Triaxial Testing to Determine the Effect of Soil Type and Organic Carbon Content on Soil Consolidation and Shear Deformation Characteristics

The purpose of this paper is to determine the effect of soil type and organic matter on the deformation characteristics of soil. We used triaxial testing to measure both the consolidation and shear deformation of soil. The novel application of this method was applied to soils from two experiments: on a clay loam and a sandy loam. The clay loam soil was from the long‐term Broadbalk Experiment at Rothamsted Research, UK, where contrasting treatments had been applied since 1843. The sandy loam soil was from a straw incorporation experiment started in 1986. The clay loam soil from selected treatments from the Broadbalk Experiment had large difference in soil organic C (SOC) content due to additions of farmyard manure (FYM) or inorganic fertilizers for over 170 yr. There were no detectable differences in SOC or microbial biomass C in the sandy loam soil where straw had been incorporated. In addition to triaxial testing, we assessed soil physical condition with measurements of aggregate stability and aggregate tensile strength. From triaxial tests of the repacked soil, we found that soil type and SOC affected the compression characteristics. We also observed that deformation characteristics are more sensitive to small changes in soil management practices designed to increase the SOC content, than measurements of aggregate tensile strength, friability, or stability. We suggest that measurement of deformation characteristics is a potentially powerful approach for detecting or predicting changes in soil physical conditions as impacted by small changes in SOC content resulting from management practices.