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Rheological Properties of Wet Soils and Clays under Steady and Oscillatory Stresses

Dep. of Plants, Soils and Biometeorology, Utah State Univ., Logan, UT 84322

View larger version (19K): [in a new window]   Fig. 1. Rheological curves of ideal materials: (a) Stress–strain relations of ideal Hookean solid and flow curve of ideal plastic material with distinct yield stress (y). Spring and slider are mechanical analogs of ideal elastic and plastic solids, respectively. (b) Flow curves of ideal Newtonian fluid and Bingham viscoplastic body, and their respective mechanical analogs, dashpot and dashpot-slider

View larger version (20K): [in a new window]   Fig. 2. The loci of observation points, initially 100 mm below the ground surface, during passage of the front and rear wheels of a tractor. Adapted from Horn and Baumgartl (1999)

View larger version (31K): [in a new window]   Fig. 3. (a) Stress function and (b) strain responses of ideal elastic (solid), ideal viscous (dashed), and real viscoelastic (dotted) materials

View larger version (74K): [in a new window]   Fig. 4. Schematic model of clay–silt–water system depicting different forms of pore spaces and pore water. Adapted from Hueckel (1992)

View larger version (53K): [in a new window]   Fig. 5. Aggregate pair model for aggregate coalescence: (a) variable definition in viscoplastically strained aggregate pair, (b) aggregate pair model before strain, (c) aggregate pair model under Hertzian strain, and (d) aggregate pair model under modified Hertzian strain

View larger version (63K): [in a new window]   Fig. 6. Rotational rheometer used in this study. (a) complete setup, (b) sensor system during measurement, and (c) arrangement of sand paper and soil sample in sensor system

View larger version (25K): [in a new window]   Fig. 7. Typical measurement results for steady state CS measurement (Millville silt loam soil at 0.28 kg kg-1 water content). (a) Stress–strain relation in log-log scale, showing the distinct differentiation of the deformation to elastic and viscous types; (b) elastic range in linear scale; and (c) viscous range in linear stress–strain rate curve (flow curve), and definition of Bingham model

View larger version (21K): [in a new window]   Fig. 8. Viscoplastic parameters of different soil and clay types as function of water content by weight. (a) Yield stress, (b) coefficient of plastic viscosity and, (c) shear modulus. Each point in the plots denotes mean of three to six independent replicates

View larger version (22K): [in a new window]   Fig. 9. Viscoplastic parameters of Na-montmorillonite over expanded water content range. (a) coefficient of plastic viscosity and (b) yield stress. Each point in the plots denotes mean of three independent replicates

View larger version (17K): [in a new window]   Fig. 10. Typical measurement results of controlled stress oscillatory test of Na-montmorillonite at frequency of 3.16 Hz and water content of 4 kg kg-1

View larger version (40K): [in a new window]   Fig. 11. Summary of viscoelastic properties of Millville silt loam soil and Fraternidad clay soil. Each point in the plots denotes mean of three independent replicates

View larger version (43K): [in a new window]   Fig. 12. Summary of viscoelastic properties of kaolinite and Na-montmorillonite clays. Each point in the plots denotes mean of three independent replicates

View larger version (24K): [in a new window]   Fig. 13. Stress–strain relationships in aggregate pair model (Millville silt loam soil at 0.28 kg kg-1 water content) subjected to steady state stress. (a) Applied contact stress and yield stress functions and (b) viscoplastic strain response as a function of real time

View larger version (35K): [in a new window]   Fig. 14. Stress–strain relationships in aggregate pair model (Millville silt loam soil at 0.28 kg kg-1 water content) subjected to two cycles (0.0681and 0.681Hz) of oscillatory stress. (a) Applied cyclic force and contact stress, (b) elastic and viscous strain components, and (c) total strain as functions of scaled time (in degrees)