硫酸盐渍土中灌注桩竖向承载力演变规律

Bored piles' vertical bearing strength evolution in sulfate saline soil

盐渍土中硫酸盐含量极高,对灌注桩具有极强的腐蚀作用从而影响其承载特性,为明确和分析混凝土灌注桩在硫酸盐盐渍土腐蚀下竖向承载力的演变规律,以及桩径、桩长对灌注桩腐蚀后承载力变化规律的影响,根据硫酸盐环境下混凝土劣化的腐蚀反应和机理,建立了硫酸盐渍土腐蚀环境下单桩承载力的评价模型;结合案例对硫酸盐渍土地区混凝土灌注桩的侧阻力、端阻力及桩体强度进行研究,分析和对比了桩长及桩径对硫酸盐腐蚀下灌注桩的承载特性演变规律的影响.结果表明:硫酸盐渍土腐蚀作用下灌注桩的侧阻力、端阻力及桩体强度均发生变化;桩侧阻力受到腐蚀产物积累、膨胀引起的桩周混凝土劣化和桩侧应力重分布的影响,同时也依赖于桩长及桩径变化;端阻力则由于单桩竖向有效面积的减小而降低;硫酸盐腐蚀作用下桩体强度降低幅度较大.由此可知,相同腐蚀条件下,增加桩径可有效提高抵抗硫酸盐腐蚀引起的承载力损失;实际设计中应考虑增加桩径的方法抵抗硫酸盐腐蚀引起的承载力损失.

Content of sulfate ions is relatively high in saline soil that can deteriorate the bearing capacities of bored pile and related studies are rarely reported.To clarify the evolution rules of bored piles＇ vertical bearing strength and the effects of pile length and pile radius on bearing strength after sulfate attack, bearing capacity evaluation model of bored pile was established based on the sulfate corrosive reactions and mechanism in sulfate corrosive condition.By combination with cases, the evolution rules of side resistance, end resistance and pile compressive strength were studied.The influences of pile diameter and pile length on bearing properties were analyzed and compared.The results show that the side resistance, the end resistance and the pile compressive strength change after sulfate corrosion.The side resistance of pile depends on stress redistribution and concrete deterioration around pile caused by sulfate corrosion products, and is also affected by the length and diameter of pile.The end resistance reduces with increasing depth of sulfate corrosion because the effective area decreases after corrosion.The compressive strength of pile decreases rapidly during sulfate corrosion process.It concludes that increase of pile diameter can enhance the resistance ability against deterioration, and the pile diameter increase can enhance the anti-sulfate corrosion ability for pile foundation design in saline area.