When tunnels in loess traverse sections of alternating soil and rock layers, variations in soil properties can induce an arching effect, potentially leading to the shear failure of the tunnel's structural components. Therefore, seismic design in these areas is particularly crucial. To address these challenges, this paper analyzes the mechanical behavior of damping joints under dynamic earthquake loads using a pseudo-static approach. Based on Bernoulli-Euler beam theory and Pasternak's dual-parameter elastic foundation beam theory, a closed-form solution is derived for the longitudinal response of tunnels in loess with damping joints under seismic loading. The solution is further validated through numerical modeling. Additionally, the study investigates the effects of filling materials (used in damping joints) and design schemes on the effectiveness of damping joints, supported by practical engineering cases. The findings indicate that installing damping joints can reduce the restraining forces on the tunnel lining, allowing the structure to better accommodate the deformation of the surrounding rock. Among the tested materials, rubber was identified as the optimal material for damping joints due to its excellent elasticity and energy absorption capacity. However, the exclusive use of damping joints may result in excessive localized deformation, potentially compromising the tunnel's normal operation. Therefore, careful design of these joints is essential. This research provides theoretical support for the seismic design of tunnels in loess in alternating soil-rock strata.

Rock joints in fault zones are commonly filled with fault gouge, where clay fillings are common. Until now, the shear characteristics of filled rock joints under different moisture contents and shear rates have not been well understood. This work investigates the mechanical behaviour of rock-like materials with clay-filled joints under compression-shear loading. A self-developed rock shear test system was used to conduct direct shear tests on rock-like materials under three normal stresses and five shear rates. Six types of natural red clay with different moisture contents were selected for filling. The coupling effects of the moisture content and shear rate on the mechanical properties of rock-like samples with clay-filled joints were investigated. Furthermore, the failure characteristics of the failure surfaces of rock-like materials after shearing were scanned via 3D scanning. The test results show that the moisture content of fillings and shear rate significantly affect the shear characteristics of rock-like materials with filled joints. The plastic limit moisture content is a critical point where the shear rate has the least effect on the shear strength. Under dry soil filling conditions, the degree of shear damage on the shear plane is the smallest. The present results can provide guidance for slope protection projects.

Due to the significant decrease in strength of loess after encountering water, loess landslides induced by rainfall are very catastrophic and widely distributed in the Chinese Loess Plateau. On September 17, 2011, a catastrophic loess landslide induced by rainfall occurred in Baqiao district, Xi'an, Shaanxi Province, China, resulting in 32 casualties and bringing great fear to the local residents. This landslide event was characterized by three individual landslides. Field investigations, geological exploration and model experiments were conducted to reveal its initiation and movement mechanisms. The results show that 1) Multiple groups of fissures in the ring-cut adits were found at a location 3 m inward from the slope surface. The minimum opening width of these fissures is 0.5 cm, and the maximum is 4 cm. The fissures develop nearly vertically and have good extensibility and connectivity. 2) the whole process of rainfall-induced landslides can be divided into 3 stages: rainfall infiltration and weight increase; crack expansion and slope deformation; slope collapse and creep deformation. 3) The volumetric water content, pore water pressure and vertical stress variation of the soil in our model all increase first and then decrease. Specifically, these three parameters increase slowly during the pretest and stabilization periods and increase fast shortly before the landslide occurrence. The volumetric water content of the soil on the side containing joints increases faster, verifying that the joints act as preferential channels that accelerate rainwater infiltration. The results of the study provide an important scientific foundation for future research on rainfall-induced loess landslides and their deep-seated mechanisms, and fill the gaps in research related to large-scale physical modeling experiments.

Buried cast iron pipelines are susceptible to damage at joints under fault movements. In this paper, a new three-dimensional soil-pipe continuum model for segmented pipelines undergoing fault rupture is introduced, in which both the nonlinear behavior of lead-caulked joints and post-peak softening behavior of dense sand are properly characterized. The rationality of the developed numerical model is validated against experimental results reported in the literature. Parametric analyses indicate that ignoring the strain softening behavior of soil would underestimate the maximum joint rotations, and the parameters of fault-pipe inter angle, cast iron-lead adhesion, and burial depth play a notable role on the magnitude of joint kinematics. Numerical fault rupture analyses are then conducted for cast iron pipelines with nominal diameters ranging from 900 to 1500 mm. Based on the numerical results, predictive solutions are developed for estimating the maximum axial translations and joint rotations under fault movements. The residuals of the proposed solutions are generally unbiased. The proposed solutions can be used to evaluate the maximum joint kinematics in terms of axial translations and joint rotations for largediameter cast iron pipelines with lead-caulked joints undergoing strike-slip fault ruptures.

The fault dislocation produces severe additional deformation on cross-fault tunnels along the axial direction, seriously threatens tunnel safety. To this end, a simplified analytical model for evaluating the mechanical behavior of segmental tunnels subjected to buried fault dislocation was established. The segmental tunnel is treated as a Timoshenko beam acting on the Vlasov elastic foundation. The plastic yield of circumferential joints, the effect of frictional resistance along the axial direction, and the deformation characteristics of overburden soil after faulting were considered. Then, the reasonability of the analytical solution is proved by 3D numerical simulation. The tunnel safety state was evaluated based on the joint deformation of the segmental tunnel. Subsequently, the effects of plastic yield behavior between segmental rings, plastic equivalent bending stiffness ratio, segment dimensions, and longitudinal bolt on the longitudinal response of the segmental tunnel linings were investigated. The results show that the simplified analytical solution proposed is reasonable in predicting the joint deformation between segmental rings when the segmental tunnel is subjected to buried fault dislocation. When the normal faulting is imposed, the segmental tunnel is dominated by tensile deformation along the tunnel axial. Under 20 cm of normal faulting, the joint opening between segmental rings is close to the deformation control value of joint waterproofing. However, the shear deformation has been significantly weakened due to the effect of faulting in the propagation process to the surface. The calculation result is too small when the plastic deformation behavior is ignored. The plastic equivalent bending stiffness ratio eta 2 inversely correlated with the maximum joint opening. Increasing the strength grade or the number of longitudinal bolts has a relatively limited effect on reducing the opening between segment rings, where the joint still has a greater risk of water leakage.

This paper proposed a new method for modelling joints, using anisotropic plate elements and elastic bar elements to address the issue that joints between panels are usually disregarded in numerical modelling. For small-scale deep excavations, which are frequently performed in the construction of various working shafts but have not been sufficiently studied, two numerical models were developed, using the No.1 Shaft of Tongtu Road Utility Tunnel in Ningbo, China, as a research object. One model considered the joints between the panels as proposed, while the other disregarded the joints as conventional. In comparison to the conventional method, the proposed method was validated due to yielding wall displacements that closely matched the results of the field monitoring, with a notable reduction in the error observed in the calculated displacements for the short side of the excavation. Furthermore, 34 numerical models were developed in order to investigate the influence of excavation length, depth, and diaphragm wall thickness on the relative differences between the calculated displacements obtained by the two models. The results of this study can provide references for the development of finite element models for designing small-scale deep excavation.

This paper presents an improved longitudinal beam-spring model on the Vlasov foundation for estimating the longitudinal deformation of the shield tunnel when subjected to the ground surface surcharge. This model incorporates an improved subgrade modulus and treats each segmental ring as a Timoshenko short beam, with each circumferential joint modeled by two mechanical springs. It can accurately reflect the discontinuous deformation, and capture the dislocation and opening deformation of shield tunnels. Two-stage analysis methodology is adopted to consider soil and tunnel interaction. The feasibility of this model is verified by comparing it with two well-documented field monitoring cases. The computed results are also compared with those based on other analytical models. The results show that the Timoshenko continuous beam overestimates the dislocation deformation, while underestimates the opening deformation. In addition, the settlement curve exhibits neither smooth nor differentiable features. Finally, this paper also conducted some parameter analysis to examine the impact on tunnel deformation, encompassing dimensions of ground surface surcharge, the dual-area loading, and the joint reinforcement. This approach provides valuable insights into how the deformation characteristics of shield tunnels are influenced by ground surface surcharge.

A new numerical-based fragility relation for cast iron (CI) pipelines with lead-caulked joints subjected to seismic body-wave propagation is proposed in this article. Two-dimensional 1600-m-length finite element models for pipelines buried in sand are developed in OpenSees. Parametric analysis is performed to investigate the influence of various parameters on the damage estimates of the buried pipelines. Numerical analyses are conducted to estimate the repair rates (RR) for CI pipelines subjected to wave propagation. The predictive model for RR is thus developed based on the numerical results and the Gaussian Process Regression approach. The model developed employs four predictor variables, namely, the peak particle velocity and wave propagation velocity along axial direction, the maximum soil shear force per unit length, and the outer diameter of pipelines, exhibiting desirable performance in terms of predictive efficiency and generalization. The performance of the developed relation is compared to several existing fragility relations. The new fragility relation can be used to estimate RR for CI pipelines with lead-caulked joints with outer diameters ranging from 169 to 1554 mm subjected to seismic body-wave propagation.

Reinforced concrete pipes (RCP) are the mainstay of urban water transmission networks. Urban development entails increased potential for blasting activities (such as subway tunneling, excavation, and demolition) as well as the risk of accidental explosions. This paper provides a detailed description of the damage evolution and deformation process of RCP under explosive loads using validated numerical simulation methods. A concise phenomenon-based method is introduced for RCP damage grading. Furthermore, a comparative analysis is conducted on the damage and deformation of RCP resulting from explosions at different locations and with varying weights. At last, this paper especially investigates and explains the impact of four commonly used joint types on the RCP's response to explosions. The research results help to enhance the understanding of damage evolution and deformation behavior of RCP (or similar structures) induced by explosion, and are also references for protection, repairing and failure identification of segmented structures subjected to explosion.