This　paper　aims　at　influence　analysis　of　approaching　excavation　on　adjacent　segments　for　twin　tunnels　with　variable　clear　spacing　located　in　Beijing,　China.　A　series　of　numerical　simulations　have　been　conducted　to　investigate　the　influence　of　approaching　excavation　on　ground　displacements　and　mechanical　responses　of　segments.　What＇s　more,　on-site　monitoring　was　conducted　at　the　position　of　the　minimum　spacing　between　the　twin　tunnels.　It　is　found　that　the　deformation　of　the　measured　segment　presents　a　pronounced　asymmetric　ovalization　when　the　second　tunnel　approaches　the　measured　cross-section.　During　the　approaching　excavation　of　the　second　tunnel,　the　normal　force　increases　gradually,　whereas　the　bending　moment　first　decreases　and　then　increases.　The　maximum　increments　of　internal　forces　in　the　measured　segment　are　both　located　at　the　regions　near　the　second　tunnel,　in　which　the　springline　and　shoulder　of　the　segment　are　mainly　subject　to　the　effect　of　the　circumferential　compression　and　axial　tension.　The　approaching　excavation　reduces　the　horizontal　displacements　of　the　ground　between　twin　tunnels　and　increases　the　ground　settlements　as　well　as　the　horizontal　displacements　of　the　ground　on　both　sides.　The　actual　tunneling　case　of　first　along　the　curved　trajectory　and　then　along　the　straight-line　trajectory　can　reduce　internal　forces　of　the　segment.