Grade beams and modified foundations are used when it is determined that soil conditions are not stable enough to support columns or gates. There is always a small amount of movement in columns. This is due to their large amount of concentrated weight on top of foundations that have a relatively small footprint. A column can weigh four to six thousand pounds (1814 – 2700 kg) and the foundation can weigh another four thousand pounds. With eight to ten thousand pounds of material sitting on top of three square feet (one square meter) of area there is high probability for settlement. Grade beams are highly recommended for double gates (bi-parting). Keeping the alignment in double gates is much more critical than single gates. When double gates are hung from columns there is good probability that they will loose their alignment 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 may want to consult with a soils engineer.