ABSTRACT

In order to reduce the liquefaction damage to detached house during earthquakes, it is essential to predict the damage using inexpensive and simple methods. Therefore, in this study, authors proposed numerical method and some ground survey methods. From the reproduction analysis using these technologies, it was found that the damage could be sufficiently reproduced by the proposed method, and it was found that the damage was affected by the strata inclination. Based on these results, we proposed two-dimensional surface wave survey and passive linear arrays that can also be used in residential areas, and confirm their superiority and simplicity.

INTRODUCTION

A large settlement and tilting of detached house have been often observed due to ground liquefaction (JGS, 2011; Yamaguchi et al., 2012). Extensive damages were inflicted to lifelines and detached houses due to widespread liquefaction and lateral spreading in reclaimed or lowland areas. Liquefaction countermeasures are effective to mitigate damage of liquefaction. However to predict these damage and to determine whether countermeasures are required, we have to conduct some field investigations to understand ground condition in detail (Kazama et al., 2018). Generally, Swedish Weight Sounding tests (SWS) were conducted as ground investigation to understand the ground bearing capacity in Japan. These results are not enough to predict these damage or to determine the necessity of countermeasures.

From these situations, the authors carried out ground investigations by using different survey techniques for two sites located in Japan and in New Zealand. In Kamisu city familiar for severe damage due to liquefaction during the 2011 off the Pacific coast of Tohoku Earthquake in Ibaraki Prefecture located east of Tokyo, four different ground survey techniques were employed. First, SWS and Dynamic Proving Test (DPT) were conducted. Later, the soil sampling was conducted. Finally, the survey of ground water level was carried out. On the other hand, passive linear arrays and two dimensional surface wave explorations were conducted in Christchurch, New Zealand. These methods not only can be easily conducted but also rapidly provide output results.

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