Report No. : -

Report Title : Design Illustrations on the Use of Soil Nails to Upgrade Loose Fill Slopes

Author : Geotechnical Engineering Office & The Hong Kong Institution of Engineers (Geotechnical Division)

Abstract

Based on the findings from a study initiated by the Geotechnical Engineering Office of the Civil Engineering and Development Department (GEO/CEDD), new design guidelines which supplement the original design guidance for the use of soil nails to upgrade loose fill slopes have been recommended, and are summarised in the report titled "Design of Soil Nails for Upgrading Loose Fill Slopes" which is jointly published by the GEO/CEDD, and The Hong Kong Institution of Engineers, Geotechnical Division (GEO-HKIE) in 2011. The new guidelines recommend the use of a hybrid nail arrangement comprising soil nails at two different orientations. A design procedure for delineating loose fill at great depths which can be assumed to be non-liquefiable is also recommended.

To demonstrate the implementation of the new recommendations given in the GEO-HKIE Report (GEO-HKIE, 2011), GEO-HKIE prepared three worked examples pursuant to the new recommendations, which are presented in this report. The first example demonstrates the procedure for adopting the hybrid nail arrangement, which is a novelty to local practitioners. The second example assumes that steeply inclined nails have to be adopted due to site constraints. The design therefore includes the provision of an embedded concrete footing which aims to reduce slope deformation. The effectiveness of the nail arrangement is verified by numerical analysis. The last example considers a fill slope with loose fill of a considerable depth, and illustrates the procedure to delineate the non-liquefiable loose fill zone by limit equilibrium method. Recommendations in respect of the selection of design parameters are also presented in the worked examples.

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