Sequence of footfalls in elephant walk after [5].

<p>The static loading conditions (loading steps 1 to 4) simulated by FEA are marked and quantified within the sequence. The leftmost loading step is loading step 1, with the elephant at a standstill. Black bars indicate ground contact of the respective foot. fl  =  left forefoot, fr =  right forefoot, hl  =  left hindfoot, hr  =  right hindfoot. See text for a detailed description of the loading steps.</p

Triaxial test results for the determination of stiffness E₅₀ [kN/m²] of Rhine sand with an initial density of e = 0.6.

<p>Blue, green and grey line: Deviatoric stress is plotted against axial strain for experiments conducted at 50 kN/m², 100 kN/m², and 150 kN/m² confining pressure, respectively. The stiffness E₅₀ is the secant stiffness over the first 50% of the deviatoric stress.</p

Grain-size distribution of Rhine sand.

<p>Grain sizes are given for characteristic values, i.e., for 10% (), 30% (), and 60% () of the sand passing the corresponding mesh size by weight.</p

Capture of elephant footprints geometry using 3D laser scanner.

<p>A total of six footprints were scanned, i.e., three pairs, each of them consisting of one forefoot imprint (right) and one hindfoot imprint (left). Each pair is pictured by a photograph (top), 3D surface plot (center), and a 2D longitudinal section plot (bottom).</p

Hardening soil model parameters.

<p>Hardening soil model parameters.</p

Results of dry density and water content profile measurements.

<p>Soil samples were obtained from the prepared test field by manual sampling with a metal tube. Samples were taken inside and outside several footprints, indicated by differing sampling depths, i.e., differing starting points of the top of the tube. Footprints are displayed schematically, for detailed information see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0077606#pone-0077606-g011" target="_blank">Figure 11</a>.</p

Geometry and generated mesh of the FEA model and interfaces.

<p>See text for a detailed description of the model.</p

3D-plot of relative density versus settlements for back analysis of applied stress [kN/m²] by FEA for a circular plate (d = 0.32 m).

<p>The diagram applies to subsoil conditions of Rhine sand. This diagram can be used to estimate the load having produced a fossil footprint if the original subsoil parameters were the same as our experimental subsoil, Rhine sand.</p

Vertical sections of FEA model at loading steps 2 to 5.

<p>Colors indicate amount of deformation.</p

Four horizontal sections of FEA model of loading step 5.

<p>Horizontal plane A is at surface, horizontal plane B is at the depth of the radius R of the circular plate that was loaded to simulate the elephant's foot, horizontal plane C is at the depth of the diameter D of the circular plate, and horizontal plane D is at twice the depth of the diameter D of the circular plate. Colors indicate amount of deformation.</p