CBD-12. House Foundations
C. B. CRAWFORD

Foundations for houses and other light structures usually receive much less attention than they should.
Perhaps the reason is that individual failures seldom result in total destruction.  Nevertheless unsatisfactory foundation performance often induces more worry and frustration on the part of the owner than any other single cause.  In most cases it is as easy to provide a proper foundation as it is to build a poor one. All that is needed is a simple understanding of the materials on which the structure is placed.

SITE SELECTION

The first opportunity to control a foundation is by the selection of the site.  While many unrelated
considerations enter into proper site selection surely the first must be concerned with foundation suitability.  Two of the most obvious questions to be answered are whether or not the site is subject to flooding or to large scale earth movements.  These are not only critical economic considerations but are possibly the only controllable factors which may cause catastrophic failure of the foundation.  Flood risk might be considered too obvious for special consideration in a note on house foundations were it not for such facts as the
following.  The $26 million Winnipeg flood of 1950 damaged 9,000 houses, 25 per cent of which were
less than five years old, indicating a trend to the use of unsuitable flood plain sites.

Four years later the floods following Hurricane Hazel caused an equal amount of destruction and resulted
in the loss of more than eighty lives due largely to unsatisfactory site selection. Soil creep down natural slopes and stream banks is a common phenomenon in many regions.  It is characterized by accumulations
at the base of the slope and by a rippled slope surface.  For obvious reasons a particular part of the
residential Southern California coastline has been named "Heartbreak Hills".
Similar real estate is available in Canada.

While creep is more likely to be a general phenomenon in certain areas the occurrence of landslides is less predictable.  The edge of any large slope should be avoided as a building site unless detailed investigation proves it to be stable.  Another extremely important consideration is the drainage of the site.  Surface water must be removed either by natural drainage or by the provision of an artificial drainage system.  Further, the ground water around basement walls must be collected in subsurface drains and removed from the site. Failure to take drainage into account in site selection and development has serious after effects.

Other important features in site selection are the occurrence of organic soils and artificial earth fills and the existence of old refuse dumps.  Organic soils and filled ground often result in large foundation settlements.  Refuse dumps may cause similar settlements but, in addition, an intolerable odour has been known to
penetrate basement walls, probably due to wicking in ground water with evaporation at the inside surface.  By far the best way to evaluate site conditions is to study the performance of existing buildings. In newly
developed regions of course this is not possible.  In addition to the common sense considerations just
mentioned it is necessary to probe beneath the surface.

SITE INVESTIGATION

Every detailed site investigation should be preceded by a surficial appraisal in order to avoid the obvious difficulties outlined above.  The next step is to establish whether or not bedrock will be encountered in any proposed excavations since this might affect foundation selection and future planning.  If the proposed site
is not solid rock the nature of the soil should be determined, in order to evaluate possible foundation
difficulties.  For the same reason the level of the groundwater table should be established.  This is the
level at which free water is encountered in the ground.
Every detailed site investigation should be preceded by a surficial appraisal in order to avoid the obvious difficulties outlined above.  The next step is to establish whether or not bedrock will be encountered in any proposed excavations since this might affect foundation selection and future planning.  If the proposed site
is not solid rock the nature of the soil should be determined, in order to evaluate possible foundation
difficulties.  For the same reason the level of the groundwater table should be established.  This is the level
at which free water is encountered in the ground.  If the groundwater table is at the surface the site is likely to be poorly drained and if special measures are not taken damage to basement walls may result.