As a specialized foundation, sub-horizontal ground anchors are distinct in application, components, and purposes. Otherwise known as “tiebacks,” they’re an integral foundation option in special cases where excavating and constructing a footing foundation isn’t possible. It’s also a popular route when it’s too difficult to construct a pile cap for a conventional wall, as opposed to vertical ground anchors that are employed when trying to avoid uplift and overturning.
At G3 Quality, a large part of our job is to guide partners and clients down the right path in terms of construction quality management. If you’re still confused as to how ground anchors could play into a construction project and specific inspection and quality verification procedures after reading, don’t hesitate to reach out to us for assistance.
Applications of Sub-Horizontal Ground Anchors
Sub-horizontal ground anchors are fitting for both temporary and permanent structures, often being used in conjunction with sheet pile, or soldier beam shoring. This allows for higher walls and more thorough excavating reminiscent of cantilever construction, which can build walls up to 15 feet high. As for sub-horizontal ground anchors, these walls can rise up to 35 feet, depending on properties in the surrounding soil that can affect structural integrity. Wall height doesn’t have to halt at 35 feet; by employing a high-strength sheet pile or soldier beams as previously mentioned, and with several tiers of ground anchors, wall height can easily surpass 35 feet.
Components of Sub-Horizontal Ground Anchors
In order to construct sub-horizontal ground anchors, construction teams will drill holes off the horizontal axis at a slight angle, usually around 15 degrees. Once the holes are drilled, a specialized prestressing system is set up before grouting the bonded length. The bonded length, or “tip portion,” serves as an anchor of sorts, distributing the prestressed force throughout the surrounding soil foundation. Lastly, the unbonded portion is secured in place with the use of an anchor head.
For an idea of how the sub-horizontal ground anchor sequence progresses, take a look at the steps below:
- Holes are drilled, at an angle, to the required length and diameter.
- Prestressing steel unit is installed.
- Primary grout is placed.
- Carry out performance and proof tests.
- Lock-off and prestress are applied.
- Secondary grout is secured.
Other Uses and Purposes
Along with their support in building taller walls and pulling deeper excavations, sub-horizontal ground anchors are especially useful in terms of workspace. Since the only part of the system that protrudes beyond the wall is a small anchorage device, an unrestricted workspace is opened up adjacent to the wall and inside the excavation site.
If you’re undergoing a construction project and require geotechnical expertise, the engineers, QA/QC technicians and inspectors at G3 Quality have the knowledge you’re seeking. We’ve contributed to countless projects up and down California, and are available to serve as your solutions-oriented quality management, inspection and materials testing expert.
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