The general term Subsurface Tensile Elements identify engineered material components contained within the earth intended to stabilize unbalanced masses. Soil nails, grouted tiebacks, and rock bolts are subsurface tensile elements.
Soil Nails. Soil nails are steel bars or tendons installed to reinforce or strengthen the existing ground. Soil nails are installed into an excavation as construction proceeds from the existing ground surface down to the proposed bottom of excavation. The soil nailing process creates a reinforced section that is itself stable and able to retain the ground behind it.
Although seemingly similar, the installation process (a hole is drilled and a nail is installed, grouted, and tested to a design load) for soil nails differs from that of grouted tiebacks. Specifically, soil nails are passive reinforcement which develop reinforcing action through nail-ground interactions as the ground deforms during and following construction. Soil nail walls provide some advantages over walls with grouted tiebacks by:
1. Eliminating soldier pile/sheeting installation and improving construction flexibility where overhead access is limited and/or in soils with cobbles and boulders.
2. Reducing right-of-way requirements by typically being shorter than tiebacks.
3. Having a higher system redundancy.
Grouted Tiebacks. Grouted tiebacks consist of a steel tensioned element (a tendon, which may be multistrands or a bar) that transfers tensile forces from the ground to a structural element. In contrast to a soil nail, a grouted tieback is an active reinforcing element which is loaded and locked-off at a specific design load.
Rock Bolts. Rock bolts consist of a steel tensioned element generally used in reinforcing a rock slope by transferring load from the unstable exterior to the confined interior of the rock mass. Rock bolts are also used as part of a rock catchment system by anchoring the catchment device
