基于BOTDA的机场道面半刚性基层裂缝扩展规律

通过室内试验与现场水泥稳定碎石基层裂缝监测试验, 采用分布式BOTDA光纤监测技术, 研究了传感光纤的应变与裂缝宽度的关系、半刚性基层早期裂缝扩展规律以及裂缝发展速率。研究结果表明: 当裂缝宽度分别为3、6、9mm时, 聚氨酯封装的传感光纤应变分别为5.9×10^-3、7.7×10^-3、10.3×10^-3, 金属基封装的传感光纤应变分别为1.5×10^-3、1.6×10^-3、2.1×10^-3, 光纤应变随着裂缝宽度的增加而增大; 当裂缝宽度为9mm时, 聚氨酯与金属基封装的光纤应变分别为内定点铝合金铠装光纤平均应变的33.2、6.8倍, 因此, 聚氨酯与金属基封装的传感光纤裂缝监测效果较好; 在现场基层施工完成后第13d, 80m长的路段出现了3处微裂缝, 此期间最大温差为2.1℃, 说明基层裂缝的产生和发展主要在第1个月, 且主要是干缩裂缝, 干缩应力是裂缝产生及裂缝间距的主要影响因素; 在施工完成后第20、77、139d, 基层底面温度分别为10.3℃、2.5℃、9.4℃, 基层底面K24+656位置裂缝处光纤应变分别为4.2×10-4、9.5×10-4、4.3×10-4, 在139d之内, 没有新的裂缝出现, 说明温缩应力对早期裂缝间距的影响较小, 主要影响裂缝宽度, 温缩裂缝主要出现在干缩阶段干缩应力较大的位置; 当上、下基层连铺时, 基层上表面与底面的裂缝位置一致, 表明水泥稳定碎石基层横向裂缝为贯穿裂缝; 基层上表面裂缝发展速率分别是基层中间和底面的3.8、2.8倍, 基层上表面的裂缝发展速率最大。

Crack propagation rule of semi-rigid base of airport pavement based on BOTDA

By the laboratory and field cement-stabilized macadam base crack monitoring tests, the relationship between sensing fiber strain and crack width, crack propagation rule in early stage of semi-rigid base, and crack growth rate were researched based on the distributed BOTDA fiber monitoring technology.Research result shows that when the crack widths are 3, 6and 9mm, the strains measured by the sensing fiber encapsulated with polyurethane are 5.9×10-3, 7.7×10-3, and 10.3×10-3, respectively, the strains measured by the sensing fiber encapsulated with metal matrix are 1.5×10-3, 1.6×10-3, and 2.1×10-3, respectively, and the fiber strain rises with the increase of crack width.When the crack width is 9mm, the strains measured by the sensingfibers encapsulated with polyurethane and metal matrix are 33.2and 6.8times as big as the average value measured by the interval fixed fiber armored with aluminum alloy respectively, so the sensing fibers encapsulated with polyurethane and metal matrix performs better for crack monitoring.In field experiment, in 13 dafter construction, 3 micro cracks were found at 80 m long road section, and the largest temperature difference is 2.1 #C during this period, which indicates that the cracks in the base generate and develope mainly in the first month and the dry shrinkage cracks are dominant.The dry shrinkage stress is the main influence factor of crack generation and crack spacing.In 20, 77 and 139dafter construction, the temperatures at the bottom surface of base layer are 10.3℃, 2.5℃and 9.4℃, respectively, and the corresponding strains measured at the bottom surface of base layer at crack location of K24+656are 4.2×10-4, 9.5×10-4 and 4.3×10-4, respectively.No new cracks emerge in base layer in 139 d, which indicates that the influence of thermal shrinkage stress on early crack spacing is very less, and the thermal shrinkage stress mainly affects the crack width.The thermal shrinkage cracks basically appear at the position where the dry shrinkage stress displays peaks in the dry shrinkage phase.When the upper and lower base layers were constructed continuously, the positons of cracks of top surface and bottom are consistent. Hence, the transverse cracks in cement-stabilized macadam base are always penetrating cracks.Furthermore, the crack growth rate on the top surface is 3.8and 2.8times the values at the middle and bottom positons, respectively, so the crack growth rate on the top surface is biggest.