Surface settlement behavior due to various active trapdoors forms in granular soils

Nima Farasat; T. Newson

Publication Title
Surface settlement behavior due to various active trapdoors forms in granular soils

Abstract

ABSTRACT: Trapdoor models serve as analog systems to study soilstructure interaction in underground structures such as tunnels and pipelines. They replicate ground load redistribution when support elements yield, providing insights into arching and settlement mechanisms. This study investigates surface and sub-surface settlement behavior of active trapdoors under 60g in centrifuge experiments with dry sand with further investigation through numerical simulations. Physical models using medium sand with varying relative densities (D_r = 3090%) were tested. Additional tests examined modified trapdoor geometries using a flexible membrane and a rigid half-tunnel shape. Soil displacements were tracked using GeoPIV. Supporting finite element analyses employed a porous elastic cap plasticity model to simulate soil behavior. Results showed that increasing relative density led to shallower and narrower settlement troughs. A flexible boundary (membrane) configuration reduced surface deformation by redistributing stresses more evenly, whereas a half-tunnel circular shape produced sharper move, localized settlements due to stronger arching. Overall, the flexible boundary promoted smoother stress redistribution, while the half-tunnel showed intermediate behavior between the flexible and the traditional rigid trapdoor conditions. These findings demonstrate how density, and boundary flexibility and shape influence surface settlements during trapdoor actuation, providing practical insights for tunnel, pipeline, and trench model design in granular soils.

Authors
Nima Farasat; T. Newson

Published In

11th International Conference on Physical Modelling in Geotechnics (ICPMG2026)

Theme

Special Session 1: Physical modelling – from Practice/Industry to Academia