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Mechanical Stresses in Soils Assessed from Bulk-Density and Penetration-Resistance Data Sets

^a Institute of Plant Nutrition and Soil Science, Kiel Univ. Olshausenstr. 40, Kiel, 24118 Germany
^b Habichtshorst 9, Garbsen 30823, Germany
^c Univ. of Hannover, Herrenhaeuserstr. 2, Hannover, 30419 Germany
^d Dep. of Agronomy, 2004 Throckmorton Hall, Kansas State Univ., Manhattan, KS 66506-5501

View larger version (14K): [in this window] [in a new window]   Fig. 1. Schematic plot of the soil packing characteristic. The linear compression line represents the greatest stress that a soil column will hold whether it has been loosened or has fresh sedimentation. It represents the normal-compacted state (NC). States diverging from this line are produced by temporary stress. They represent the precompacted state (PC).

View larger version (20K): [in this window] [in a new window]   Fig. 2. Packing characteristic (void ratio vs. vertical gravity stress z) of Profile 1 (Luvisol). Filled symbols are measured values, showing the precompacted state for the first five values. It approximates the 60-cm depth. The line, also for Profile 1, shows the normal-compacted state, calculated by extending the linear regression of the normal-compacted state from the lowest three data points.

View larger version (22K): [in this window] [in a new window]   Fig. 3. Mean penetration resistance (PR) values and their standard deviations in relation to soil depth. The straight line shows the assumed hydrostatic stress distribution, which defines the boundary conditions for the evaluation of the stresses at rest coefficient K0 and the depth of the precompression stress. Soil depths with PR values greater than this line characterize the precompacted state.

View larger version (13K): [in this window] [in a new window]   Fig. 4. Relation between the rest coefficient values obtained on the basis of bulk densities, K0(Db), (x axis) and on the basis of penetration resistance, K0(PR), (y axis) as shown in Fig. 2 and 3 for three soils derived from glacial till at multiple depths under agricultural use. The positions of the symbols reflect the different influence of moisture tension on soil strength at different bulk densities. Symbols in the normal-compaction (NC) area (K0 1) are not shown; only symbols in the precompacted (PC) area are shown.