(0.1-5.0). Early stopping was applied to reduce overfitting, terminating training when validation performance did not improve for 25 consecutive boosting rounds. Three optimisation objectives were tested: maximisation of Kling-Gupta Efficiency (KGE), and minimisation of MAE and RMSE. KGE was computed as: = 1 − √( − 1)2 +( −1)2 +( −1)2 (Eq. 1) where is the Pearson correlation between observed and predicted Δ , = / is the bias ratio, and = / is the variability ratio. MAE was used for model selection because the target was the one-step deformation increment in millimetres, making errors directly interpretable. It is also less sensitive than RMSE to isolated large errors. RMSE was retained as a complementary metric, and KGE to assess correlation, bias, and variability. 3. RESULTS 3.1 MT-DInSAR time-series analysis MT-DInSAR vertical displacement time series were extracted for 85 monitoring points on the TSF dam. Figure 1 summarizes the spatial evolution of cumulative vertical deformation from 2020 to mid-2025, based on 166 Sentinel-1 acquisitions per point. In 2020, cumulative deformation is low in magnitude and spatially heterogeneous, with modest uplift over parts of the downstream flank and localized subsidence along the crest, consistent with early-stage operational conditions. In 2021, the pattern becomes more organized: uplift dominates the eastern and downstream portions, while a continuous subsidence develops along the crest and central dam body, consistent with simultaneous raising and consolidation. By 2022, deformation is characterised by widespread subsidence across the dam face, associated with primary and secondary consolidation of foundation soils. These are well-established geotechnical processes typically observed at laboratory scale, but here they are manifested clearly at field scale. From 2023 onwards, a spatially concentrated subsidence depression becomes evident, centred in the west–central sector and extending towards the downstream slope. This deformation footprint is spatially coincident with the Stage 4 construction period (April–November 2023) and persists into 2024–2025, indicating sustained settlement in the west–central sector, while the eastern flank remains comparatively more stable over the same period. 2020 2021 2022 2023 2024 2025
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