It looks very much as though they have cut a triangular shape into the grass which has been concreted to support the starboard undercarriage leg of the aircraft. Looking at the ‘conga’ line of aircraft on RWY 23 the last but one (777?) overhangs the runway by a considerable margin on both sides neccessitating Concorde having to move that bit onto the grass to give enough room for safe passage.

Regards,

kev35