Testing the Integral Suspension Pressure Method for Particle-Size Analysis with the Pario Device: Accuracy of Results.

The particle-size distribution (PSD) is one of the fundamental soil properties. To determine the proportions of the fine fractions silt and clay, sedimentation experiments are used. Most common are the Pipette and Hydrometer method. Both need manual sampling at specific times. Both are thus time-demanding and rely on experienced operators. Durner et al. (doi:10.1002/2016WR019830) recently developed the Integral Suspension Pressure method (ISP), where a continuous PSD is estimated from the temporal evolution of the suspension pressure at a certain measurement depth in a sedimentation cylinder. It requires no manual interaction after start and thus no specialized training of the lab personnel. The aim of this study was to test the precision and accuracy of new method with a device called PARIO, which is developed by the METER Group. We aimed to answer the following research questions: (1) Are the results obtained by PARIO reliable and stable? (2) Are the results identical to the ones that are obtained with the Pipette method as reference method? The experiments were performed with a quartz silt material and with three real soil materials. PARIO measurements were done repetitively on the same samples in a temperature-controlled lab to characterize the repeatability of the measurements. Subsequently, the samples were investigated by the pipette method to validate the results. We found from replicate and repetitive measurements that the statistical error for the silt fraction was in the range of 2% for the quartz material to 3% for the soil materials. Since the sand fractions, as in any sedimentation method, must be measured explicitly and are used as fixed parameters in the PARIO evaluation, the error of the clay fraction is determined by error propagation from the sand and silt fraction. The PSD’s obtained with the PARIO corresponded very well with the results of the Pipette method.