This paper presents an experimental study on the uplift behaviour of both pipes and strip plate anchors buried in sand. A total of 24 plane-strain uplift tests were performed using an image-based deformation measurement technique, by which the influences of anchor/pipe embedment ratio, sand relative density and pipe roughness on the load-displacement responses and associated failure and deformation mechanisms were systematically investigated. It was observed that the overall uplift responses of pipes and strip anchors were essentially similar. The peak uplift resistance of a strip anchor tended to be greater than that of a pipe at shallow depths, but the difference reduced as the sand-pipe interface frictional strength and the embedment ratio increased. Image analysis shows that the peak resistance of a shallow strip anchor/pipe was mobilised through the formation of an inverted trapezoidal block, bounded between a pair of inclined shear zones. The inclinations of the shear zones were dependent on sand dilatancy, and its average angle to the vertical for a strip anchor is slightly larger than that for a pipe. The shear zones initiate from the edges of an anchor invariably, whereas the initiation points may lie above the pipe waist, varying with sand-pipe interface conditions. These observations were used to modify a limit equilibrium method and a cavity expansion approach for predicting the peak uplift resistance of shallow pipes in sand. The modified methods were validated using a database of 125 shallow pipe uplift tests assembled from the literature. After the modifications, a good agreement with the overall database was shown, with average errors of less than 6%.

This paper presents a fabric tensor-based bounding surface model accounting for anisotropic behaviour (e.g. the dependency of peak strength on loading direction and non-coaxial deformation) of granular materials. This model is developed based on a well-calibrated isotropic bounding surface model. The yield surface is modified by incorporating the back stress which is proportional to a contact normal-based fabric tensor for characterising fabric anisotropy. The evolution law of the fabric tensor, which is dependent on both rates of the stress ratio and the plastic strain, rules that the material fabric tends to align with the loading direction and evolves towards a unique critical state fabric tensor under monotonic shearing. The incorporation of the evolution law leads to a rotational hardening of the yield surface. The anisotropic critical state is assumed to be independent of the initial values of void ratio and fabric tensor. The critical state fabric tensor has the same intermediate stress ratio (i.e. b value) and principal directions as the critical state stress tensor. A non-associated flow rule in the deviatoric plane is adopted, which is able to predict the non-coaxial flow naturally. The stress–strain relation and fabric evolution of model predictions show a satisfactory agreement with DEM simulation results under monotonic shearing with different loading directions. The model is also validated by comparing with laboratory test results of Leighton Buzzard sand and Toyoura sand under various loading paths. The comparison results demonstrate encouraging applicability of the model for predicting the anisotropic behaviour of granular materials.

This paper presents an experimental study on the pullout behavior of a vertical plate anchor buried in sand under lateral loading, using the digital image correlation (DIC) technique. Based on image analysis, the influences of anchor embedment ratio, sand relative density, and sand–plate interface friction on the failure and deformation mechanisms were discussed. With lateral displacements, the plate anchor experienced passive soil pressure in the front and active soil pressure from the behind. It is observed that the passive failure surfaces varied from approximately linear to be curved and finally became locally rotational with increasing embedment ratios, which indicated that the failure mode transitioned from general shear to be local shear gradually. The failure process is progressive in nature, and the critical embedment ratio is sand-state dependent. With an increasing relative density of sand, the front passive failure zone became larger, whereas the scope of the active failure zone reduced. A wider range of soil may be mobilized by plate anchors of a greater interface frictional strength, leading to enhanced anchor capacity, and this effect decreased with increasing anchor embedment ratios and vanished for deep anchors. The test findings can provide useful visualized data for the development and verification of relevant theoretical models.

This paper presents a unified analytical solution for elastoplastic stress analysis around a cylindrical cavity under biaxial in situ stresses during both loading and unloading. The two-dimensional solution is obtained by assuming that the connected plastic zone is statically determinate and using the complex variable theory in the elastic analysis. It is shown that the biaxial state of initial stresses applies significant influences on the stress distribution around the inner cavity. Under biaxial far-field stresses, the asymptotic conformal mapping function predicts that the outer boundary of the statically determinate plastic zone is in oval shape in Mohr–Coulomb materials. The major axis of the elastic–plastic interface lies in the direction of the greatest far-field compression pressure during loading, whereas it is along the perpendicular direction during unloading. The loading and unloading solutions are validated by comparing with the results of numerical simulation and other analytical solutions. In the assumed states, the new solution provides an accurate analytical method to capture the biaxial in situ stress effect in the prediction of the plastic failure zone and calculations of the static stress field and the elastic displacement field around a cylindrical cavity within an infinite medium.