DIYbanter - View Single Post - Wet clay soil unsuitable for deck foundation, or not?

wrote:
As I've mentioned previously in other threads, I'm in the process of
building a deck. At the moment, I've just dug holes 5 feet into the
ground in preparation for pouring concrete pier-columns (the
foundations which my deck will rest on). However, as soon as these
holes were dug I noticed they would partially fill up with water,
seeping in from the surrounding (clay) soil). I've drained them once
with a sump pump, and I thought the holes would stay dry until I could
pour the concrete into them, provided the weather remains dry til then.
However, despite continued dry weather conditions, this morning I
noticed that the holes have filled with water again. I surmise this to
be related to my neighbor leaving his lawn sprinkler on the night
previous, and that water seeping into the ground from that is what is
entering my holes. All this has got me thinking... Will my concrete
pier-columns be stable enough to hold my deck properly since the
surface soil they will be buried in is obviously prone to holding
water? Right now the weather is dry because it is summer. But most of
the year it rains a lot here (Vancouver). If water from a neighbor's
sprinkler can saturate my future foundation soil so readily, can I
expect it not to turn into an unstable, sinking, muck when the heavy
rains return.

Responses please and thanks,
Ken

There shouldn't be a problem, as long as the clay stays
wet. The problem would be if the clay dried out,
because then it would shrink and shift the footings.

Bill Gill