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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。
The research on the mechanical strength of concrete-frozen soil contact surface mostly focuses on the mechanical test of the contact surface between prefabricated concrete samples and permafrost. However, compared with engineering practice, the in-situ concrete in frozen soil and the frozen concrete The research on mechanical strength of frozen soil contact surface is seldom involved. Based on the test method of cast-in-place concrete in frozen soil, the direct shear test of the frozen contact strength of concrete-frozen soil under different water-cement ratio, ice content and frozen soil temperature was carried out. The results show that under the test conditions, due to the difference of the thermal conductivity of coarse and fine aggregates and hydration heat erosion intensity, the cast-in-place concrete in frozen soil will lead to the fluctuation of the contact surface between concrete and frozen soil. Affected by this factor, the roughness strength of the rough contact surface increased by 71.9% compared with the smooth contact surface. The stress concentration caused by the rough contact surface makes the shear stress intermittently increase and jump during the shear failure. In the composition of the freezing strength, with the increase of the roughness of the contact surface, the value of φ contributes more to the increase of the freezing strength than the value of c. The water-cement ratio increased from 0.4 to 0.6, the thermal conductivity of concrete decreased, the contact surface became smooth and the freezing strength decreased. When the soil moisture content increased from 15% to 30%, the freezing strength increased and the water content continued to increase To 40%, the freezing strength decreases; under different temperature conditions, the overall temperature of frozen soil decreases and the freezing strength increases correspondingly. Based on the above results, when designing the bored pile in the permafrost region, it is recommended that the concrete be used with 0.4-0.5 water-cement ratio.