An apparatus and procedure for 1-g modeling of press-in assembled open caisson shaft construction in soft urban underground spaces

Abstract

As metropolises expand, to accommodate infrastructure such as transport systems, ventilation networks, and utilities, underground spaces must be developed. In congested metropolitan cities characterized by soft ground conditions, press-in methods for open caisson shafts have emerged as a preferred construction technique. However, the geotechnical response of surrounding soils especially in heterogeneous grounds remains complex and insufficiently understood during press-in assembled open caisson construction. This paper presents a 1-g modelling apparatus and procedure for simulating press-in assembled open caisson construction. The system replicates vertical sinking and staged excavation processes while allowing detailed observation of soil displacement and settlement. Transparent soil was prepared to replicate silty clay and clay region from silica-based mixtures with matched refractive indices. Soil displacement fields in real time were captured using combined laser assisted imaging with Digital Image Correlation (DIC) system. Results reveal typical behavior in silty clay with deformations localized near the cutting edge and remained comparatively restricted with penetration, indicating partial drainage and a stiffer response. However, clay revealed wider propagation zones and larger displacement magnitudes at deeper penetration, consistent with plastic flow and undrained softening. This apparatus effectively investigated soil-structure interaction during caisson installation, showing the substantial influence of soil strata and penetration depth on ground movements. For future studies it offers a platform for improving predictive modeling, geotechnical design, and risk mitigation in urban underground construction.