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The deformation of long–short supporting piles in soil–rock combined strata, which involves the cooperative working effect, is not easy to be analyzed by the theoretical method, and the deformation mechanism is not precise. Therefore, the deformation and mechanical characteristics of long–short supporting piles are investigated in this work by numerical simulation and field monitoring. The results show that for deep excavation in soil–rock combined strata, the lateral deflection curve converges rapidly below the excavation face, and the maximum point is located near the soil–rock interface. The bending moment of long and short piles increase simultaneously at each excavation stage, showing a remarkable cooperative working mechanism. The ratio number of long piles has a more significant impact on the internal force of the pile beneath the weathering line. Parameter analysis indicates the soil thickness and the rock deformation modulus have a considerable influence on the stability of deep excavation and the internal force of the supporting structure. For a given soil thickness, the embedded depth of long piles should be increased with increased softness and weathering of the underlying rock mass. Meanwhile, for deep excavation with thin overlying soil and hard rock mass, as described in this paper, the design of long–short supporting piles tends to be safe. The diameter of supporting piles and the number of short piles can be optimized to meet a reliable and economical design requirement, provided that the performance of the supporting structures can meet the design requirement in practice. [ABSTRACT FROM AUTHOR]