Driveway Gate Posts and Footings in Limestone

Thirty inches is the minimum depth for a driveway gate post, and the figures kept at driveway gates georgetown museum house on bloor push it to forty-two where the ground is clay near Georgetown, TX. Rock changes the answer in the other direction, since a post drilled into solid limestone needs less concrete than one in soft ground.

How deep does a post go?

The depth follows the weight and the width of the leaf. A single swing leaf up to six feet takes a post thirty inches deep, and a heavy ten foot leaf takes forty-two or more. A slide gate or a cantilever gate carries its counterweight on a footing that is wider and deeper than a swing post, since the load tips toward the track.

What does limestone soil change?

Limestone soil is shallow and hard across much of Williamson County and the Texas Hill Country. A drill rig cuts through it slowly, and a hand auger stops at the rock. When rock is reached above the planned depth, the post is set into the rock with a smaller hole, dowels are drilled in, and the concrete is poured around them. The rock holds the post better than soil would, and the hole is often narrower than a clay footing.

What does clay do to a footing?

Clay swells when it is wet and shrinks when it is dry, and the cycle pushes on the footing. Near the San Gabriel River the swing can be an inch or more over a season. A footing in clay is drilled wider at the base than at the top, so the cone of concrete resists heaving, and the top is shaped to shed water away from the post.

What size post and what concrete?

A driveway gate post is four inch square steel tubing at minimum, with a wall of one quarter inch for a heavy leaf. A hinge post for a ten foot iron leaf is six inch tubing. The post is filled with concrete, welded to a cap, and primed inside and out. A post that will be galvanized or powder coat finished is sealed so that water cannot sit inside.

The concrete is a structural mix, poured in one lift, and tamped to remove voids. A full cure takes seven days, and the leaf is not hung on the post until the concrete has reached that age.

How is the post set plumb?

The post is braced in two directions with a level on two faces, and the bracing stays until the concrete sets. A post that leans by an eighth of an inch at the top becomes a half inch gap at the free end of a twelve foot leaf. The hinge post is set first, the latch post is set to the leaf, and any adjustment is made before the concrete is placed.