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As a novel type of supporting system, servo steel struts have been employed frequently in deep excavations adjacent to important infrastructures. However, the studies concerning the effect of servo steel struts on restraining deformation have not been consummated, and further detailed explorations are required. This study presents the performance of a deep excavation with servo struts based on on-site measurements, including wall deflections, ground settlements, and axial force of struts. To analyze in-depth the supporting effect of servo struts on restraining deformations, the wall deflections and ground settlements obtained from field observation are compared with those in existing studies. Furthermore, the behaviors of conventional struts and servo steel are numerically analyzed and compared. The results indicate that compared with conventional struts, servo steel struts can effectively bring the wall deflections caused by excavation under control. Installation of servo steel struts is an effective measure to reduce the rate of ground settlements but has little effect on the overall settlement trend. Different from the conventional struts, the upper part of the wall is pushed back by servo steel struts, resulting in a wall deformation in an S-shape and increasing the maximum deformation depth. The negative bending moments against the upper part of the wall are significantly greater than those supported by conventional struts. [ABSTRACT FROM AUTHOR]

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• Developed a hydraulic loading system to carry out a full-scale loading test. • The asymmetric unloading load of the three-ring segment is realized. • The influence of initial confining pressure loading method is considered. • The influence of foundation pit excavation on tunnel structure is explored. To explore the internal force and deformation response law of the Hangzhou subway shield segment under the influence of the excavation and unloading of the side foundation pit, the self-developed "shield segment hydraulic loading system" was used to carry out full-scale loading tests on the three-ring staggered assembled segments. A preloading loading test were performed before the formal experiment to determine the loading method of the initial confining pressure. Analyzed the change mechanism of the internal force and deformation of the segment structure are influenced by factors such as the foundation pit and the tunnel clear distance. A numerical model is established based on the experimental results, and the influencing parameters that are difficult to complete in the experiment, such as the depth of the tunnel, are analyzed in detail. The research results show that the equal load maintains a balanced state of the segment to the greatest extent, and its internal force and deformation results are large, which is suitable for this experiment. After the excavation of the foundation pit, the maximum positive and negative bending moment increases, while the maximum axial force decreases. The average maximum recovery rate of tunnel section is 15.6%. Moreover, the additional internal force and deformation of the segment will increase with increasing deformation parameters of the envelope structure and decrease with increasing clear distance between the foundation pit and the tunnel. The bending moment of the segment is more sensitive to changes in the confining pressure, the convergence change can be controlled within a limited range, and the trend of the change in the internal force of the bolt shows differences. The numerical model established in this paper can better analyze the stress state of the tunnel. When the tunnel is buried deep in the slightly upper position of the excavation surface of the foundation pit, the unloading effect that is received is largest. [ABSTRACT FROM AUTHOR]

For piggyback pipelaying operations, current-induced force and its effect on the piggyback pipe have not been thoroughly studied. In the present study, an improved method in hydrodynamic load calculation and structural modelling is proposed to simulate the pipelaying of a piggyback pipeline. In order to obtain the mean drag and lift force coefficients for the piggyback pipeline subjected to different inflow angles, two-dimensional Computational Fluid Dynamics (CFD) simulations are performed by modelling the piggyback pipeline as two cylinders attached to each other without gap. Then, the acquired force coefficients are used to calculate the hydrodynamic loads through a user-defined function in OrcaFlex based on a cross-flow principle approach. The interaction between the pipeline and the piggyback cable is modelled using two types contact elements which are ring penetrator and non-penetrating contact. The present proposed method is compared with other two widely used engineering methods based on (1) the equivalent diameter and (2) two separate cylinders without accounting for hydrodynamic interaction, in terms of the top tension, and the bending moments at Hang-off Clamps (HOC) and sagbend of the pipeline. The comparison shows that the two widely used engineering methods are not always conservative in force and response predictions. Hence, it is important to consider the hydrodynamic and structural interactions between the piggyback cable and the pipeline. With different current directions, the bending moments at the HOC predicted by the present method vary from 40% lower to 100% higher than those predicted by the two widely used engineering methods. • The influence of piggyback pipeline modelling methods on the calculation of installation loads in deepwater is investigated. • An improved method that considers the interactions between the pipeline and the piggyback cable is proposed. • Drag and lift coefficients on the pipeline and piggyback cable are computed using 2D CFD simulations of flow past two adjacent smooth circular cylinders. • A user-defined function is implemented to calculate the hydrodynamic forces on the pipeline and the piggyback cable. • The proposed model can capture the hydrodynamic and structural interactions between the pipeline and the piggyback cable. [ABSTRACT FROM AUTHOR]

In order to research the theory for the variety of transverse forces of the adjacent shield tunnels caused by foundation pits excavation, the effect mechanism of foundation pit excavation on the adjacent shield tunnel was analyzed. The sidewall unloading model of the foundation pit, considering the deformation of the retaining structures, was introduced to calculate the additional stress of soil caused by foundation pit excavation. On this basis, the additional confining pressure variation model of the adjacent shield tunnel was established, considering the influence of the longitudinal deformation. Take the deep foundation pit project by the side of the shield tunnel of Hangzhou Metro Line 2 as a case study, the variation in confining pressure distribution of the adjacent shield tunnel caused by foundation pit excavation was analyzed, and a simplified finite element model was established to calculate the internal force of the segment ring structure. Moreover, the influence factors were analyzed, such as the deformation of the foundation pit retaining structure, the clearance between the foundation pit and the adjacent tunnel, and the buried depth of the tunnel. The present study suggests that the foundation pit excavation reduces the confining pressure of the adjacent shield tunnel, increases the absolute value of bending moment and shear force, and decreases the axial force at the top and bottom of the tunnel's segment ring. With the increase in the deformation of the foundation pit's retaining structure, the absolute value of the additional confining pressure on the adjacent tunnel increases, and the response of the bending moment to the foundation pit excavation unloading is more obvious than the variation in the confining pressure. When the buried depth of the adjacent shield tunnel is deeper than the excavation depth of the foundation pit, the influence of the excavation on the tunnel will be obviously weakened. With the decrease in the distance between the pit and tunnel, the influence of the excavation on the tunnel will be enhanced. [ABSTRACT FROM AUTHOR]