Experimental Study on Shear Strength of Fulvic Acid-Contaminated Red Clay

To investigate the effect of fulvic acid on the shear strength of red clay, the red clay was mixed with different contents of fulvic acid powder to prepare samples and saturated with distilled water. Direct shear tests were carried out on the samples with soaking ages of 7 d, 14 d, and 28 d to analyze the effects of different dosages of fulvic acid and soaking time on the shear strength of red clay samples. The test results show that the addition of fulvic acid will reduce the shear strength of the soil samples. With the increase of fulvic acid incorporation, the shear strength of the samples increases and the internal friction angle decreases, respectively. With the same amount of fulvic acid, the longer the soaking time, the greater the cohesion and the smaller the internal friction angles. The active functional groups of the fulvic acid, such as carboxyl groups, hydroxyl groups, carbonyl groups, and methoxyl groups adsorbed on the surface of soil minerals, wrapping on the surface of soil particles and forming a bonding effect between the soil particles, thus affecting the shear strength indexes of the soil.