CBD-12. House Foundations Con't.
C. B. CRAWFORD

FOUNDATION SELECTION (con't)

Until it is completely fixed, top and bottom, the full vertical load has been applied, and the concrete or
mortar has completely cured, the structural resistance of a normal basement wall to lateral forces is not
very great.  During construction therefore, the wall is especially subject to failure or to damage which will later permit leakage.  Special care should be taken during this period to prevent the accumulation of water next to the wall before backfilling and to keep heavy construction equipment away from the wall during
and after backfilling.  Lateral earth pressures are increased by vertical loads but if equipment is kept at a distance from the wall equal to its depth it will have little detrimental effect.  The slow settlement of backfill often causes appreciable damage to steps, walks and adjacent slabs and results in a depression around the
building which collects roof run-off water.  This annoying situation can be avoided by proper placing of backfill.  In most cases a light tamping of the backfill in thin layers is all that is required.  The placing of backfill is extremely important if footings are to be founded on the fill and expert advice should be sought.
It is usually possible and wise to avoid disturbing the soil beneath a footing.  Fine-grained soils draw in
water when they freeze, causing, in some cases, a considerable increase in volume.  Silty soils are especially
susceptible to "frost heaving".  Coarse-grained soils are not susceptible.  This ground heaving commonly causes considerable damage to improperly founded attached garages and porches.  It may also affect house foundations that have been left unheated in winter.  Where fine-grained soils occur footings must be placed at depths below the penetration of frost.


CONCLUSION

This note has attempted to show the necessity for general site evaluation and the advantages to be gained from studying the soils at every building site.  Reference is made to the standard terminology which bas
been developed to facilitate the accurate recording of soil information. Typical construction difficulties are associated with various types of soil and the solution of common problems is shown to be unusually simple.

• The reader is referred to the "Guide to the Field Description of Soils for Engineering