4-03. PRELIMINARY ASSESSMENT OF FOUNDATION DESIGN AND 

 CONSTRUCTION CONSIDERATIONS 



This section of the report will concentrate on possible 

 foundation support systems, construction impacts and foundation 

 costs for each of the proposed major building elements of the 

 planned development. These issues are generally determined by 

 considering the various effects of: building geometry, typical 

 column/wall loads and subsurface soil and groundwater 

 conditions. For purposes of this report, building loads were 

 estimated by H&A assuming loads in the typical range of steel 

 or concrete construction. Each of the proposed structures, as 

 defined previously, will be discussed separately. Our specific 

 comments follow. 



1. Office Structure and Below Grade Parking Area 



Based on subsurface soil conditions presented in Figures 3 

 and 4, anticipated building loads and the 30 to 40 ft. 

 excavation required for construction of the planned three 

 of four level below grade parking garage, it is 

 anticipated that individual spread footings bearing on the 

 glacial till soils may be used for support of the office 

 structure. This foundation type is recommended since the 

 required excavation for garage construction will remove 

 the miscellaneous fill and organic soils which are 

 generally unsuitable as foundation bearing materials. 

 Typical allowable bearing pressures for glacial till soils 

 in the Boston area range between 5 and 20 tsf (tons per 

 sq. ft.). Recommendation of an allowable bearing pressure 

 for the glacial till will require additional analysis and 

 subsurface explorations in combination with an evaluation 

 of the active column loads anticipated by the structural 

 consultant. 



Excavation of the three to four level garage area will 

 require construction of a cofferdam to retain the earth 

 and provide a groundwater cutoff. Groundwater control is 

 of primary concern, particularly in those areas adjacent 

 to the harbor, where existing groundwater levels are up to 

 2 5 to 3 5 ft. above the lowest garage level. 



Based on an evaluation of subsurface conditions and the 

 results of in-situ permeability testing, the use of either 

 interlocking steel sheet piling or a concrete diaphragm 

 wall (slurry wall) constructed with adequate penetration 

 into the glacial till soils were evaluated for use as 

 temporary excavation support for the garage. Both of 

 these options would theoretically provide adequate control 

 af groundwater seepage into the excavation, however, due 



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