터널로 인한 지하수 영향 저감방안 연구

Abstract

Recent road and railroad construction projects show prominent trend to design most of the routes linearly, for the purpose of increase of the running speed and reduction of transportation time. Moreover, it has been more and more increasing that most of the routes in the projects are composed of tunnels and bridges to minimize the damage of the natural environments by slope cutting and to perform the real construction to be environmentally sound. However, some road and railroad construction projects which were started after 2000 provoked delay of the projects and lawsuit problems, because the impacts of the groundwater outflow during tunnel excavation was dealt with superficial experiences rather than scientific verification. Therefore, this study was focused on establishment of overall improvement plan for groundwater impact assessment in construction projects including rock tunnel excavation, taking 1) the forecast of environmental impacts on tunnel groundwater outflow with objective and scientific criteria and 2) the real operation status of the construction sites into consideration. The goal of this study is to perform; 1) systematic analysis and rearrangement of groundwater impact by tunnel excavation during road and railroad construction, 2) provision of applicable mitigation plan and examination of environmental impacts due to tunnel groundwater outflow, 3) formation of the schemes which can be applied to future EIA, and 4) provision of reasonable guideline for appropriate impact forecast, assessment, and establishment of the mitigation plans during EIA of tunnel-included projects. As a result of the analysis of four environmental conflict cases related tunnel groundwater outflow, representative caused of the groundwater impacts were; 1) the failure of effective mediation among the stakeholders, 2) inadequate decision of optimal execution time for the groundwater impact investigation, 3) overall drop of the investigation results caused by omission of several investigation items, 5) imperfection of related legal items, and 6) the absence of environmental audit plan during tunnel operation. Moreover, the environmental audits, which are mainly composed of regular measurement of tunnel outflow rate, will be more and more important because it can help to grasp the change of secondary natural environment due to tunnel groundwater outflow. The environmental assessment of tunnel groundwater has the target to forecast the drawdown and amount variation of the domestic groundwater near the planned routes due to tunnel excavation. As usual, numerical method of groundwater flow modeling is used for the EIA of tunnel groundwater. The program packages used for the groundwater modeling are different each other, depending on the case of regional groundwater level variation in whole tunnel or small-scale groundwater level variation in narrow fracture zone. In this study, the analysis results of two real EIA cases showed that the difference of unit amount of groundwater outflow per the length of tunnel was comparatively large according to the applied modeling programs. The analogue study of Japan and America showed that numerous discussion and mediation among stakeholders with sufficient time and extensivve scale of scientific impact investigation supporting the result of the discussion were indispensable for solving the environmental conflict due to tunnel groundwater outflow. As conclusions, the integration of the study results could suggest the improvement plan for mitigating the impact of tunnel groundwater. detailed items of the improvement plan were as follows; 1) elucidation of detailed investigation method for tunnel groundwater impact assessment on current laws and systems, 2) decision of timing of the tunnel groundwater impact assessment under current EIA system, 3) establishment of the assessment and mitigation criteria for review organization, and 4) improvement factors for the side of the project leader. Considering the systems, processes, and required time of current EIA, it could be firmly decided that tunnel groundwater impact assessment should be performed according to appropriate scientific investigation procedures, especially for the construction projects including tunnel excavation. The draft stage of EIA could be the most appropriate timing for the tunnel groundwater impact assessment.