Observed And Calculated Behaviour Of A Geotextile Reinforced Embankment On A Soft Compressible Soil

An instrumented test embankment was constructed to failure on a soft compressible organic clayey silt deposit at Sackville, New Brunwick, Canada in Sept./Oct., 1989. This embankment consisted of an unreinforccd section and a section reinforced with a relatively high strength polyester woven geotextile. The instrumentation, field performance and analyses of these embankment are examined in this thesis.;The observed responses of pore pressure, settlement, heave and lateral displacements in the foundation soil and the strain in the geotextile are correlated and failure of each embankment is discussed. An account of the development and propagation of cracks in relation to the construction and the interpretation of failure for each embankment is also discussed. The excess pore pressure response and soil deformations showed some evidence of the susceptibility of the soil to progressive failure. The actual failure was of a plastic (or visco-plastic) type and no classical-type of abrupt failure was encountered during the construction of either of these embankments.;A numerical model is developed to perform fully coupled large strain elasto-plastic consolidation analysis with Modified cam-clay material behaviour using 15-noded cubic strain triangular elements. The viscous/creep effects and the potential strain softening behaviour of the soil are not considered in this numerical model. The test embankment was back analyzed using information obtained from the field investigation together with engineering properties of the soils and geotextile obtained from laboratory tests. The results of finite element analysis using this model are shown to be in reasonable agreement with the observed performance. The deformations at large depth and the large settlements and heaves observed in the field at high embankment thicknesses could not be predicted satisfactorily using this model.;Finite element analyses are used to study the sensitivity of embankment behaviour to variations in the foundation soil and embankment fill properties. The influence of the variation of over consolidation ratio (OCR), the coefficient of earth pressure at rest (K{dollar}\sb{lcub}\rm o{rcub}{dollar}), angle of internal friction, Poisson\u27s ratio and the permeability of the foundation soil as well as the effective friction angle of the embankment fill are examined. This sensitivity study indicated that the effective friction angle ({dollar}\phi\sp\prime{dollar}), K{dollar}\sb{lcub}\rm o{rcub}{dollar} and OCR of the foundation soil are all important parameters and therefore should be measured or estimated carefully. Furthermore, uncertainties regarding the Poisson\u27s ratio did not affect the results of the analysis significantly but the uncertainties regarding permeabilities of the foundation soil or effective friction angle may have a significant influence on the behaviour of such reinforced embankments on soft soil.;Both small strain and large strain undrained finite element models are also used to back analyze the reinforced embankment. The effect of changing the undrained shear strength profile on the behaviour of this embankment is examined. The failure of the reinforced embankment could be predicted accurately by a small strain undrained finite element analysis using the mean shear strength profile (between the field vane and the CAU triaxial and constant volume direct simple shear tests in the lab)

Characterisation of a lightly stabilised granular material by indirect diametrical tensile testing

Lightly stabilised granular materials with cementitious binders are generally characterised by their stiffness modulus and this paper examines the use of monotonic and cyclic load indirect diametrical tensile (IDT) testing to determine the stiffness characteristics of these materials. The experimental programme included the determination of density, IDT strength and static and dynamic moduli from monotonic and cyclic load IDT testing for a typical freshly quarried aggregate granular base material stabilised by the addition of 3-5% slag-lime slow-setting binder under a narrow range of moisture variations. The IDT tests were conducted on 28 days cured samples prepared by gyratory compaction. Details of an IDT testing arrangement with internal displacement measurement for performing cyclic load testing to obtain reliable data are also discussed. This study indicates that cyclic load IDT testing could be used reliably for determining the dynamic stiffness modulus of a lightly stabilised granular material with a newly proposed equation