基坑降水开挖对邻近铁路高架桥的影响区研究

Study on the influence zone of dewatering in deep excavation adjacent to railway viaduct

以国内首例下穿城际铁路结构的基坑工程——深圳轨道交通12号线和平站为依托,建立了基坑近接铁路高架桥降水开挖有限元模型,对邻近高架桥进行近接影响区研究,以期对地铁车站基坑施工过程中邻近桥梁的状态进行预测。研究结果发现:在仅考虑基坑降水开挖时,桥梁墩顶水平位移比竖向位移更容易超限,当桥坑间距为0.341~3.029倍基坑开挖总深度时墩顶位移会超过极限值,当桥坑间距大于3.664倍基坑总深度时墩顶位移会始终小于警戒值(极限值的60%);将铁路高架桥受邻近基坑降水开挖的影响范围划分为三类大区和五类小区,根据桥坑间距及基坑开挖深度预测桥梁结构状态,在仅考虑基坑降水开挖时,邻近铁路高架桥30号和31号桥墩随着基坑开挖会存在位移超限的可能,因此现场采取隔离桩和旋喷桩的组合加固措施来保证桥墩安全;数值计算结果及现场监测结果吻合性较好,均表明采用的加固措施能保证桥梁结构的安全。

Based on the first deep excavation project beneath an intercity railway structure in China,the Heping Station of Shenzhen Rail Transit Line 12,a finite element model of the dewatering during excavation was established to study the influence zone of the adjacent railway viaduct,to predict the state of the adjacent bridge during the construction of the underground station excavation.The study results reveal that the horizontal displacement of the bridge pier top is more likely to exceed the limit than the vertical displacement when considering only the dewatering,and the displacement of the pier top will exceed the limit when the spacing between the bridge and excavation is 0.341~3.029 times of the total excavation depth,and the displacement of the pier top will always be less than the warning value(i.e.60%of the limit)when the spacing exceeds 3.664 times of the total excavation depth.The range of the railway viaduct affected by the adjacent excavation dewatering is classified into three areas and five subareas;the structural safety state of the bridge is predicted according to the spacing between the bridge and excavation pit,and the depth of excavation.Considering the dewatering only,the displacement of railway viaduct pier Nos.30 and 31 will exceed the limit possibly.Therefore,the reinforcement measures including isolation piles and rotary high jest grouting are adopted to ensure the safety of the piers.The numerical calculation results are consistent with the field monitoring results,which indicates that the reinforcement measures adopted could ensure the safety of the bridge structure.