OVERVIEW:
The Gilbert, a new 16-story building, is now rising on 295 STELCOR® micropiles installed by Posillico. Upon completion, the new building at 1912 First Avenue will be dedicated to seniors, offering 153 affordable-housing units across 131,316 square feet. This site is adjacent to the 14-story Draper Hall building, which is also standing on STELCOR.
CHALLENGE:
The foundation needed to be installed adjacent to an existing structure, so vibration needed to be limited. The stratigraphy of the site consisted of soft organic material for the top 30’ with loose sands below. The original design called for pressure grouted micropiles bonded into the sand to address this condition.
In addition, voids were encountered during installation on the east side of the site. During installation in this part of the site, the piles consistently hit obstructions or tough drilling at about 20’ below grade and all the grout would be lost. The grout loss was so drastic that the installation crew described it as akin to flushing a toilet. The area was investigated, and it was determined that about 25 piles were effected by this soil condition.
SOLUTION:
Posillico proposed Stelcor DDM piles to provide the same capacity as the pressure-grouted micropiles and provide a solution that would eliminate possible disturbance and vibration to the adjacent structures. The grout head and lateral strength needed to be maintained at pile locations where the voids were encountered on site. A drill rig was used to install 18” casings to 25’ below grade. The Stelcor piles were then installed through the casing and continued to an additional 25’ to provide the same embedment as was tested in the load test phase.
By changing to the Stelcor DDM pile, we were able to drastically shorten the schedule and provide a savings to the owner. See other STELCOR CASE STUDIES.
INSTALLER:
Posillico, Inc.
LOADS:
170 kips allowable compression
40 kips allowable tension
40 kips allowable tension
Safety factor of 2
PILE DETAIL:
STELCOR® 1400
16” tip or drive plate
14” corrugated grout column
11” solid grout column
8” reverse auger
5.5” O.D. X 0.476″ W.T. – 80 ksi central shaft
SOILS + EMBEDMENT DEPTH:
The stratigraphy of the site consisted of soft organic material for the top 30’ with loose sands below.