In-situ monitoring of displacements and stability evaluation of slope based on fiber Bragg grating sensing technology

Abstract

A new type of in-place inclinometer based on fiber Bragg grating(FBG) sensing technology and the related analysis method are presented. Based on the linear relationship between the wavelength change of FBG and strain, the strains at different measuring points on the new in-place inclinometers are obtained. Using the classical beam bending equation and finite difference method, the displacements of the inclinometer can be calculated. This new type of in-place inclinometer overcomes certain disadvantages of the conventional in-place inclinometer, such as low accuracy, poor durability, and complex operation. Laboratory calibration results verify the reliability of the new in-place inclinometer and its analysis method. For a cut slope along the Panzhihua-Tianfangcun highway, three new FBG in-place inclinometers were placed in three vertical boreholes in the same cross-section of the slope, ensuring that the inclinometers passed through the potential slip surface. Then the field monitoring started. Monitoring data derived from the inclinometers are collected and analyzed. An optimal model is adopted to calculate the position of the potential slip surface and the factor of safety of the slope, which is well compared with the results obtained from Bishop's method. It is shown that the method presented provides a new and reliable approach for assessment of slope stability based on slope monitoring data. 首先介绍基于光纤布拉格光栅传感技术的新型原位测斜仪及其分析方法。根据光纤布拉格光栅波长变化与应变之间的线性关系求得原位测斜仪各测点的应变,然后通过梁的弯曲理论公式和差分算法,由测点应变计算出原位测斜仪各点的位移。该原位测斜仪克服了传统原位测斜仪精度低、耐久性差、操作繁琐等缺点。室内标定试验验证了该新型原位测斜仪和分析方法的有效性。针对攀田高速公路一路堑边坡,将3套新型光纤光栅原位测斜仪安装于该边坡同一剖面的3个钻孔里,并保证测斜仪贯穿了边坡内的潜在滑裂面,对该边坡进行现场监测。假设边坡滑动面为圆弧形,根据当前监测结果,以3个孔原位测斜仪所测应变之和最大为目标函数,以原位测斜仪在边坡坐标系中的位置和滑裂面的形状为约束条件,建立最优化数学模型来推求潜在滑裂面的具体位置。根据经典Bishop条分法计算得到了该潜在滑裂面对应的边坡安全系数,以评估该边坡当前的稳定性。本方法在基于边坡监测成果的边坡稳定性评估方面提出了新的可靠的途径。