The Westfield Century City Mall construction team had an approach to the excavation like we had not encountered before.  An existing low-rise office building already occupied the site.  It already had a 4 level basement.  The contractor determined that, while the foundation system for the new mall extension and the below grade parking decks would be completely different than that of the existing building’s, it would be cheaper to leave the basement walls in place for reuse.  This eliminated the need for conventional steel soldier piles and lagging.  A bracing scheme was developed that held back the walls with a tieback on a strongback supporting the wall at the existing decks but out of the way of the proposed decks.  The strength of the existing wall was key to the brace layout.  Deep utilities and a bridge pier plagued the tieback coordination.  On sides where adjacent structures already existed to matching depths, a cantilever pile was used to hold the wall upright while the decks were replaced.