In order to reduce the volume of reclaimed soft ground formed by dumping of dredged soil, the vacuum consolidation method with prefabricated vertical drains (PVD) is one of the most effective methods, which has been frequently applied in Japan. However, it was reported in this method that the PVD installed in the soft ground was bended along with the consolidation settlement. Moreover, the drainage performance of PVD might be decreased due to such bending effect. A series of laboratory tests were performed to evaluate the bending effect on the consolidation behavior in PVD. First, the large scale model tests were performed to measure the shape of PVD bended by the vacuum consolidation. In these tests, the clay slurry at a water content of 150% was consolidated under the vacuum pressure of 60 kPa in the consolidation cells, which were 5 m in height and 30 cm or 76 cm in diameter. It was confirmed in these tests that the bending shape of PVD was explained by the buckling model of a column on an elastic foundation. Second, the permeability test for bended PVD was carried out to evaluate the drainage performance of bended PVD. In this test, PVD were used as sample and the flow rate under a given water head difference was measured. Consequently, it was revealed that the drainage performance of PVD was depended on the curvature and the number of bending points of PVD. Finally, the bending effect of PVD on its consolidation rate was discussed based on all the test results performed in this paper.
This paper comprehensively describes the result of groundwater flow modeling using data of hydraulic responses due to construction of Mizunami Underground Research Laboratory (MIU) in Mizunami, Gifu, in order to update hydrogeological model based on stepwise approach for crystalline fractured rock in Japan. The results showed that large scale hydraulic compartment structures which has significant influence on change of groundwater flow characteristics are distributed around MIU. Furthermore, it is concluded that hydrogeological monitoring data and groundwater flow modeling during construction of deep underground facilities are effective for hydrogeological characterization of heterogeneous fractured rock.
The dry shrinkage cracking of mud paste shows complex dynamical behavior due to some combinations of multiple physical processes such as dry-wet cycle, changing of grading composition in the paste, etc. In this work, we reveal the fractal dimension of cracking patterns on the bentonite pastes, also discuss the time-series variations and coarse mixtures variations. Additionally, we investigate the influence of dry-wet cycle on crack patterns and fractal dimensions. Consequently, the fractal dimensions of mudcracks increased as the cracks propagated, and they converged towards a constant value. And, we found the fractal dimension of mudcracks is closely related to their volumetric shrinkage rate. In contrast, although no significant relationship between crack length and fractal dimension was observed, the dry-wet cycle experiment indicated that bentonite paste may reproducibility their cracking points which occurred in the past.
The 2011 off Pacific coast of Tohoku Earthquake measuring Mw of 9.0 caused significant liquefaction in the Tokyo Bay area, which had been in its peak period of land reclamation projects since the World War II. In order to identify factors affecting liquefaction-induced damage to roads, the authors extracted values of road subsidence at total 224 points in Urayasu city, Chiba prefecture, from a subsidence map of the liquefied ground obtained from Airborne LiDAR surveys before and after the earthquake. The result indicates that the values of subsidence along arterial roads with thicker roadbeds are larger than those of residential roads. This feature is implemented in the empirical formula to describe road subsidence in terms of liquefaction potential index PL. In addition, improvement effects of liquefaction countermeasure are quantitatively examined on the subsidence map of the liquefied ground.