Abstract
AT the meeting of the Paris Academy of June 26, M. Daubrée read a note on the geological conditions of the Channel tunnel. The works connected with the tunnel comprise three phases:—(1) Scientific researches; (2) preparatory works; (3) execution of the tunnel itself. The first phase was devoted to purely geological investigation, in the form of minute exploration of the French and English coasts, exact and detailed investigation of the sea-bottom in the Strait, borings made on terra firma which verified the nature, thickness, and inclination of the strata, and gave an approximate idea of the hydrological condition. Since 1879 the second phase has been entered on by verifying the previous scientific data, and preparing for the execution of the tunnel itself, experimenting in small galleries with machines and tools capable of being ultimately used in a work of exceptional importance. On the French coast, the geological investigation established a slight bulging of the beds at the place known as the Quenocs. On account of this bulging the inclination of the strata, which, in the strait is towards the north-north-east, is found, along the cliffs,of Blanc Nez, turned towards the south-east, and the slope which, according to the first orientation, in the neighbourhood of the Quenocs, is about 0.05 m. per metre, is found, in the second, to be nearly 0.09 m. It is important then, to find in what conditions this bulging may modify the physical conditions of the banks forming the base of the Rouen chalk. For this purpose the French Association had dug, near Sangatte, two shafts of a depth of 86 m., which met the gault at 59 m. below the hydrographic zero, adopted in the maps in which the geological explorations of 1875–6 are recorded. The digging of these shafts, one of them 5.40 m. in diameter, showed that all the white chalk and the upper part of the Rouen chalk are water-bearing. These strata had thus to be abandoned.
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The Channel Tunnel . Nature 26, 229 (1882). https://doi.org/10.1038/026229a0
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DOI: https://doi.org/10.1038/026229a0