Stress-Controlled Direct Shear Tests of Straw Fiber Reinforced Loess

The loess tends to behave in an instable manner when subjected to external loads since it is characterised by metastable structure, high porosity, and water sensitivity. Therefore, the Chinese Loess Plateau has been deemed as a landslide-prone area in northwest China. This study explores the potential use of the loess-waste straw mixture as an alternative backfill material to improve the stability of loess against shallow slope failure and functionalise the agricultural solid waste. The displacement-controlled direct shear tests aim to document the baseline shear strength parameters of the loess specimen with and without waste straw inclusion, whereas the stress-controlled direct shear tests reveal the temporal relations of horizontal and vertical displacement under given shear stresses. The increase in cohesion, induced by the effect of waste straw inclusions, contributes the most to the increase in shear strength, and it is predicted using the perpendicular model. The measured results are generally in line with the prediction. Further, the stress state at failure in a displacement-controlled direct shear test and a stress-controlled direct shear test for same specimen under equal testing conditions shows good correspondence to each other irrespective of testing method, and their results approximate a single failure envelope.