Chap. XXVI.

SEA AND DOCK WALLS

1527

the heads of the bearing piles; the sheeting pileswere spiked to an inner waling of the samesize, and the whole was covered with 4-inchclose planking, on which the walls, which were°f brick, rested: their thickness at bot-tom is 10 feet, at top 4 feet 6 inches; theheight is 24 feet 6 inches, and it batters 5 feet.The counterfort at the back is 9 feet thick, andprojects at bottom 8 feet, and at top 3 feet6 inches from the back face of the wall.

Retaining walls built of stone in some ofour tidal harbours are 12 feet in thickness atthe base and half that width at the top; inmany instances the face is curved with a radiusof 80 feet, to allow the nearer approach of thevessels to be loaded and unloaded: and thefenders of oak, which are placed perpendicularly,are secured by iron ties.

It is important to carry the foundations of allretaining walls to the depth of 6 or 7 feet belowthe bed of the harbour or basin where they areconstructed, and to protect them at the toe byrows of piles ; in many places the oak fendersare capped with iron, and lewis iron eye-boltsare introduced to secure vessels.

Where the soil of the foundations is soft, atimber platform is generally laid below thefootings, the toe of which is protected by sheet-piling.

Pig. 2806.

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Fig. 2808.

The Brunswick Wharfat Blackwally wholly ofiron, was constructed in1834. A trench 6 feetin depth was dug alongthe intended line, and thetimber guide-piles after-wards driven: the ironpiles, which are in twoheights, with a socket-joint secured by a screw-bolt, were then driven atintervals of 7 feet, andthe intermediate spacespiled in: each sheet-pileis secured at the top bytwo bolts to the upper-most wall of the wood-work behind: the iron

Fig. 2809. BRUNSWICK WHARi',

5 £ 4