The improved integral suspension pressure method (ISP+) for precise particle size analysis of soil and sedimentary materials
Wolfgang Durner, Sascha C. Iden
Abstract
The Integral Suspension Pressure (ISP) method is a technique to determine the continuous particle size distribution (PSD) of soil materials by inverse modeling of suspension pressure data in a sedimentation experiment. The objective function in ISP includes externally determined sand fractions and a time series of measured suspension pressures. Practical experience with ISP has shown that the precision of the method for the clay fraction is not satisfying. In this contribution, we present a further developed method called "ISP+" to improve the accuracy. This is achieved by additionally including in the objective function the dry particle mass of a collected subsample of the suspension containing fine material, mainly clay. This regularizes the inverse problem and reduces the uncertainty of the determined PSD in the fine particle range. The application of the methodology is illustrated with five soils tested with an adapted PARIO™ system (METER Group AG, Munich, Germany). The results show a significantly improved precision of the ISP+ results in the range of silt and clay particles and very good agreement with the pipette method, which serves as the reference. The measurement time could be reduced from 8 h (ISP) to about 2 h (ISP+) without affecting the accuracy.