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KEEP IT SIMPLE: FOUNDATIONS FOR ADDITIONS by Stephen Coyle Connect new to old — without forms,, footings,or frost *Soil Bearing Values Allowable Material bearing (tons/sq.ft.) Massive crystalline bed rocks,(granite,gneiss,trap rock,etc.)in sound condition 1 00 Foliated rocks (bedded limestones;schist,slate)sound condition 40 Sedimentary rocks (hard shales,siltstones,sandstones,soft limestones),sound 15 condition Hard pan;gravel,sands,exceptionally compacted 10 Gravel,sand-gravel mixtures;compact 6 Gravel,loose;coarse sand,compact 4 Coarse sand,loose;sand-gravel mixtures,loose;fine sand,compact;coarse sand,3 wet,confined Fine sand,loose;fine sand,wet,confined 2 Stiff clay 4 Medium stiff clay 2 Soft clay 1 *Values are for general reference only.Consult engineers and local codes for allowable values To design a foundation,you must first determine the soil's bearing capacity at the footing level. When underlying soils have been previously disturbed,contain expanding clays,or are filled with organic debris such as stumps and peats you must excavate down to undisturbed or