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

Abstract

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.

Centrifuge model studies on soil-nailed slopes subjected to seepage

“…Deepa and Viswanadham (2009) conducted centrifuge model tests with and without soil-nails and presented that increase in vertical as well as horizontal spacing of nails and decrease in nail length reduced the stabilizing effect. Rotte and Viswanadham (2013) reported that slope facing helped to retain the soil mass effectively behind it and it prevented the local failure of the soil between the nails at the toe of slope.…”

Centrifuge and Numerical Model Studies on the Behaviour of Soil-Nailed Slopes with and without Slope Facing

“…An onboard central processing unit placed on the swing basket allows to record data from various transducers continuously. The scaling considerations of parameters related to soil, slope and soil-nails need to be satisfied and are discussed by Rotte and Viswanadham (2013).…”

“…A seepage simulator unit was used to allow seepage of water through soil-nailed slopes during the tests. The details and working operations of seepage simulator unit was discussed in detail by Rotte and Viswanadham (2013).…”

“…After completion of each layer, specially designed L-shaped plastic markers made of thin transparency sheets were placed at a distance of 20 mm from the slope face to study the movement of soil during the test. The detailed procedure of construction of slope model, insertion of nail with facing was discussed in detail by Rotte and Viswanadham (2013). All the slope models were instrumented with the help of pore pressure transducers (PPTs) to measure the development of pore water pressure within the slope and linearly variable displacement transformers (LVDTs) to record the surface settlements of the slope during the test.…”

Editorial

“…In the third paper Rotte and Viswanadham (2013) examine the influence of soil nail inclination and facing material types on the stability and deformation behaviour of soil-nailed slopes subjected to seepage flow at 30g in a series of instrumented centrifuge model tests. Tests were carried out on 5V:1H slopes both with and without soil nails.…”