2016 – Geotechnical Characterisation of a Tropical Residual Soil in an Embankment Abutment

James Penman, Terence Jibiki, Len Murray, and Mark Rynhoud

Two earthfill embankments are being constructed to form an impoundment in a mountainous region with a tropical climate. The embankment abutments are underlain by tropical weathered rock/soil including a significant thickness of residual soil. Previous slope failures within the area, including a 150 m wide failure of a construction access road, have been potentially due to weakness of the residual soil. In order to quantify the potential risk to the embankments, a geotechnical characterisation program consisting of in situ and laboratory testing was completed to determine the shear strengths and loading response within the residual soil material. This paper summarises the geotechnical investigation program and characterisation of this tropical residual soil in the context of the embankment stability.

Results of laboratory direct simple shear testing are presented and compared to common empirical methods for estimating the undrained shear strength of both over-consolidated and normally-consolidated materials using index properties and/or over-consolidation ratios. Methods used for comparison include those proposed by Skempton (1952 & 1957), Bjerrum-Simons (1960), Lambe & Whitman (1969) and Wroth & Houlsby (1985) for normally consolidated material and Ladd (1977) and Jamiolkowski et al. (1985) for over-consolidated material.

The results of in situ testing, including pocket penetrometer data and field shear vane data, are also presented.

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