May is Soils Support Building and Infrastructure
The International Year of Soils is nearly half underway. The Soil Science Society of America’s theme for the month of May is “Soils Support Building and Infrastructure.”
Soil is essential as the foundation of our buildings and infrastructure. The strength and composition of the soil is a key determinant for whether we can build a structure on it and how big a structure can be. A famous example of when builders took for granted just how important it was to understand the soil prior to building can be seen in the construction of the Tower of Pisa in Italy. More famously known as the “Leaning Tower of Pisa;” this bell tower was erected on soil that was too soft on one side to properly and evenly support its weight. Thus, since its construction in 1173, the tower has been leaning to one side. The approximate tilt of the building is 3.99 degrees or put another way, the tower is displaced 3.9 meters (12 feet 10 inches) off center from where it should be if it were perfectly perpendicular to the ground.
Not only does soil provide physical support to stabilize buildings and structures, it also often provides material for the construction of the buildings themselves. Worldwide, an estimated 50% of the population lives in houses made of soil.
The use of soil as building material has been in use for centuries and has come back en vogue as an eco-friendly building solution. Traditional earthen homes are typically found in one of the following building styles: cob, adobe, rammed earth, and/or earthbag.
Cob: Cob is a building material that has been in use since prehistoric times. It is composed of subsoil, water, some form of fibrous organic material and sometimes lime. Cob is an inexpensive material that is both fireproof and resistant to seismic activity. It is a popular form of architecture used in English homes, but has also been found in some of the oldest man-made structures in the Middle East, Arica and even the eastern United States.
Adobe: Adobe is very similar to cob, but is first formed into bricks and dried in the sun before being used to build structures (cob is directly made into walls). Adobe is made up of sand, clay, water and some kind of fibrous or organic material like sticks, straw or manure. Adobe is typically associated with the Southwest in American culture as many Native American groups including the Anasazi, Hopi, and Zuni Indians, who used it to build their pueblos. The largest known structure to have been made using this technique is the Bam Citadel in southeastern Iran. The citadel covers an expanse of 44 acres and has been dated back to between the 6th or 4th centuries BCE and may possibly be even older.
Rammed earth: Rammed earth is also very similar to both cob and adobe. It is a technique that uses natural raw materials like earth, chalk, lime or gravel. The process involves using a compressed, damp mixture that has sand, gravel, clay and sometimes an added stabilizer. Rammed earth is also fireproof and is efficient at storing heat. This form of construction has been found on every continent except Antarctica. One of the earliest known use of this technique can be found along the Yellow River in China where you can find Neolithic rammed earth structures that date back to 5000 BCE.
Earthbag: The earthbag method was influenced by military bunker construction and temporary flood control building methods. This building style uses polypropylene or burlap bags that are filled with earth, typically moist subsoil with enough clay to be cohesive, that are then stacked atop each other and tamped down. The pioneering architect and builder of the earth bag style, Nader Khalili, has also posited that this would be the most effective construction method for any future colonization of the Moon or other planets.
Beyond building with the soil itself, many other building materials like brick, concrete, stucco, and lumber all have important roots in the soil, too. And humans aren’t the only species to see the merit of using soil to build our homes and structures—many animal species also make use of this valuable resource.
A prime example of how animals use the soil for shelter can be seen in the mound building of termites. The specific species of termites that build mounds can be found in Africa, Australia and South America. They are known for constructing elaborate homes out of the soil that contain numerous intricate inner chambers and often have their own ventilation systems. These mounds have been found to be as big as 30 meters (roughly 98 feet) in diameter.
The use of soil for building and infrastructure both directly and indirectly gives new meaning to the expression “home soil,” and hopefully sheds light on just how integral soil is in supporting and sustaining all life.
Find out more interesting facts about the important role soil plays in supporting our infrastructure and so much more by visiting the NACD Soil Health pages. You can also check out the Soil Science Society of America’s International Year of Soils webpage for more materials on this month’s theme.
