Search Results (3)

Seismic intensity measures (IMs) can directly affect the seismic risk assessment and the response characteristics of underground structures, especially when considering the key variable of burial depth. This means that the optimal seismic IMs must be selected to match the underground structure under different buried depth conditions. In the field of seismic engineering design, peak ground acceleration (PGA) is widely recognized as the optimal IM, especially in the seismic design code for aboveground structures. However, for the seismic evaluation of underground structures, the applicability and effectiveness still face certain doubts and discussions. In addition, the adverse effects of earthquakes on tunnels in soft soil are particularly prominent. This study aims to determine the optimal IMs applicable to different burial depths for horseshoe-shaped tunnels in soft soil using a nonlinear dynamic time history analysis method, and based on this, establish the seismic fragility curves that can accurately predict the probability of tunnel damage. The nonlinear finite element analysis model for the soil–tunnel interaction system was established. The effects of different burial depths on damage to horseshoe-shaped tunnels in soft soil were systematically studied. By adopting the incremental dynamic analysis (IDA) method and assessing the correlation, efficiency, practicality, and proficiency of the potential IMs, the optimal IMs were determined. The analysis indicates that PGA emerges as the optimal IM for shallow tunnels, whereas peak ground velocity (PGV) stands as the optimal IM for medium-depth tunnels. Furthermore, for deep tunnels, velocity spectral intensity (VSI) emerges as the optimal IM. Finally, the seismic fragility curves for horseshoe-shaped tunnels in soft soil were built. The proposed fragility curves can provide a quantitative tool for evaluating seismic disaster risk, and are of great significance for improving the overall seismic resistance and disaster resilience of society. Full article

Accurately estimating the stability of horseshoe tunnel faces remains a challenge, especially when excavating in rock masses. This study aims to propose an analytical model to analyze the stability of the horseshoe tunnel face in rock masses. Based on discretization and “point-by-point” techniques, a rotational failure model for horseshoe tunnel faces is first proposed. Based on the proposed failure model, the upper-bound limit analysis method is then adopted to determine the limit support pressure of the tunnel face under the nonlinear Hoek–Brown failure criterion, and the calculated results are validated by comparisons with the numerical results. Finally, the effects of the rock properties on the limit support pressure and the 3D failure surface are discussed. The results show that (1) compared with the numerical simulation method, the proposed method is an efficient and accurate approach to evaluating the face stability of the horseshoe tunnel; (2) from the parametric analysis, it can be seen that the normalized limit support pressure of the tunnel face decreases with the increasing of geological strength index, GSI, Hoek–Brown coefficient, m_i, and uniaxial compressive strength, σ_ci, and with the decreasing of the disturbance coefficient of rock, D_i; and (3) a larger 3D failure surface is associated with a high value of the normalized limit support pressure. Full article

Limited drainage tunnels face pore water pressure, water inflow, and permeability challenges. At present, there is little systematic analysis and research on the lining water pressure of sub-sea tunnels, and there is a lack of verification of relevant engineering examples and field monitoring data. Based on the numerical simulation method, this paper discusses the lining water pressure and its reduction coefficient of the horseshoe section tunnel, which is verified by an engineering example. Based on many numerical simulations, the recommended value of the water pressure reduction coefficient considering the thickness of the grouting ring and grouting effect is put forward. The stress law and safety of tunnel lining under different water reduction coefficients are studied, and the safety of lining is evaluated combined with the measured data of lining stress. The results show that the numerical simulation has been well verified. Considering the water pressure according to the water pressure reduction coefficient method proposed in this paper can ensure the structural safety of tunnel lining. The method of lining water pressure reduction coefficient proposed in this paper can provide a reference for the subsequent lining design of the sub-sea tunnel. Full article