8UBMARINK TfNNELINO 207 



inland shafts, flooded a section of the tunnel, but the pumps 

 removed this water within a week. 



In order to construct the portion of tunnel traversing the 

 line of the great spring, the water was diverted into a side 

 heading below the level of the tunnel, leading to the old shaft, 

 win-nee it was pumped, and the fissure below the tunnel was 

 filled with concrete, over which the invert was built. An 

 attempt to imprison the spring, on the completion of this 

 length of tunnel, having resulted in imposing an excessive pres- 

 sure on the brickwork, leading to fractures and leakage, a shaft, 

 29 ft. in diameter, was sunk at the side of the tunnel at this 

 point in 1886, and pumps were erected powerful enough to 

 deal with the entire flow of the spring. 



The tunnel was opened for traffic in December, 1886, and 

 gives access to a double line of railway, connecting the lines 

 converging to Bristol with the South Wales railway and the 

 western lines. The pumping power provided at the shaft con- 

 nected with the great spring, and at four other shafts, is capable 

 of raising 66,000,000 gallons of water per day, the maximum 

 amount pumped from the tunnel being 30,000,000 gallons a 

 day. The ventilation of the tunnel is effected by fans placed 

 in the two main shafts on each bank of the estuary, and the fan 

 in the Monmouthshire shaft is 40 ft. in diameter, and 12 ft. 

 wide. The tunnel gives passage to a large traffic, numerous 

 through-trains between the north and southwest of England 

 making use of it 



