Testing the improved Integral Suspension Pressure method ISP+ with the PARIO™ device

The integral suspension pressure method (ISP) uses pressure measurements in a soil suspension to derive the particle size distribution (PSD) in the silt range in high resolution. The sedimentation process is mathematically simulated and the simulated suspension pressure at a fixed depth in the sedimentation cylinder is fitted to an observed time series. The PSD is determined by numerically solving the inverse problem. The methodology is implemented in a commercial apparatus named PARIO that is produced by METER AG, Munich.

Practical experiments with PARIO indicated that the accuracy of the method to determine the clay fraction was not as high as expected from theory, which may partly be caused by the error propagation from the independently determined sand fractions. Durner and Iden (2019) thus proposed an extension of the experimental protocol called ISP⁺, which makes the inverse problem better-posed and allows shorter experimental time. After a sedimentation time of few hours, a part of the suspension is drained laterally from the sedimentation cylinder through an outlet, collected and oven-dried. The resulting dry mass of the soil particles is integrated into the objective function of the inverse problem. This markedly reduces the uncertainty of the identified PSD towards the finest particles. We present experimental results from PARIO measurements evaluated by the ISP⁺ method and illustrate the new experimental design and the improvement of accuracy for the clay fraction.

Reference: Durner, W., & Iden, S. C. (2019, January). ISP+: improving the Integral Suspension Pressure method by an independent measurement of clay content. In Geophysical Research Abstracts (Vol. 21).