A　gap　formation　underneath　pipelines　could　be　observed　during　tunneling　beneath　existing　buried　pipelines,　thus　altering　the　pipeline-soil　interaction　behavior.　However,　the　most　existing　analytical　approaches　typically　do　a　full　contact　assumption　for　brevity.　For　such　purpose,　we　aim　to　present　an　analytical　approach　coupling　the　effect　of　gap　formation　underneath　pipelines　by　considering　the　buried　pipeline　as　an　Euler-Bernoulli　beam　on　tensionless　foundation.　The　pipeline　can　be　divided　into　three　segments　according　to　pipeline-soil　interaction　behavior,　and　then　the　bending　behaviors　of　each　segment　are　formulated.　The　deflection　and　bending　moment　of　the　pipeline　caused　by　tunnelling　underneath　from　the　proposed　approach　are　compared　and　validated　with　centrifuge　testing　data　and　existing　analytical　solutions.　The　effects　of　pipeline-soil　stiffness　ratio,　pipeline　buried　depth,　tunnel　buried　depth,　tunneling　induced　volume　loss,　and　tunnel-pipeline　intersection　angle　on　the　pipeline　responses　are　further　discussed.　The　results　indicate　that　gap　formation　underneath　pipeline　can　be　observed　indeed　for　shallowly　buried　pipeline　and/or　larger　pipeline-soil　stiffness　ratio.　The　proposed　analytical　approach　provides　a　theoretical　guideline　to　predict　the　responses　of　existing　pipelines　to　tunnelling　underneath.　©　2024,　Korean　Society　of　Civil　Engineers.