Specialty Anchor Systems
Helical anchors and auger cast or driven piles are excellent alternatives for many monopole or tower foundation projects and can be also the perfect solution for a retrofit design. Frequently they’re the only answer for building sites in marshy areas, to minimize wetlands disturbance or to work in confined areas. Speed and economy are also benefits of certain applications.
Auger Cast Piles
Helical Anchor Systems
The helical screw pile anchor is one of the easiest and quickest foundation systems to install for guyed and self supporting towers. A skid steer or backhoe with a 12,500 – 15,000 ft.-lb. drive motor with an internal torque monitoring device is the only heavy equipment you will require on site to install the anchors. Excavated soil removal is normally non existent except for some minimal spoils from the tower base installation. The vibration free installation and minimum ground disturbance makes the anchor system an excellent candidate for environmentally sensitive areas and locations where heavy equipment normally can not operate. The anchors are not suitable for installation in soils that have rock or cobbles.
Helical systems can be utilized to anchor a new guyed tower installation or serve as a foundation for additional guy wires on an existing structure that requires retrofitting. The number of anchors per guy wire will depend upon soil conditions and anchor loads. Two or more helical anchors may be required to support one wire on a tower, whereas two anchors with a spreader beam and fan plate can accommodate four wires on another structure. Helical anchor systems have been designed and used to support guyed towers over 400’ tall with a basic wind load design of 110 mph.
Upon applying torque to the shaft, the helix shape of the bearing plate creates a pulling force that keeps the anchor advancing downward into the soil. An extension rod is then attached and the process is continued until the anchor reaches the design depth or maximum torque. Depending upon the guy wire loads and soil conditions, the anchor might have to be installed to depths exceeding 90 feet. Helical anchors with either square or round shafts can work equally as well in medium to dense sand or firm clay.
Grouted minipiles can use the helical anchor to provide for bearing loads required for new self supporting towers, equipment platforms and shelters or anchor retrofits. When the anchor is advanced downwards in the soil, an attached lead displacement plate forces soil outward to create a cylindrical void around the shaft. From a reservoir at the surface a flowable grout fills this void, encapsulating the shaft. Additional extensions and displacement plates are added until the helical bearing plates reach the load-bearing soil. The piles are then capped for the tower’s anchor bolts or secured to a grade beam or an existing shaft to affect interaction.
For pricing and additional information we recommend that you contact our valued helical anchor manufacturers, distributors and installers to discuss your site-specific requirements.
Auger Cast Piles
Auger cast piles can be utilized for the foundation for a new monopole or tower and can be effective in retrofitting existing foundation designs.
Ranging in diameter from 4” to 36”, the piles are installed by rotating a continuously flighted hollow shaft auger into the soil to a specified depth. High strength cement grout is pumped under pressure through the hollow shaft as the auger is slowly withdrawn. The resulting grout column hardens and forms an auger cast pile. Reinforcing, when required, can be installed while the cement grout is still fluid or, in the case of full length single reinforcing bars, through the hollow shaft of the auger prior to the withdrawal and grouting process.
Since the auger cast piles are drilled there is less noise and vibration than a driven pile and it avoids the potential of damaging existing structures. No casing is required since the earth filled auger maintains the shape for the pile hole during drilling. While withdrawing the auger, the induced grout provides the lateral pressure to keep the hole open. It also exceeds the pressure per foot of the depth of the soil and displaces the existing soil for the entire length of the pile.
Many drilling rigs are small enough to work with as little as 10 feet of headroom or the auger can be placed at an angle to accommodate any retrofitting design requirement.
For pricing and additional information we recommend that you contact our valued auger cast installation contractors to discuss your site-specific requirements.
If you are near a Lousiana bayou, a New Jersey bog, a South Carolina sensitive wetlands area, or similar environments throughout the country, chances are your only tower foundation option available is to install driven piles.
The driven pile is a relatively long, slender column, provided to offer support or to resist the structure’s forces. They’re made of preformed material having a predetermined shape and size that can be physically inspected prior to and during installation. They’re installed by impact hammering, vibrating or pushing into the earth.
Driven piles are usually installed to an established criteria such as a minimum blow count per unit penetration or a minimum penetration. Variable subsurface conditions can require piles of different lengths. Driven piles may either be cut off to shorten their length or spliced to extend their length. Splice designs are required to meet or exceed the strength of the pile itself. One length does not have to accommodate all site conditions. This allows driven piles to easily adapt to variable site conditions to achieve uniform minimum capacity with high reliability, thus eliminating uncertainty due to varying site conditions.
Driven piles can be the most cost effective deep foundation solution in marshy or sensitive wetlands areas. The wide variety of materials and shapes available for driven piles can be easily fabricated or specified for high structural strength, allowing them to be driven by hammers to increased working loads thus requiring fewer piles per project, resulting in substantial savings in foundation costs. Pile driving contractors will either provide you with pricing to cap off the piers for your tower anchorage design or make available a list of capable contractors.
For pricing and additional information we recommend that you contact our valued pile driving contractors to discuss your site-specific requirements.