Ground water flow into tunnels driven in aquifers with variable head is evaluated for the construction period as well as for the time life of a tunnel to which ground water is allowed to enter, as is the case in tunnels driven with the associated purpose of water reclamation. The time-dependent behaviour of water inflow from the transitory construction stage up to the permanent state after completion is likewise established for tunnels driven in constant head aquifers.
On evalue le flux d'eau dans les tunnels excaves dans des nappes phreatiques à charge variable, aussi bien pour la periode de construction que pour la duree de vie utile d'un tunnel dans lequel on permet l'entree de l'eau de sous-sol après sa construction, tel est le cas des tunnels excaves ayant pour but additionnel de procurer de l'eau potable. On etablit aussi le comportement dans le temps, le debit qui penètre dans le tunnel, depuisl'etat transitoire de la construction jusqu'à l'etat stationnaire après la construction pour les tunnels excaves dans des nappes phreatiques à charge hydraulique constante.
Der Grundwassereindrang in Tunnel, die in wasserfuehrende Schichten mit schwankenden Grundwasserspiegeln getrieben wurden, wird bewertet, sowohl fuer die Bauperiode als auch die aktive Zeit, in der der Grundwassereindrang in den Tunnel erlaubt ist, wie es der Fall von Tunnel mit der gleichzeitigen Zielsetzung der Wassergewinnung ist. Ebenso wird das zeitabhangige Verhalten des Wassereindrangs von der voruebergehenden Bauperiode bis zum stationaren Zustande nach Fertigstellung fuer Tunnel, die in konstanten Grundwasserspiegeln getrieben wurden, festgestellt.
Seepage towards tunnels being driven in constant head aquifers can be predicted for the under construction transitory stage, as close as the - permeability and effective porosity of the sub-- soil mass are known, BELLO, 1974. In many instances the after construction water inflow has none or little interest, because the tunnel lining is impermeable in the general case. However, for -- water reclamation projects involving tunnels --- along the waterways, the possibility of allowing groundwater to get into the tunnel, to increase - the volume reclaimed acquires relevance, mostly because this additional water can be gained with out increasing the construction cost of the tunnel. BELLO, 1974, developed a procedure to estimate the amount of water inflow for both the transitory and the stationary stages for a tunnel driven at a constant rate in a constant head aquifer. This paper deals with the relationship between time and water inflow after the end of the excavation for the above mentioned case and also for that one in which the tunnel is driven in - a variable head aquifer. For both cases the transitory stage is the most important for the reconstruction-period, because during this time takes place the larger amount of seepage and it must be handled to allow tunnel driving, whereas the stationary stage is of most importance - when it becomes necessary to know the water inflow after construction, to base on it the financial characteristics of a water reclamation project. This relation is of 'great help to analyze the - variation of pumping equipment required for maximum and final total inflow discharges to a tunnel; as it has the same form of the equation defining the average unit discharge e, its value can be read from the corresponding curve in figure No.1, once the value of TF is known. The theoretical behavior of total water inflow established above has been compared with, the - discharge actually measured in a part of the -- Emisor Central tunnel, driven north of Mexico - City as part of the deep sewage system of the - metropolitan area. The total discharge shown - in relation to time corresponds to a length of n, made tributary to a shaft for seepage handling to outside the tunnel. As can be seen in Fig. 3, actual and predicted discharge values are in good agreement; the subsoil conditions assumed in the development of the mathematical model were well accomplished in this part of the tunnel, as the aquifers are recharged not only by annual rain but also by an underground water flow coming from the near highland areas.
The mathematical model developed for constant head aquifers, has been extended to cover the variable head aquifers case, which is present in a tunnel under construction across the Las - Cruces mountain range, which runs in a north -- -south direction in the western part of Mexico City. The aquifers in the mountainous area are recharged by rain in annual periods, as it has been proved by the comparison of annual rain -- volume in the area and the water inflow getting into another tunnel operating in the same area from 25 years ago, and in which provitions for - groundwater penetration were made.
