Earthquakes　can　be　extremely　damaging　to　tunnelling　through　active　fault　zones.　By　defining　the　damage　evolution　state　of　concrete　model　and　refining　the　grading　of　concrete　tensile　damage　degree　by　combining　the　crack　width　and　tensile　damage　evolution　parameter,　and　then　taking　the　under-construction　Taiyuan　City　Urban　Rail　Transit　Line　1　Phase　I　project　interval　tunnel　crossing　Jiaocheng　fault　zone　as　the　engineering　basis.　A　three-dimensional　refined　model　simulating　the　fault　displacement　was　established　by　using　ABAQUS　software,and　the　effects　of　three　key　parameters,namely,protection　length,joint　location　and　thickness,on　the　mechanical　response　and　fracture　resistance　of　the　tunnel　structure　with　variable　cross-section　mitigation　measures　are　analysed.The　results　show　that:the　use　of　variable　cross-section　measures　is　conducive　to　reducing　the　overall　damage　of　the　cross-fault　underground　tunnel　structure;the　use　of　tensile　damage　state　classification　to　assess　the　damage　of　the　tunnel　structure　can　determine　the　location　and　extent　of　the　damage;the　tunnel　structure　is　prone　to　tensile　damage　when　the　fault　is　moving　and　the　damage　is　widely　distributed;the　appropriate　protection　length　is　necessary　to　maximise　the　mitigation　effect　of　the　variable　cross-section　measures;The　overall　damage　to　the　tunnel　structure　and　the　extent　of　damage　can　be　reduced　by　selecting　the　appropriate　lining　position　and　thickness;the　variable　section　lining　structure　effectively　controls　the　extent　of　lining　damage　caused　by　the　fault,avoids　the　occurrence　of　the　tunnel　collapse　phenomenon,and　achieves　the　purpose　of　improving　the　seismic　resilience　of　the　underground　structure　across　the　fault.　©　2024　Editorial　Board　of　Journal　of　Basic　Science　and　Engineering.　All　rights　reserved.