CONSTRUCTION MONITORING OF URBAN TUNNELS AND SUBWAY STATIONS

Monitoring of tunnels and subway stations during construction using in-situ geotechnical instruments plays multiple essential technical roles. During early construction stages, it provides a factual basis for quantitative assessment of the proposed design and selected construction technology. If needed, such field measurements also can be used to guide modifications or refinement of the construction procedures, particularly at critical portions of the underground project. On the other hand, systematic instrumentation measurements taken at reasonably spaced control sections along the proposed alignment of a project can be utilized to document the overall performance. Such valuable records also can be used in a database for the design of similar future tunnels and for subway development. From the point of view of applied research, field measurements gathered during construction monitoring provide badly needed records for reviewing and improving the existing design procedures and validating new analytical tools, as well as for formulating effective directions of future research needs to match the mounting development of underground space. This paper outlines the basic requirements of a successful construction monitoring program for urban underground projects, based on 15 years of experience in the design and implementation of more than 10 instrumentation test sections, mainly for tunnels and subway stations in Egypt and Canada. Some details of the most reliable in-situ instruments are also given. Finally, examples of different layouts of the monitoring programs implemented at different underground projects are presented, with some typical results.