Speaker
Description
Air pluviation is a well-established technique for preparing sand specimens for model and laboratory tests. In this method, dry sand is discharged from a hopper onto a perforated plate that controls the rate of bulk flow. Below this plate, layers of wire mesh or parts of similar geometry are installed to distribute the grains as uniformly as possible across the specimen surface. The distance between the lowest mesh layer and the specimen surface (i.e., the drop height), along with the rate of bulk flow, governs the resulting void ratio and, consequently, the relative density. Achieving a high degree of homogeneity—both in terms of density and grain-size distribution, i.e., avoiding segregation—is essential. Only a well-controlled and reproducible specimen preparation allows for the reliable derivation of soil parameters in element tests or the validation of system responses in geotechnical boundary-value problems using physical modelling.
To validate the suitability of the air-pluviation technique for a specific sand prior to large-scale model testing, a framework was developed that enables systematic investigation with a limited number of experiments. Particular emphasis was placed on assessing specimen homogeneity in pluviated samples of comparably large dimensions and identifying material-specific application limits of the method. Air-pluviation trials were performed with varying rates of bulk flow and drop heights. The resulting specimens were deconstructed layer by layer and subdivided into several sampling volumes to quantify homogeneity throughout the sample and, within a single test configuration, to quantify the influence of drop height.
For density determination, volumes of subsamples were measured at comparatively high spatial resolution using a 2D laser profile scanner; density was then obtained by weighing the extracted material. Additionally, granulometric analyses of the subsamples were conducted using a high-resolution optical device (Camsizer). Across two test series, it was demonstrated that air turbulence within the specimen can lead to non-uniform density distributions; however, this effect can be eliminated by a minor improvement of the pluviation device.