• HSI enables in-situ, non-destructive determination of real CPB concentration after curing, addressing the gap left by core sampling and strength tests.
• Spectral reflectance of CPB increases with concentration from 61wt% to 73wt%, with characteristic absorption peaks at 1407 and 1917 nm; reflectance at 1407 nm correlates linearly with concentration.
• SVM achieved superior classification accuracy (98.24%) compared with optimized KNN (95.03% at K=3), providing stable and precise concentration identification.
• The proposed method supports intelligent backfill control and goaf stability management, reducing risks from concentration deviations caused by groundwater inflow and segregation.