Report No. : GEO Report No. 264

Report Title : Review of the Approach for Estimation of Pullout Resistance of Soil Nails (2012), 49 p.

Author : W.M. Cheung & K.W. Shum

Abstract

Pullout resistance is one of the key parameters for the design of soil nails. At present, methods for estimating pullout resistance are not unified as reflected by the many approaches used in different technical standards and codes of practice. As part of a series of soil nail studies for the development of Geoguide 7, a review of the design methods and safety factors adopted by Hong Kong and overseas, including the US, Japan and some European countries (the UK, France, and Nordic countries), for estimation of pullout resistance of soil nails has been conducted.

As part of the review, about one thousand of field pullout test data have also been collected from LPM sites for analysis. About 84% of the tests were conducted in weathered granite and volcanic rocks. The rest were conducted in other types of materials such as fill, colluvium and moderately decomposed rock.

In summary, each of the design methods has its merits and limitations. The field pullout test results indicate that the pullout resistance is generally higher than the theoretical value given by the effective stress method. This suggests that although the method has limitations, it gives a safe solution under the ground conditions and construction practice in Hong Kong.

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