GM Pontiac A-line Existing Foundations
May 07, 2021
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| STATEMENT OF PROBLEM At bid time CCC received the 1950 Albert Kahn facility record drawings of the plant. This set had two foundation drawings, showing two different column foundation types for the plant. One drawing showed all footings, one drawing showed all caissons. It was unknown by GM which was the as-built condition. This was important based on the new scrap tunnel, which needed to be designed to run in-between the existing foundations. Other reference Kahn drawings created after original building was built, showed the foundations to be footings. Because of this, IBI completed the tunnel design based on footings. However when CCC excavated the area the column foundations were found to be caissons. IBI was required to re-design the tunnel to work with the existing caissons while also not narrowing the tunnel width or greatly impacting the scrap conveyor design. This required careful engineering for raising the tunnel floor over the caisson bells and tying the walls into the caisson shafts. IBI was able to successfully engineer this difficult area in a short time frame in order for CCC to order rebar and maintain schedule. COURSE OF ACTION IBI Group quickly re-designed the tunnel based on existing column caisson foundations. However, if IBI had not been able to provide a timely and robust solution, it may have delayed the installation of the tunnel do to delay in rebar shop drawings/material ordering. LESSON LEARNED When as-built conditions are unknown at the start of design the D/B team needs to not only clarify the design assumption, but also consider the impact if the as-built condition is suspected to vary. It needs to be a known risk variable in the construction schedule. |
