Shear strength of surface soil as affected by soil bulk density and soil water content

This paper proposes a new method to measure the soil strength parameters at soil surface in order to explain the processes of soil erosion and sealing formation. To simulate the interlocks between aggregates or particles with in top 2 mm of the soil, a piece of sandpaper 130 particles cm(-2)) was stu ck on the bottom face of a plastic box of diameter of 6.8 cm with stiffenin g glue and used as shear media. The soil strength for the soils from sandy loam to clayey loam was measured with penetrometer and the new shear device at soil surface at different bulk density and soil water content. The norm al stresses of 2, 5, 8, 10 and 20 hPa were applied for the new shear device . The results indicated that significant effect of bulk density on soil str ength was detected in most casts though the difference in bulk density was small, ranging from 0.01 to 0.09 g cm(-3). It was also indicated that the m easurement with the new shear device at soil surface was reproducible. The changes in soil shear strength parameters due to changes in bulk density an d soil moisture were explainable with the Mohr-Coulomb's failure equation a nd the principles of the effective stress for the unsaturated soils. The im plications of the method were later discussed. (C) 2001 Elsevier Science B. V. All rights reserved.