Laboratory measurement of soil mechanical parameters for an annually mouldboard ploughed versus unploughed soil

Shear tests is a common way of measuring the soil’s cohesion and angle of internal shearing resistance. Especially, for annular shear devices the result may, however, be somewhat erroneous due to the soil escaping in radial direction from below the annulus. This paper describes experiments with shear tests on large samples of undisturbed cores brought into the laboratory from experimental plots in the field. The shear tests were performed by means of a ring shear device of a new design. The shear head was constructed in such a way that the normal stress against the soil surface was maintained not only below the shear ring, as conventionally, but also inside and outside the annulus. During the tests, the soil was under controlled water tension of 6 kPa. Two soil treatments were considered: annually mouldboard-ploughed and unploughed. sults showed no significant difference between the two treatments concerning cohesion and angle of internal shearing resistance. Likewise, no significant difference was found regarding the shear deformation modulus. Concerning this parameter it was, in addition, found to be independent of the normal stress. The annually ploughed soil was found to be more compressible than the unploughed.