桩基内力长期监测中的蠕变影响分析

Analysis of creep influence in long-term pile stress test

以黄土地区桩基浸水试验为代表的桩身内力长期监测过程中,桩身混凝土除发生弹性应变外还会发生蠕变,以往工作中往往忽略了混凝土在轴力长期作用下蠕变对测试结果的影响,但蠕变真实存在,它对内力测试结果的影响程度以及如何消除其影响值得研究。根据现场实测试验资料对比分析表明,长时间的桩基内力测试应考虑桩身蠕变的影响;基于混凝土蠕变的相关理论,推导了从实测应变中扣除桩身蠕变的公式;从消除蠕变影响角度分析了黄土桩基浸水试验中应采取的措施,其关键技术是控制试验桩的混凝土强度等级,在桩顶附近设置标定段,并保持标定段混凝土的温度和湿度恒定,且与下部桩体一致,获得具有代表性的蠕变度函数曲线。

Besides elastic strain, creep would also occurred in long-term pile stress test represented by pile immersion test in loess regions for concrete pile; and the influence of creep occurred under long-term axial stress was usually be overlooked in the past when calculating stress of pile body. But creep is a real existence, influence degree of creep and how to eliminate its effect are worth studying. Based on comparative analysis of field test data, how the concrete creep affect the analytical results of pile stress is studied; and the conclusion shows that the overlook of concrete creep will lead to wrong distribution rules of axis force and friction. A formula, which calculates axial force of pile and can eliminate the creep influence, is derived from some basic theory on creep. Some measures needing be taken in pile immersion test of loess regions to attain representative creep curve are presented; mainly include： controlling the concrete strength grade of test pile, setting calibration section near pile top and keeping concrete＇s temperature and moisture constant in this section and are in the same with lower pile.