Load and resistance factor design of soil nail walls

Peiyuan Lin, Jinyuan Liu, Xian-Xun Yuan

In the proceedings of: GeoRegina 2014: 67th Canadian Geotechnical Conference

Session: Transportation Geotechnics

ABSTRACT: This paper presents the determination of resistance factors for the design of soil nail walls (SNWs) according to the Canadian Highway Bridge Design Code (CHBDC). This study adopts the load factors and target reliability indices from the CHBDC and performs reliability analyses by using the Rackwitz-Fiessler iteration to calculate the resistance factors for external, internal, and facing failures of SNWs. SNWs with different heights and in various soil conditions are used in the determinations of those resistance factors. Several influencing factors including wall height, wall geometry, nail spacing, nail inclination, and drillhole diameter are investigated to check their impacts on the resulting resistance factors. The geometry of the wall is found to be of most importance while other factors have comparatively less influence. Finally, a set of preliminary resistance factors are recommended for the CHBDC to develop the LRFD for SNWs. RÉSUMÉ Cet article présente la détermination des facteurs de résistance pour la conception de murs d'ongle du sol (SNWs) selon le pont de la route Code canadien sur le (CHBDC). Cette étude adopte les facteurs de charge et les indices de fiabilité cible de la CHBDC et effectue des analyses de fiabilité en utilisant l'itération Rackwitz-Fiessler pour calculer les facteurs de résistance des défaillances externes, internes, et en regard des SNWs. SNWs de différentes hauteurs et dans différentes conditions de sol sont utilisés dans les déterminations de ces facteurs de résistance. Plusieurs facteurs influencent notamment la hauteur du mur, la géométrie de la paroi, l'espacement des ongles, inclinaison, et le diamètre de forage sont étudiés pour vérifier leur impact sur les facteurs de résistance résultant. La géométrie de la paroi se trouve être la plus grande importance alors que les autres facteurs ont une influence relativement moins. Enfin, un ensemble de facteurs préliminaires de résistance sont recommandés pour la CHBDC pour développer le LRFD pour SNWs. 1 INTRODUCTION Soil nailing is an important earth retention technique for highway construction and maintenance, e.g., reinforcing existing slopes and supporting excavations for roadway widening. As another alternative to mechanically stabilized earth (MSE) structures and other retaining wall systems, soil nail walls (SNWs) are competitive because of their cost-effectiveness and fast construction. There are several typical failure modes that must be considered when designing an SNW, i.e., external, internal, and facing failures. External failures refer to failures of overall stability, sliding stability and bearing capacity. Bearing capacity failure is not investigated in this study since SNWs normally are not built in or over soft, fine-grained soils (Lazarte 2011). Internal failures include nail pullout and nail fracture in tension. Facing failures mainly refer to flexural failure and punching shear failure of the wall face and tensile failure of headed-studs. The current design practice to prevent those potential failures is based on the working stress design (WSD) (FHWA 2003, GHKSAR 2008), by which a factor of safety (FS) is designated to control the safety level that the structures should achieve. The FS is defined as the ratio of the overall resistance of a system to the total loading effects that the system has to carry. The WSD approach might induce considerable inconsistency of safety levels among different design scenarios, even that these design scenarios are all dictated to achieve the same FS. The load and resistance factor design (LRFD) approach, which was initiated by structural engineers for steel and concrete structural design in the 1970s, considers variability in the design equations by defining load and resistance factors (LRFs) (Melchers 1999, Nowak and Collins 2012). The direct benefit of using the LRFD over the WSD is more consistent safety levels under different design scenarios. The LRFD approaches are adopted in the Canadian Highway Bridge Design Code (CHBDC 2006) both for bridge and associated structures, including several soil-reinforcing techniques such as ground anchor and MSE structures. Although the design philosophy of soil nailing is conceptually similar to that of the ground anchor application, Clause 6.10 in the CHBDC (2006) for ground anchor design explicitly points out that it only applies to soil and rock anchors, but not to soil nailing systems. Therefore, the LRFD for SNWs has to be developed, given that soil nailing is popular in western Canada and is extending its popularity to nationwide. This paper addresses the development of LRFD that is pertinent to the CHBDC (2006) against external, internal, and facing failures of SNWs. Resistance factors are calculated based on the load factors and target reliability indices that are specified in the CHBDC (2006). Influencing factors such as wall height and geometry, nail spacing and inclination, and drillhole diameter are also examined to understand their impacts on the calculated resistance factors. Preliminary resistance factors are suggested in the end for application.

RÉSUMÉ: and resistance factor design of soil nail walls Peiyuan Lin, Jinyuan Liu & Xian-Xun Yuan

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Cite this article:
Peiyuan Lin; Jinyuan Liu; Xian-Xun Yuan (2014) Load and resistance factor design of soil nail walls in GEO2014. Ottawa, Ontario: Canadian Geotechnical Society.

@article{GeoRegina14Paper333,author = Peiyuan Lin; Jinyuan Liu; Xian-Xun Yuan,title = Load and resistance factor design of soil nail walls ,year = 2014}