Exploring the correspondence between precompression stress and soil load capacity in soil cores

- Precompression stress of unstructured soil samples increase asymptotically with over time of soil cores preparation.
- Precompression stress from two-line intersect method overestimates the soil load bearing capacity.
- Applying in the field loads equal to precompression stress would progressively increase soil compaction.

The soil precompression stress (σp) has been used as an estimator of the soil load bearing capacity, but a few researches have evaluated the correspondence to each other. In this study, we first evaluated in prepared soil cores the time needed for σp to reach a quasi-stable state. Afterwards, we waited the same time for using another set of soil cores to evaluate the changes on σp after the soil core received loads equal to its σp. The two experiments were performed using two Rhodic Hapludox (RH1 and RH2) and one Typic Paleodult (TP). In both experiments the σp was denominated as σp2R, because it was calculated using the two-line intersect method proposed by Dias Junior and Pierce (1995). In the first one, σp2R increased asymptotically over time after sample preparation. When the increasing rate of σp2R decreased down to 0.05 kPa d−1, we assumed that the increase in soil structure strength over time was small and had little effect on σp2R, which took place at 21 days for RH1, 26 days for RH2, and less than 1 day for TP. The second experiment was performed after these times of structure strengthening. Four times in each soil, the σp2R was measured (σp2Ri) and this value was applied as a new load on the soil. Thus, σp2Ri was assumed as the maximum load previously received by the soil core, which was related to the subsequently measured σp2R(σp2Ri+1). The results indicate that σp2R overestimated the maximum load previously received by the soil, because the σp2Ri+1 was generally greater than σp2Ri. Also there were evidences that applying on soil a load equal to σp2R can increase soil compaction. If this tendency is confirmed by further studies using more sensitive techniques to evaluate soil structure changes, as computed tomography, the load limit to be applied to the soil should be less than σp2R, because loads equal to such value may overcome the soil load bearing capacity and progressively increase in the degree-of-compactness.