Predicting Wall Deflections for Deep Excavations with Servo Struts in Soft Clay

Axial forces can be artificially adjusted in deep excavations braced with servo struts to reduce excavation-induced deformations. The interactions among the servo strut, retaining wall, and retained soil must be considered to predict the excavation-induced deformations and axial force adjustment. According to the beam-spring model, this study advances a simplified method to calculate the wall deflections generated by excavation with adjustable axial forces in struts. The proposed method incorporates the coupling relationship between the alterations in the earth pressure and wall displacement to consider soil-wall interactions. A mixed boundary, including force boundary and spring boundary, is introduced in the equilibrium equation to simulate the adjustable forces in the servo struts. The recommended method accounts for the soil-wall-strut interactions. Two real excavation cases supported by traditional and servo steel struts, respectively, validate this study's findings. Comparisons between the predictions and measurements demonstrate the effectiveness of the proposed method. Projections and measurements indicate that the servo struts reduce the maximum wall deflection, which decreases significantly with the increased axial force. Importantly, the retaining wall moves outside the excavation if excessive axial forces are applied in the servo struts. (c) 2023 American Society of Civil Engineers.