回填土钻孔灌注桩-承台混凝土水化作用效应现场试验

混凝土早期水化作用释放大量热量,会引起桩身温度和桩身应力变化,从而影响桩基承载性能。通过开展现场试验,研究回填土地基中钻孔灌注桩-承台混凝土水化热对桩身及桩基周围土体的影响,实测并分析了桩身及桩基周围土体温度随时间、深度的变化规律和桩基应力随时间的变化规律。研究结果表明,试桩混凝土浇筑完成后,0.7 d时桩体不同深度处的温度均达到最大值,21.4d时其温度基本稳定;桩体温度随时间变化规律可分为快速上升、快速下降、缓慢降低和基本稳定4个阶段。承台混凝土水化热效应仅对桩基周围浅层土体温度有一定影响,当深度大于3 m时,其对土体的温度作用效应基本可以忽略。桩基约束应力变化表现为先迅速增长再缓慢下降最终趋于稳定,最大约束应力值与混凝土轴心抗拉强度十分接近。

Field Test on Concrete Hydration Effect of Bored Pile in Backfill Soil

The early hydration of concrete will release a lot of heat, which will cause the change of temperature and stress of pile body, thus affecting the bearing capacity of pile-cap. Through field tests, the influence of hydration heat of bored pile-cap concrete on pile body and soil around pile foundation is studied. The variation of temperature of the pile foundation and the soil around pile along depth and with time, and the stress history of pile foundation are measured and analyzed. The results show that the temperature at all depths of the pile reaches its maximum value at day 0.7 after the completion of concrete pouring. At day 21.4, the temperature of the pile is basically stable. The law of temperature variation with time can be divided into four stages: rapid rise, rapid decline, gentle decrease and basic stability. The hydration heat effect of cap concrete has only a certain effect on the temperature of shallow soil around pile foundation. When the depth is more than 3 m, the effect of hydration heat on the temperature of soil can be neglected. The confinement stress of pile foundation first increases rapidly, then decreases slowly and finally tends to be stable. The maximum confinement stress value is very close to the axial tensile strength of concrete.