基于光纤光栅传感技术敞口混凝土管桩应力测试现场试验

基于4根足尺敞口混凝土管桩现场试验,在桩身刻槽预埋串联式的FBG传感器,成功地将准分布式FBG传感技术应用在贯入过程中桩身轴力的测试,研究了敞口混凝土管桩稳态贯入过程中桩端阻力和桩侧摩阻力的变化规律。试验表明：FBG传感技术能够准确分离桩端阻力和桩侧摩阻力,测试效果较为理想。桩端阻力和桩侧总摩阻力沿深度变化曲线反映土层的工程性质,桩端阻力受土层变化影响明显,硬质土层界面处桩端阻力平均增幅78.5%；桩侧摩阻力进入圆砾层时出现峰值,平均增长幅度为20.2%。桩端位于非硬质土层,桩端阻力、桩侧摩阻力变化不明显。贯入过程中桩身轴力变化曲线表明桩身下部侧摩阻力明显大于上部侧摩阻力。

Field Tests on Stress Measurement of Open-Ended Concrete Pipe Piles Based on Fiber Bragg Grating Sensing Technology

In order to measure the pile stress during installation, quasi-distributed FBG sensing technology has been implemented successfully in static load test through the pre-embedded tandem in pile groove. Four full-scale open-ended concrete pipe piles are used in the field tests to illustrate the proposed measurement methodology, and to study the evolution discipline of open-ended concrete pipe piles toe resistance and side resistance during installation. The test results indicate that FBG sensing technology is advantageous in that side resistance and toe resistance can be separated precisely ignoring the temperature effect. The variation of side resistance and toe resistance basically reflects the soil parameters difference during installation. Toe resistance is more susceptible to soil parameters than side resistance and it increases about 78.5% when jacked into the bearing layer. However, side resistance increases only about 20.2% when pile enters the round gravel layer with the peak. Toe resistance and side resistance vary slightly where toe is not located on bearing layer. Variations of pile shaft force indicate that side resistance in upper is greater precisely than bottom during installation.