A　large-scale　3D　combined　geomechanical　model　test　is　conducted　in　this　study　to　investigate　the　mechanical　characteristics　for　linings　of　asymmetrically　closely-spaced　twin-tunnels　constructed　in　sandy　ground.　A　series　of　experimental　results　(i.e.,　excavation　and　overloading)　effectively　reveal　the　mechanical　features　of　the　linings　and　the　stress　release　and　displacement　characteristics　of　the　sandy　ground　for　asymmetrical　twin-tunnels　during　the　excavation　and　overloading　under　the　condition　of　great　buried　depth　(vertical　stress)　and　high　stress　coefficient　(the　ratio　of　lateral　to　vertical　stress).　Afterward,　numerical　analyses　are　conducted　by　a　finite　difference　program　FLAC3D　to　verify　experimental　results.　The　influences　of　construction　sequence,　stress　coefficient,　clear　distance　and　lining　stiffness　on　mechanical　behaviors　of　linings　and　stratum　are　discussed　in　some　details.　The　experimental　results　show　that　during　the　excavation　of　the　asymmetrically　closely-spaced　twin-tunnels,　the　linings　are　in　a　state　of　compression.　The　lining　of　the　smaller　diameter　tunnel　which　excavated　later　is　susceptible　to　bias　pressure.　The　bending　moment　located　on　the　lateral　side　of　the　larger　diameter　tunnel　close　to　the　smaller　diameter　tunnel　decrease　when　the　smaller　diameter　tunnel　is　excavated.　The　change　of　stress　release　direction　in　the　middle　soil　pillar　is　the　main　reason　that　results　in　the　change　of　stress　state　in　linings.　The　overloading　process　only　causes　the　bending　moments　increasing　continuously,　but　not　affect　the　basic　distribution　patterns　in　linings.　Numerical　results　indicate　that　if　the　smaller　diameter　tunnel　is　excavated　first,　the　continuous　tunneling　of　the　larger　diameter　tunnel　will　cause　sharp　changes　in　lining　moment　of　smaller　diameter　tunnel,　but　it　will　not　cause　serious　adverse　effects　on　the　existing　tunnel　lining　(larger　diameter　tunnel)　if　the　larger　diameter　tunnel　is　excavated　first.