Research on the Experiment for Dilatancy of Unsaturated Silty Clay in Different Matrix Suctions

Dilatancy is one of the most important mechanical properties of soil, and it makes the deformation characteristics of the soil becoming more complex. Most soil is unsaturated in engineering practice, so it is completely necessary to research the dilatancy of the unsaturated soil considering the matrix suction. This paper studies the direct shear test of the unsaturated silty clay about dilatancy by GDS unsaturated back pressure shear apparatus (UBPS). We have summarized the unique regularity about the dilatancy of unsaturated silty clay with the changing of the matrix suction and got that the matrix suction can resist the vertical load in unsaturated silty clay. When the matrix suction is greater than the vertical load, the cohesive force among soil particles can resist the effect of vertical pressure, so the unsaturated silty clay would appear the phenomenon of dilatancy. When the matrix suction is less than the vertical load, unsaturated silty clay would appear the phenomenon of negative dilatancy (negative dilatancy is shear contraction). The value of dilatancy is increasing with the increase of the matrix suction of unsaturated silty clay under the same vertical load. The matrix suction can directly affect the surface tension of the contractile membrane, thereby affect the bonding strength between the soil particles.