Effects of bulk density and moisture content on selected mechanical properties of sandy loam soil

Standard triaxial compression tests were carried out on an agricultural sandy loam soil to assess the effect of soil dry bulk density and moisture content on soil mechanical properties, namely, cohesion, internal friction angle, Young's modulus of elasticity and Poisson's ratio. Regression analyses were performed to establish mathematical relationships for simulating the variation in these mechanical properties as a function of dry bulk density and moisture content. These relationships were developed for six typical field moisture contents ranging from 3 to 22% d.b., and various dry bulk density levels ranging from 1.15 to 1.82 Mg m(-3). Results showed that all mechanical properties increased with dry bulk density, except the internal friction angle that was an independent property. Cohesion, Young's modulus of elasticity and Poisson's ratio decreased with moisture content, except that the Poisson's ratio increased after the moisture content exceeded 17% d.b. However, the internal friction angle was also independent of moisture content. The regression equations developed to relate the soil cohesion, Young's modulus of elasticity and Poisson's ratio with moisture content and dry bulk density were quite simple, and had high determination coefficients ranging from 0.92 to 0.96. The regression equations indicated that the three mechanical properties varied linearly with moisture content and non-linearly with dry bulk density. Quadratic relationships were detected for the variations in properties studied and dry bulk density. These equations may be used for prediction of the variation in the mechanical properties (except internal friction angle) of sandy loam soils for any combination of moisture content and dry bulk density. Establishing these equations can be considered an advantage from an economical point of view because of avoiding the need of carrying out the costly triaxial compression test.