View site development images. Playing a part in the construction of one of Portland's most prominent landmarks in the downtown skyline, Coffman Excavation removed over 200,000 c.y. of soil to make way for the Oregon Convention Center Expansion. Working at night, the bulk of the soil was removed in just under two months. After completing the mass excavation, Coffman Excavation crews constructed the building pad, excavated and backfilled the footings and pile caps and mass backfilled the exterior walls. Site finishes is yet to come. When complete the Oregon Convention Center Expansion will have added 407,000 s.f. including a two level parking garage, new ballroom and new meeting and exhibit space. Coffman Excavation is proud to have played a major role in helping to construct this world-class landmark in our community that will be enjoyed by many in the decades to come. Jim Shannon Sr. Project Manager/Sponsor To learn about our other project experience, review Our Clients list.