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The Thames Tunnel (continued)
On March 6 the proprietors paid a visit to the Tunnel, and were highly satisfied with what they saw. On that evening Sir Isambard writes:—
It is of absolute necessity now to provide for everything that is conducive to the more expeditious management of the frames, and to a greater facility in getting up the brickwork. If these two points are realized, then indeed we may soon expect to be moving at a good rate—not less than I have held out, namely, 3 feet per 24 hours.
March 11.—Received early in the morning a report from Armstrong stating that the water was completely stopped—that it had been stopped during the night. Aware that we had passed the gravel, it was of course expected that we were under the clay; means were therefore resorted to, to drive clay and oakum at the tail of the top staves, which was productive of a very good effect. The great shield was soon entirely free of water. This shows the efficiency of the shield to oppose difficulties which could not have been overcome without the complete protection it affords, under almost any circumstances. Indeed this has been a tedious operation since January 25, when the water first burst upon No. 5, at the front of the shield. The miners as well as the bricklayers have worked with great spirit and perseverance through the whole, during a period of 44 days. The well that was made at the front of the shaft has been of use in acquainting us with the extent of the open ground we had to pass through. It will be made a useful opening for ventilating the works. By means of this well we have been able to apply the lead pipes with which the water has been diverted: it is not therefore a useless expense. Things were put in better order to prepare for a more expeditious way of working. Directions were given to place the frames in a better condition. Isambard is still too unwell to go to the Tunnel. [marginal note: Water stopped as expected.]
March 25.—Went to the Tunnel with Isambard. Found that a considerable fall of ground had taken place again at the right side. No one could account satisfactorily for it. I inspected it, and directed that, after making it good, flat bars of iron be driven at the head of the side staves, in order to pin it up, and in order to enable the miners to get at the solid ground. It is verv bad and extremely dangerous; the ground is evidently the same as that which, in the report of the first attempt, was found so loose as to have dropped upon the works, leaving a large cavity above, when it is said the man ascended and made good the hole. We should be warned by this, lest we should meet another as fatal as it ultimately was on that occasion. [This observation refers to the driftway of 1807] [marginal notes: Consideral slip of ground: how to check it and Very dangerous]
April 24.—By Armstrong’s report the water is entirely out, and the men at work in the morning in removing the dirt, &c. Isambard engaged at the Tunnel, where I am not yet able to attend as often as I could wish. Everything goes on well, much through his exertions.
May 11.—One hundred feet will be completed to-night.
May 22.—The top plate over the frame No. 1 has been cracked without any particular violence or stress. It appears that it is nothing but the change of temperature that is the cause of that rupture. The accident justifies the opinion I have of cast-iron not being safe upon traction, and the precaution of having had wrought-iron bolts at the back of the frames. [These were vertical rods which took the tensional strain.] Without these bolts what would have become of the shield, if one casting was to break? The fracture was accompanied with a loud report like that of a gun. Isambard was in the works at the time of breaking: nothing could have prevented it. [marginal notes: The shield being too much out, resolved to move it bodily.]
May 25.—I observed that nothing whatever had been gained to recover the deviation [the shield had gradually worked 2 feet 3 inches to the westward], which subjects us to so much inconvenience and loss of time. The only way to bring the shield right is by taking the frames sideways.