<p>In the construction and renovation processes of underground spaces in dense urban environments, there is an increasing demand for space-intensive layouts and special-shaped cross-sections. To address the requirements for special-shaped cross-section design and lightweight structures, this study, against the backdrop of construction of underground road ramp junctions, proposes a servo structural agent for special-shaped cross-sections and its underground excavation method with no foundation pit construction by integrating traditional underground structures with intelligent perception and servo strut control. This agent embeds servo components into the structural system and performs active force control through sensing of stress and deformation. Compared with traditional structures, servo structural agent can adaptively balance the load changes induced by excavation, thereby reducing component size and deformation. On this basis, an undercutting construction method and process are proposed, utilizing dual shield tunneling parallel construction and underground excavation to replace the traditional large working shaft schemes. Through numerical simulations of typical conditions, the servo structural agent is shown to reduce maximum deformation by 30% and peak internal forces by 10%. The related work provides novel approaches for underground excavation construction and safety control in urban areas with dense underground road networks.</p>