现浇混凝土-冻土接触面冻结强度直剪试验研究

关于混凝土-冻土接触面的力学强度研究多集中于预制成型混凝土样（块）与冻土接触面的力学试验研究，而与工程实际更为接近的冻土中现浇混凝土、冻结稳定后混凝土-冻土接触面的力学强度研究则少有涉及。基于冻土中现浇混凝土的试验方式，开展了不同水灰比、含冰量及冻土温度条件下，混凝土-冻土复杂接触面冻结强度的直剪试验研究。结果表明：试验条件下，由于混凝土中粗、细骨料导热系数及水化热侵蚀强度不同，冻土中现浇混凝土会导致混凝土-冻土接触面发生起伏变化。受该因素影响，粗糙接触面较光滑接触面的冻结强度增大71.9%。粗糙接触面引起的应力集中，使得剪应力在剪切破坏过程中出现间歇性增大、跳跃。在冻结强度构成中，随接触面粗糙程度的增大， φ值对冻结强度增长的贡献要大于c值。水灰比由0.4增至0.6，混凝土导热系数降低，生成接触面趋于光滑，冻结强度减小；土体含水量由15%增大至30%时，冻结强度增大，含水量继续增大至40%时，冻结强度减小；在不同温度条件下，整体呈现冻土温度降低冻结强度相应增大的趋势。基于上述结果，多年冻土区灌注桩设计时，建议混凝土采用0.4~0.5水灰比。

Direct shear tests of freezing strength at the interface between cast-in-situ concrete and frozen soil

Previous experimental study of interface strength between concrete pile and frozen soil has focused more on the mechanical properties of the interface between precast concrete block or specimen and frozen soil with less information about direct shear test of freezing strength between cast-in-situ concrete and frozen soil.Based on a new specimen preparation method,a series of laboratory direct shear tests of the interface between cast-in-situ and frozen soil were performed.The results show that because of difference in thermal parameters of concrete,the interface between cast-in-situ concrete and frozen soil appears irregular model.Freezing strength of rough interface will increase by 71.9％ as compared with that of smooth interface.Stress concentration occurs on the rough interface,resulting in stress intermittently increasing and jumping in the shear failure process.With the increase of roughness at the interface,ψ contribution increase more than c contribution increase by degree.Thus ψ can play more important role in the growth of freezing strength.When water cement ratio increases from 0.4 to 0.6,with the thermal conductivity of concrete decreasing,the interface becomes smoother and the freezing strength will decrease;when water content increases from 15％ to 30％,freezing strength will increase first and then decrease;when water content increases to 40％,freezing strength will decrease.Thus,it is recommendedthat 0.4 ～ 0.5 is a reasonable water cement ratio,according to this study.