Analysis of Liquefaction and Its Mitigation for Soil Under Open Foundation of Structure—A Case Study of Road Project in West Bengal, India

Liquefaction of loose to medium dense, saturated, cohesionless sandy soil deposit endangers the stability of open, i.e., shallow foundation of structure under seismic loading condition due to loss of shear strength of underlying liquefiable soil and subsequent occurrence of excessive settlement. This paper presents the typical case study of assessment of liquefaction potential of the loose to medium dense sandy foundation soil deposits having high water table as found through geotechnical investigations at one ROB structure location along the project road of NH-31D from “Siliguri (Ghoshpukur)” to “Alipurduar (Salsalabari)” in the northern part of West Bengal. Since the said project road is located in the “Seismic Zone IV” of “IS 1893 (Part 1): 2016 (Reaffirmed 2021)” (IS 1893 (Part 1):2016 (Reaffirmed 2021)—Criteria for Earthquake Resistant Design of Structures, Part 1: General Provision and Buildings (Sixth Revision), Bureau of Indian Standards (BIS), New Delhi.), so there was susceptibility of liquefaction of loose to medium dense saturated cohesionless soil explored under the open foundation of substructures. The structures having shallow foundations were not feasible due to the presence of liquefiable depth of soil beyond the proposed founding level at those identified locations of substructures. Hence it was essential to do the appropriate mitigation measure against liquefaction of the foundation soil deposits. The “vibro-probing method” of densification for loose to medium dense saturated sandy soil was adopted as the effective and economic mitigation measure against probable liquefaction in seismic condition. The paper discusses about the said ground treatment method of densification for loose to medium dense saturated sandy deposits under the open foundations of substructures. The field geotechnical investigation work by SPT method of sounding was conducted at the post-ground treatment stage and the liquefaction potential for the treated foundation soil was also assessed to verify the efficiency of adopted mitigation measures against any possibility of liquefaction during earthquake.