waterproofed pressure mat if constructed at the lowest 

 grade level. Therefore, a slab-on-grade with a permanent 

 underdrainage system beneath is required for hydrostatic 

 pressure relief. A typical underdrainage system consists 

 of a system of perforated PVC pipe placed within a layer 

 of crushed stone. The PVC pipes are interconnected to 

 transport the inflow of groundwater into collection pits 

 where sump pumps are utilized to remove accumulated 

 groundwater. Underdrain design, groundwater infiltration 

 rates and pumpage will be determined by a number of 

 factors including diaphram wall penetration below the 

 lowest slab level and proximity to the harbor. 



2. Pier Structure 



Unlike the Office Structure, no below grade levels are 

 anticipated for the pier structure which extends out into 

 the harbor. Since the fill and underlying organic soils 

 are not considered suitable for support of the proposed 

 structure, building loads must be transferred to the 

 natural, inorganic soils below; therefore the pier 

 building will require a deep foundation system. 



Based on waterfront construction constraints, a pile 

 foundation system was considered as the only technically 

 feasible foundation system. From our analysis of the 

 subsurface information, high capacity piles driven to end 

 bearing in the glacial till at a depth of approximately 35 

 to 50 ft. below the top of the existing warehouse floor 

 (El. 114.0+) appear to be the most appropriate. These 

 pile lengths assume piles are driven 10 ft. into the 

 glacial till soils. However, additional borings should be 

 conducted within the area of the proposed pier structure 

 to more completely define the bearing strata and to allow 

 for a better estimate of pile lengths. 



Currently in the Boston area, precast-prestressed concrete 

 piles are generally the most economical foundation element 

 for use as end bearing piles. Maximum design loads for 

 this pile type are 134 tons/pile (14-in. square) and 175 

 tons/pile (16-in. square) according to the current 

 Massachusetts State Building Code. Precast-prestressed 

 concrete piles are also resistance to corrosion in the 

 salt water environment, a significant consideration for 

 this structure. 



Note that the Massachusetts State Building Code requires 

 the completion of a pile load test for all piles with a 

 design capacity in excess of 50 tons. Completion of such 

 a- test must be included in this project. Pile spacing and 



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