基于BOTDA分布式光纤传感技术的双排圆形桩变形特性及内力研究

Research on deformation characteristics and internal forces of double-row circular piles based on BOTDA distributed optical fiber sensing technology

为了解双排圆形桩在基坑支护中的变形规律和内力分布特性,结合BOTDA分布式光纤传感技术和深层位移监测技术对双排桩在基坑开挖过程中的变形及内力响应进行测试.通过在前、后排桩分别布设传感光缆,采集了从基坑开挖过程到稳定后的应变对双排桩的变形特性及内力,并引入数值模拟与之对比分析.研究结果表明:光纤监测推算的桩身扰度与相应位置的测斜监测的桩身侧向位移曲线规律基本一致,基坑整体变形较小且处于稳定状态,双排圆形桩起到了很好的支护效果;通过监测应变能真实反映桩身内力分布及传递规律,对比数值模拟成果,双排桩实测弯矩剪力值明显小于模拟值,分布规律基本一致,在前、后排桩上的系梁连接点及坑底以下2 m附近的弯矩较大,后排桩分担的荷载大于前排桩的;基坑开挖完成后,坑底以上土压力的分布形式呈现“上下部小,中部大”的中凸特征,实测土压力值也小于经典土压力法理论计算值.

In order to understand the deformation laws and internal force distribution characteristics of the double-row circular piles in the foundation pit support,the deformation and internal force response of double-row piles in the process of foundation pit excavation are tested by means of BOTDA distributed optical fiber sensing technology and deep displacement monitoring technology.By laying sensing optical cables in the front and rear piles respectively,the strain from the excavation process to the stability of the foundation pit is collected to study the deformation characteristics and internal forces of the double-row piles,and the numerical simulation is introduced for comparative analysis.The result shows that the pile disturbance calculated by the optical fiber monitoring is basically consistent with the pile lateral displacement curve of the corresponding position inclination monitoring.The overall deformation of the foundation pit is small and in a stable state,and the double-row circular piles have a good supporting effect.By monitoring the strain energy,the internal force distribution and transfer law of the pile body are truly reflected.Compared with the numerical simulation results,the measured bending moment and shear force values of the double-row piles are significantly smaller than the simulated values,and the distribution law is basically the same.The bending moment at the connecting point of the tie beams on the front and rear piles and near 2m below the bottom of the pit is larger,and the load shared by the rear piles is greater than that of the front piles.After the excavation of the foundation pit is completed,the distribution of earth pressure above the bottom of the pit shows a convex characteristic of"small in upper and lower parts and large in middle parts".The measured earth pressure value is also less than the theoretical value calculated by classical earth pressure method.