1010 N BROADWAY EVCC 2018-01-01 MF Import

PROPOSED LIBERTY HALL,EVERETT COMMUNITY COLLEGE Everett,Washington TABLE 3. BEARING CAPACITIES FOR PARTIAL OVEREXCAVATION AND REPLACEMENT Foundation Locations Allowable Bearing Overexcavation Depth Pressure(psf) Required2(feet) Zone I(Gridlines 1 through 6) 6,000 None s Zone II(Gridlines 6 through 7) 4,000 1 .4* (49 IJ 2,500 2 Zone III(Gridlines 7 through 3') 3,000 3 2,000 3 Zone IV(Gridlines 3'through 7') 2,500 t 4 3,000 5 Notes: 1 See Figure 3 for a summary illustration of the allowable bearing capacity delineation. 2 Overexcavation should be completed as described in the text of this report. Perched groundwater was observed within 6 of the 7 borings. The contractor should be prepared to handle groundwater seepage, if encountered during foundation excavations. Ground Improvement-Drilled Aggregate Piers Ground improvement may be considered to decrease the size of the shallow foundations within Zones II through IV and to reduce excavation of unsuitable soils below foundations. Ground improvement techniques include drilled aggregate piers, stone columns, dynamic compaction, and grouting (to name a few). In our opinion, drilled aggregate piers such as GeoPiersTM will be the most cost-effective ground improvement technique, other than overexcavation and replacement. Up to 12 feet of compressible silt/clay soils exist under portions of the east end of the building footprint. The GeoPierTM system would include drilled aggregate piers extending through the compressible fill and silt/clay deposits and at least 3 feet into the underlying medium dense to dense glacial soils. Drilled aggregate piers will range up to about 15 feet long and should be planned to extend to the bottom of the foundations and within two feet of floor slabs. Our analyses have assumed that floor slab loads are at 350 psf or less. Installation of the aggregate piers typically includes drilling two to three foot diameter holes and filling them with crushed aggregate. Crushed aggregate is placed into the hole in one-foot lifts and compacted using a hydraulic densification system to create a column (pier) of crushed aggregate. Uplift resistance can be achieved by installing plate anchors at the base of the pier during construction. The drilled aggregate pier would support moderate foundation loads (both bearing and uplift) and reduce post construction settlement to an acceptable amount. An allowable bearing pressure of 6,000 psf can be assumed for shallow foundations bearing above areas improved using GeoPiers. GeoPiers can also be used to support the floor slabs if the risk of potential settlement of the silt/clay soils is not acceptable. Based on our experience, we anticipate that the system may include the following elements for support of the design loads: Drilled aggregate piers 24 to 36 inches diameter. GEOENGINEERS June 10,2010 Page 13 Filo No.;636-010-0C