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ON THE DOVER HARBOUR WORKS. 485 
to the inclined approach leading from the promenade level, a masonry 
abutment, founded on concrete cylinders carried down to the chalk, was 
formed close to the Granville Clock Tower at the west end of the 
Esplanade. 
The viaduct is built in spans of 40 feet, each pier consisting of three 
hollow wrought-iron piles strongly braced together. The width at deck 
level is 30 feet, and provides for a central roadway of 18 feet, and a 
footpath on each side of 6 feet. The level of the deck is 19 feet above 
high water of ordinary spring tides, and it is therefore not liable to 
damage even in the heaviest seas. At three points in the length of the 
work, the number of piles in a few bays is increased to five, giving a deck 
width of 56 feet, while the spans are reduced to 20 feet. Considerable 
additional stability, both laterally and longitudinally, is thus obtained. 
On the piers so constructed longitudinal lattice girders carry a platform 
or deck of corrugated iron plates. 
The ordinary section of the viaduct, and the section at the centre 
stiffening bays were shown. 
At first the piles were fitted with steel points, and were driven about 
25 feet below ground level, inclusive of about 15 feet into the chalk 
which exists over the whole of Dover Bay. Contrary to expectation, the 
bearing power of these piles was not found sufficient, and cast-iron screws, 
3 feet 6 inches in diameter, were substituted for the steel points. 
The screws for a few piers proved satisfactory under the 100 tons 
dead weight test to which each centre pile was invariably subjected, but 
during the application of the test load at a pier about 200 feet from the 
shore, the pile, much to the surprise of all present, suddenly sank about 
20 feet vertically. Borings taken at close intervals round the site of the 
pile showed that its position was exactly at the bottom of a cavity in the 
chalk, the surface of which sloped down to the pile in all directions. 
The accident proved that the quality of the chalk was extremely 
variable, and a change in system became necessary. The method adopted 
for the remaining length of the viaduct is shown on the diagram. Under 
the centre of each pier a cast-iron cylinder 8 feet in diameter was sunk 
into the chalk and filled with concrete, the centre pile or column being 
erected on a granite block bedded therein. The two side piles, on which 
the loads are considerably less than on the centre, were, after the accident 
‘before described, fitted with cast-steel screws 4 feet in diameter, and no 
further trouble has been experienced. 
It may be interesting to members to learn that when the excavations 
in the cylinder on the site of the pile which failed reached the depth to 
which the screw had originally penetrated, the blade was found broken 
into three pieces, having parted from the boss very close to the pile shank. 
The explanation of the accident appears to be that parts of the screw 
blade were bearing on hard chalk or flints, while other parts, as well as 
the point of the boss, were in soft material lying in the cavity indicated 
by the borings as already described. 
The corrugated deck of the viaduct will be filled with concrete as 
soon as the outer or solid portion of the pier is completed. The surface, 
both of roadway and footpaths, will be formed of asphalte. 
The solid masonry portion of the pier has a length, including the head, 
of 1,650 feet, with a width at quay level of 35 feet, and at foundation 
level of 48 feet. The general level of the surface is 10 feet above high 
‘water, but at the inner end this rises on a gradient of 1 in 40 to meet 
