Investigation into some soil strength parameters using a locally developed soil shearing equipment

Abstract

A mechanical device was designed and fabricated for in situ measurement of soil strength parameters such as soil cohesion, soil adhesion, angle of soil internal friction, soil to metal friction angle, soil penetration resistance and soil bulk density.  The equipment was tested on the field at soil depth interval of 10 cm ranging from the soil surface to the depth of  30 cm following the standard procedures for the measurement of these soil strength parameters at soil moisture contents of 16.71% and 20.15%.  At soil moisture content of 16.71% dry basis, soil cohesion and soil adhesion were 5.313 and 6.968 kN/m² and 3.745 and 4.234 kN/m² at the soil surface and at soil depth of 30 cm respectively.  At soil moisture content of 20.15%, soil cohesion and soil adhesion were 4.703 and 6.533 kN/m² and 2.961 and 4.181 kN/m² at the soil surface and at soil depth of 30 cm respectively.  The comparison of soil cohesion and soil adhesion with soil bulk density gives a linear relationship at the same moisture content.  The soil penetration resistance was found to have different values but followed the same trends or exhibit the same characteristics that is; the initial increment in the values of the penetration resistance at the first 15 cm depth and the values fall as the depth increases when tested under different soil conditions and time.  The highest soil shearing stress was at the soil surface, while the least was recorded the depth of 30 cm, thereby showing that the shearing stress of soil decreases with depth and the strength of soil reduces with increase in soil moisture content.  Also, the highest point of soil resistance to penetration was recorded at the soil depths of between 15 and 20 cm.

Keywords: soil strength parameters; soil cohesion, soil adhesion, soil penetration resistance