C. T. Gnanendran

On equivalent granular void ratio and steady state behaviour of loose sand with fines

Void ratio has traditionally been used as a state variable for predicting the liquefaction behaviour of soils under the critical state soil mechanics framework. Recent publications show that void r...

Modified state parameter for characterizing static liquefaction of sand with fines.

An experimental study was carried out to investigate the static liquefaction behaviour of sand with a small amount of plastic and nonplastic fines. Five series of tests were conducted in drained and undrained conditions. The drained test results indicate not only that the failure line coincides with the critical state, but also that the development of volumetric strain during shearing was not sensitive to the initial confining pressure. In both isotropically and anisotropically consolidated undrained tests, a so-called “reverse behaviour” was consistently observed. The results were also interpreted in the critical state framework. The critical and steady state (CS/SS) data were found to trace along the same curve in e–log( p′) space, irrespective of the stress history and effective stress paths. A comparison between the isotropic consolidation line (ICL) and critical state (CS) curve showed that a small amount of fines can significantly change the shape and position of the ICL relative to the CS curve. Fu...

Characterization of cementitiously stabilized granular materials for pavement design using unconfined compression and IDT testings with internal displacement measurements

This paper presents the findings of a laboratory investigation on the characterization of a freshly quarried granular base material lightly stabilized with slag-lime cementitious binder involving unconfined compression (UC) testing and indirect diametrical tensile (IDT) testing, both with internal displacement measurements. The UC test investigation involved the determination of the unconfined compressive strength (UCS) and four different types of stiffness moduli from both internal and external displacement measurements. The IDT testing included the determination of IDT strength as well as the static and dynamic stiffness moduli (i.e., SSM and DSM) of the lightly stabilized granular base material from monotonic and cyclic load IDT testing. This study indicates that the stiffness moduli of a lightly cementitiously stabilized granular base material can be determined consistently from UC testing by measuring the deformations internally, and the modulus is more reliably defined as either the tangent modulus at half the ultimate stress or secant modulus at 0.02% strain. The UC stiffness modulus could be estimated reliably from the corresponding UCS value using the regression relationships established from this study. The IDT strength was determined to be equal to 0.1143 times the UCS value and this conforms to the recommendation given in design guides such as AUSTROADS. Moreover, the IDT, DSM, and SSM of a lightly cementitiously stabilized granular base material could be estimated from the UCS of the same material using the correlations developed in this paper which could be used in pavement design.

Strain measurement and interpretation of stabilising force in geogrid reinforcement

Abstract The stabilising force provided by a layer of geogrid reinforcement embedded in the body of a sloped fill subjected to loading from a footing located near the crest was investigated through a laboratory model study and the results are reported in this paper. This study indicates that the geogrid reinforcement could be instrumented more reliably with strain gauges installed in pairs, i.e., on top and bottom faces of the geogrid, at each location across the geogrid reinforcement and the use of the average strain minimises the influence of flexural strains in the geogrid. If only one strain gauge per location is used, the tensile strain and geogrid force estimated on the basis of nominal stiffness would not be accurate particularly at low load levels and considerable caution is required when using such an approach. The study demonstrates that the accuracy of the estimated stabilising force in the geogrid reinforcement could be enhanced by calibrating each pair of gauges as installed in position since each gauge installed at different locations across a geogrid sample would behave differently. Details of a relatively simple tensile testing method developed for calibrating these gauges and the use of calibration results for assessing the gradual development of stabilising force in the reinforcement in relation to the foundation load are discussed.

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.

The influence of compaction method and density on the strength and modulus of cementitiously stabilised pavement materials

Australian practice is moving towards the utilisation of gyratory compacted samples tested by indirect diametrical tensile testing for determination of both modulus and fatigue life of cementitiously stabilised pavement materials. At the same time, conformance testing is expected to remain an unconfined compressive strength and density based assessment. The influence of material density on the strength and modulus of these materials is important as differing densities are achieved in the laboratory and the field. The effect of compaction method, where different test methods are used for characterisation and conformance testing, is also important. An investigation was undertaken to determine the influence of both dry density and compaction method on the strength and modulus of reclaimed pavement material stabilised with a slag-lime binder. As a prelude, the influence of compaction method and the addition of binder to the host material on the optimum moisture content and maximum dry density were also determined. The gyratory compactor protocol required to achieve densities equivalent to Standard Proctor compaction was determined and the influence of the addition of binder to a host material was found to be material specific. Whilst the compaction method (at the same dry density) had no significant influence on the strength and modulus of these materials, the density had a significant impact on both strength and modulus.

Geotextile strain in a full scale reinforced test embankment

Abstract A geotextile reinforced test embankment was constructed on a soft organic clayey silt deposit at Sackville, New Brunswick, Canada in September/ October 1989. A relatively high-strength polyester woven geotextile (ultimate strength of 216 kNm−1) was used as reinforcement. The reinforcement was instrumented with a number of electrical resistance, electromechanical and mechanical gauges. The details of this instrumentation and field performance of the geotextile reinforcement during the construction of this test embankment are described in this paper. The field data indicated that the strain in the geotextile was comparatively small (typically less than about 0·7%) up to an embankment thickness of 3·4 m. The strain increased to a maximum of about 2% when the embankment thickness was increased above 4·1 m, suggesting the initiation of movement (or yielding) of the foundation soil. A large increase of strain was evident for thicknesses exceeding 5·7 m and the available evidence indicates that the soil approached failure at a fill thickness of about 5·7 m. The strain increased to over 8·5% when the embankment was first constructed to 8·2 m thickness and then failed as the soil continued to deform at constant fill thickness and the geotextile strain increased until failure (inferred tearing) of the geotextile occurred. After the embankment failed at a thickness of 8.2 m, the addition of more fill did not result in any

Determination of Fatigue Life of a Granular Base Material Lightly Stabilized with Slag Lime from Indirect Diametral Tensile Testing

Stabilization of granular materials with low percentage of slow setting binders, such as slag lime, for constructing new pavements and/or rehabilitation of existing granular pavements has economical and environmental benefits. The fatigue life of a lightly stabilized granular material under traffic type repeated or cyclic loading is an important consideration for pavement design involving this material and it is the focus of this paper. In particular, this paper examines the use of indirect diametrical tensile (IDT) testing with internal displacement measurement for determining stiffness and fatigue life of a granular base material lightly stabilized with slag-lime cementitious binder. An extensive laboratory investigation involving monotonic and cyclic load IDT testing was carried out to determine the strength, stiffness, and fatigue life of a granular material stabilized lightly with 3–5% slag lime and to establish relationships for predicting the fatigue life. Fatigue life was established using two met...

Indirect diametrical tensile testing with internal displacement measurement and stiffness determination

This paper examines the indirect diametrical tensile (IDT) testing method and its suitability for determining the tensile strength and stiffness modulus properties of a lightly cementitiously stabilized granular base material that are required for the design of a pavement structure involving this material. A new IDT testing setup with internal deformation measurement is presented in this paper. The suitability of this testing arrangement for determining the tensile strength and stiffness characteristics of a lightly stabilized granular base material was examined by studying the IDT strength and stiffness characteristics of two typical granular base materials stabilized with 3–5 % slag-lime and 1.5 % general blend cement-flyash. This study indicates that the internal deformation measurement setup presented in this paper for IDT testing is suitable for carrying out both monotonic and cyclic load IDT tests to determine the IDT strength, static stiffness modulus, and dynamic stiffness modulus properties of lightly cementitiously stabilized granular base materials reliably and consistently.

Determination of c and φ from IDT and Unconfined Compression Testing and Numerical Analysis

AbstractThis paper presents an alternative criterion (simplified method) to determine the cohesion (c) and internal angle of friction (φ) properties for two granular materials lightly stabilized with slag lime and general blend (GB) cement–fly ash using indirect diametral tensile (IDT) strength and unconfined compressive strength (UCS). The c and φ values of the stabilized materials obtained on the basis of this criterion were related to the IDT strength and UCS. The results suggest that the c and φ can be estimated using this criterion and the c can be accurately related to either the IDT strength or UCS for lightly cementitiously stabilized granular materials. However, the IDT strength is a better characteristic than the UCS to estimate the c. To validate the criterion, the c and φ obtained from the proposed criterion were input in the numerical analyses of IDT testing with Mohr-Coulomb failure criterion using FLAC2D finite difference software. The predicted tensile stress–horizontal diametrical deforma...