Advances in Soil Nail Design and Construction

摘要

The new FHWA Geotechnical Engineering Circular No. 7 - Soil Nail Walls -Reference Manual (GEC 7) (Lazarte et al. 2015) provides updated guidance for design and construction. The information presenting in this paper is based in Lazarte et al. (2015). The GEC 7 introduces a framework for the design of soil nail walls that takes into account factors of safety (FS) as previously used in allowable stress design (ASD) and integrates Load and Resistance Factor Design (LRFD) principles. Design is limited to ASD-based slope stability procedures because LRFD-based slope stability analysis procedures are not available. Therefore, a soil nail wall design must use ASD-based stability calculations to quantify loads and slip plane geometries, and then take those values and perform LRFD checks. Hollow Bar Soil Nails (HBSNs) have been increasing in popularity and usage since the technology was introduced about 20 years ago (Cadden et al. 2010) and HBSNs are now addressed in GEC 7. HBSNs are advanced into the ground for their full design length with a sacrificial bit using grout as the drilling fluid; thus drilling, grouting, and tendon installation are all accomplished as part of one single process. HBSNs are particularly advantageous in collapsing ground conditions where the simultaneous injection of grout through the tendon during drilling keeps the drill hole from collapsing. Due to their installation method, the procedures for HBSN installation, design, corrosion protection, and load testing require special considerations.