Anchor construction commences with a detailed review and understanding of the anchor construction specification and project drawings. Dimensions and properties of permanent materials including all-thread-bar, plates and grout are determined. Additionally, for rock bonded anchors, the minimum embedment into rock, referred to as the bond length, is also required.
Bar anchors typically consist of three main components, the bond length, the un-bonded length (if so designed) and the anchorage head. The bonded section of the anchor is developed in competent rock or soil and the load is therefore transferred into the underlying formation. Solid bar anchors are more suitable for compact soils that are not prone to collapse and in rock formations.
Bonded bar anchors maximize the potential benefit of the subsurface characteristics. The design engineer reviews the available geotechnical information including core borings and unconfined compressive strength of the formation in developing the anchor design calculation. These design calculations are used to establish the theoretical minimum bond length. Once mobilization to site occurs, the theoretical design parameters are validated in a pre-production testing program. Upon successful testing, bar anchor production commences using the same operational parameters.
The challenge on this project was to provide deep foundation support for a 2.0 million gallon capacity Type III wire-wound, pre-stressed concrete water tank. Subsurface challenges included an under laying of soft clays present at the site. Rock anchors were chosen to both bridge the soft clays and transfer the load into competent rock to support the structure and to counter any uplift force.
kip vertical tension load
lf of drilling
Anchors constructed with high strength bars are drilled and grouted into bedrock and/or soil in order to resist forces. Structures need anchors to counteract the uplift and other forces acting on foundations.
For this project, the Design Engineers were faced with the complex geological conditions with high structural loading and as always were looking for the best economical value in their approach to the work. Rock anchors were selected to maximize the benefits of the under laying rock formation and to accept the heavy compressive loads and to counter any uplift forces. The structural loading of the water tank is transferred from the concrete floor(s) and ultimately down through the anchors into the under laying rock formation. Rock anchors provided the best value on this project because the designers were able to calculate the diameter, length of the bond zone and the specifics of the materials that made up the anchor to formulate the precise performance necessary to achieve the design criteria. The subsequent project design called for the installation of (96) 1.375” Grade 150 Epoxy coated bar anchors designed to handle vertical tensile loads of 113 kips. The anchors were drilled through driven 9.625” pipe piles, including a 2’ concrete plug at the bottom of the casing, and grouted. Five anchors were tested to confirm design and installation. Application specific designs such as these ensure the proper foundation element is developed to maximize the benefits and contribution of the actual subsurface characteristics.