Engineering Wonders of the World
Volume III

316 ENGINEERING WONDERS OF THE WORLD. Rot had reduced the upper layer of timbers to a powder very similar in appearance to coffee grounds, and the decayed material was full of what is commonly known as “ eel- worms.” Above these timbers the masonry was cracked and flaked in all directions, and it was apparent that an alarming state of affairs existed in regard to the whole of the foundation. The problem of saving the edifice from ruin was hardly capable of easy solution. Pending a decision, the important preliminary step was taken of pumping cement into every cavity and crevice, as also into all the voids left by the decayed timber. To carry out this valuable work the grouting machine invented by the late Mr. James Greathead (see vol. i., p. 61) was brought into operation. Beneath the nave columns vertical piles were found. It was supposed that these had been baulks of larch, but in some instances nothing except powder remained. The form of the original timber was seen impressed in the clay, but the wooden pile had completely rotted away, leaving only a cylindrical hole with the dust particles at the bottom. At every step the utmost caution had to be observed, and the tower was dealt with pier by pier. In the first instance, on the east and west sides, quite clear of Grillage pier, an excavation was Beams ma(je 24 feet long and 6 feet placed. ® wide, extending to the same depth as the old foundation. The two holes, dug with the greatest possible care, were filled in with concrete, in which what are techni- cally known as “ grillage beams ” were placed, with the object of distributing over the whole area of the new work the weight to be borne. A cavity 2 feet 6 inches deep and 9 inches wide was then cut or “ jumped ” through the lower masonry of the pier, and a steel girder, measuring 24 inches by 7 inches, was threaded through to rest on grillage beams in the con- crete blocks. Old Pier Foundations removed. To prevent subsidence resulting from the deflection of the girder when it received its load, steel wedges were driven in under each end of the beam. Initial deflection was thus secured, and the further sinking of the pier became impossible. The girder was next built into position with blue brick in cement, and grouted up. Four steel beams were thus inserted in succession, and properly secured in like fashion. In this way the immense weight of the pier was quietly and safely transferred from the rotten timbers to the steel girders, resting on the thick bed of concrete. This work was accomplished in turn under each of the four piers supporting the tower. The next endeavour was to get rid of all the old cracked masonry and decaying wooden beams at the base of the piers, some of th© latter having been cracked through. It was not deemed safe to remove more than a fourth of these materials at once, and as the débris was cleared away the space was filled up with concrete in cement. The result of this splendid piece of labour is that to-day each pier stands upon about 560 square feet of solid concr&te, instead of upon the old defective foundation, which would inevitably have involved a catastrophe of an appalling character. When once the piers had been rendered perfectly safe and sound, the task of taking down the defective nave columns began. One after another they were dis- mantled and rebuilt in a Church so.'vcd strictly vertical position, as much of the old masonry as remained available being utilized ; but owing to the transverse strains that had been brought to bear upon the columns before the work of restoration commenced, two blocks out of every twelve on an average had been broken and rendered useless. Holy Trinity Church, Hull, was in this way saved in the nick of time, to the intense delight of the whole population.