Experimental study on tensile strength of granite residual soil during drying and wetting

The tensile strength of remolded granite residual soil under different water content conditions, during wetting and drying, was investigated using a self-made horizontal direct tension apparatus. The variations in tensile strength and the microcosmic mechanism of shrinkage crack formation and development were elucidated from the perspectives of suction stress and cementing force. Experimental results indicated that the tensile strength of granite residual soil initially increased and then decreased under different water content conditions. During the wetting process, the tensile strength followed a similar trend, but the peak strength (10 kPa) was lower compared to that under different water content conditions (22 kPa). The drying process exhibited three stages of tensile strength variation: a linear increase stage, a stationary stage, and a slight decrease stage. The peak value of the tensile strength during drying was much higher (reaching approximately 84 kPa) than that under different water content conditions and the wetting process. The tensile strength of remolded granite residual soil was solely controlled by suction stress under different water content conditions and in the wetting process. However, in the drying process, the tensile strength was also influenced by the cementing force, resulting in a peak value four times higher than that under different water content conditions and seven times higher than that in the wetting process. Suction stress served as the source of tensile stress in the soil during the drying process, and the development of cracks caused by suction stress led to a reduction in the overall tensile strength of the soil. Suction stress acted as both a contributor and a destroyer of soil tensile strength. During the drying process, the soil sample exhibited weakly acidic pH and gradually weakened hydrophilic ability. This led to the formation of stronger binding forces within the soil skeleton. Consequently, for soil samples with the same moisture content, the tensile strength during the drying process was much greater than in the other two situations. This study provides an alternative perspective on the source of soil tensile strength and its main controlling factors.