Abstract
During the 2015 Gorkha Earthquake (Mw7.8), extensive soil liquefaction was observed across the Kathmandu Valley. As a densely populated urban settlement, the assessment of liquefaction potential of the valley is crucial especially for ensuring the safety of engineering structures. In this study, we use borehole data including SPT-N values of 410 locations in the valley to assess the susceptibility, hazard, and risk of liquefaction of the valley soil considering three likely-to-recur scenario earthquakes. Some of the existing and frequently used analysis and computation methods are employed for the assessments, and the obtained results are presented in the form of liquefaction hazard maps indicating factor of safety, liquefaction potential index, and probability of ground failure (PG). The assessment results reveal that most of the areas have medium to very high liquefaction susceptibility, and that the central and southern parts of the valley are more susceptible to liquefaction and are at greater risk of liquefaction damage than the northern parts. The assessment outcomes are validated with the field manifestations during the 2015 Gorkha Earthquake. The target SPT-N values (Nimproved) at potentially liquefiable areas are determined using back analysis to ascertain no liquefaction during the aforesaid three scenario earthquakes.
Highlights
Soil liquefaction is one of the common seismic consequences that frequently lead to significant structural damage during earthquakes (Setiawan et al 2017)
After the 2015 Gorkha Earthquake, NBC (2020) has recommended an earthquake of Mw8.4 with a peak ground acceleration (PGA) of 0.36 g for the Kathmandu Valley. All these recommended scenarios were used in the analysis of liquefaction susceptibility in terms of factor of safety (FOS), liquefaction potential index (LPI) and probability of ground failure (PG)
A larger part of the Kathmandu Valley is considered to be highly susceptible to soil liquefaction during seismic activities owing to its geological, geotechnical, and hydrogeological conditions
Summary
Soil liquefaction is one of the common seismic consequences that frequently lead to significant structural damage during earthquakes (Setiawan et al 2017). Surface manifestations of liquefaction have been well recorded during various earthquake events, such as Nepal-Bihar Earthquake (1934, Nepal), Alaska Earthquake (1964, USA), Niigata Earthquake (1964, Japan), Loma Prieta (1989, USA), Kobe Earthquake (1995, Japan), Chi-Chi Earthquake (1999, Taiwan), Bhuj Earthquake (2001, India), Chile Earthquake (2010), Emilia-Romagna (2012, Italy) and Gorkha Earthquake (2015, Nepal) (Ansal and Tönük 2007; Novikova et al 2007; Sharma et al 2018; etc.) All these manifestations have led to an understanding that liquefaction occurs mostly in fine loose and saturated silty sands, low-plastic silty clays, and non-plastic silts as a result of substantial loss of material shear strength (Jalil et al 2021).
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