I don't mean the basement (aka D6) - I mean the ground floor, i.e., the whole of the downstairs corridor (D1 to D57). With the exception of D6 these are all normal gates with aircraft parked at the end of airbridges.

For those not familiar with D Pier - D Pier is shared between Schengen and non-Schengen, and operates on two levels. If your flight is a non-Schengen flight you access your gate from the ground floor. If your flight is a Schengen flight you access it from the upper floor. Every D gate has two numbers, a "downstairs" one and an "upstairs" one.