New photos of Apple Campus 2 show concrete foundation work, rebar installations

Three new aerial photos of Apple's Campus 2 construction site show rapid progress being made on the main circular building's foundation, including rebar work for below grade retaining walls and the addition of interior "tunnels."

The images, shared on Twitter by KCBS traffic reporter Ron Cervi, come nearly three weeks after the last batch of photos showed initial progress on the "spaceship's" substructure.

As seen above, it appears preparations are being made to pour the concrete foundation that will serve as a base for the three-story building. Of note is rebar work being done to retaining walls ringing the build's perimeter, which will likely be paired with a comprehensive drainage system to avoid water ingress and lower level flooding.

Cervi's flyover also reveals crews have been digging out troughs in the central courtyard area, the purpose of which is not yet known. The "tunnels" are accompanied by what looks to be pipes, concrete stanchions and metalwork to be used as part of the build's substructure.

Apple won final approval for its Campus 2 headquarters from the Cupertino City Council last November after late cofounder Steve Jobs presented original architectural plans in 2011.

In July, a full-scale segment of the main structure's glass and metal facade was constructed in Germany for materials demonstration and testing. Included in the mockup was a distinctive eave feature with integrated air vent that will cycle fresh air throughout the building, illustrating just one of many novel ideas applied to Campus 2's design.

Construction of the large main office building is slated for completion by 2016, though it is unclear if other structures like an above-ground parking lot, auxiliary office space and maintenance buildings will be done in the same time frame.