地铁工程对兰州断陷盆地地下水环境的影响分析

Impact from subway project on groundwater environment in Lanzhou fault basin

为研究地铁1号线对兰州断陷盆地浅层地下水环境的影响程度,根据地下水长期监测资料,采用Vilual MODFLOW模型,预测了地铁工程引起的地下水流场变化程度及影响范围,并采用水质化学分析方法,对地下水水质影响趋势做了研究。结果表明:兰州地铁建成后对断陷盆地浅层地下水径流阻滞作用明显。预测地铁运营前5 a水位上升幅度最大,后5 a趋于平缓;10 a时上升较大的区域为地铁沿线南侧西客站至文化宫站,升幅达2.10~2.80 m,其中小西湖站水位最大雍高2.81 m,北侧“迎水面”奥体中心站到马滩站区间水位平均雍高约1.50 m;预测影响范围为0.8~1.2 km。通过对多年水质监测数据分析认为,随着含水层溶滤及矿化作用增强,水中溶解性总固体和SO4^2-、Cl^-离子增加,对水下建(构)筑物基础的腐蚀增强。针对地铁工程建设产生的主要地下水环境问题,提出了建立地下水监测系统、人工调控地下水流场和污染管理等三项保护措施建议。研究成果可为今后兰州市地下空间建设规划提供一定的科学依据。

In order to study the impact from Lanzhou Metro Line 1 on the shallow groundwater environment of Lanzhou Fault Basin,the changing degree and impacting range of the groundwater flow field caused by the construction of the metro project are predicted by means of Vilual MODFLOW model in accordance with the long-term monitoring data of the groundwater therein,while the trend of the impact on the quality of groundwater is studied through the relevant method of chemical analysis of water quality.The results show that the retardation effect from the construction of the metro on the runoff of the shallow groundwater in the fault basin is obvious after the completion of Lanzhou Metro.It is predicted that the rising amplitude of water level is to be the maximum during the first 5 a of the operation of the metro,and then tends to be smooth in the next 5 a,while the area with the lager rising amplitude at 10a is the zone from the West Railway Station to the Cultural Palace Station along the southern side of the metro line with the rising amplitude of 2.10~2.80 m,in which the maximum raising of water level at Xiaoxihu Station is 2.81 m.The mean raising of water level of the section between Olympic Sports Center Station to Matan Station at the northern water-facing side of the metro is about 1.50 m with the predicted impacting range of 0.8~1.2 km.Through the analysis on the multi-year water quality monitoring data,it is considered that the relevant corrosions from the increases of the total dissolved solids and SO4^2-and Cl^-ions in water on the foundation of the underground building(structure)are increased along with the increases of the leaching and mineralizing effects of the aquifer.Therefore,three protection measures,i.e.establishment of groundwater monitoring system,artificial regulation of groundwater flow field and pollution management,are proposed herein for the main groundwater environmental problems caused by the construction of the metro project.The study result can provide a certain basis for the construction planning of the underground space in Lanzhou.