Axial Force Coherence Study of Servo Steel Strut Loading in Soft-Soil Deep Excavation

The coherence of axial force between steel struts in excavation (axial force coherence) is an important factor affecting the axial force control of servo struts. To understand the law of axial force loss of adjacent struts caused by servo struts loading, this paper proposes a calculation method based on the theory of nonlimiting earth pressure. First, the diaphragm wall is simplified to a simply supported beam with both endpoints free horizontally, the soil on both sides of the diaphragm wall is divided into n small sections ( n as big as possible) along the depth direction, and the average nonlimiting earth pressure combined force within each section is calculated. Second, a system of nonlinear force-displacement equations is constructed by applying the “graph multiplication” method to calculate the combined nonlimiting soil pressure and deflection of the wall from the axial force of the servo steel strut at each level. The Newton–Raphson method is applied to obtain a recursive equation for the wall displacements. The accuracy of the method is verified by comparison with field measurements. Then, based on the method in this paper, the effect of prestressing and adjustment on the axial variation of each strut course is investigated. The method can provide a reference for the loading scheme of servo steel struts in deep excavation in soft-soil areas.