“If you have built castles in the air, your work need not be lost; that is where they should be. Now put the foundations under them.”
– Henry David Thoreau, Walden
Shipping containers have been an integral part of Mr. Dirch Olsen’s life for the last 42 years. Now he is laying the foundation (literally) for his own dream home, which will feature converted shipping containers. Mr. Dirch Olsen’s container home is being constructed in Irene, an area that can be fairly unstable from a construction perspective. Dolomite rock occurs throughout a large part of the land south of Pretoria, including Irene. Dolomite, while very hard, is susceptible to being gradually dissolved by acid water. This causes cavities to form, and this eventually leads to subsidence and sinkholes.
John Deppe, the architect responsible for designing Olsen House, will be building on top of a type of foundation known as a ‘raft’ in order to minimize the risk of damage to the structure if subsidence or sinkholes occur. The foundation will function in a similar way as a raft would on water: by ‘floating’ on the ground. The load imposed on the foundation will be spread across its entire footprint. This enables the foundation to maintain structural integrity while allowing for some ground movement.
Building such a foundation is not an easy undertaking, and begins with creating a compacted soil ‘mattress’. This mattress consists of graded material that is compacted in layers 150mm thick until a specific strength is reached.
The site for Olsen House seems fairly flat at first glance, but the soil ‘mattress’ required far more graded material than initially expected in order to compensate for the fall of the ground. While the ‘mattress’ required more material than anticipated, the ground is flat enough to allow for machinery and materials to be transported over it with relative ease.
Once the soil is prepared, steel-reinforcing is laid down. The steel-reinforcing will provide almost all of the tensile strength to the foundation, and is a unique and critical component of the design.
Finally, concrete is poured over the steel-reinforcing to create a steel-reinforced concrete platform that is capable of tolerating a loss of support from a sinkhole of up to 7m in diameter. Interestingly, crushed dolomite is frequently used as an aggregate in concrete. It is quite poetic that the same underground rock that makes building the Olsen House foundation difficult, is also one of the major construction components.
The Olsen House foundation is the perfect blank slate, awaiting the containers that will be a major component of the home.
“Of the many foundations upon which humans rest, words are probably the most solid.”
– Nikki Giovanni, Acolytes