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The paper investigates the effect of stress history and shallow embedment on centrifuge cone penetration tests in sand. A series of centrifuge cone penetration tests were performed in loose and dense silica sand at g-levels ranging between 20 and 100 with corresponding overconsolidation ratio (OCR) between 1 and 5. Based on the measured cone tip resistance (qc) profiles, improved empirical correlations have been proposed with depth factors (fD) to impart additional flexibility in accurately back predicting sand relative density (RD) at shallow embedment in normally consolidated (NC) sands. The qc - RD correlations are then extended to capture overconsolidation effects in cone tip resistance, which is broadly consistent with the changes in compressibility and in-situ lateral stresses taking place in sands with increasing OCR levels. The proposed expressions allow accurate quantification of depth corrected CPT profiles in soils of varying overconsolidation ratio, for application in the interpretation of model tests on shallow foundations and anchors and in shallowly buried structures such as pipelines. The expressions also have application for interpretation of field CPT profiles where the thickness of interbedded layers is of similar order of magnitude to the cone diameter.

The paper examines the merit of a two surface plasticity model through an optimised calibration procedure and assesses the model performance in capturing the response at both element and system level. The governing equations are based essentially on the parent two surface plasticity model developed by Dafalias and Manzari (2004) with some simple yet practical changes to enable realistic predictions for monotonic loading along different load paths. This is achieved by scaling the influence of state parameter based on a normalised measure of anisotropy, thus leading to suitable change in dilatancy and plastic modulus for different loading directions. The paper presents a simple optimisation technique for calibrating the model parameters, providing an objective approach to reduce the uncertainties in parameter determination that leads to good agreement with responses measured in drained and undrained triaxial tests. The model has also been implemented for the boundary value problem of a buried circular plate anchor and a surface circular footing. Comparisons of the simulated responses with those measured in centrifuge tests demonstrate the potential of the model, whilst also pointing to the challenges in capturing the global response at all strain levels, even for rather simple boundary value problems.

his paper investigates the uplift capacity of horizontal plate anchors in sand through finite element analyses and centrifuge experiments. Finite element simulations adopt a sophisticated bounding surface plasticity model that accounts for stress and density dependent behaviour, as well as loading and fabric related anisotropic effects in sands. Failure mechanisms at peak anchor capacity show that failure occurs progressively, with a marked decrease in mobilised friction angle within the shear bands close to the anchor edge. Numerical simulations of a large set of centrifuge experiments on rectangular, strip and circular plates at different relative densities and stress levels are in good agreement for dense conditions, but perform poorer for loose conditions due mainly to the open cone yield surface in the bounding surface model. Equivalent comparisons with current limit equilibrium methods highlight the challenges in direct application of element level strength equations. Finally, the paper proposes a modified limit equilibrium solution based on a ‘rigid-block’ failure mechanism extending to soil surface, but with anchor factors that encompass the results from the finite element simulations. The modified solution provides a higher level of agreement with results from a large database of plate and pipeline test data than existing limit equilibrium methods.

A new wave generator (or cam) is proposed (Maiti, Patent 1995) to drive the flex gear of strain wave gearing i.e., harmonic drives with gear pairs of pure involute profiles. The cam profile is made of circular arcs at the two contact zones and shifted elliptical curves for the other zones. The geometric constniction is made in such a way that tip interference is properly avoided for both engagement and disengagement with nominally stubbed or full depth involute gears. The theories are established to verify other geometric and gearing conditions. Evidently, in the existing products (all are patented design) the profiles are non-involute and none of them offers ideal gear kinematics. It is expected that this new harmonic drive will offer the best gearing kinematics and will have desired accurate performance.