Variation of the critical‐state boundaries of an agricultural soil

Abstract

Summary The critical‐state theory can be applied profitably to analyse the mechanical behaviour of agricultural soil. Critical‐state parameters and other soil properties are affected by the microstructure and unsaturated nature of agricultural soils. We determined the critical‐state boundaries of an agricultural soil in both saturated and unsaturated triaxial tests and examined the effects of matric suction and initial structure on critical‐state boundaries. On the compression plane, the presence of air and matric suction in the pores of unsaturated soil significantly affected critical‐state boundaries by increasing compressibility, λ On the deviatoric stress‐mean net stress plane, the strength increased with matric suction. On this plane, the critical‐state lines for the unsaturated tests had non‐zero intercepts. For a given soil structure, the frictional parameter M remained fairly constant with matric suction change. However, a change in the initial microstructure resulted in a change in M , causing the position of the critical‐state line to ‘pivot’ in state space.