the tunnel structure. If the leak is not extreme, you monitor it every year or every several years and then decide what to do.

• In case of a new tunnel with icing close to the portals, you see where the water comes into the tunnel and when appropriate or necessary, those tunnel areas can be injected and sealed, especially when the tunnel lining is made out of reinforced concrete.

• During fires, do they cut the ventilation to reduce oxygen?

• No. In a tunnel a special ventilation is activated during a fire to suck the smoke away from the fire and people can rescue them selves to the next emergency exit without having to go through deadly smoke. 

• Because the tunnel is a closed tube, the biggest problem is the extreme heat which could result into the collapse of the tunnel structure which is dangerous for the rescue groups and fire fighters.

• Ventilation and heat have to be considered in the design of the tunnel structure.