Effect of Moisture Content on the Shear Strength Parameters

Abstract

The variation of moisture content in the field may occur due to fluctuation in groundwater level due to climatic variation, drainage condition, porosity, density of particle, etc. These variations of moisture content in the soil directly affect the shear strength of soil. Laboratory study to evaluate the shear strength of the compacted soil remoulded with proctor density under varying moisture content and further allowing compacted soil to undergo saturation may help to understand the similar condition of compacted field with fluctuating water levels. To stimulate the field condition, triaxial shear tests were conducted with consolidated undrained (CU) method on MI (Inorganic silt of medium plasticity) type of soil. Two field conditions were modelled in laboratory study. In the first case, specimens were remoulded at 98% maximum dry density (MDD) at varying moisture content (w), considering it in a partially saturated state, as B-factor measurement is less than 0.9. In the second case, specimens were remoulded from same sample, as done in first case and further saturated with the help of back pressure system in a controlled manner exhibiting B-factor > 0.9, representing saturated state of soil. The deviator stress–axial strain graphs are plotted at incremental confining pressures (σ3) and analysed at different remoulded moisture contents. It was observed that deviator stress increases with increase in σ3 and decreases with increase in moisture content. However, deviator stress obtained in the partially saturated samples is much higher than saturated samples. The maximum stresses obtained are also employed to understand modified failure envelopes and shear strength parameters with respect to total stress measurement. Based on the results, it was found that the moisture content is the dominant factor affecting shear strength. Angle of internal friction ‘ϕ’ plays an active role in controlling the shear strength of MI type of soil. The cohesion has little effect on shear strength of soil. This paper discusses the effect of moisture content on shear strength parameters of MI type of soil tested in triaxial loading under incremental confining pressures.