Proceedings of the 17th African Regional Conference on Soil Mechanics and Geotechnical Engineering

The mechanism involved in ground improvements with vacuum assisted prefabricated verticaldrains (PVDs) for road embankments is essentially 3-dimensional (3-D) but could reasonably well approximatedas axisymmetric. In this context, axisymmetric unit cell modelling generally provides a very good representationfor Finite Element (FE) modelling. However, it carries significant limitations in terms of the scopeof the analysis. Hence, to get an understanding of the overall deformational behaviour of the foundation soilbeing improved, a full scale Plane Strain (PS) FE model would be necessary. In this paper, conversion of axisymmetricunit cell to an equivalent PS model is carried in the context of a vacuum consolidation project.Foundation soft soil is modelled using an elastic-viscoplastic (EVP) model which accounts for the time dependentbehaviour of soft clay. Results of this PS conversion is compared with the axisymmetric FE solution. Stabilityof the embankment is also analysed using maximum lateral displacements

Proceedings of the 11th International Conference on Geosynthetics

Prefabricated vertical drains (PVDs) with vacuum suction have helped to shorten the con- solidation time significantly in ground improvement projects. This method is claimed to be more effective and economical in consolidating deep soft clay layers. However, recent research has shown that the vacu- um suction applied to PVD near the ground surface may not penetrate the full depth (i.e. along the full length) of the PVD and the actual effects of the vacuum suction on the consolidation of the clay are not clearly understood. In this paper, an innovative approach is presented to model the vacuum suction distri- bution along the PVD using Finite Element (FE) modelling. Complex vacuum distributions, close to ellip- tical in shape is modelled and validated against field performance monitoring data. Moreover, the effects of this vacuum distribution on the deformational behaviour of the soft clay are also discussed

Proceedings of the XVI Pan-American Conference on Soil Mechanics and Geotechnical Engineering (XVI PCSMGE)

Vacuum consolidation can be used to accelerate the soil consolidation inground improvement projects. Capped Prefabricated vertical drains (CPVDs) is an improved method where vacuum is applied to each PVD separately. This is particularly useful if the area is inundated or have a high permeable sand layer or seam. Vacuum consolidation in an actual project is much challenging to model and predict the performance. This is due to the switching on and off of the vacuum pump, accidental failures of the pump etc. in the field and they need to be incorporated in the analysis. In this paper an elasto-viscoplastic (EVP) model, capable to simulatesuch instances, is presented and is validated against a field case reported from a landreclamation project in Singapore

Dynamic modulus and fatigue testing of lightly cementitiously stabilized granular pavement materials

This paper examines the characterization of a granular material lightly stabilized with slag-lime cementitious binder particularly utilizing the monotonic and cyclic load IDT testing method. An extensive laboratory investigation was carried out to determine the mechanical properties of the lightly stabilized granular material and to establish fatigue life relationships by IDT testing and typical results obtained from this ongoing research are presented in this paper. This study shows that the static stiffness modulus and dynamic stiffness modulus of the stabilized material increases with binder content and showed little change with moisture content variation around the optimum moisture content. Fatigue life relationships were established using two methods, namely the approach of determining the number of cycles for 50% reduction in the stiffness compared to the initial stiffness and the energy ratio method, and they both showed similar linear relationships. It is therefore concluded that cyclic load IDT testing can be used reliably to characterize lightly stabilized granular materials with slag-lime in terms of their strength, stiffness modulus and fatigue life relationships

Determination of stiffness modulus and poisson's ratio of lightly stabilized granular materials from indirect diametral tensile testing

Lightly cementitiously stabilized granular materials are generally characterised by their tensile properties that are required for the analysis and design of a pavement structure involving these materials. Tensile properties include tensile strength, stiffness modulus, and Poisson's ratio. However, there are limited studies on the mechanistic determination of stiffness modulus and Poisson's ratio of lightly stabilized materials; rather, a magnitude of Poisson's ratio is often assumed. This paper examines the use of monotonic and cyclic load indirect diametral tensile (IDT) testing to determine the Poisson's ratio and stiffness modulus of lightly stabilized granular materials. The experimental program included the determination of IDT strength, static and dynamic stiffness modulus, and Poisson's ratio for a typical freshly quarried granular base material stabilized by the addition of 0.5 to 3 % cement-flyash and 1.5 to 3 % slag-lime slow-setting binder. A new IDT testing setup to measure both the horizontal and vertical deformations along the diameters of an IDT specimen was developed and the tests were conducted on 28 days cured samples prepared by gyratory compaction. Details of the new IDT testing arrangement with on-sample deformation measurement for performing monotonic and cyclic load testing to obtain reliable data are discussed. This study indicates that the proposed IDT testing setup with on-sample deformation measurement could be used reliably for determining the tensile properties of lightly stabilized granular materials including the Poisson's ratio.Scopu

Fatigue characterization of lightly cementitiously stabilized granular base materials using flexural testing

The fatigue characteristics of a lightly stabilized granular material under traffic loading are important considerations for the design of a pavement containing such material. This paper examines the use of flexural testing with on-sample midspan deflection measurement for determining fatigue characteristics of lightly stabilized granular base materials. The experimental program included cyclic load flexural testing to determine the stiffness modulus, fatigue life, and damage characteristics of a granular material stabilized lightly with 1-3% cement-fly ash and to establish relationships for predicting the fatigue life. Fatigue life was estimated using the energy ratio approach and compared with the number of load cycles required to break the specimen. Empirical relationships are proposed to relate the fatigue life with tensile strain and stress ratio similar to those proposed in the literature. Progressive damage due to fatigue and permanent deformation accumulation with increases in the load cycles is also presented in this study. 2016 American Society of Civil Engineers.Scopu

Settlement analysis of foundation soil over long time and comparison with field performance

This paper models the consolidation of the foundation soil of a wide geogrid reinforced embankment close to its centre-line. An elastic viscoplastic model has been used for the analysis. A creep function that takes into account of the non-linear nature of creep has also been incorporated in this model. The predicted results are compared with the field measurement data and with the analysis results obtained using two other models (i.e. Kutter and Sathialingham, 1992 and modified Cam-Clay)