Wall deformation of a zone-divided deep excavation with concrete servo struts in Hangzhou soft clay

Traditional prestressed struts often suffer from axial force loss and challenges in force adjustment; in contrast, the effectiveness of servo steel struts in controlling excavation induced deformations is widely documented. However, conventional servo steel struts are limited in large or irregularly shaped excavations. To address this, concrete servo struts have emerged as an innovative alternative. This study investigated the supporting effects by comparing wall deformations associated with concrete servo struts against those of traditional concrete struts. The installation of hydraulic jacks on a single side of the concrete servo struts results in asymmetrical wall deformations. Specifically, the area adjacent to the hydraulic jack was defined as the Directly Supported Area (DSA), while the opposite end was termed the Indirectly Supported Area (ISA). Under the influence of the servo system, the wall deformation profile in the DSA exhibited a distinct S-shape, significantly differing from the deep-seated movements observed in the ISA and the Traditionally Supported Area (TSA). Monitoring results indicated that both DSA and ISA exhibited reduced wall deformations compared to those in TSA. The average maximum deformation was 0.11% of the excavation depth in the DSA, compared to 0.16% in the ISA and 0.29% in the TSA. Furthermore, post-installation data showed that deformation in the DSA remained stable or followed a downward trend, whereas deformations in the other two areas continued to increase. Notably, the depth of maximum wall deformation remained primarily governed by the on-site soil properties rather than the support type. Overall, concrete servo struts provide superior deformation control, particularly within the DSA. • The mechanism of wall deformation under concrete servo struts was revealed. • Deformation difference at both ends of the concrete servo strut was compared. • Average wall deformation to excavation depth ratio of concrete servo strut was 1.1‰. • Wall deformation of concrete servo strut was 38% of traditional concrete strut.