Deformation Response of Retaining Walls to Axial-Force Regulation in Deep Excavations with Servo Steel Struts

Servo steel struts enable active adjustment of support forces during deep excavation, but the retaining-wall response to force adjustment and the influence of spatial force allocation among multiple struts remain insufficiently understood. This study investigates a soft-soil deep excavation supported by multiple servo steel struts using a two-dimensional finite-element model validated against field wall-deflection measurements. The analysis progresses from individual-strut adjustment to two-strut force combinations and four-strut force allocation, followed by an assessment of the influence of small-strain soil-parameter variation. Results show that the effectiveness of individual-strut regulation depends strongly on excavation stage and strut depth. As excavation proceeds, the influence of upper struts decreases, whereas deeper struts become increasingly effective. At Stage 8, increasing the force of Strut 7 from 300 to 1000 kN/m reduces the maximum wall deflection and maximum bending moment by approximately 25% and 39%, respectively. For two-strut regulation, different force combinations produce relative variations exceeding 30% in maximum wall deflection and 50% in maximum bending moment in some later-stage cases. Under a prescribed total four-strut force, low-deflection configurations exhibit a nonuniform and sequential allocation tendency, with additional force preferentially assigned to deeper struts before extending upward. Soil-parameter variation changes the magnitude and dispersion of the regulation benefits, with a more pronounced influence on bending-moment response than on wall deflection. These results highlight the combined importance of excavation stage, strut depth, and spatial force allocation in servo-strut regulation.