The　columnar　jointed　basalt　(CJB)　in　the　dam　site　of　the　Baihetan　hydropower　station　exhibits　noticeable　geometric　anisotropy.　The　current　constitutive　relationship　based　on　a　quadrangular　columnar　structure　fails　to　truly　represent　the　natural　characteristics　of　the　CJB.　To　address　the　stability　problem　of　the　diversion　tunnel　at　the　dam　foundation,　the　mechanics　of　composite　materials　and　Goodman　superposition　principle　were　employed　to　establish　improved　three-dimensional　constitutive　relations　for　pentagonal　and　hexagonal　CJBs.　The　constitutive　relations　of　three　types,　including　the　quadrangular　prism　CJB,　were　optimized　by　considering　the　impact　of　transverse　joints　and　internal　staggered　zones.　The　mechanical　parameters　of　the　Baihetan　CJB　were　appropriately　evaluated　using　the　three　constitutive　relations,　and　the　achieved　results　demonstrated　that　the　determined　elastic　moduli　of　the　three　improved　constitutive　models　were　consistent　with　field　results.　Subsequently,　the　three　anisotropic　constitutive　models　were　employed　for　numerical　simulations　of　the　diversion　tunnel　excavation　in　the　Baihetan　CJB　stratum.　Strain　field　tests　were　conducted　at　different　locations　within　the　tunnel,　and　an　empirical　method　was　proposed　that　combined　statistical　data　on　the　shape　of　CJBs　at　the　site,　which　can　effectively　predict　the　deformation　of　the　surrounding　rock.　The　theoretical　and　numerical　results　provide　crucial　reference　values　for　engineering　optimization　design.　©　2023　Elsevier　Ltd