Yukihiro Morikawa

Effect of Reinforcement on Bearing Capacity of Foundations

To increase bearing capacity of a foundation, geosynthetic is laid beneath the foundation. In previous research, the authors investigated the reinforcement mechanism by changing the length and the laying depth of the reinforcement (Nakai et al, 2009). In the present study, to get more bearing capacity, the reinforcing effect in the case that each edge of the reinforcement is fixed with the soil is investigated. For this purpose, 2D model tests and the corresponding non-linear finite element analysis are carried out. In these tests and simulation, the depth of the reinforcement is changed under constant length of reinforcement. Reinforcing effects, under concentric and eccentric load, are discussed. It is revealed that a significant increase of the bearing capacity is observed in the model tests when the reinforcement is set up in the ground with an appropriate depth under both concentric and eccentric loads. The results of numerical simulation - in which the stress-stain behavior of the soil and the frictional behavior between soil and reinforcement are properly taken into consideration - show good agreement with the observed results.

NUMERICAL ANALYSIS ON MECHANISM OF LIQUEFACTION NOT ONLY IN MAIN EARTHQUAKE BUT ALSO IN AFTER SHOCK

ABSTRACT: During the 2011 Great East Japan Earthquake, liquefaction occurred in the reclaimed ground in the wide area of east Japan. In some areas, liquefaction happened in the aftershock was even more serious than what happened in the main shock. For this reason, the liquefaction that happened a long time after the earthquake caused not only by the main shock but also the multiple aftershocks within a short period of time, is intensively investigated in recent years. In this paper, particular attention is paid to the characteristic features of the liquefaction and its consequent consolidation-induced settlement. Based on the observed data, a series of dynamic-static analyses, considering not only the earthquake loading but also static loading during the consolidation after the earthquake shocks, are conducted in a sequential way just the same as the scenario of the earthquake. The calculation is conducted with 3D soil-water coupling finite element-finite difference (FEFD) analyses based on a rotating-hardening elastoplastic constitutive model. From the analyses, it is recognized that small sequential earthquakes, which cannot cause liquefaction of a ground in an independent earthquake vibration, cannot be neglected when the ground has already experienced the liquefaction after a major shock. In addition, the aftershocks have great influence on the long-term settlement of the soil layers with low permeability. It is confirmed that the numerical method used in this study can describe the ground behavior correctly under repeated earthquake shocks.

EFFECTIVENESS OF CRASHED TILE IN COUNTERMEASURE AGAINST LIQUEFACTION

Liquefaction usually occurs in many sandy grounds during earthquake including Japan. Liquefaction causes damage of structures by making floatation or subsidence of them, and reduces the necessary performance of the structures. For example, stability of retaining wall based on skeleton weight of the structure is reduced due to subsidence and inadequate support which causes the destabilization of the structure. In addition, the light weight underground structure suffers damage such as floating due to the reduction of shear strength of soils during liquefaction. The damage occurs not only to the civil engineering structures (roads, bridges, etc.) but also to the residential buildings which makes the building unusable. On the other hand, Aichi Prefecture (Japan) is a center of the production of tiles where the crushed tile can be used as recycling materials for a measure of soil liquefaction. In this research, we have investigated the material property of the crushed tile and examined the effectiveness of countermeasure against liquefaction by shaking table tests. It is found that liquefaction of the ground can be reduced using crushed tiles because of its high friction and drainage properties. In the research, we found that the anti-liquefaction manhole which was backfilled by clashed tile floated only by 1/3 of the magnitude observed in the case of without countermeasure against liquefaction.

Countermeasure against liquefaction using crushed tile

Liquefaction is a common phenomenon of the sandy ground in an earthquake. It leads to the floatation of underground structures or subsidence of structure in the ground. Formerly, the phenomenon was associated with the main shock that lasts for relatively a short time. In recent years, however, it has been found that the bearing capacity of soils may also decrease during short-term seismic motions that occur multiple times (aftershocks) in the same way as in a long-term seismic motion. Crushed tiles abundant in Aichi Prefecture (Japan), a center for tile industry, are one of the promising recycling materials for a countermeasure against soil liquefaction. This research investigates the effectiveness of these tiles as a countermeasure against liquefaction for a long-term seismic motion and short-term multiple aftershocks in case of small structures, and confirms their physical and mechanical properties.