This paper introduces thirteen kinds of typical excavation failures widely encountered in practice in China along with corresponding failure mechanisms and damages to adjacent structures and facilities. Emphasis is placed on investigation of longitudinal slip failure during excavation of subway station, which frequently occurs but rarely receives serious attention. This investigation is based on a sliding event in Hangzhou, China, in which a soft earthen slope about 13 m high inside an uncompleted subway station underwent massive slip failure. Slide debris travelling on sloped terrain caused the detachment of braced steel pipe struts and breakage of interior columns and two concrete struts atop them. Fortunately, an efficient contingency plan was executed right after the event; thus, potential catastrophic collapse of the entire earth supporting system, a domino effect of the massive sliding, was avoided. Postfailure investigations in terms of ground survey, visual inspection, and numerical analyses show that for this three-step earthen slope with an overall slope gradient (including benches) of 1 vertical (V) to 3 horizontal (H) ($1\mathrm{V}:3\mathrm{H}$ ), the sliding took place at the uppermost 6-m slope and there was no sign of sliding in the lower 7 m of slopes ($1\mathrm{V}:2\mathrm{H}$ ) atop firm to stiff clayey strata. The steep local slope gradient ($1\mathrm{V}:1.75\mathrm{H}$ ) of the uppermost slope overlying weak muddy clay was the predominant factor triggering the sliding; probabilistic stability analyses indicate a high slip failure probability of 88.92%. Degradation of soil strength resulting from soil deformation was mitigated by negative excess pore water pressure associated with excavation (unloading); consequently, the uppermost slope did not show signs of potential sliding during the excavation. Following postexcavation dissipation of negative excess pore water pressure accompanied by decreasing of soil shear strength, the uppermost slope underwent an abrupt sliding failure 7 days later. Apart from its recognized effectiveness in limiting lateral wall displacement, quick soil removal was helpful for keeping the soft earthen slope temporarily stable during excavation. To ensure stability of soft earthen slopes underlain by weak subgrades, a slope gradient no steeper than 1V:3H is essential. Based on sensitivity analysis results, optimal slope angles corresponding to strength parameters of soft subsoils are proposed for future excavations. To prevent slip failure of soft earthen slopes, one cost-effective solution is to install recyclable steel sheet pile vertically penetrating through a potential slide at the deepest point of the estimated critical slip surface.

An algorithm for calculating the effective ratio of the transverse bending rigidity is established based on the segment longitudinal joint bending stiffness. With the knowledge of this effective ratio, the bending rigidity of a modified uniform rigidity ring is fully defined. To verify this developed algorithm, the effective ratios and convergence deformations of the modified uniform rigidity rings obtained with different methods are compared. Moreover, the responses of the modified uniform rigidity ring model under loading obtained from this algorithm are compared to those obtained with the existing generally accepted beam-spring model. The results show that although the bending moments obtained from these two models are different, the axial forces, horizontal convergent deformations, and vertical convergent deformations are quite consistent with each other. The modified uniform rigidity ring model built on the developed effective ratio algorithm is applicable for the analysis of the tunnel convergence deformation and the interaction between the tunnel structure and the ground during operation. This modified uniform rigidity ring model is simpler and easier to use than the beam-spring model; thus, the significance of the developed algorithm for the effective ratio of the transverse bending rigidity is demonstrated.

Composite laminated bolted joints are increasingly used in the aerospace industry, and most researchers are involved in the study of the failure behavior of composite bolted joints’ structures. Because of the complexity and stability of the structure, precisely predicting the damage evolution and failure behavior of the composite laminated bolted joint becomes rather difficult. In this paper, an asymptotic damage model is proposed to predict the failure behavior of the composite bolted joint structure. The model is based on the frame of mainstream criteria and some improvements are made to adapt to the particularity of composite laminated bolted joints. Combining the damage model with the finite element method, the failure behavior of single-lap and double-lap bolted joint structures are predicted and analyzed. In order to guarantee the reliability of the model, the corresponding experimental study is conducted, and the results show that the simulation curve and the experimental data are in good agreement. This damage model can further predict the failure behavior of various types of complex composite laminated bolted joints effectively.

The prediction of settlement is of great significance to tunnel management during operational periods. The permanent settlement of Hangzhou Qingchun Road crossing-river tunnel under traffic loading is investigated in this paper. A simple and practical prediction formulation for engineering practice is proposed. The proposed formulation takes the effect of principal stress rotation into consideration, which is not considered in a previous formulation. This formulation is validated by tests results, and the constants in formulation are determined. The stresses in subsoil induced by traffic loading are calculated through a three-dimensional dynamic finite-element analysis. Then the permanent settlement of a typical section of the crossing-river tunnel is calculated using the calculated stresses and proposed formulation. The predicted permanent settlement is in fairly good agreement with the field monitoring data. The presented prediction method can be a practical approach for engineering practice.

An analytical formulation involving residual force is proposed to predict the displacement of an existing structure by simplifying the tunnel as an infinite Euler–Bernoulli beam resting on a two-parameter Pasternak foundation. The feasibility is confirmed by two actual measurements at sites in the published literature. Parametric studies—including consideration of jacking force alone, jacking force and ground loss, and jacking force and equivalent bending stiffness—are carried out to study the influence on the deformation of the existing tunnel. The results show that the residual jacking force can decrease the settlement of the existing tunnel, but the significance of its effect varies under different engineering conditions. With the increase in ground loss, the beneficial effect of jacking force in preventing further aggravation of tunnel settlement gradually becomes obvious, and the jacking force can reduce the deformation more effectively when the tunnel has lower bending stiffness. As a result, it is recommended that some effective measures should be adopted to maintain sufficient residual jacking force in the segments, so as to prolong the life of the tunnel.