According to the size and connecting characters of soil particles, soil is discomposed into two components as matrix and reinforcement particles respectively with a demarcation size fixed at 0.075mm to investigate the influence of the microstructures on soil strength. Based on the strain gradient theory, a multi-scale matrix-reinforcement particle model was established to study the trans-scale properties of soil strength which indicates that the soil strength is related to the intrinsic length scale, the strain gradient, the matrix properties and the gradation and size of reinforcement particles. A series of consolidated and undrained compression tests of unsaturated remoulded soil were designed to study the trans-scale properties of soil strength. The results showed that: the yield stress of soil increased as the reinforcement particle size decreased, displaying the trans-scale properties of soil strength. The research result is significant to the development of strength theory of soil.
