Identification of Possible Liquefaction Zones Across Guwahati and Targets for Future Ground Improvement Ascertaining no Further Liquefaction of Such Zones

Abstract

Liquefaction is associated with the loss of shear strength of soil, causing considerable damages. The Northeast Indian region has experienced many major (M ≥ 7.0) to great earthquakes (EQs) such as 1869 Cachar EQ and 1897 Shillong EQ. As a consequence, Guwahati city had faced large scale damage and significant induced effects such as liquefaction during past EQs. At present, Guwahati is the largest business hub of the northeast India. Further, Guwahati is also amongst the list of cities, Government of India has shortlisted to be developed as “smart city”. For these reasons, the city attracts lots of infrastructural growth in the times to come. In the present work, the liquefaction potential of Guwahati subsoil is evaluated. For the purpose, seismic scenarios experiences during 1869 Cachar EQ (Mw = 7.5), 1897 Shillong EQ (Mw = 8.1), average horizontal seismic coefficient given by IS 1893 (Part 1): 2016 (seismic zone V) and maximum amplified peak ground acceleration (PGA) values obtained based on site-specific subsoil data are considered separately. In-situ subsoil properties are obtained from 244 boreholes (BHs) till 30 m depth and maps showing possible liquefiable zones across Guwahati are developed. In addition, maps showing target SPT-N value ($$N^{improved}$$), to be obtained at above liquefiable zones after ground improvement, ensuring no further liquefaction, are also developed. Thus, the present study collectively identify zones which may undergo liquefaction during future EQs and further, how much improvement in the subsoil strength properties are required so that the above found liquefaction can be avoided, is also estimated. Obtained results and proposed values will provide very useful information to field engineers regarding where and how much ground improvement is required for avoiding future liquefaction. In addition, the present study is very helpful for city planning and microzonation studies.