When we set our students longer projects in any field, we tended to call them 'extended' or 'in-depth' projects, with the former being more prevalent.

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Note added at 1 hr (2012-11-19 14:46:53 GMT)
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The Spring term is focused on a design project that asks students to explore the notion of neighborhood and
how this complex definition is played out in the 21st century city, where your best friend is 3000 miles
away,where you meet on Facebook and you have nevervisited your local corner-shop? The term starts with
aproject where we will use time based media to observe and record several London neighborhoods and their
changing character over a short time period to establish a first notion of a genuis loci. This is followed by an
extended design project that pursues notions, qualities and the restructuring of the neighborhood.
The term is supported by shorter workshops, Technical Studies, History & Theory Studies and Media
Studies. Students will deploy ideas and lessons learned in the initial phase to develop their own approach.
http://www.aaschool.ac.uk/downloads/briefs2010/fy_Brief2010-...

The semester is structured around an extended design project that will be investigated in considerable depth. The
project is broken into five discrete sub-projects which will be completed and reviewed at defined times.
The schedule requires you to generate a developed conceptual design by midterm (including diagrammatic designs
for structural and mechanical systems), then to develop selected elements and systems of the building to a detailed
level, and finally to revisit and revise the entire design in light of the implications of the detailed development.
http://arch.usc.edu/sites/default/files/classes/Edit Cou...

An alternative might be 'detailed design project'.