Chance Helical Anchors
Since the early 1960s, Chance Helical Anchors have been used in the electric transmission industry as the primary guy anchor solution. Today, Chance Helical Anchors are finding increased popularity in civil construction applications because of the versatility and cost-effectiveness of this uplift (tension) restraint solution. Chance Helical Anchors extend bearing plates through soft, loose or expansive surface soils into stable strata with minimal disturbance. Discover the predictable, cost-effective, quickly installed alternative to traditional uplift restraint methods.
Helical anchors are commonly selected for earth anchoring applications because they are quick to install and can be proof-tested and loaded immediately with no concrete to cure or de-watering of the excavation to deal with. Helical anchors are often chosen over traditional anchoring methods such as concrete deadmen or grouted anchors in order to overcome limited accessibility or the presence of a high water table.
Helical Tiebacks from Chance
A tieback anchor is a segmented deep foundation system with helical bearing plates, welded to a central steel shaft. Load is transferred from the shaft to the soil through these bearing plates.
Tieback anchors are installed by rotating the anchors into the ground with rotary drilling equipment. Once the minimum depth is obtained, the capacity can be determined by reading the installation torque and correlating it to the holding capacity ratio. Capacities up to 55,000 pounds per anchor can be obtainable with this system.
Benefits for Using Chance Helical Anchors
- High production capabilities
- Minimal vibration or displacement of soil during installation
- Instant load capacity
- Installation Torque continuously monitored
- No spoils removal (ideal for contaminated site conditions)
- Easily installed in areas with limited access
Helical Anchor Installation
Chance Helical Anchor Installation Overview
A helical anchor is used to resist tensile loading. For these tension only anchors, square shaft helical anchors are the logical choice. The helical anchor is segmented with helical bearing plates welded to a central steel square shaft. Load is transferred through the shaft to the soil through the bearing plates. Anchors are couple together with couplings, and the only limit to installation depth for these anchors is soil density. Engineers can achieve whatever depth makes sense economically.
Since the plates are helical, they do not auger, but rather screw into the soil with minimal disturbance. Helical bearing plates have a standard 3″ pitch and are spaced at far enough distances from enough apart that they bear load independently of each other; therefore, the load capacity of one is not influenced by adjacent plates.
Anchor Installation Details
Central steel shafts are available in two different types: Square Shaft (SS) series or Round Shaft (RS) series. The Type SS series are available in 1-1/4″ to 2-1/4″ square sizes. The Type RS series are available in 2-7/8″ to 7-5/8″ diameter sizes. Type SS-RS combinations are also available for compression applications in soil conditions where dense/hard soils must be penetrated with softer/loose soils above the bearing strata.
Segments or sections are joined with bolted couplings. Installation depth is limited only by soil density and practicality based on economics. A helical bearing plate or helix is one pitch of a screw thread. All helixes, regardless of their diameter, have a standard 3″ pitch. Being a true helical shape, the helices do not auger into the soil but rather screw into it with minimal soil disturbance. Helical plates are spaced at distances far enough apart that they function independently as individual bearing elements; consequently, the capacity of a particular helix on a helical anchor/pile shaft is not influenced by the helix above or below it.
The first section or lead section contains the helical plates. This lead section can consist of a single helix or up to four helices. Additional helices can be added, if required, with the use of helical extensions. The helices are arranged on the shaft such that their diameters increase as they get farther from the pilot point. The practical limit on the number of helices per anchor/pile is four to five if placed in a cohesive soil and six if placed in a cohesion less or granular soil.
Plain extensions are then added in standard lengths of 3, 5, 7 and 10 feet until the lead section penetrates into the bearing strata.
Chance Helical Wall Anchoring System
The success of the Helical screw anchor system is based on decades of similar use of Chance anchors by electrical utilities. The proven reliability and engineered predictability of the system’s performance gives you anchors that are permanent, economical, and hassle-free. Engineered for dependability and long-term stability, the Chance Helical Wall Anchor System features exclusive anchoring techniques, tools, designs, and sizes that make other foundation methods a thing of the past. It provides a smart, cost-effective solution for bulging, bowing, or cracked walls.
There is no grout used so installed anchors can be tested immediately, and concrete trucks or grout pumps are not required. They can be installed in almost any weather using conventional drilling equipment. The Chance Anchors from MDTI have predictable holding strength in all soils.
The AB Chance Helical Wall Anchor System components include: Lead Helix, Extension(s), Anchor Termination, Wall Plate (or C-channel for blocked foundations). The installation steps include:
- The foundation is prepared for anchor installation by drilling 3” diameter holes at each anchor location from the inside to the outside.
- After the Helical anchor is screwed into the inactive soil, it is then extended through the drilled hole in the wall.
- From the inside, a wall plate (or a steel 6” C-channel for blocked foundations) is attached to the anchor and secured tight.