Groundwater level lowering effects for reducing damage to existing residences during earthquakes

抄録

Numerous structures, including residences and buildings, were damaged severely not only in Tohoku but also in Ibaraki, which is adjacent to Fukushima, one Tohoku prefecture affected by the Great East Japan Earthquake that struck on 11 March 2011. One difficulty presented by the great earthquake is the method used to reconstruct damaged residences. Another difficult issue is how to maintain the stability of existing structures on sandy soil deposits with high ground water level (GWL) against the coming great earthquakes. Those structures are endangered by liquefaction-induced damage, particularly vulnerable are aged structures that experienced the great earthquake. This study specifically examines a proposal for reducing the settlement and deformation of existing structures on sandy ground during earthquakes. Model tests were conducted under normal gravity (1 × g) conditions to examine the effects of groundwater level lowering techniques with and without sheet pile walls installed along the sides of structures. Analysis of the test results showed the following: (1) Severe structural settlement occurred when no sheet pile walls on sands with high water level had been installed. However, the longer the sheet pile walls had been installed, the more they reduced settlement during earthquakes. (2) Furthermore, the combined use of sheet pile wall installations and a decrease in groundwater level engendered the greatest reduction in structural settlement. (3) It is greatly advantageous from a practical perspective that it is not necessary to attach sheet pile walls to the side walls of structures when the groundwater level becomes lower. Therefore, it is strongly recommended that groundwater lowering techniques should be combined with sheet pile installation for reducing the damage to existing residences during earthquakes.