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In the elasto-plastic constitutive model, bulk modulus is one of the most important parameters to control the change of effective stress under undrained condition. However, the experimental research on bulk modulus of sand during liquefaction has not been conducted so far. In this paper, therefore, the bulk modulus of Toyoura sand was measured directly during liquefaction using a hollow cylindrical torsional shear testing device equipped with a volumetric strain control device. This study found that the bulk modulus corrected by membrane penetration effect during liquefaction process is constant under relatively high confining pressure, and that the stress dependency of bulk modulus during liquefaction process is different from that during swelling process.

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In this study, a new methodology by using the X-ray CT scan is proposed for estimating void ratio of sandy soil.The general problems in high resolution X-ray CT scan such as beam hardening and ring artifact had been successfully settled up using thin metal plate filter and some calibration process. In order to calculate the void ratio of sand from its CT image, the procedures and algorithm for CT image processing are developed. CT scan tests for Joomunjin sand are carried out to verify its applicability to void ratio testing.

: It has been generally recognized that the conventional rockfall protection nets have several problems to actual field application in the aspect of shock absorption, lack of pullout bearing capacities, and net damages. Because of the recognition, authors have tried to develop a new rockfall protection system consisted of shock absorption parts and hexagonal net configuration. In the previous research by the authors, the performance of the newly developed rockfall protection system has been investigated through the laboratory tests and the full-scale testing. In this study, subsequently, numerical analysis program is organized to make a confirmation of the structural stability and performance. For the correct design procedure of the hexagonal net system, it is essential to understand the various mechanical behavior of the entire system. It is also important to be reproduced the systematic characteristics of the system acquired by laboratory and full-scale testing by numerical analysis in order to carry out the numerical experiment to understand various mechanical behavior of the system. As a conclusion, the hexagonal net has better performance in mechanical and physical behavior compared with that of the rectangular net. Furthermore, due to the hexagonal net shows a good performance in aspect of the load distribution, it gives a good alternative in long-term management of the rockfall protection net.