Influence of nail inclination and facing material type on soil-nailed slopes

The performance of a soil-nailed slope is significantly influenced by the slope geometry, nail parameters and facing material types. The objective of the present study was to examine the influence of nail inclination and facing material types on the stability and deformation behaviour of soil-nailed slopes subjected to seepage flow at 30g. A series of centrifuge model tests were carried out on 5V:1H slopes with and without soil nails. Bored and grouted soil nails including nail heads were modelled using thin aluminium tubes coated with a thin layer of sand-smeared adhesive. Two different nail inclinations of 10 and 25° with the horizontal were adopted with two different material facing types. All the models were thoroughly instrumented with displacement transducers for measuring surface settlements of the slope and pore pressure transducers to capture the development of the phreatic surface within the slope during the centrifuge test. In addition, the centre column of soil nails were instrumented at their mid-length to measure nail forces at the onset of seepage flow during the centrifuge test. A digital image analysis technique was employed to arrive at displacement vectors placed on the front elevation of the slope and markers attached to the facing to monitor face movements. Stability analysis of soil-nailed slopes with nail inclinations ranging from 0° to 30° in increments of 5° with the horizontal was carried out to ascertain optimum nail inclination for a 5V:1H slope with facing. The results indicate that stabilising the earth slope subjected to seepage using soil nails has a significant effect on the stability and deformation behaviour of the slope and is strongly influenced by nail inclination and the facing material type. For an identical type of facing and nail layout, a 5V:1H slope stabilised with soil nails inclined at 10° was observed to perform better than a slope stabilised with soil nails inclined at 25°. The measured nail forces were found to be on the higher side for a slope stabilised with soil nails inclined at 10° than at 25°. The observed centrifuge model tests were found to corroborate well with results of the slope stability analysis.