Conferência do Prof. F. Tatsuoka

(actual Vice-Presidente da IGS - International Geosynthetics Society):

"2004 Niigata Chuetsu Earthquake: Reconstruction of Geogrid-reinforced Soil Retaining Walls with a Full-Height Rigid Facing"

(dia 8 de Abril de 2005, às 15h00 no pequeno Auditório do centro de congressos do LNEC)

ABSTRACT

On October 23, 2004 at 17:56 PM (Japan local time), a magnitude 6.8 earthquake struck 80 km to the South of Niigata, on the West coast of Honshu, Japan. The earthquake epicenter was 195 km (120 miles) North-Northwest of Tokyo, Japan. This is one of the deadliest earthquakes to hit Japan in the last decade. Compared to the damage to steel-reinforced concrete structures, the scale and extent of the damage to soil structures and its effect on the transportation system and associated civilian life were much more extensive. In particular, a number of embankments that had been constructed in narrow valleys and on slopes, where ground and surface water tends to concentrate, experienced the greatest damage. The effect of heavy rainfall two days before the earthquake resulted in the backfill becoming more saturated than under typical conditions. Three embankments on the Jo-etsu railway line constructed on the slope on the right bank of Shinano River completely failed and are a typical example of the damage done by the earthquake.

These failed embankments were reconstructed into four geogrid-reinforced soil (GRS) retaining walls within two months after the failure. The GRS retaining
walls had a full-height rigid facing (i.e., a thin slightly steel-reinforced concrete facing) constructed using the staged construction method . This type of GRS retaining wall was chosen to reconstruct the failed embankments for the following reasons:
1) Several GRS retaining walls of this type performed very satisfactorily during the 1995 Hyogoken-nambu Earthquake (the so-called 1995 Kobe Earthquake). A number of conventional-type retaining walls (gravity, leaning,masonry, and cantilever RC) failed during the Kobe earthquake and many were reconstructed into GRS retaining walls within a short period of time.
2) For this case, it was estimated that this type of GRS retaining wall is superior to other types of structures (i.e., conventional sloped embankments supported by RC cantilever walls that are supported with a pile foundation, bridges, etc.) in terms of construction costs, construction time, and performance in terms of deformation and ultimate stability.

This case history further validates that geosynthetic-reinforced soil retaining walls can be a very competitive construction method for critical wall structures, such as railways and highways.