Failure: Building Overturn
Location: Niigata, Japan
Type: Earthquake – Liquefaction
On June 16. 1964, the city of Niigata experienced a magnitude 7.5 earthquake. Kawagishi-cho, a complex of eight 4-story apartment buildings with approximate dimensions of 30m by 8m, was built on reclaimed land. During the earthquake, the complex experienced severe soil settlement, resulting in various degrees of tilting of up to 80° from the vertical (photo 1) [a]. Although the buildings had been designed and constructed to withstand the violent shaking, the soils beneath the foundations turned to “quicksand”. These reinforced concrete buildings sank into the earth and tilted [b].
The earthquake caused the peak surface acceleration of 0.16 g’s near the site. The buildings, which were built with shallow foundations, tilted because of the shear strength of the liquefied sand diminished during the earthquake. This process became known as liquefaction. Civil and geotechnical engineers around the world immediately became aware of the devastating potential of earthquake-induced ground failures that were rarely considered before in the design process. [d]
Liquefaction is a phenomenon in which the strength and stiffness of a soil is reduced by earthquake shaking or other rapid loading. Liquefaction occurs in saturated soils: that is, soils in which the space between individual particles is completely filled with water. The water exerts a pressure on the particles that influences how tightly they are pressed against each other. Prior to an earthquake, the water pressure is relatively low. However, earthquake shaking can cause the water pressure to increase to the point where the soil particles can readily slide by each other. Earthquake shaking often triggers this increase in water pressure; however, construction-related activities, such as blasting, can also cause an increase in water pressure [e].
As more and more projects are being constructed in hazardous locations, the threat of liquefaction has grown. However, through careful evaluation and engineering, the risks of liquefaction can be mitigated. Since that Niigata earthquake, the methods of Earthquake Drains and Vibro-replacement have been developed so as to mitigate the risk liquefaction [f].
The video below demonstrates the concept of liquefaction. Sand (loose sediment) was used and water added to create a saturated soil similar to that in nature.
[a] Milutin Srbulov, page 164, Practical Soil Dynamics: Case Studies in Earthquake and Geotechnical Engineering