Grade beams and modified foundations are used when soil conditions are not stable enough to support columns or gates. There is always a small amount of movement in columns due to the large amount of concentrated weight on top of foundations that have a relatively small footprint. A column can weigh 4,000 - 6,000 Lbs (1814 – 2700 kg) and the foundation can weigh another 4,000 Lbs. With 8,000 - 10,000 Lbs. of material sitting on top of 3 square feet (one square meter) of area, there is high probability for settlement.
Grade beams are highly recommended for bi-parting (double) gates as maintaining alignment is much more critical than single gates. When bi-parting gates are hung from columns, there is a high probability they will become misaligned within a short period of time.
Foundations can be modified to prevent settlement by altering their size and depth to accommodate soil conditions. If you are in doubt of your soil conditions you should consult with a soil engineer.
