New drilling techniques and the design of adits of long hydro tunnels

The choice of number and length of adits for construction of long hydraulic tunnels has received attention in the past, among others, by the authors (1981) because finding a solution bearing significant factors in mind (like economy of adit lengths, the presence of geologic controls or topographic peculiarities, the need of adequate rock cover, construction timing) for the choice of the most convenient layout defines a difficult optimization problem. New drilling technologies seem to have substantially modified the overall cost scheme thereby altering the optimal tunnel layout and configuration. Upon a review of the progress experienced in this field since the previous paper by the authors appeared, this paper examines some consequences of the new drilling schemes on the optimal layout of the tunnel and adits.