Deformation and reinforcement of piled bridge foundations on weathered mudstone slopes

Introduction: With the rapid development of China’s highway system, the construction of bridges spanning valleys in mountainous regions has become inevitable. In these areas, the deformation of bridge foundations must be strictly controlled, often through slopes reinforced with anti-slide piles. Materials and methods: Departing from the conventional “landslide–stabilizing pile” paradigm, this study adopts a holistic system perspective by modeling the “bridge pile–anti-sliding pile–weathered mudstone slope” as an integrated finite element method (FEM) framework, with the Qiezang Bridge on the Linxia–Dahejia Expressway as a case study. The horizontal displacement of the bridge foundation and anti-piles serves as the principal optimization target. Results: The installation of the rear-row anti-pile (P1) alone reduced the maximum horizontal displacement of the bridge foundation from 6.67 mm to 5.07 mm, corresponding to a 24.0% decrease. This confirms that a single-row configuration at the rear effectively enhances the deformation resistance of the foundation. By adjusting the location of the front-row anti-pile (P5) under the prevailing geological conditions, an optimal position of p x = 2.0 m was identified in the case of double anti-slide piles reinforcement. Conclusions: Comparative results indicate that the interaction between piles and soil is highly complex, due to the combined effects of lateral parabolic loads from soil thrust, lateral triangular loads from pile deflection, and soil resistance acting on the piles. Given the prevailing geological setting, the lateral displacement of P5 decreased from 51.2 mm to 34.0 mm at a position of p x = 2.0 m, representing a reduction of 17.2 mm (33.6%) and remaining the horizontal displacement of the bridge within the allowable limit. This provides a quantitative basis for reinforcing bridge foundations on weathered mudstone slopes.