Soil failure patterns and draft as influenced by consistency limits: An evaluation of the remolded soil cutting test

Abstract

Soil failure patterns play an important role in obtaining a better understanding of the mechanical behavior of soils. Despite the large number of studies over the past few decades, a better understanding of soil failure patterns and its relation to soil and tool parameters for particular soils such as dry land and paddy has not been developed. This study investigated soil failure patterns and related draft at sticky, plastic and liquid consistency limits and the sticky point of dry land and paddy soils. A soil cutting test rig was developed to perform soil cutting at three consistency limits (sticky limit, plastic limit and liquid limit) and the sticky point of soil, three rake angles (15°, 30° and 45°), and three operating depths (30mm, 50mm and 70mm). A flat triangular shaped tool operating at a constant speed of 10mms−1 was used in all experiments. Soil failure patterns were observed and recorded using a digital camera, and draft per unit displacement was measured by load cells attached to the soil bin. A direct relationship between soil failure patterns or draft and the consistency limits of soil was found. Brittle failure was obtained at the sticky limit, chip forming failure was observed at 15° rake angle and 30mm depth, and bending failure with little strains of elements at 30° and 45° rake angles and 50mm and 70mm depths at plastic limit, while flow failure was linked to the liquid limit of the soil. At the sticky point, flow failure was observed at an operating depth of 30mm and 15° rake angle, while flow with considerable bending and no strains of elements occurred at 50mm and 70mm operating depths and 30° and 45° rake angles. However, bending was more prominent at 70mm depth and 45° rake angle. The draft at the sticky limit, plastic limit and sticky point was cyclic in nature, whereas at the liquid limit it was comparatively diverse and fading. The highest draft was found at the plastic limit, and the lowest at the liquid limit. Since the soil failure patterns may change with moisture content, soil type and particle size distribution within the same textural class, consistency limits can provide clearer and more accurate definitions of soil failure patterns than moisture content levels alone.