Soil–Structure Interaction and Arching Effect for Buried Flexible Pipelines in an Induced Trench: Experimental and Numerical Investigation

Abstract

Flexible culverts have been widely used in underground engineering, but the deformation control of buried flexible pipelines during trench backfilling remains challenging. In this study, foamed concrete was introduced as a lightweight backfill material below the pipe springline, with a maximum relative height of 0.5 D , and its influence on pipe–soil interaction and soil arching behavior was investigated through 1 g physical model tests and numerical simulations. The soil arching effect was evaluated using the relative deformation of the pipe and the normalized vertical stress ratio λ = σ _v / σ _i within a 1 D range of crown, where λ _min and λ _max were used to characterize load reduction and stress concentration, respectively. Based on these indices, the influence of foamed concrete height, pipeline number, and pipe diameter ratio on earth pressure distribution and structural deformation were analyzed. The experimental data showed reasonable agreement with the numerical results in terms of the overall deformation pattern, internal force distribution, and stress redistribution characteristics, indicating that soil arching played a major role in governing the mechanical response of the pipe–soil system. The results show that foamed concrete placed below the pipe springline effectively reduced pipe deformation by improving support stiffness around the pipe invert and lower pipe region, but it also restrained the differential soil deformation required for the development of positive soil arching above the crown. Compared with the single-pipe configuration, the double-pipe configuration produced an overlapping arching effect between adjacent pipes and formed a double-arched stress redistribution pattern in the surrounding soil. Parametric analyses further indicated that the modulus and height of foamed concrete, pipe diameter, burial depth, trench base width, and pipe clearance significantly affected λ _min , λ _max , and the development of soil arching.