Supporting structure of expansive soil excavation slope and construction method

The invention provides an expansive soil excavation side slope supporting structure and a construction method. The expansive soil excavation side slope supporting structure comprises a plurality of graded side slopes, an intercepting ditch is formed in the slope top of the uppermost side slope, and a foot protection retaining wall is arranged at the slope bottom of the lowermost side slope; inter-stage platforms are arranged between the adjacent side slopes, and platform drainage ditches are formed in the inter-stage platforms; a plurality of main sewers supported by sand-free water-permeable concrete are longitudinally and uniformly distributed in each stage of side slope, a plurality of herringbone branch sewers supported by sand-free water-permeable concrete are transversely and uniformly distributed among the main sewers, the branch sewers are communicated with the main sewers, the main sewers and the branch sewers divide the side slope into a plurality of areas, and grass is sprayed and planted in each a