Research on the Strength Characteristics of Red Soil Amended by Biochar

In order to investigate the effect of biochar on the strength characteristics of red loam, a number of experiments were carried out in the red loam of northern Guangxi Province, including a direct shear test, a scanning electron microscopy (SEM) test, and an X-ray diffraction (XRD) test of red loam, bagasse biochar–red loam, and rice platycodon biochar–red loam. The aim of this study was to determine the effects of different biochar contents, types, and particle size ranges on the shear strength of the improved soils. The results showed that both bagasse biochar and rice platycodon biochar could effectively improve the shear strength of soil, and the shear strength increased first and then decreased with the increase in biochar content and reached the peak value when the content of biochar reached 6%. Under vertical pressures of 100 kPa, 200 kPa, 300 kPa, and 400 kPa, the shear strength of the two improved soils increased by 53.39%, 52.52%, 43.43%, and 47.08%, respectively, and 54.56%, 23.89%, 33.71%, and 47.78%, respectively, compared with that of plain soil. In addition, the grain size was negatively correlated with the shear strength, and the shear strength of the sample increased with a decrease in the grain size, in which the biochar in the range of 0~0.5 mm had the best effect on the strength improvement of the red loam. The results of this study provide theoretical and technical support for revealing the evolutionary mechanism of red loam strength and coping with soil erosion in red soil areas.