Depth-Resolved Deformation Monitoring and Short-Term Forecasting with Multipoint Extensometers in Hydraulic Tunnels

Multipoint extensometers measure rock movement at several depths, but channel plots can obscure changes between anchors. We linked exported readouts to conversion coefficients, formed adjacent-anchor states and forecast the next reading using actual observation intervals. Records from a pumped-storage water-conveyance system comprised 20 instruments, 65 channels, 45 segments, 2898 segment observations and 2667 forecast samples. Numerical reconstruction matched 4209 of 4211 displayed displacements within 10−6 mm; it did not independently calibrate the instruments. We assessed 84 seven-day forecasts on two later monitoring dates. Direct ExtraTrees residual correction gave the lowest mean absolute error (MAE), 0.024819 mm. A validation-selected magnitude gate changed 13 forecasts and reduced MAE from the persistence value of 0.026113 to 0.024915 mm (4.59%). A lagged linear comparator gave 0.026001 mm. The gated nominal 95% interval covered 82/84 observations and was 10.38% narrower than the persistence interval at the same observed coverage; common-calendar calibration covered only 77/84. Instrument-held-out refitting improved 2 of 19 instruments. Source-linked segment states support depth-specific record review. The small forecast gain should be treated as a local analytical result until calibration, independent monitoring rounds and an instrument-level uncertainty budget are available.