Fiber reinforcement has been demonstrated to mitigate soil liquefaction, making it a promising approach for enhancing the seismic resilience of tunnels in liquefiable strata. This study investigates the seismic response of a tunnel embedded in a liquefiable foundation locally improved with carbon fibers (CFs). Consolidated undrained (CU), consolidated drained (CD), and undrained cyclic triaxial (UCT) tests were conducted to determine the optimal CFs parameters, identifying a fiber length of 10 mm and a volume content of 1 % as the most effective. A series of shake table tests were performed to evaluate the effects of CFs reinforcement on excess pore water pressure (EPWP), acceleration, displacement, and deformation characteristics of both the tunnel and surrounding soil. The results indicate that CFs reinforcement significantly alters soil-tunnel interaction dynamics. It effectively mitigates liquefaction by enhancing soil stability and slowing EPWP accumulation. Ground heave is reduced by 10 %, while tunnel uplift deformation decreases by 61 %, demonstrating the stabilizing effect of CFs on soil deformation. The fibers network interconnects soil particles, improving overall structural integrity. However, the increased shear strength and stiffness due to CFs reinforcement amplify acceleration responses and intensify soil-structure interaction, leading to more pronounced tunnel deformation compared to the unimproved case. Nevertheless, the maximum tunnel deformation remains within 3 mm (0.5 % of the tunnel diameter), posing no significant structural risk from the perspective of the experimental model. These findings provide valuable insights into the application of fibers reinforcement for improving tunnel stability in liquefiable foundations.

Immersed tunnels, as a form of underwater transportation engineering offering numerous advantages, have been widely deployed in coastal and riverside cities. However, due to the shallow burial and underwater characteristics, immersed tunnels present significantly different surrounding soil and water environments compared to land-based tunnels. Currently, there is limited research on the seismic analysis of submarine immersed tunnels, raising questions about the direct application of the methods of land-based tunnels. In this study, the Davidenkov soil constitutive model is introduced to simulate the strong nonlinearity of deep sedimentary soil in marine areas. The Coupled Acoustic-Structure (CAS) method is employed to simulate the dynamic interaction between seawater and seabed. A time-history analysis model is developed to capture the coupling interactions between seawater, seabed, and tunnel structure. The effects of the soil-tunnel contact mode and seismic input method on the seismic responses of immersed tunnels are investigated in detail. Seismic response characteristics of immersed tunnels are analyzed from four perspectives: distribution of tensile damage in the tunnel, maximum inter-story drift ratio, maximum bending moment, and tunnel inclination angle in the cross-sectional direction. The results indicate that the overlying seawater and sand compaction piles negatively impact the seismic performance of immersed tunnels in the scenarios of this study. Furthermore, their impact pattern and extent are closely correlated with the intensity of the input seismic motion.

Zhuanyao dwellings faced significant seismic risks in rural regions of China. Therefore, a shaking-table test was performed to explore the seismic performance of Zhuanyaos and validate the finite-element simulation results. The results showed that the damage to the pier and roof levels of Zhuanyaos was more severe after earthquakes, resulting in a noteworthy increase in the displacement responses of these two levels compared to that of the vault level. The damage to the front structure (Yaolian) and mid-pier of the Zhuanyao were more severe than the damage to the back wall and side pier, respectively, which caused a significant reduction in acceleration responses of Yaolian and mid-pier. Following the crack development, dynamic response, and field investigation, three typical collapse modes of Zhuanyaos were presented. Subsequently, the parametric analysis was conducted using a verified finite-element simulation method. The results show that using the catenary arch can reduce earthquake damage in Zhuanyaos. Increasing the width of the middle pier can improve the seismic performance of Zhuanyaos to a certain extent; however, it may exacerbate local damage to the structure. Besides, the high seismic vulnerability of Zhuanyaos stemming from an increasing thickness of overlying soil cannot be ignored.

Earthen houses are practiced as a traditional and low-cost housing in many countries around the globe. These houses were exposed to unacceptable earthquake (EQ) risks despite their environmental benefits. Past earthquakes including the recent past 2017 Tripura EQ has evidenced significant damages mostly in earthen/masonry houses which are built in a non-engineered manner. In this context, the current study aims to investigate the seismic behavior and failure patterns of both unreinforced and using proposed retrofitted rammed earth model houses (with and without openings) built using typical Tripura soils having higher silt content using unidirectional shake table experiments on total 26 physical models. Besides, both seismic strength and structural stability are also examined for retrofitted earthen houses. The study indicates that, proposed novel low-cost natural fiber made textile encasing reinforcement technique has exhibited promising seismic performance of such houses from the view point of structural strength and ductile behavior as compared to traditional cementitious additives and fiber blended stabilized retrofitted houses as well untreated houses. The fundamental lateral period of model unreinforced and reinforced houses found within the range of 0.08 to 0.15 s respectively which indicates increased stiffness of walls due to strengthening may decrease the lateral period maximum up to 46.67%. On the other hand, the maximum increase in seismic strength was observed in order of 4.50 to 6.31 times in the case of bitumen treated bamboo fiber textile based encased houses with L-shaped bamboo splint corner reinforcement whereas traditional cementitious stabilized method has offered maximum 1.13 to 1.83 times increment in lateral strength. Further, the effect of different parametric variations such as area of openings (doors and windows), thickness to height ratio, variation in compaction methodologies on seismic performances of unreinforced rammed earthen houses were also studied in detail. Finally, regression based closed form predictive expressions for seismic strength of rammed earthen houses and without retrofitting are proposed herein. The performed cost analysis study will also help to assess the effectiveness of proposed strengthening techniques.