Evaluating Penetration Resistance and Wheel Sinkage Response to Soil Water Suction Changes in a Draining Clay Soil1
- Reuven Steinhardt2
To facilitate the development of subsurface drainage design criteria for the reduction of soil compaction, the relation between the bearing capacity of nearly saturated soil and its water suction(s) is analyzed for a cone penetrating into the soil and for a sinking tractor wheel. Approximate equations are developed, from basic soil mechanic theory, for certain soils under a limited range of suction and loading conditions. The main assumptions are attainment of plastic equilibrium during dynamic loading and independence of the soil deformation process and its shear failure pattern of suction. The penetration resistance-suction model shows that a linear response to suction changes can be expected, characterized by a modified bearing capacity-suction factor (Ns) which may be estimated from the mechanical and water properties of the soil. The wheel sinkagesuction model predicts the relative change in wheel rut depth in response to loading (inflation pressure) and suction changes, by means of the same Ns parameter. Tests were conducted in plowed (P1) and unplowed (P0) irrigated plots of a clay soil, utilizing a cone penetrometer and a tractor with differentially loaded and differentially inflated rear wheels. Variations in penetration resistance with suction were successfully predicted, assuming local, intermediate, and general shear failure in the subsoil, and in the plow-layers of P1 and P0, respectively. The relative change in wheel rut depth with suction was found predictable, provided S > Smin. The transition from S > Smin to S < Smin was characterized by an inversion of sinkage response in P0, and by a transition from vertical to horizontal soil compaction or flow in P1.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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