Abstract
This article describes the main stages involved in the construction of the vertical shafts (large-diameter vertical wells), which are necessary for the subsequent construction of the tunnel´s sections. The different risk situations existing during the construction of the Eastern Drainage Tunnel in the valley of Mexico City (in Spanish, "Tunel Emisor Oriente") are analyzed. In order for this 52 km-long and 7.5 m-wide tunnel to carry part of the city’s sewage, 25 shafts must first be built, ranging from 55 to 150 meters deep. The magnitude of such a project implies working in different geographical areas and varied geological strata involving the presence of groundwater, which increases the risks due to possible landslides or flooding during excavation. As digging will occur in different types of soil, varying procedures must be used depending on soil type. Likewise, due to the magnitude of this kind of project, detailed scheduling and planning are required as simultaneous works on different fronts are necessary to meet deadlines. The study mentions that, while projects like these involve high risks for workers, analysis of activities and situations are conducted precisely to demonstrate that such risks can be considerably reduced.
Highlights
1.1 History of the Project of the Eastern Drainage TunnelMexico City’s metropolitan area is built over a closed watershed, it was composed by a system of lakes comprising five large lakes: Texcoco, Xaltocan, Zumpango, Xochimilco and Chalco.During the highest raining seasons, the five lakes merged into one of an area of more than two thousand square kilometers
The underground works of the drainage system and the subway in Mexico City, by their magnitude and subsoil characteristics, left great knowledge in the construction of shafts in soft soils; this has resulted in the possibility of having an advanced planning of the construction of the shafts and to obtain the labor risks analysis to minimize the possibility of having accidents (Méndez 2009)
Even when it has been noted that risk analyses are an indispensable tool in the security and hygiene areas, many corporations still consider that labor risk prevention represents only a great expense, and they do not see it as an investment, originating that risk analyses are a simple requirement to be met and not an opportunity to avoid risks of accidents on site
Summary
Mexico City’s metropolitan area is built over a closed watershed, it was composed by a system of lakes comprising five large lakes: Texcoco, Xaltocan, Zumpango, Xochimilco and Chalco. During the highest raining seasons, the five lakes merged into one of an area of more than two thousand square kilometers. This explains the periodical flooding the inhabitants of the region suffered since the foundation of Tenochtitlan (Aztec capital before the Spaniards conquered it and changed its name to Mexico), as well as the great importance to make draining works in order to control and extract rainwater and sewage from the valley. In order to fully solve the draining system problem, it was decided to build a new tunnel below the city: The Eastern Drainage Tunnel “EDT” (Tunel Emisor Oriente in Spanish), with a capacity of 150 m3 per second of polluted water. The total estimated cost of the Project was 12 billion pesos (National Water Commission, 2011)
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