Two-dimensional physical modelling of soil displacements above trapdoors

Geosynthetic reinforcement has been increasingly used over voids or piles in soft soil to support embankments and minimise differential settlement. Due to differential settlement, soil arching is formed and less pressure is applied onto the reinforcement. This problem is often simulated using trapdoor tests. The reinforcement effect on displacement and soil arching has not been fully understood. In real applications, multiple voids or multiple spans of piles exist under embankments. The effects of multiple voids or spans of piles on displacement and soil arching have not been well investigated. This paper reports a series of two-dimensional trapdoor tests conducted to investigate soil displacements above single and double trapdoors without or with reinforcement. Analogical soil, made of aluminium bars, was used as embankment fill. Paper was used as reinforcement. Two different embankment heights were investigated. The experimental tests showed that both embankment height and reinforcement reduced the vertical displacement on the top of the embankment, and higher embankment caused more soil failure at the edge of the stationary support but reduced the vertical stress on the reinforcement. The maximum tensile strain happened at the edges of the trapdoor. Trapdoors spaced at twice the trapdoor width did not cause much interaction between each other.