How are underground structures constructed?

Some of you have been asking me how underground structures are built, so here’s a simple summary.

There are two methods of excavation, drill-and-blast and using the tunnel boring machine. Drill-and-blast is a cyclical procedure, where the rocks are first drilled, blasted with explosives, ventilation is created, then the overhanging rock is supported by rock bolts or concrete, and the whole process repeats itself (Zhao & Tan, 2012). 

Drill-and-blast process. Picture taken from www.mtr-shatincentrallink.hk/en/construction/construction-methods

Using the tunnel boring machine on the other hand is a continuous procedure (Zhao & Tan, 2012). The tunnel boring machine looks like a ferocious, teeth-baring earthworm enlarged up to a 100 times. I know, earthworms do not have teeth, but just imagine a set of nasty spiralling teeth in them, and you have a tunnel boring machine! The Cutterhead, which is the front part of the elongated machine, contains roller cutters. Pushing the machine in and rotating the Cutterhead helps to crack hard rocks (Zhao & Tan, 2012).

Tunnel boring machine. Picture taken from www.dlr.de

Both methods have their strengths and weaknesses and they are used for different rock types and ground conditions. For example, the tunnel boring machine can work on soft to the very hard rocks, but it fails in drilling rocks of differential geology, where strong rocks are mixed with weak rocks. Drill-and-blast is suitable for differential geology but it cannot cope with groundwater seepage (Zhao & Tan, 2012).

Therefore, before tunnelling works can take place, engineers have to investigate the underground properties, like rock types and the level of groundwater infiltration to choose the appropriate excavating process.

Literature cited:

Zhao, J. & Tan, S. B. (2012). Underground space development in Singapore rocks. PTRC and NCUS Workshop on Underground Space and Rock Cavern Development in Singapore, NTU. 17 January 2012.

Is underground space the answer to our problems? (journal review)

In the journal article, “Sustainable Development and the Use of Underground Space”, underground tunnels and buildings are hailed to be the solution to sustainable development. Roberts’ (1996) idea of sustainable development was one that limits imports, has efficient and effective infrastructure systems, maximises the use of urban and rural lands, and produces cost-effective exports with the least waste. Municipal waste should also be re-used as inputs for agriculture.

By limiting imports, Roberts is suggesting that agriculture has to be expanded to meet the needs of a growing population. He argues that rural areas should be kept as agricultural lands, which means that development and construction has to be focused in already urbanised areas. He envisions that “future megacities will be concentrated, attractive and healthy places to live, surrounded by rural areas”.

However, such a plan is difficult to accomplish for countries with small land areas (such as Singapore). Farming in these small countries can hardly meet the demands of the population. Expanding farming would mean that urbanized lands have to be retreated for ‘rural’ lands. Although high intensity farming can help increase output with the restricted space, it is usually too costly for long-term dependency. Of course, such a move would be going against the nature of economics because it would be forcing countries with no comparative advantage in agriculture to grow their own food. On another note, it is possible that instead of having agriculture, the intended lands for farming can undergo reforestation which can reduce the overall carbon footprint of the country.

According to Roberts, using underground space has many benefits to the environment in terms of resource recycling, reduction of vehicle carbon emission, recovery of farm lands, and energy savings.

The first benefit he talked about is resource recycling. In order to reduce waste, the waste products of one industry can be the raw materials of another. Industrial parks can be connected via underground tunnels, for the transportation of waste products to the industry that can use them, for the construction of combined waste treatment plants (which can be more efficient as the scale is bigger), and the exchange of cooling/heating waste water (water used for cooling purposes that is heated up and no longer useful can be passed on to industries that require heated water). Of course, all these would need a low-energy delivery system located underground. Such an idea is feasible and has great potential to reduce wastage and even lower energy consumption, but it is only practical in counties with highly diversified industries. Otherwise, it is very unlikely for one industry to find the waste products of another as potential raw materials.

Photo from Jamiecphotos.com

The second benefit of using underground space would be the reduction of vehicle emissions. By developing an efficient and reliable underground mass public transportation system, it would encourage commuters to switch to the cheaper and faster alternative which is underground. This would decrease the number of motor vehicles on the road. Less petroleum would be used and less carbon dioxide and acidic gases would be emitted. Since transport, in particular motor vehicles, is a significant contributor to anthropogenic carbon emissions in Asia and most likely the whole world, a reduction in vehicle volume would definitely alleviate the pressures of global warming (Ohara et al., 2007). Such a massive transportation system would be best situated underground because the ground can snuff out the high decibels generated by the rapidly moving trains and also the system would be protected from destructive natural forces like hurricanes and even earthquakes. 

Lastly, Roberts highlighted the most important function of underground structures which is energy savings. Underground structures can reduce the amount of energy required for the running of factories, transportation, offices and homes. It was indicated in the article that studies have shown that decreasing energy consumption by as much as 50% would have no reduction in standard of living. This proves that lowering our energy needs would have almost no trade-offs to living quality. He also wrote that “improvements in energy efficiency will be more economical than developing new supplies of energy”.  I believe that this is the most optimum measure in the present moment. While alternative sources of energy are being developed, we should cut down on our use of energy as much as possible until a viable source is found. Research on renewable energy is imperative and the government should pump funds into research. But at the same time, we need to actively reduce our exorbitant energy usage to minimise the damage done to our environment.

In conclusion, the use of underground space is a potential solution to a sustainable future, but it is not the best or only solution. This is because the effectiveness of underground structures may not apply to every country and construction costs are high. It is recommended that larger developed countries explore the use of underground space in those aspects suggested by Roberts and assess the advantages. Developing countries should also start taking an interest in underground structures and draft out plans of their future land use. They should also conduct exploratory studies to determine the feasibility of underground projects. Singapore is still relatively new to underground structures and more improvements can be made to expand underground transportation systems and make it more efficient.

Article reviewed:

Roberts, D. V. (1996) Sustainable Development and the Use of Underground Space. Tunnelling and Underground Space Technology. 11 (4). p. 383-390.

Literature cited:

Ohara, T. A. et al. (2007). An Asian emission inventory of anthropogenic emission sources for the period 1980–2020. Atmospheric Chemistry and Physics. 7(16). p. 4419-4444.

Surprise interview segment

Dr Jose C. E. Mendoza on underground living, the environment and outer space (?)

What is your opinion on living underground?

You know, I’m a biologist, so I love the outdoors, I love to be in open spaces. Or else I would feel quite claustrophobic. That being said, if it is a necessity, I don’t mind using the underground for things like storage, but not as living space. I have faith in the ingenuity of people, they can make conditions underground as close to the surface as possible.

What kind of structures do you think should be placed underground?

[He chose everything except residence of course!] Offices, schools, retail, sports facilities, research labs (definitely!), and transport (We’re already doing that right?). But I think what’s most important is that we make good use of the space and do not affect the aesthetics of the land. Actually, I would prefer to live under water, I mean we can get a sense of space there. Or maybe even outer space! We always have those fantasies to colonize the moon. Underground living is something really new to me.

Given that Singapore is facing land constraints and a likely increase in population, how do you think we should plan our land use? (E.g. building upwards, building downwards, reclaim land, clear land)

I think that going upwards or downwards doesn’t make any difference, because when you are building upwards you are also preparing for building downwards. We should exhaust all possible lands first. You see, Singapore is both a city and a state. I would say Singapore is more of a city than a state.

So you’re definitely against the clearing of land?

We should intensify the use of land that are already quite built up rather than use those small patches of forests. Keep these patches, increase the connectivity between Bukit Timah Reserve and the Central Catchment. And if we want to build underground we have to do site explorations to see if Singapore is suitable for underground constructions. It must also be cost-effective.

Do you think that underground buildings are better or worse for the environment?

I’m just thinking what do we do with the rocks that are being excavated?

We can use the excavated rocks for reclaiming land.

Aha! So that is the problem. [Gives a wide grin]

Oh, so you think land reclamation is not good?

Yea, reclaiming land is not good. Because where are we going to reclaim our land from? Most likely mangroves at the coastline. It’s going to affect mangrove areas which have a lot of biodiversity. In Singapore, there is concern to preserve biodiversity. We still don’t know what biodiversity we have in the coastal areas. You don’t know until you do a proper study… This is a very boring response hor? [Not at all, Dr Mendoza :D] When you build something underground you will disturb what is on the surface. Just like the plan to build the CIL [Cross Island Line] under the CRR [Central Catchment Reserve], when you drill underground, it could lead to a crack in the rocks, and then what? [Prompts me for the answer. Err…animals in the reserve would be affected?]

Actually, we can use the excavated rocks for paving roads too.

Paving roads ah… Do we need so many roads?

What we should be thinking is what exactly is fuelling this demand for space? A lot has got to do with economic growth. We can just live with less, lower our ecological footprint, then we don’t need all that space. We cannot always create solutions to our problems, we have to change our mindsets. If there is an option to live with less, I’d go for that option.

What would you like to know about underground structures?

Erm, how they’re built, what are the applications in Singapore, what are the impacts on the environment, and what kind of psychological problems would it bring. [I guess that’s more work for me!]

Quote of the day from Dr Mendoza: “Do we need all that space?”

P.S. I would like to thank Dr Mendoza for his patience in sharing his thoughts with me, even though I just sprung out of nowhere without giving him time to prepare. 

[Date interviewed: 13 October 2014]

Underground Structures in Singapore Part 2: The industries

Jurong Rock Caverns

Land in Singapore is so precious that simply using it to store commodities is such a waste. The Jurong Rock Cavern is a 130-metre-deep cave under Jurong Island that stores oil like naphtha and condensate (JTC, 2014). It is meant to free up surface space so that space above the ground can serve other important uses instead of just storing hydrocarbons.

Photo from JTC, 2014

Interesting facts about the Jurong Rock Caverns (Lim, 2014):

1.       This project took 6 years of planning and 8 years of construction.

2.       Why so long? Because the cavern is hollowed out using explosives and it takes 1.5 to 2 years for each cavern to be excavated.

3.       The caverns made available 60 ha of land on the surface.

4.       The caverns are the deepest known public construction in Singapore, deeper than the deep tunnel sewerage system (remember this from our NEWater field trip?)

5.       The 3.5 million m³ of rock excavated will be utilised for land reclamation and laying roads.

6.       During the caverns’ opening ceremony, Prime Minister Lee Hsien Loong announced that this project exemplifies Singapore's determination to develop a petrochemical industry, despite our limited land area and the likely effect of the coming UN Framework Convention on Climate Change treaty on carbon emissions.

Underground Science City

Photo from Straits Times

When we think about an underground research lab, we would probably think of an evil villain’s secret lab where all the genetic experiments, flasks full of weird chemicals or robotic assistants are hidden. Well, there are plans to build an underground research lab in Singapore, not for mad scientists of course, but for research and development. JTC is considering the proposal of an underground Science City to be located underneath Kent Ridge Park (not too far from NUS!) which could house “4200 scientists, researchers and professionals” (Feng, 2012). The Science City would consist of 40 connecting rock caverns and up to four levels worth of commercial space (Feng, 2012). According to the Straits Times report (2012), building a science city beneath the ground can make use of the ground’s natural isolation against noise and vibration and can easily contain the fall-out of hazardous substances.

If underground structures are so great, why hasn’t Singapore built more of them? The answer lies in the cost of constructing underground buildings. The differential rock geology of Singapore’s ground makes excavation more expensive (Chin, 2013). An example would be the harder granite and norite rocks found in Bukit Timah and Bukit Gombak respectively (Sharma et al., 1999). On the other hand, the sedimentary rocks in Jurong are quite weathered, making them easier to excavate. According to the Straits Times report by Chin (2013), the cost of building one storey below ground is the same as building three storeys on the surface. This can be very expensive judging by the number of underground structures we have to build to compensate for those above ground. Hence, unless Singapore has exhausted all means of cost-effective land use, underground structures are not likely to dominate the country in the near future.

Stay tuned to the next post for something really interesting and unexpected (I hope)!

Literature cited:

Chin, D. (2013) Singapore’s (costly) underground ambitions. The Straits Times. 10 September 2013.

Feng, Z. K. (2012) JTC looking at plan for underground science city. The Straits Times. 14 November 2012.

JTC Corporation. (2014) Jurong Rock Caverns. [Online] Available from http://www.jtc.gov.sg/RealEstateSolutions/Pages/Jurong-Rock-Caverns.aspx. [Accessed: 12 October 2014]

Lim, L. (2014) Singapore opens S$950m underground rock cavern at Jurong. Channel News Asia. [Online] 2 September 2014. Available from: http://www.channelnewsasia.com/news/singapore/singapore-opens-s-950m/1341836.html. [Accessed 11 October 2014]

Sharma, J. S., Chu, J. & Zhao, J. (1999) Geological and Geotechnical features of Singapore: An Overview. Tunnelling and Underground Space Technology. 14(4). p.419-431

Underground structures in Singapore Part 1: The underground campus

NUS is no small campus. It has so many faculties and facilities- Science, Engineering, libraries, the SRC... Utown was even added recently to provide the booming student population with more lecture theatres and recreational places. Yet we somehow feel that these are not enough. We need more classrooms, more lecture theatres, more sports amenities, more laboratories. But we are already squeezing the very last land space we have, any more and the school would lose its beauty and liveability. At this point you might have guessed. Yes, go underground!

Both NUS and NTU have just finished their exploratory research on the feasibility of underground development. NUS vice-president of campus infrastructure, Yong Kwet Yew mentioned in an interview by the Straits Times that going below ground can allow the space of Kent Ridge campus to be maximised while keeping the present green and open spaces aboveground. He raised the possibilities of “sports facilities, classrooms, libraries, auditoriums and even research laboratories, data centres and parking structures”. However, there was no real proposal for the construction of these buildings and Dr Yong called for more studies on ways to make underground areas more comfortable such as using natural illumination.

As for NTU, there are plans to build a four-storey underground learning centre and a three floors worth of sports hall below ground. The lucky NTU students would one day get to swim in an underground swimming pool! (Feng, 2013)

What about SMU you may ask? SMU already has an underground link-way that connects the five major buildings and the Bras Basah MRT station (The Business Times, 2013).

Is the idea of expanding underground good news for you? If we cache some of our buildings underground the surface would look less ‘cluttered’. We can afford to have more trees and even wildlife. It would be a wise move to shift air-conditioned buildings below the surface since they would then require less energy for cooling. However, for large scale buildings like libraries and auditoriums, safety measures have to be thoroughly studied and communicated to students. Hence, for a start, laboratories should still remain on the surface due to the higher risk of a fire hazard where the effects would be more rampant in underground enclosed spaces.

When we talk about studying, we probably would not think it a big deal to have it underground, but when it comes to actually living underground permanently that is when we would start hesitating.

Literature cited: 

Feng, Z. K. (2013) NUS, NTU complete studies on underground campus. The Sunday Times, Home. p.18. [Online] 14 July 2013. Available from http://newshub.nus.edu.sg/news/1307/PDF/CAMPUS-st-14jul-p18.pdf. [Accessed 3 October 2014]

The Business Times. (2013) NUS, NTU look into underground expansion. p.8. [Online] 24 September 2013. Available from http://www.smu.edu.sg/sites/default/files/smu/news_room/smu_in_the_news/2013/sources/sept24/bt_20130924_1.pdf. [Accessed 3 October 2014]

The 2 challenges

The two key challenges of building underground residences are lighting and ventilation. Sure, we can install numerous lights and use powerful air-conditioning like what we have in our underground MRT stations and shopping centres. However, that would negate the savings in electricity that underground buildings are said to bring (remember the temperature stability and lower energy requirements to heat/cool them?). I’m sure our immediate response in a basement carpark is to get out of that place as soon as we can, find the nearest door to air-con! At three storeys below ground, the air is just humid, stagnant and warm.  If we are to switch on all the lights and air-conditioning units at full power every single day, 24/7, think about the crazy energy usage! We might as well be better off squeezing on the surface. Besides, living in a windowless environment with ‘white light’ all the time isn’t healthy for us in the long run. Just imagine living in your office or tutorial rooms, that kind of man-made feeling might just drive us to depression. That’s why we need an energy-efficient ventilation system and natural light.

One energy-saving ventilation system currently used by the Ewha Campus Centre building in Seoul, South Korea is the thermal ventilation system. In such a system, there will be an underground labyrinth where air from outside can be forced in and heat is lost to the ground (Song et al., 2014). The cool air can then be enjoyed by occupants of the building. This system has been proven to be effective as the yearly energy demand for conditioning outdoor air decreased by 31.3% (Song et al, 2014). Engineers can also consider pumping air underground to ensure good ventilation. By allowing air to enter low enough, it can be sufficiently cooled by the earth and sink below to reach the people. Meanwhile, warm air generated by the population can rise up via another set of shafts. Hopefully more innovative technologies will come about as more and more governments consider underground structures.  

Natural light from the sun has many benefits: it increases visual performance, hence heightening alertness and concentration, it soothes the mind and it induces the skin to produce vitamin D which is important for calcium and phosphorus absorption from food (Hughes, 1987). As such, if we are able to simulate natural light, replacing artificial fluorescent lamps with lighting that emits rays of similar wavelengths as that of the sun, then we can achieve maximum bodily functions and comfort. It is not too difficult to simulate natural light as we only need to select the correct wavelengths. Also, the “remote skylight” technology proposed by Ramey in the Lowline can be combined with natural simulation to create a pleasantly lighted environment for the underground dwellers. 

Picture taken from Lowline (2014)

Other forms of renewable energy sources such as solar or even kinetic can be considered to power the lights in the underground building as well.

If you ever miss the natural breeze and sunlight, you can always take the elevator (or stairs, if you’re not that deep into the ground) to the surface where nature would be more beautiful since there would be less tall buildings fighting for space.

Literature cited:

Hughes, P. C. (1987) The use of simulated natural light in the design of earth-sheltered environment. Tunnelling and underground space technology. 2 (1). p.75-81.

Song, S. Y., Song, J. H. & Lim, J. H. (2014) Effectiveness of a thermal labyrinth ventilation system using geothermal energy: A case study of an educational facility in South Korea. Energy for Sustainable Development. 23. p.150-164.

There's a garden under my home!

Remember the no-sunlight-and-all-concrete-walls depressing scenes? We talked about how unliveable that kind of environment would be like. Well, it is not impossible to have greenery in the depths of the crust. In fact, projects are underway for the world’s first ever underground park, located in New York! 

Picture from www.kickstarter.com

The Lowline is a proposal for a community park underneath the bustling city of New York, in a long abandoned trolley terminal (The name is inspired by the successful highline park in New York). The team behind the project even overcame the challenge of providing sunlight to the plants using nothing but a few reflective dishes. The “remote skylight” as it is called is the brainchild of James Ramey, the co-founder and creator of Lowline. The technology harvests natural sunlight from aboveground and concentrate the rays onto a focal point after which the light energy is transferred underground via fiberoptic tubes and spread across the facility by interconnecting reflective domes on the ceiling (Lowline, 2014). With that, plants can photosynthesize in an otherwise dark room. By using natural sunlight, it also means that electricity is not needed to power bulbs in the day time.

You can find out more about the Lowline project by watching their promotional video:

 And, of course, they succeeded in building their prototype! They have proven that it is very possible to have a park full of healthy trees and shrubs below the ground. Residents in that area can relax at the park even when it is raining or freezing cold in winter.

According to Asimov (1989), one advantage of living underground is to make space aboveground, so that forests need not be cleared for more urbanisation. People can enjoy nature both underground and above, and the ecosystems on the surface would be in better shape.

Would you like an underground park in Singapore too? With greater wildlife and forests conservation by not touching present forests, it looks like living underground can truly make us a garden city!  

Literature cited:

The Lowline. (2014) Project. [Online] Available from: http://www.thelowline.org/about/project/. [Accessed: 20 September 2012].

Asimov, I. (1989) The advantages of underground living. Los Angeles Times, ProQuest Historical Newspapers. [Online] 2^nd June. P D2.

(I'll be using the Harvard referencing style from here on)