The　storage　of　liquefied　natural　gas　(LNG)　in　underground　coal　mine　tunnels　offers　numerous　advantages,　with　the　fracturing　characteristics　of　surrounding　rock　under　cryogenic　conditions　(−162　°C　at　the　lowest)　closely　tied　to　the　safety　of　the　storage.　However,　a　substantial　knowledge　gap　persists　within　the　entire　temperature　range,　presenting　a　significant　challenge　in　our　understanding.　The　innovation　of　this　work　lies　in　the　comprehensive　study　of　fracture　toughness　and　the　revelation　of　damage　mechanisms　in　both　dry　and　saturated　rock　across　a　complete　temperature　range　from　−162　to　20　°C.　Both　dry　and　saturated　cracked　straight-through　Brazilian　disc　(CSTBD)　sandstone　specimens　underwent　treatment　at　various　temperatures　(20,　−40,　−80,　−120,　and　−162　°C)　through　liquid　nitrogen　cooling,　with　subsequent　testing　of　fracture　toughness.　The　results　indicate　that　the　fracture　toughness　of　dry　sandstone　experiences　a　marginal　decrease　(∼5　%)　with　lowering　temperatures.　In　contrast,　the　reduction　in　fracture　toughness　for　saturated　sandstone　is　more　pronounced,　reaching　approximately　30　%　from　room　temperature　to　a　cryogenic　critical　temperature　(above　−40　°C).　Interestingly,　within　the　critical　temperature　range　to　−162　°C,　the　fracture　toughness　of　saturated　sandstone　remains　relatively　stable.　At　ultralow　temperatures,　dry　sandstone　exhibits　failure　cracks　that　are　more　crooked　due　to　shrinkage　damage.　On　the　other　hand,　saturated　sandstone,　subjected　to　ultralow　temperature　treatment,　displays　crooked　failure　cracks　with　branched　cracks,　attributed　to　frost　heaving　damage.　Consequently,　the　damage　mechanisms　under　cryogenic　conditions　are　identified　as　shrinkage　damage　and　frost　heaving　damage.　For　dry　sandstone,　shrinkage　forces　can　induce　some　microcracks　between　mineral　grains　and　cementation,　but　the　number　of　cracks　is　limited.　In　contrast,　both　shrinkage　and　frost　heaving　forces　can　lead　to　more　microcracks　in　saturated　sandstone.　Comparative　analysis　of　experimental　results　suggests　that　frost　heaving　damage　is　the　primary　mechanism　in　saturated　sandstone.　It＇s　important　to　note　that　for　sandstones　with　different　cementation　types　and　porosity,　the　main　damage　mechanism　may　vary,　requiring　further　research.　These　findings　contribute　to　a　more　accurate　stability　evaluation　of　LNG　underground　storage.　©　2024