The benefits of Earth anchor

The earth anchor provides a safe and reliable foundation solution with a lower material and labor cost than the typical foundation options. Essentially, earth anchors work the same way as helical piles and ground screws but with much less steel, greater adjustability, and without the need for the specialized installation equipment. Although a few different earth anchor products are on the market, in general they all work similar to a toggle bolt by driving a small (few inches long) steel tip into the ground using a steel rod. The steel tip is driven into the ground with a pneumatic hammer, or by hand with asledge hammer, and is attached to a steel cable. For the Earth anchors, they are typically driven to a depth of around 2 to 4 feet below grade. Once in place the steel rod is removed leaving behind the steel tip and cable. Theabove gradeportion of the cable is then attached to a hand-cranked winch which is cranked until the cable resists in tension. Below grade, the tension on the cable causes the steel tip to rotate 90 degrees which then causes the longer side of the steel tip to be in direct bearing with the soil. The steel tip is held in place by the weight of the soil above and the internal friction within the soil. The angle that this internal friction spreads out at varies depending on the soil type but if this angle was taken as 45 degrees, an earth anchor driven down 3 feet would engage a cone of soil above it with a volume of almost 30 cubic feet. This high volume of soil provides great uplift resistance for a minimal amount of material and labor all while using the existing soil (instead of concrete) to provide uplift resistance.

The most appealing aspect to an engineer or buildingofficial,is that every single earth anchor can be load tested to provide the most accurate and reliable results. The results of each test can be summarized and provided to the engineer of record and building official for review and approval. Since the earth anchor assembly requires the cable to be in tension in order to engage the anchor portion, it is easy to install a gage to measure the cable tension when the cable is cranked. This allows the anchors to be installed in most soil types and to any depth as long as the anchor is loaded to the tension requirements pre-determined by the engineer. The factor of safety can be kept at a minimum since every single anchor can be tested.

For example, if the engineer determines that the uplift demand on an anchor is 500 lbs., the engineer may require the anchor to be tested to 750 lbs. (factor of safety of 1.5). The installer would then drive the earth anchor, and crank each cable to 1,000 lbs. of tension. If the level of tension is reached without the earth anchor pulling out of the ground, the anchor passes the test regardless of the embedment depth, soil type, etc. If the earth anchor pulls out of the ground, it can be re-driven to a deeper depth and the test repeated. This way, the exact capacity of the anchor is known and proven without the need for an expensive geotechnical report,large scalepile driving equipment, or any amount of concrete.

Essentially, earth anchors work the same way as helical piles and ground screws but with much less steel and without the need for the specialized installation equipment. Helical piles and ground screws resist uplift loads in the same way and are commonly tested to ensure the most efficient depth is specified for thesite specificsoil conditions, but unlike earth anchors, helical piles and ground screws often come in preset lengths makingin fieldmodifications more difficult than earth anchors.