Optimization of Zoned Excavation and Servo Strut Systems for Deep Excavation Groups Adjacent to Historic Buildings in Soft Soil

Deep excavation groups in soft soil can endanger adjacent historic buildings. This paper presents a 3D finite element analysis of a project in Ningbo, employing the HSS constitutive model. Three excavation schemes were compared. The small-zone staged excavation from near to far proved optimal: relative to the conventional large-block scheme, it reduced maximum wall displacement on the heritage-building side by 37.0% and building tilt by 54.0%; servo struts were then introduced in the critical sub-excavation and optimized via response surface methodology. A layered control hierarchy was revealed—wall bulging is governed by the third and fourth struts (F3 ≈ F4 > F2), and mean settlement by the third strut (F3 > F2 ≈ F4). Building tilt control relies on synergistic action of all three struts (F3 > F2 > F4), with significant antagonistic interactions among struts at high force levels. The optimal combination (F2 = 1200 kN, F3 = 1800 kN, F4 = 1550 kN) limits maximum tilt to 0.380‰, well below the 1.0‰ code limit, and remains robust under various weighting scenarios.