Narrow Results

The current bridge pile foundation design specifications in China provide only general principles for karst areas and do not provide a method to calculate the safe cave roof thickness or the vertical displacement of the pile foundation. Additionally, previous studies have not adequately considered the interaction between bridge pile foundations and caves under seismic loads. Therefore, the national design code does not provide an effective basis or reference for calculating the seismic performance of pile foundations in complex karst areas. This study establishes a numerical model of the pile-foundation-cave interaction system. The dynamic responses of the pile foundation displacement, stress, plastic strain, and bending moment subject to ground motion after inversion are analyzed. The effects of different factors on the safe cave roof thickness and vertical displacement of the pile foundation are investigated, and multiple regression models are obtained and optimized. Finally, parametric sensitivity analysis is conducted for each influencing factor. The results demonstrate that the safe cave roof thickness is between 2.5m and 5.7m and the vertical displacement is between 0.0075m and 0.06m. The sensitivity factors for the safe cave roof thickness in the case where the cavern shape is simplified to a rectangle, in descending order, are the rock cohesion, pile diameter, initial load at the top of the pile, cave size, and the peak value of ground motion. The sensitivity factors for the vertical displacement of the pile foundation, in descending order, are the peak value of ground motion, initial load at the top of the pile, cave size, and pile diameter. The conclusions provide valuable insights into the design optimization of rock-socketed pile foundations in karst regions.

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Tropical karst is highly sensitive to surface and subsurface changes, with natural and anthropogenic factors contributing to its potential degradation and overexploitation. Thus, the appropriate management and protection of karst environments are needed. This study aims to determine the anthropogenic-driven changes in the karst landscape and groundwater resources of El Nido, Palawan Province. Interferometric Synthetic Aperture Radar (IfSAR), LandSat 8, and Google Earth imagery were used for pre-field geomorphological and land cover delineation. Semi-detailed stratigraphic surveys and rock sampling were conducted. In-situ water quality testing and sampling were done to obtain physicochemical parameters such as pH, conductivity, and total dissolved solids. Focusing on preliminary findings from El Nido, petrographic characterization and microfossil age dating have shown that the limestone is composed of Middle Permian faunal assemblage. Geomorphological analysis shows that the area is dominated by karst towers, remnant valleys, sinkholes, and caves. Georesistivity surveys reveal that the water-saturated layer becomes thicker in the extensive floodplains of Villa Libertad, Dewil Valley, and Villa Paz. In contrast, the town center has a thin and permeable water-saturated layer that is approximately 2-3 m thick. Fecal coliform, nitrates, and sulfates are relatively higher in groundwater collected from karst areas in the urban and tourism center.