ارزیابی تاثیر روانگرایی خاک بر ساختمان کم ارتفاع در زلزله Meinong The impact evaluation of soil liquefaction on low-rise building in the Meinong earthquake

Introduction On February 6, 2015, a local magnitude (ML) 6.4 earthquake struck southern Taiwan. Te epicenter was at 22.92° north and 120.54° east with a focal depth of 14.6 km according to the Taiwan Central Weather Bureau (CWB). Te epicenter was near the town of Meinong in Kaohsiung City and thus was called Meinong earthquake. No signifcant damage was reported in the epicentral region. However, serious damages occurred approximately 30 km west of the epicenter in Tainan City. Te collapse of the 16-story Wei Guan complex building (30 km from the epicenter) resulted in 115 deaths and caused the greatest public concern. Apart from this tragic event, the liquefaction-induced damages also caused considerable concern. Tis paper presents major preliminary observations on the liquefaction-induced damage. Te severe building damages centered on Huian and Sanmin Streets in Tainan City. From old geographical information, we know that these areas are fll reclamation from old fsh or farm ponds, and it is not surprising that the construction of these reclaimed areas had poor quality control. Since seismic stations were far from these areas, there is some doubt as to the exact PGAs. To better understand the efect of site responses in these areas, this study used the several simplifed approaches to consider site response analyses and quantify the amplifcation efects of the sites subject to the Meinong earthquake for comparison. After that, several common simplifed methods with the information provided by 13 Standard Penetration Test (SPT) boreholes and 5 Cone Penetration Test (CPT) soundings were used to estimate the liquefaction potential index (LPI) during the Meinong earthquake. Te liquefaction evaluation results combined with the soil characteristics were used to explain the failure mechanism of the damaged buildings. It was also found that the estimated damage severity was not consistent with the feld conditions if the local site efect was not taken into account, because this results in the underestimate of the PGA at the site. Besides, the performance of the simplifed methods in moderate magnitude earthquake was reviewed based on the collected case histories. Te sensitivity of fnes content in liquefaction assessment was also evaluated. Liquefaction‑induced damages to building structures Based on a feld investigation by a survey team from the National Center for Research on Earthquake Engineering (NCREE), the locations of major liquefaction sites are shown in Fig.  1 along with the epicenter and the CWB seismic stations. Te estimated peak ground accelerations range from 0.15 to 0.25g in this general area. Te major liquefaction sites include Annan (LI), Sinshih (L2), Wenhe (L3), Zhengju (L4), Dawan E (L5) and Xinhua (L6). Te frst four sites are residential areas and liquefaction led to diferent levels of structural damage. Te last two are free-feld sites located on farm land, and thus, no damage was reported. According to the defnition of ground failure index (GFI) (Table  1) proposed by Bray and Stewart (2000), the most severely damaged areas were located at the Annan, Sinshih, Wenhe and Zhengju sites where substantial settlements and tilts of buildings are summarized in Table  2. In this paper, the liquefaction evaluation mainly focuses on the two most severely damaged areas in the Annan and Sinshih Districts.