Kenta YOSHII
Cyclic shear strength of medium soil sampled at landfill failure in Takamachi housing development
Satoru OHTSUKA
In 2004 Mid-Niigata Earthquake, a lot of infrastructures were seriously damaged by the main shock and sequent aftershocks recorded as 7 and 6 higher in Japanese seismic intensity scale. It is remarkable that many natural slopes and landfills failed by sequent earthquakes. The disaster area had much rainfall by typhoon 23 before the earthquake occurrence and it enlarge the damage of soil structures greatly. It is pointed out as a complex disaster of earthquake and rainfall.
This study reports an investigation work on the Takamachi housing development in Nagaoka city, where circumferential landfill was seriously damage by the earthquake.
Cut soil composed of sand and silt was used for fill material. It is classified into silt sand. The strength property is not clear because it posses both properties of silt and sand. This study conducted a series of cyclic loading tests of fill soil sampled at the slope failure site. The effect of saturation degree on cyclic shear strength was also investigated. By making clear the shear property of landfill material, the cause of slope failure was examined by the inversed slope stability analysis.
The conclusions obtained in this study are shown in the followings.
(1) Cyclic shear strength of landfill soil sampled at landfill failure site in Takamachi housing development was made clear. It was observed to cause partial liquefaction for cyclic loading in case of void ratio as e=0.9 corresponding to landfill condition.
(2) Different liquefaction strength curves were obtained for void ratio. By the decrease in saturation degree, the cyclic shear strength of unsaturated soil naturally increased, but the initial stiffness was found to decrease.
(3) By the inverse analysis of slope failure, the seismic intensity was obtained as 0.15 for the earthquake in case of saturated condition at the slip line constituted along the former ground surface. It expresses the possibility of slope failure without any rainfall.
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