Nondestructive volumetric quantification of irregular shaped soil samples using close-range photogrammetry

The main purpose of this study is to introduce a noncontact and nondestructive methodology to determine the volumetric properties of irregular shaped bulk soil specimens using close-range photogrammetry. To this accomplishment, 3D models of soil specimens were reconstructed by using a computational technique called Structure from Motion (SfM). This technique uses multiple overlapping photos of the same object from different perspectives to generate a 3D reconstruction. A cylindrical shaped calibration object was produced by a high precision mechanical lathe tool for the evaluation of the accuracy of the proposed technique. The SfM method and the Archimedes test setup were verified for regular shaped solid calibration object by obtaining 0.020% and 0.051% relative errors in volume with respect to production dimensions. In order to verify the proposed methodology, bulk soil specimens were prepared by compacting soils from three different soil classes with two different energy levels. The compacted soils were broken into pieces and irregular shaped bulk soil specimens were obtained. Volumes were measured through photogrammetric and conventional technique. Inevitably, paraffin wax coating was used for the bulk soil specimens for the Archimedes method, and drawbacks were experienced. Volume and bulk density comparisons of irregular shaped bulk soil specimens were made between the Archimedes displacement method and the proposed one. The errors for the bulk specimens are experienced slightly higher than that of the calibration object. This is attributed to the discrepancies originated from the paraffin wax, in this study