Geomaterials with different grain size distribution, particle shape, and other micro-structural features exhibit various mechanical properties due to those features. In addition, even if soil specimens are sampled from the same geological stratum or prepared in a similar manner, the test result may vary depending on their micro-structural differences. Therefore, evaluating the effects of such micro-structural features will lead to advances in methods for evaluating the mechanical properties of the ground. In the conventional geotechnical investigation method, undisturbed samples (i.e., cores) are taken from the original ground, after which various types of laboratory tests must be performed to measure their properties, etc. depending on the purpose. On the other hand, if it were possible to use an X-ray CT scanner to acquire images of the micro-structural features of the ground, perform CT image and numerical analyses, and conduct simulated soil tests using 3D printing technology, it would enable the evaluation of the various mechanical properties of the core samples, which would be highly useful in practice.

We 3D-printed the micro-structural data detected in CT images, and performed triaxial compression tests of such simulated test specimens, and thus were able to prove that the unique behaviors as the granular materials (such as stress dependency and dilatancy behavior), which the original gravel material resembles, could be recreated, confirming its applicability as an appropriate soil testing method.

In addition, we conducted DEM-SMAC coupled analyses (in which models are created by DEM from particle structures, and the flow of pore fluids is computed) to address the issue of water permeation in the ground, and were able to confirm that the findings were highly consistent with the results of the constant head permeability tests in which simulated test specimens were used.

In this study, we have been developing equipment that will be able to perform X-ray CT scanning of core specimens on site. We are analyzing the images acquired in experiments, and examining the discrete element method and the mechanical property evaluation method that utilizes 3D printing technology.