A New Approach to Explore the Surface Profile of Clay Soil Using White Light Interferometry

In order to have a better understanding of the real contact area of granular materials, the white light interference method is applied to explore the real surface morphology of clay soils under high stress. Analysis of the surface profile indicates that there exists a support point height z(0) with the highest distribution frequency. A concept of a real contact region (from z(0) to z(0) + d(90); d(90) represents the particle size corresponding to 90% of the volume fraction) is proposed by combining a surface profile with the particle size distribution of clay soil. It was found that under the compressive stress of 106 MPa–529 MPa, the actual contact area ratio of clay soil varies between 0.375 and 0.431. This demonstrates an increasing trend with the rise of stress. On the contrary, the apparent porosity decreases with an increasing stress, varying between 0.554 and 0.525. In addition, as the compressive stress increases, the cumulative frequency of apparent profile height (from z(0) − d(90) to z(0) + d(90)) has a concentrated tendency with a limited value of 0.9.