Construction is Under Way!
August 12, 2008
Now into the sixteenth week of on-site construction activities, Mirabella at South Waterfront continues forward with positive progress (visible at lower center-left in the above photograph, taken from the 15th floor eco-terrace of the OHSU Center for Health & Healing).
A bird’s-eye view of the Mirabella construction site from the northwest shows the two major pieces of equipment performing the primary activity at this time: placement of driven grout pilings. The crawler with the red lattice boom (shown at right in the above photo) suspends an auger that is used to pre-drill through the silt layer to the top of the native gravel layer. The large orange-colored crawler with the black lattice boom (shown near the approximate center of the site in the above photo) is suspending the pile driver. The earthen ramp at the midblock of SW Curry Street continues to facilitate construction access into the site. Mass excavation holds steady at approximately 75% complete with only the earthen access ramp and pending excavation for the massive mat slab to support the tower structure remaining.
Also visible in the above photo (far right), across SW Bond Avenue from the site, electrical workers are installing new temporary poles on the west side of Bond Avenue, which will replace two that have been removed from the jobsite on the eastern side of Bond Avenue. The poles are used to support the overhead electrical lines that power the Portland Streetcar. This switchover was required to facilitate the pending arrival and subsequent operation of the tower crane, a primary element to construct Mirabella. The switchover occurred in one day and did not impact Streetcar operations.
Visible in the above photo is the compressed-air-driven pile driving rig (the pile driver is suspended by the lattice-boom crawler at left in the photo). At the far right in the photo, the continuous-flight auger is visible (suspended from the red lattice-boom crawler). In this photo, a grout-injected pile has just been driven and the reinforcing steel (‘rebar’) cage (shown vertically suspended to the right of the pile driver) is being positioned for placement into the grout filled pile.
Prior to being driven, a shaft for each piling is pre-drilled through the silt down to the top of the native gravel layer (roughly 30-feet below the jobsite base, seen above). The pile driver is then placed into the pre-drilled shaft and the grout-injected piling is subsequently driven into the native gravel layer until the required structural bearing capacity is achieved.
Visible in the above photo is a close-up view showing the placement of the reinforcing steel (‘rebar’) cage into the driven grout pile (the pile driver is visible to the left of the rebar cage). Over 500 driven grout piles will be placed through the summer and into the fall.
