Steel　slag,　a　by-product　of　steelmaking,　can　be　used　as　backfill　material　for　energy　structures,　and　the　granite　residual　soil　is　a　common　soil　type　in　civil　infrastructure.　The　thermal　conductivity　of　backfill　materials　and　soils　surrounding　the　piles　is　the　crucial　parameter　which　has　influence　on　the　heat　transfer.　In　this　paper,　the　steel　slag　and　granite　residual　soil　were　treated　by　enzyme-induced　carbonate　precipitation　(EICP)　and　the　effect　of　the　different　number　of　treatment　cycles　(N)　on　the　thermal　conductivity　of　EICP-treated　specimens　was　also　investigated.　The　thermal　conductivity　was　determined　by　the　transient　plane　source　method　(TPS).　Moreover,　X-ray　diffraction　(XRD)　and　scanning　electron　microscope　(SEM)　tests　were　carried　out　to　investigate　the　microstructure　of　the　EICP-treated　specimens.　The　results　showed　that　the　thermal　conductivity　of　steel　slag　and　granite　residual　soil　specimens　can　be　significantly　enhanced　using　EICP　treatment.　The　thermal　conductivity　of　bio-cemented　specimens　increased　as　the　N　increased.　The　maximum　values　of　thermal　conductivity　were　obtained　for　steel　slag　with　a　particle　size　=　0.55 mm,　CCC　=　6.17%　and　N　=　12,　and　for　granite　residual　soil　with　density　=　0.7 g/cm3,　CCC　=　3.38%　and　N　=　12.　The　heat　transfer　mechanism　was　revealed　through　microstructure　analysis　and　it　was　discussed　how　the　different　patterns　of　CaCO3　crystal　precipitation　caused　the　different　ratios　of　thermal　conductivity.　©　2023,　The　Author(s),　under　exclusive　licence　to　Springer-Verlag　GmbH　Germany,　part　of　Springer　Nature.