Research conclusions: (1)The displacement in top of the front pile in portal double—row pile is obviously small than that of single—row pile and double—row pile without coupling beam，when the distance between two rows is big．(2)The max．moment and shearing force in the front pile are close to the back pile and the absolute value of positive moment and shearing force are close to the negative moment and shearing force．The coupling beam has an obvious effect on coordinating the moment and shearing force between the front pile and the back pile．(3)The parametem choice of the karst soil is an important influence factor on design of friction pile．(4)Portal double—row pile has lateral rigidity to effectively restrain the lateral deformation of exterior—protected construction．(5)To the side slope of expansive soil，the excavation and support should be conducted in time during engineering to reduce the disturbance of the water content and soil body by the engineering．(6)The numeral calculation should be adopted along with the experience for ensuring the stability of side slope．.