铁路隧道放射性全周期监测方法与评价

Life Time Monitoring Method and Evaluation of Radioactivity in Railway Tunnel Construction

为研究地下工程建设过程中地下岩石中天然放射性对隧道和周边人居环境的影响,以福建省某双线高速铁路隧道建设项目途经的两条连续花岗岩隧道为例,开展施工前、施工期间和隧道贯通后全周期跟踪监测。施工期和隧道贯通后,隧道及周边场所放射性属正常范围,且施工期施工人员和运营后检修人员所受附加内、外照射剂量之和满足相关限值要求,隧道伽马辐射剂量率和空气氡浓度满足“施工期>隧道贯通后>施工前背景”的规律,且施工期伽马剂量率幅度变化较大。隧道内伽马剂量率主要受燕山早期第三阶段岩体中铀含量较高的影响,其次是钍含量的影响,同钾含量的相关性不大,基本表现出“燕山早期花岗岩>辉绿玢岩>燕山晚期花岗岩>震旦系楼子坝群千枚岩/变质砂岩/板岩”的规律。相较于传统的地表沿线放射性监测或钻孔监测,采取全周期监测能更为有效地获取隧道建设阶段的放射性变化和特征,给出放射性工程防治建议,保障隧道施工和后期运营安全。

In the process of underground engineering construction,the gamma rays of natural radionuclides in surrounding rock may produce radioactive harms over construction workers and the surrounding environment,which is related to local lithology,tunnel environment,formation structure and other factors,and performs as the radionuclide⁃containing dust generated by tunnel face blasting and excavation,radon and radon daughters emanating from tunnel rocks and rock crevasses,radioactive tunnel seepage and construction waste,etc.In order to reveal the influence of natural radioactivity in rocks on the tunnel or surrounding settlements during the construction of underground engineering,two continuous granite tunnels of a two⁃track high⁃speed railway tunnel construction project in Fujian province were selected as cases for life time monitoring was before construction,during construction and after construction.According to the test results,the surface⁃ground gamma radiation dose rate and air radon concentration conformed the rule of‘construction period>final state detection>pre⁃construction background-during the construction period and the completed state.The sum of the internal and external radiation dose received by the builder and maintenance worker met the relevant limit requirements.The influence sequence of element content over gamma dose rate in the third stage of the early Yanshan orogeny from high to low is:uranium,thorium,potassium.The gamma dose rate showed the rule of granite of Early Yanshan Orogeny>diabase-porphyrite granite of Late Yanshan Orogeny>phyllite/metamorphic sandstone/slate in Sinian Louziba Group.Futhermore,the radioactivity in and around the tunnel kept the normal range and met the relevant standard requirements.Compared with the traditional surface⁃ground or drilling exploration,the life time monitoring is more effective to obtain the changes and tendency of radioactivity over the whole construction period,and provided references on radioactive prevention and control to ensure the safety of construction and operation.