Friday, January 20, 2006


Joe Dahmen of MIT was kind enough to answer some questions about himself, the Great Wall of MIT and his thoughts on rammed earth in general.

Read on!

1. Tell us a little about you: your background, education, interests, what you do now, how you came to do it.

JD: I am a Master of Architecture Student in my final semester at MIT. Prior to coming to MIT I worked as a carpenter in Portland Oregon and a builder in Marfa, Texas, where I worked on projects with traditional unstabilized adobe bricks.

2. When and how were you first exposed to rammed earth?

JD: Last year I traveled to Andalucia, Spain, to research a paper on Moorish Bridges built of stone. During an interview with an archaeologist in Algeciras he pointed out walls of a fortification over 1300 years old built of rammed earth (which they call tapial). I was intrigued that walls could last that long without the addition of concrete or any other energy-intensive products.

3. How did the MIT wall come about? What was your role in that?

JD: Following my return to MIT I showed some slides of the rammed earth in Andalucia to Professor Ochsendorf, my advisor, who has been interested in rammed earth for some time as an environmentally sustainable alternative to concrete. We drew up a proposal to evaluate the feasibility of using rammed earth in New England and received research funding form the Boston Society of Architects about a month later. As the project moved forward we wanted to locate the test wall in a publicly accessible place, which turned out to be the courtyard of an MIT building at 275 Massachusetts Avenue. The wall actually fills dual functions, reclaiming a disused courtyard for the School of Architecture while providing evidence about weathering and appearance of rammed earth. We proposed to build the wall there and received funding from the School of Architecture, MIT Council for the Arts, and a variety of other sources within MIT. Eventually we also attracted funding from Sasaki Associates, Inc., an international architecture firm with an office in Boston that is interested in sustainable building methods.

4. Can you talk about the soil selection process? Why did you use the soil you used? What kind of soil analysis did you perform? Did you do any compressive strength tests?

JD: I had read a number of books that suggested that portland cement was not necessary if the clay content of the soil was high enough, although in the US it is standard practice to add at least 5% portland cement to satisfy building codes. During the spring I traveled to Europe (supported by a grant from MIT and the Architectural League of NY) to view historic and contemporary rammed earth buildings in climates similar to that of New England. Many rammed earth buildings in the Rhone Valley of France are 300 years old and were built with soil straight out of the ground. On the same trip I interviewed Martin Rauch and Roland Keable, two of the foremost contemporary rammed earth builders in Europe, both of whom suggested that the use of Portland cement was not necessary if proper detailing is used and the clay content is high enough (approximately 30%).

Initially we wanted to use a site soils, but the wall is sited on filled marshland of the Charles River, so the soil has almost no clay at all. I visited a number of quarries and stone yards as well as construction sites where excavation was going on looking for suitable soil sources, but the soil for around 10 miles around Cambridge has very little clay in general. Eventually we decided to engineer the soil from a mixture of Boston Blue Clay and sand and gravel. Boston Blue Clay is a marine clay deposited about 10-15,000 years ago that is prevalent at depths of 30-60 feet beneath grade all over the city. Anytime a large building is built they have to dispose of the clay after excavating for the foundation.

We performed a number of proctor compaction tests to find the optimal moisture content for compaction. Also we did some spalling tests by freezing samples, as well as unconfined compression tests. Following these tests we were able to convince a local building firm to donate 12 tons of the clay from a building site at Harvard, about a mile away.

5. How was the City of Cambridge with regards to this project? Did you need a permit? Did you need to have an engineers report? Who did the engineering?

JD: We did the engineering for the wall; the permit system in Cambridge states that no permit is required for masonry walls 6' high and under. So we built it 6' high.

6. Can you talk about the foundation? I saw in one picture what appeared to be concrete piers. What's going on there?

JD: The wall rests on a pier and beam foundation of reinforced concrete. This allowed use to save approximately 80% of the concrete that would have been used in a continuous footing, while still providing resistance to heaving from frost. The posts penetrate 5' below grade (Frost line is approx. 4' in New England) with flared bottoms to spread out the weight.

7. Can you talk about the wall structurally? How much rebar is in there? How thick was the rebar? How far apart did it have to be spaced? Have you had any problems with Cracking?

JD: The wall is completely unreinforced. We have see a small amount of cracking at the cold joints (where different compacted sections come together) in the wall but otherwise it is doing fine.

8. Who designed the form work? How difficult was it to form up the wall?

JD: I designed the formwork, with the help of Shuji Suzumori, who helped build the wall as he was researching his Masters thesis on concrete formwork. It was pretty straightforward; the relatively small size of the wall (two sections, each approx. 30' long) meant that we did not try to slipform it, but rather built one side, compacted it, and moved that formwork to the other side. We did change from horizontal to vertical walers in the second section.

9. What are your thoughts on rammed earth as a material for home building? Do you think rammed earth will ever account for 1% of all new homes building in north America? Why or why not? What stands in the way?

JD: I think that there is great potential for rammed earth in many different markets in the United States, including housing. However, rammed earth, like any material, is not a panacea-- it should be used only if it is appropriate to the concerns of a particular project. For the applications where rammed earth is appropriate, two things stand in the way: economics and attitudes. By mechanizing the process we hope to address the former; the latter is already changing. According to Rick Joy, a rammed earth is becoming a status symbol in the Tucson area. As more architects use the technique to create striking contemporary designs, the appeal will only increase. Certainly environmental concerns will only grow more important as time goes on.

10. Do you have any rammed earth plans for the future?

JD: We are now developing a proposal for rammed earth sound barriers along interstate highways in Massachusetts and elsewhere

1 comment:

Lou said...

very interesting and informative, thank you...
Lou Villalon