Full-scale investigation into top-down construction of fully prefabricated structures retaining deep excavation

Given the scarcity of systematic field measurements for fully prefabricated top-down excavations, this study presents a comprehensive field investigation of a building basement excavation in Huzhou, China, integrating the TAD (Trench cutting Assembled Diaphragm wall) method with fully prefabricated top-down construction. Continuous monitoring examined lateral deflection of the retaining structure, strut axial forces, wall and column heave and settlement, and ground surface settlement. The fully prefabricated system outperformed conventional cast-in-place structures in deformation control. The ratio of maximum lateral deflection of the TAD wall to excavation depth ranges from 0.05% to 0.22%, and maximum ground settlement outside the excavation is limited to 0.46‰-1.5‰ of excavation depth. The prefabricated strut system combined with servo control achieves optimized distribution and active regulation of axial forces. Field data reveal a collaborative wall-strut-base slab mechanism: prefabricated struts take up load immediately, and the prefabricated base slab provides timely rigid restraint. Systematic comparisons with conventional cast-in-place diaphragm walls in Shanghai, Hangzhou, Suzhou, Boston, and global databases show that deformation indices of the fully prefabricated TAD system lie at the lower bound of statistical range. This study provides key field evidence and design references for fully prefabricated underground engineering.