Title:
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The use of discrete piles for infrastructure slope stabilisation
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Real piles used to stabilise a railway embankment near Tonbridge, Kent, have been instrumented with strain gauges and inclinometer tubes to measure pile bending moment and displacement. Pile bending and displacement was monitored over a period of two years. Lateral soil displacements of 8mm were measured to a depth of 4m. Much of the pile loading occurred as a result of regarding of the granular rockfill originally placed on the embankment surface as a construction platform, although early loading occurred as the result of the instability of the slope. The top of the pile in an upslope direction as it was restrained within the failing mass of soil. This bending behaviour is contrary to that assumed during design of the piles. Analysis of the piles was carried out using both the elastic program ALP and the finite difference program FLAC3D. The elastic analyses were used to back analyse the measured pile behaviour, and to investigate the stiffness properties of the soil materials. The finite difference analysis was able to incorporate the construction sequence and demonstrate the impact of the slope regarding on pile behaviour. The finite difference analysis did however calculate smaller bending moment than measured in the pile, mainly because it was found to be difficult to incorporate the change in pore pressures in the slope due to rainfall, and to model the exact instability of the slope (the real pore pressures were not measured). The use of elastic analysis was studied as a means of pile designs. There is often no site specific soil stiffness data available, but despite this it was found to be more satisfactory than the limit equilibrium calculations commonly used at present.
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