Soil nailing is an earth retaining technique used to stabilise existing slopes and support excavations. The stability post construction can change due to variation in groundwater, resulting in a reduction of effective stress in the soil. Nine centrifuge model experiments were performed investigating the influence of reducing the effective stress within the model by water inundation. The models tested were 1/10th scale. The full-scale prototype excavation was a three metre high cutting with a slope angle of 70°. The corresponding forces developed in the nails and displacements developed are assessed.


Soil nailing is an earth retaining technique used to stabilise existing slopes and support excavations, both as temporary and permanent works. The long term stability of the excavation post construction can change due to a number of factors, i.e. nail degradation, failure of the facing. One particular aspect is changes of groundwater resulting in changes of effective stress conditions in the soil. The long-term performance of soil nailed excavations is a major unknown to those designing the soil nail systems because there are very few over 20 years old. Those observed for long-term performance have been monitored for a period typically 2–5 years after construction (FHWA, 1996). Hence, the response of the soil nailed structure to changes in ground conditions within the soil are not well established. The aim of these studies was to investigate the contribution made by soil nails to maintaining the stability of a steep sided cutting during the excavation process and a period of water inundation. The technique of centrifuge modelling was used to investigate the processes. The investigation considers the influence of changes in effective stress conditions on the stability of the slope and the increased contribution of the nails to maintain stability under these conditions.

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