Red　clay　was　a　special　roadbed　filling　soil　that　was　easy　to　expand　and　shrink　because　of　the　characteristics　of　high　liquid　limit　and　high　porosity,　leading　to　the　appearance　of　a　large　number　of　cracks.　In　order　to　understand　the　cracking　mechanism　and　nonlinear　fracture　failure　process　of　red　clay,　the　fracture　toughness　and　crack　sensitivity　of　red　clay　with　different　saturation,　compaction　and　gravel　content　were　analyzed　by　three-point　bending　cracking　experiment　and　Image　processing　technology,　and　then　the　cohesive　crack　model　was　established　to　describe　the　fracture　toughness.　The　results　showed　that　the　cracking　process　of　red　clay　could　be　divided　into　three　stages:　crack　incubation　period,　crack　initiation　and　propagation　period　and　visible　cracks　appearance　stage.　There　was　a　conic　function　relationship　between　fracture　toughness　and　saturation　and　a　positive　correlation　between　fracture　toughness　and　compactness.　The　influence　of　gravel　content　on　the　final　fracture　path　of　red　clay　was　the　most　significant,　while　the　effects　of　saturation　and　compaction　could　be　ignored.　In　addition,　the　fracture　toughness　converted　from　the　cohesive　crack　model　was　basically　as　the　same　as　the　measured.　This　work　provided　a　basis　for　theoretical　analysis　and　numerical　calculation　for　the　fracture　toughness　of　red　clay　under　three-point　bending.　©　2024　Elsevier　Ltd