Abstract: A elastoplastic constitutive model based on Mohr-Coulomb criterion was constructed to explore the limit bearing characteristics of bridge pile foundation in strongly alkaline marsh area based on the transformation among strength, cohesion, and internal friction angle. First of all, the water curing strength and corrosion strength of pile foundation concrete were measured by field test and laboratory test. The internal chloride ion concentration of concrete was measured by EDS analysis and element analysis. The convection depth of chloride ions inside the concrete was determined by an indoor electron microscopy test. In subsequence, the concrete specimens in the corrosive alkaline environment are divided into the spalling zone, the corroded zone and the non-corroded zone. The relation between corrosion depth and post-corrosion strength of concrete exposed one year was calculated by formula. Results demonstrated that with the increase of ratio of corrosion thickness to diameter of uncorroded pile, the ultimate bearing capacity of the transverse axial direction of a single pile reduced gradually, but the reduction gradually attenuated. The increase of pile length helped little to the improvement of ultimate bearing capacity of single pile transversely. The vertical ultimate bearing capacity of single pile also decreased gradually, and such decline also slowed down. Within the same range of corrosion thickness, the reduction of vertical ultimate bearing capacity of large-diameter single pile was greater than that of small-diameter single pile.

Key words: pile foundations, ultimate bearing capacity, strongly alkaline marsh area, chloride ion, corrosion thickness, Mohr-Coulomb criterion, elastoplastic constitutive model