Precise knowledge of the post-peak constitutive response occurring within shear bands in sands is of keen interest in geomechanics, particularly for accurate modelling of progressive failure phenomena. There is mounting evidence that the displacement field within shear bands in sands is non-uniform and distinguished by distinct meso-scale features: namely, particle force chains. Experimental validation of such features will help elucidate the precise nature of the deformation field within shear bands. This paper presents experimental evidence of the kinematic signatures of force chain activity within shear bands in sands. The meso-scale kinematics are quantified from digital-image-correlation-based, grain-scale displacement analyses performed on digital images of specimens undergoing plane strain compression. As in previous work, the data reveal distinct, systematic patterns in the kinematics along the length of the shear band, which serve as indirect evidence of force chain build-up and collapse. Herein, local volume changes are shown to integrate into this pattern. Temporal changes in these patterns with the progress of deformation are also tracked. It is argued that the changes observed in the kinematics from softening to critical state provide a physical, meso-scale explanation for the progress of global stress–strain response through the post-peak regime.

Within shear bands in sands, deformation is largely non-affine, stemming primarily from buckling of well-known force chains and also from vortex-like structures. In the spirit of current trends toward multiscale modeling, understanding the links between these mesoscale deformational entities and corresponding macroscale response will form the basis for the next generation of sand behavioral models and may also aid in efforts to understand jamming-unjamming transitions in dense granular flows in general. Experimental methods to quantify and characterize such subscale kinematics, in particular in real sands, will play critical roles in these efforts. Digital Image Correlation (DIC) is a fast growing experimental technique to nondestructively measure surface displacements from digital images. Here, DIC has been employed to identify and characterize the development of vortex structures inside shear bands formed in dense sands during plane strain compression. A rigorous assessment of the DIC method has been performed, in particular for subscale behavioral characterization in unbonded granular solids, and guidelines are offered for accurate implementation. While DIC systematically overestimates shear band thickness, a methodology has been devised to compensate for this overestimation. Shear band thickness for four different uniform sands were found to range between 6 and 9 grain diameters, and for a well-graded sand between 8 and 9.5 grain diameters. These determinations agree with visual inspections of grain kinematics from the image data, as well as recent theoretical predictions.

This article addresses the question of whether the viscoelastic behavior of asphalt pavements, as part of the factors that impact the rolling resistance, might lead to substantially higher energy consumption of road traffic, as compared to non-dissipative pavements. In the context of sustainable development (fuel consumption, gas emission), this is a current issue for the pavement design community. This problem is tackled by a theoretical approach which consists in computing the Structure-induced Rolling Resistance (SRR) for a vehicle by using the mechanical response of a layered viscoelastic medium excited by moving loads (i.e. tires of the vehicle). The structure-induced power dissipation is shown to be proportional to the integral over contours of the applied loads of the pavement deflection, times the outward normal to these contours. Following the developed approach, the determination of the SRR force engendered by the structure-induced dissipation is obtained from the computation of the deflection of the viscoelastic pavement to an assumed pressure distribution. Such an approach applied to a thick asphalt pavement allows the SRR for a typical road structure to be evaluated as a function of temperature and speed. A non-dimensional analysis is also presented to extend the results to some other contexts. Under the assumptions made for the derivation of the SRR, the main conclusion of the case study is that the extra fuel consumption for a vehicle resulting from the viscoelastic behavior of asphalt pavements is small.

As shown by strains measured on full scale experimental aircraft structures, traffic of slow-moving multiple loads leads to asymmetric transverse strains that can be higher than longitudinal strains at the bottom of asphalt pavement layers. To analyze this effect, a model and a software called ViscoRoute have been developed. In these tools, the structure is represented by a multilayered half-space, the thermo-viscoelastic behaviour of asphalt layers is accounted by the Huet-Sayegh rheological law and loads are assumed to move at constant speed. First, the paper presents a comparison of results obtained with ViscoRoute to results stemming from the specialized literature. For thick asphalt pavement and several configurations of moving loads, other ViscoRoute simulations confirm that it is necessary to incorporate viscoelastic effects in the modelling to well predict the pavement behaviour and to anticipate possible damages in the structure.

This article presents a method to compute the response of a viscoelastic layered half-space to a moving load when interlayer slip is considered. The Navier equations of equilibrium are solved for each layer in the frequency domain. The solution in the spatial coordinate system is subsequently obtained by means of Fast Fourier Transform and quadrature rules applied to integrable singularities. Following the global solution technique, the developed method compiles all the interface and the boundary conditions within a global matrix and it solves a unique linear system per couple of wave numbers. This method proves to be effective and is validated in an elastic case by comparison with the ALIZE-LCPC software that implements the Burmister axisymmetric solution. The influence of the interface sliding condition on the response of a layered viscoelastic medium is studied through an application to pavement structures. In this application, the effect of the load speed on vertical and horizontal profiles of the longitudinal strain and the normal stress is analyzed. It is shown, inter alia, that the maximum extension in the medium is not systematically observed at the location of an interface and that, as expected, low speeds and interlayer slip are more damaging to the structure when either a strain or a stress criterion is considered