季节冻土区深基坑混凝土桩冻融效应分析

Analysis of freezing-thawing effect of deep foundation pit concrete pile in seasonal permafrost region

东北某越冬深基坑工程,由于季节性温度变化,桩后土体内温度重新分布呈现较明显的温度梯度变化规律。基坑冻深与温度和持续时间有关,当温度30 d降至-11℃时冻深约为1 m,而当温度45 d降至-22℃时,冻深约为2 m与当地标准冻深基本一致。支护桩身位移受冻土压力影响变化明显,最大位移由冻前桩身位置变化为冻后桩顶位置,位移超过了规范允许限值,现场及时采取了保温防冻措施,控制了位移发展。此外,由于冻融后土体强度的衰减,土压力有了显著的提高,通过现场监测数据和数值分析结果对比,掌握了基坑桩身位移随温度变化的发展规律,为基坑的安全越冬提供了充分的理论依据。

In a deep foundation pit in northeast China,due to seasonal temperature changes,the temperature redistribution of the soil behind piles shows obvious temperature gradient.The freezing depth of foundation pit is related to temperature and duration.When the temperature drops to-11℃for 30 d,the freezing depth is about 1 m.When the temperature drops to-22℃for 45 d,the freezing depth is about 2 m,which is basically consistent with the local standard freezing depth.The maximum displacement changed from the position of the pile before freezing to the position of the pile top after freezing.The displacement exceeded the allowable limit of the code,and the heat preservation and anti-freezing measures were taken timely to control the displacement development.In addition,due to the attenuation of soil strength after freezing-thawing,the soil pressure has been significantly increased.By comparing the field monitoring data and numerical analysis results,the development law of the pile displacement of foundation pit with temperature is grasped,which provides a sufficient theoretical basis for the safety of the foundation pit over winter.