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The unloading relaxation caused by excavation for construction of high arch dams is an important factor influencing the foundation's integrity and strength. To evaluate the degree of unloading relaxation, the long-short term memory (LSTM) network was used to estimate the depth of unloading relaxation zones on the left bank foundation of the Baihetan Arch Dam. Principal component analysis indicates that rock characteristics, the structural plane, the protection layer, lithology, and time are the main factors. The LSTM network results demonstrate the unloading relaxation characteristics of the left bank, and the relationships with the factors were also analyzed. The structural plane has the most significant influence on the distribution of unloading relaxation zones. Compared with massive basalt, the columnar jointed basalt experiences a more significant unloading relaxation phenomenon with a clear time effect, with the average unloading relaxation period being 50 d. The protection layer can effectively reduce the unloading relaxation depth by approximately 20%.