Abstract: Underpinning pile-soil nailing (UPSN), a composite structure of underpinning piles and soil nailing, is a new retaining technology. Base on the hypothesis that the underpinning pile top load is equal to the upper structural load with its settlement greater than that of the underpinning pile top, the retaining characteristics of UPSN are analyzed; and its deformation coordination mechanism and load transfer path are discussed. The computing methods of lateral deformation, vertical settlement and inner force are proposed. Parametric analysis shows that UPSN can obviously reduce the deformation and internal force of supporting structure compared to conventional composite soil nailing; the deformation and internal force increases as the upper structural load and horizontal spacing of the micro-pile increases; less affect as the embedded depth of micro pile increases.

Key words: underpinning pile, soil nailing, lateral deformation, settlement, deformation coordination