English：

In the design and construction of foundation excavation engineering in composite soil and rockstrata, adopting the support form of long and short suspended piles without rock shoulders is an innovativeattempt compared to traditional pile⁃supported design schemes. However, due to the relatively fewpractical application cases of the long and short suspended pile support method, its force and deformationcharacteristics have not been fully studied and clarified in academia and engineering practice. This studyfocuses on the support effect and optimized design of the long and short suspended pile retaining structurein foundation excavation engineering of composite soil and rock strata, by constructing a three⁃dimensional numerical model based on actual engineering cases for analysis. The results show that theelastic fulcrum method, which considers soil and rock strata, can simulate to a certain extent the changesin the interaction between the soil within the pit and the supporting structure during the deformationprocess of the foundation excavation support structure, which is closer to the actual situation. Infoundation excavation with soil and rock strata, the support system of long and short suspended pileswithout rock shoulders and without prestressed anchors can ensure the stability of the support. Comparedwith traditional suspended piles, the support structure of long and short suspended piles in foundationexcavation with soil and rock strata exhibits different internal force and deformation patterns, with thepeak internal forces and displacements occurring in the soil layer area from the soil⁃rock interface to thesecond support. When implementing the support scheme of long and short suspended piles, it isrecommended that the embedment depth of the long piles should at least reach the level of the fourthsupport and be embedded into the slightly weathered rock layer. While the short piles are recommendedto be embedded up to the third support and ensure they are completely embedded into the moderatelyweathered rock layer. The deformation patterns of long and short suspended piles can be summarized intothree types. The first one for rock⁃embedded piles and suspended piles embedded in slightly weatheredrock layers,the second one for suspended piles embedded in moderately weathered rock layers, the thirdone for suspended piles embedded in strongly weathered rock layers and soil layers.