Seawall Collapse on the Detroit River

Several weeks ago I was asked to conduct a forensic investigation of  260 feet of collapsed seawall.  At a cost of $900,000 to replace, I was intrigued at the construction characteristic of the seawall.  Constructed in the 1920s, it was comprised of 3 rows of wood piles capped with a 6 foot wide by 6 feet deep concrete cope.  The wood piles had been completely submerged from the day they were installed, and were still in good condition.  The concrete cap, however, was in a severly deteriorated condition.  In the 1920s they did not know about air entrained concrete.  As a result, the exposed concrete surfaces did not withstand the annual freeze thaw cycles which erroded the concrete.  What I find amazing is that, notwithstanding the primitive nature of the concrete, the seawall has existed in a harsh environment for over 90 years.  The structural nature of the seawall has served it well.