e outer doors. ease, two inches in thickness. The shoulder, more- guished from that of the caisson. over, gives room to shore up if it should be necessary. As the material is excavated the caisson will sink Preparatory to launching the caisson, the river bot- The roof of the working chamber is five… … upper layers being framed in these operations is in carefully between the quite extensive, as will struts and ties of the be seen from our front trusses. The timbers of the page engraving. By a whole caisson, both walls and roof, are securely drift- and a fairly level bed was prepared on which it…
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