Innovative Model for Settlement Calculations in Organic Soils

Abstract

The settlement of organic soils is dependent on the relative proportions of organic and mineral fractions and the degree of organic solids decomposition. The characteristics of the organic and mineral fractions significantly impact organic soils behavior. Experimental compression data for peat moss and mixtures of organic fibers with kaolinite or fine sand show a linear relationship between the organic fraction (by weight) and void ratio for constant stress levels. Over the range of possible organic content, this relationship is nonlinear for mixtures of organic fibers with montmorillonite. Decomposition in fibre-clay soils reduces volume of organic solids and produces changes in compressibility parameters. Use of the ignition test for measurement of the organic fraction permitted changes in the degree of decomposition to be monitored concurrently with changes in compressibility and vane shear strength. Void ratio parameters, based on experimental data, permitted calculation of equilibrium void ratios in terms of the organic fraction and pressure. An innovative model is proposed which permits calculation of equilibrium void ratios directly for any combinations of stress level and organic content. The proposed model eliminates the need for using compression index in settlement calculations associated with organic soils. Decomposition of organic solids at a constant over-burden pressure contributes additional volume change. Volume change caused by the loss of organic solids for soils mixtures involving organic fibers with sand, kaolinite, or montmorillonite can be readily predicted. New compression parameters for several soil mixtures revealed that organic soil behavior is complex and is dependent on organic fraction and type of mineral present.