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Retaining structures
Published in Rodrigo Salgado, The Engineering of Foundations, Slopes and Retaining Structures, 2022
A tieback is an anchor that exerts a restraining force on the retaining wall. It is usually a cylindrical hole with a steel cable separated from the soil by grout. The cable is firmly connected with the wall. The tieback develops its resistance by side friction with the soil beyond the potential sliding wedge. Little to no side resistance exists between the tieback and the potential soil wedge. Tiebacks are usually preloaded to 150% of their design load, and that load is locked in. They differ from soil nails mostly in this regard: soil nails develop side resistance against the surrounding soil throughout, including along the contact with the potential sliding wedge, and soil nails are not preloaded. This makes for a much less stiff response from soil nails, which will only mobilize their resistance after significant movement of the wall has taken place.
Braced excavations
Published in An-Bin Huang, Hai-Sui Yu, Foundation Engineering Analysis and Design, 2017
A tieback is a prestressed, grouted ground anchor installed in soil or rock that is used to transmit the applied tensile load into the ground. The basic components of a tieback include: (1) the anchorage, (2) the unbonded length, and (3) the anchor (or tendon) bond length, as schematically shown in Figure 6.9. The anchorage is the combined system of anchor head, bearing plate, and other mechanical components that facilitate transmitting the tensile force from the tendon to the excavation wall. The unbonded length is the part of the tendon that is free to elongate while transferring the tensile force from the bonded tendon to the excavation wall. The tendon bond length is that length of the bonded tendon capable of transmitting the applied tensile load into the ground. The anchor bond length should be located outside of the active failure zone.
Special Topics
Published in Bungale S. Taranath, Tall Building Design, 2016
In slurry wall construction, a trench is dug in the eventual location of the perimeter walls. A bentonite slurry is pumped into the trench as it is excavated, to keep the trench open against caving of the surrounding earth. Prefabricated reinforcing steel is lowered into the trench, and concrete is placed through a tremie to create a reinforced concrete wall around the site perimeter. After the concrete is cured, excavation of the structure begins. As the excavation progresses below surrounding grade, tiebacks are drilled through the exposed concrete wall and through the surrounding soil into the rock below to provide stability for the excavation.
Three-dimensional numerical analysis of corner effect of an excavation supported by ground anchors
Published in International Journal of Geotechnical Engineering, 2022
Alireza Ahmadi, Mohammad M. Ahmadi
In the 3D numerical model, cable elements were used to model tiebacks. These elements are one-dimensional axial elements that can be anchored or grouted so that they develop forces and provide a shearing resistance along their length in response to relative motion between the cable and the grid. They behave as elastic, perfectly plastic materials that can yield in tension and compression but cannot resist bending moments (Itasca 2013). In the 3D model, two cable elements were used to model each tieback. The first cable element was created to model the free-stress length of each tieback, and it had the properties of strands. The second cable element was created to model the grouted length of each tieback, and it had the parameters of strands, grout, and soil-grout interface. These two cable elements were attached to each other at the end of the free-stress length and at the start of the grouted length. Beam elements were used to model soldier piles. These elements are two-dimensional elements with three degrees of freedom at each end node.