Building on soft ground: How can skyscrapers be built on landfill in Boston?

Building in Boston presents some difficult challenges for architects and engineers. First of all, more than half of Boston's land is actually fill that was added to the existing shoreline, at various times between the 1600's and the 1950's. Where there is not fill, much of the soil is actually many feet of gravel and sand (deposited during the last Ice Age). Perhaps more importantly, the bedrock under Boston is quite deep. Beneath the several feet of fill you would find a layer of "Boston Blue Clay" many feet deep - in many cases, over a hundred feet deep! This clay is quite soft and not at all suited to holding up heavy structures such as skyscrapers.


What are your options, as an architect or engineer?

- Dig a foundation (using a pile system, perhaps) that allows the structure to rest above the ground surface.

- Create a "floating" foundation that allows you not to have to dig all the way to the bedrock but will hold up the structure.


Your Task:

You have been contracted to build a high-rise apartment building with an open park area at ground level. The soil, as in much of Boston, is sand. The bedrock is much too deep for you to rest the foundation directly upon it. Design a "floating pile" system that uses a minimum of materials and requires the least amount of excavation, but that will still hold the most weight. At the same time, the building may not sink more than a minimum amount (1 cm on our model), and any subsidence should be uniform.

You are to build a working model of the foundation, with a platform representing the building's floor. Weight will be added to the floor to represent the weight of the building itself.

You will build your model and set it into a large basin of sand, or you may construct your foundation within the sand, and then build your model on top. Your foundation may not rest on the bottom of the container (that would be like resting on the bedrock).

You will be given a container and sand to work with, along with water to keep the sand damp as needed. You will also be given a glue gun and glue sticks, and other assorted tools.

The only material you may use for the actual foundation of the building is a limited number of popsicle sticks.

Want to know more about foundations? Here's a link to some background information about building foundations.