X-ray CT analysis of pore structure in sand

The development of microfocused X-ray computed tomography (CT) devices enables digital imaging analysis at the pore scale. The applications of these devices are diverse in soil mechanics, geotechnical and geoenvironmental engineering, petroleum engineering, and agricultural engineering. In particular, the imaging of the pore space in porous media has contributed to numerical simulations for single-phase and multiphase flows or contaminant transport through the pore structure as three-dimensional image data. These obtained results are affected by the pore diameter; therefore, it is necessary to verify the image preprocessing for the image analysis and to validate the pore diameters obtained from the CT image data. Moreover, it is meaningful to produce the physical parameters in a representative element volume (REV) and significant to define the dimension of the REV. This paper describes the underlying method of image processing and analysis and discusses the physical properties of Toyoura sand for the verification of the image analysis based on the definition of the REV. On the basis of the obtained verification results, a pore-diameter analysis can be conducted and validated by a comparison with the experimental work and image analysis. The pore diameter is deduced from Young–Laplace's law and a water retention test for the drainage process. The results from previous study and perforated-pore diameter originally proposed in this study, called the voxel-percolation method (VPM), are compared in this paper. In addition, the limitations of the REV, the definition of the pore diameter, and the effectiveness of the VPM for an assessment of the pore diameter are discussed

Sediment consolidation in ephemeral river: the effect of applied loading on soil properties and dredging method selection

Bengawan Solo River, a typical large ephemeral river in Indonesia, is facing stream problems induced by the erosion and deposition of sediment. Imbalance between these two phenomena on the riverbed can lead to excessive sedimentation, increased risk of flooding, and formation of sandbars. One proposed solution to address this problem is dredging. However, this process can have potential negative effects on the environment, such as removal or destruction of the biota in the dredged materials, increased turbidity, as well as coverage of the benthos in the vicinity. Also, different dredging methods are needed to suit sediments with different properties. Therefore, the knowledge of the deposited sediment properties is required so that appropriate methods can be selected. The sediment characteristics were obtained by performing laboratory tests on physical and consolidation properties and shear strength tests of a soil sample. The results indicate that the materials were broadly grouped into sandy sediment in downstream areas and clayey sediment in estuary areas. The distribution of sediment properties varies with depth because of subsequent erosion and deposition over time. Additionally, the distribution also shows that sand content decreases as the origin of sample approaches estuary areas. Erosion is predominant at locations with small hydraulic radius and high flow velocity, mostly at downstream areas, whereas deposition is predominant at locations with a large hydraulic radius and low flow velocity, specifically at estuary areas. The shear strength increases as the loads imposed by the self-weight of sediment layer increase. The analysis suggests that sediments cannot be eroded naturally as they have a shear strength that exceeds the small-capacity dredging method (t . 20 kPa); therefore, the removal of excess sediment in such areas requires dredging methods of larger capacities (such as grab dredger)