Comparison of soil strength data obtained in situ with penetrometer and with vane shear test

Measurement of the in situ cone penetration resistance (PR) is the only easily available and direct measurement of the actual in situ soil strength. Soil strength varies frequently due to changes in soil moisture conditions, which affects trafficability of soils quite unexpectedly. To generalize the information obtained from penetration resistance data, two of the authors [Hartge, K.H., Bachmann, J., 2004. In situ evaluation of the soil consolidation state by using penetration resistance data. J. Plant Nutr. Soil Sci. 167, 304–308] proposed a simple site specific analysis for the interpretation of the depth-dependent penetration resistance characteristics. In this paper, results of comparison of PR data with independently measured vane shear (VS) data were used to assure the plausibility of this approach for deeply developed non-layered soil. The focus of this paper is to prove the validity of the underlying basic assumption that the horizontal stress component begin to dominate the vertically measured penetration resistance and can further be used to characterize the intensity of agricultural landuse systems with respect to the compaction status of the soil. The procedure applied consists in assigning PR-values to the principal stress (σx) as a function of depth normalized by the PR-value of the greatest accessible depth, which is limited by the length of the probe. PR data were measured on three pasture sites after clearing the secondary virgin forest 12, 50 and 150 years ago. Results show that the duration of cattle grazing could significantly be detected by using either PR data or VS data. These results confirm the general feasibility of this simple experimental approach to evaluate the compaction state of soil from easy obtainable PR data.