this square surface, together with SU 8313 seems to represent a floor built after 8317 and abutting walls 8238 and opus signinum 8264. It is also probable that this surface does not belong to a floor surface. it may be a trace of a staircase leading to a second floor held by the arch construction.
Series of Floors in Room I-11
photo taken from the east
photo taken from the west
photo taken from north