Emphasis on Inspection and QC/QA Figure 2. Solid bars for soil nails shown with gray and purple epoxy coating (left); partially encapsulated by sheathing (right). Photos courtesy DYWIDAG-Systems International. • Transfer tensi le loads to the surrounding ground through shear stresses (i.e., bond stresses) along the grout-ground interface. • Develop resistances that can be estimated with established design procedures. • Have long-term, demonstrable cor- rosion protection to ensure adequate, long-term performance of the system. • Interact structurally with the facing of the excavation. • Are load-tested according to prescribed methods. • Are routinely subject to construction QC/QA, according to established procedures. Like its 2003 predecessor, GEC 7 2015 provides information to assist owners in identifying and managing the main risks associated with soil nail wall projects. To this end, guidelines for construction of safe and cost-effective soil nail walls are included in terms of: (a) the types of information that owners should provide for contracts; (b) the activities that design engineers should perform (either on design/bid/bui ld or design/bui ld procurements); and (c) the expected tasks to be performed by the contractor. New Construction Materials and Applications Since the first edition of GEC 7, new bar types and other related materials have emerged for the construction of soil nail walls. For example, a wider selection for fusion-bonded epoxy coatings now exists. Epoxy coating can now be found in different 76 • DEEP FOUNDATIONS • MAY/JUNE 2015 Figure 3. Sculpted natural rock-like soil nail wall facing. Photo courtesy Con-Tech Systems, Ltd. types including green, gray and purple, and in various thicknesses. The green epoxy coating is flexible and suitable for application over bent steel reinforcement. Generally, the gray and purple coatings are less flexible but have greater chemical resistance than the green coating (Figure 2). The purple epoxy coating is considered to be best suited for harsh environments. Sculpted wall facing, which has been used since the early 1990s, is now listed as an alternative to traditional final facing options, such as plain shotcrete, cast-in- place (CIP) concrete, and precast concrete panels. While sculpted wall facings can increase construction costs, they can offer owners an aesthetically attractive option (Figure 3). The CIP concrete wall of this figure was hand sculpted to resemble stone, and the final surface was stained to match the surrounding environment. Similar to its predecessors, GEC 7 2015 emphasizes the need to provide thorough inspection as part of a construction QC/QA program. The manual includes guidelines for better construction practices and contains an entire chapter devoted to “Construction Inspection and Performance Monitoring.” The document highlights key construction aspects, from assessment of the stand-up time of initial cut to the inspection and testing of materials, as well as observation of excavation, hole-drilling, bar installation, grouting and shotcreting. The section on soil nail load testing has been expanded and improved to both reflect the LRFD format and better practices developed by industry over the years. As an example of recommended practice for assessing material per- formance, the manual discusses how shotcrete test panels are prepared, cored and tested for compressive strength to verify their quality, strength and consistency (Figure 4). Design Philosophy The design philosophy of GEC 7 2015 hinges on: (a) ASD stability calculations based on limit-equilibrium principles, using soil nail design software; and (b) LRFD checks using results from ASD-based slope stability calculations. Therefore, this design framework allows users to:
