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Two basic methods are available to us in selecting the foundation type and allowable loads. These are the <br />standard penetration test and consolidation -swell testing. Ultimately, the bearing capacity of the foundation <br />soil depends upon the size and shape of the foundation element, the depth below the surface, and the <br />physical characteristics of the supporting soil or gravel. <br />Due to the shrink /swell potential of the upper fat clay soils, we recommend that no foundation elements <br />bear directly on this clay. Below we have provided shallow foundation options for footings bearing either <br />directly on the native sands and gravels or on compacted structural fill (from the removal of at least 3 feet <br />of the upper native lean /fat clay soils). Another possible option, that was not a part of the scope of this <br />investigation, is for deep foundations bearing in the bedrock. If this option is pursued, additional deep <br />geotechnical borings will be required to determine /provide foundation design criteria. All options need to <br />be evaluated with respect to potential movement, current material availability and economic feasability. It <br />should be noted that due to the shallow groundwater table, de- watering will probably be required to install <br />foundations regardless of the option chosen. <br />Pad Footing Foundations <br />Where the foundation will bear through any unsuitable fill and /or lean /fat clay soils and be placed on the <br />native undisturbed silty sands, the foundation could be a pad footing foundation designed for a maximum <br />allowable bearing capacity of 1,750 pounds per square foot (dead load plus full live load). Where <br />foundations will bear directly on the native sandy gravels, the maximum allowable bearing capacity may <br />be increased to 3,000 p.s. f. <br />If these excavations are deeper than practicable another alternative would be to over - excavated the native <br />clay soil by 3 feet in depth (and 3 feet beyond the edge of all foundation elements) and then backfill with <br />compacted and tested structural fill. Replacement material shall consist of imported, non - expansive <br />4 <br />