X-ray computed tomography-based evaluation of the physical properties and compressibility of soil in a reclamation area

Nowadays, land reclamation by dredged soil has become an effective solution to the growing demand for land resources in coastal areas. However, the widespread dredger fill (artificial deposits in reclamation area) can compress the underlying soil layers, causing different degrees of land subsidence and posing a threat to infrastructure in relation to agriculture. Therefore, it is necessary to facilitate an understanding of the physical properties and compressibility of soil in the reclamation area. X-ray computed tomography (CT), as a non-destructive method, can provide insight into the structure of soil. In this paper, 44 undisturbed soil samples comprised of dredger fill, sandy silt, muddy clay, clay, and silty clay, were collected from ten 55 m deep boreholes in Chongming East Shoal reclamation area in Shanghai. CT and conventional tests were conducted on all soils. The coefficient of variation of the scanning-slice-related standard deviation was used to evaluate the soil heterogeneity, which reflects the spatial variability of the arrangement of soil particles. The results indicated that the slice-related coefficient of variation had a reliable capacity to evaluate the soil heterogeneity; the averaged Hounsfield (AHu) values of the soil sample had a significant statistical correlation with the conventional-test-derived physical properties (wet bulk density, dry bulk density, gravimetric water content, and porosity). The AHu values essentially reflected the relative amounts of soil particles and water in saturated soil. The granulometric compositions that can lead to denser arrangements of soil particles tended to have higher Hu values. A linear relationship was also found between AHu values and the compression index, which may help to predict the compressibility of the soil. As a rule, these findings open new avenues for research into the physical properties and compressibility evaluation of varied types of soil.