Condition to move
To move your column, since it is not anchored, depends only on the friction force ##F_f## between your column and the ground. The condition before it begins to move is:
$$ F_f > \mu W$$
Where ##\mu## is the coefficient of friction (static) and ##W## is the total weight of your column. If the wind (or anything else) pushes harder than ##F_f##, the column will slide.
Considering a coefficient of friction of 0.5 (as an example; depends on the materials of the column and the ground) and a weight of 600 lb (=
75 lb/ft³ * 8 ft³) for a completely gravel-filled column, a force of 300 lb would move the column.
Condition to tip
For tipping, you need to consider the moments. The applied force ##F_a## times the height of application ##h## will tip the column if it is greater than the reaction moment of the weight. Since the weight should be acting at the center of the column and the normal force will be at the edge of the column just before tipping, the distance between the two forces is half the width of the column, thus:
$$F_a h > W\frac{d}{2}$$
Or:
$$F_a > W\frac{d}{2h}$$
Where ##d## is the width of the column. If the wind (or anything else) pushes harder than ##F_a##, the column will tip. If ##F_a## is greater than ##F_f##, then it will slide, and it should never tip.
Considering a weight of 600 lb and a force applied at the tip of the column (8 ft), a force of 37.5 lb would tip the column.
Considering the force is acting at the middle of the column (4 ft), a force of 75 lb would tip the column.
Because the tipping force is less than the friction force, it will tip before it slides.
These numbers are obtained before the application of a safety factor. And with the simplicity of the analysis and the potential risks of an error, I would used a safety factor of
at least 5 (maybe 10), i.e. divide these forces by 5.
Even a force of 75 lb @ 4ft high is something
that a human can easily produce.
