1-g shaking table tests on seismic enhancement of existing box culvert with partial ground-improvement method and its 2D dynamic simulation

An underground structure buried in a soft ground located in a seismic-active region may experience intolerable deformation due to earthquake loading. The collapse of Daikai Station of the Kobe subway line during the 1995 Hyogoken-Nambu Earthquake demonstrated that underground structures may also sometimes be at high risk for failure in a huge earthquake. In particular, box culverts constructed in a soft ground with a thin overburden are vulnerable to earthquakes. Some previously constructed box culverts do not meet the present requirements of seismic design standards. In this paper, numerical analyses and 1-g shaking table tests are conducted to evaluate the effect of partial ground improvement (PGI) as a seismic countermeasure for the above-mentioned existing box culverts. Particular attention is paid to the optimum pattern of PGI that can most efficiently reduce the impact of an earthquake on a box culvert. The underground structure of Daikai Station is taken as an example and its physical and geometric conditions are used to model the box culvert in the analyses and the tests. In order to accurately consider the influence of the soil-structure interaction (SSI) on the underground structures, both the soil and the box culvert are considered in the analyses and the shaking table tests. Four different patterns of PGI are considered. Based on the analyses and the tests, an optimum pattern for the PGI of existing box culverts is proposed.