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At the bedrock section of the auxiliary shaft of the Tong-ting coal mine, the sidewall has varying degradation degrees in different parts. The part on which water flowed is barely corroded, whereas the moist part near the pouring joints is seriously corroded. We first studied the mechanism of this phenomenon by chromatography, X-ray diffraction, and energy-dispersive X-ray spectroscopy. We then used simplified models built by particle flow code software (i.e., particle flow code in three dimensions, PFC3D) to analyse how increasing degradation depth affects compressive strength and failure patterns. The results were as follows. (1) Gypsum and calcite in corrosive water were supersaturated. The part on which water flowed was protected by the crystallized precipitation on the concrete. By contrast, the degradation of the part where water flowed through pouring joints was aggravated by internal crystallization and dissolution. (2) PFC3D numerical simulation indicated that decreases in vertical ultimate stress were strongly linearly correlated with degradation depth. As for the −355.5 m damaged part, reinforcement should be conducted before degradation depth reaches 250 mm. (3) No obvious signs were observed prior to the failure of the corroded sidewall. Therefore, the development of degradation depth should be monitored before degradation parts are reinforced., U pomoćnom oknu rudnika ugljena Tong-ting u pojasu temeljne stijene pojedini dijelovi zida pokazuju različite stupnjeve propadanja. Područja na kojima je tekla voda malo su korodirana, dok su vlažni dijelovi uz izljeve izrazito korodirani. Mehanizmi te pojave najprije su proučavani kromatografijom, rendgenskom difrakcijom i energijski disperzivnom rendgenskom spektroskopijom. Veza između dubine korozije i tlačne čvrstoće te obrasca sloma analizirana je pojednostavljenim modelom utemeljenim na kôdu toka čestica (kôd toka čestica u tri dimenzije, PFC3D). (1) Voda je prezasićena s obzirom na gips i kalcit. Dijelovi preko kojih je voda tekla zaštićeni su precipitatom na betonu. Nasuprot tome, propadanje je pojačano kristalizacijom i otapanjem u nutrini izljeva. (2) Numerička simulacija modelom PFC3D pokazuje linearnu vezu između smanjenja vertikalnog maksimalnog naprezanja i dubine degradacije. Oštećeni dio na −355,5 m trebat će pojačati prije nego korozija dopre do 250 mm dubine. (3) Nisu bili uočeni jasni pokazatelji propadanja prije sloma korodiranog zida. Stoga treba pratiti napredovanje propadanja prije nego uništeni dijelovi budu ojačani.