1532

THEORY AND PRACTICE OF ENGINEERING.

Book II.

In some instances, in forming sea walls, timber and stone may be introduced together,and particularly when the banks are loose and subject to slip, or are acted upon by the''land-springs. A stone wall carried up in frout of the work, supported at the back bystrong wooden piles strutted and braced, and afterwards filled in with concrete, or puddled

Fig. 2825.

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Fig. 2826.

with clay in the manner of a cofferdam, will have great strength, and resist any force towhich it may be opposed: a row of sheet piles round the face of such walls, as well as thebuttresses, prevent any irruption, and planking the whole foundations over binds them intoone entire mass. It is sometimes advisable in face of a cliff to form a temporary defence,by driving in double rows of piles, and filling up the space between with clay or earth im-

pervious to water: the weight acting against such a dam should be always resisted by atimber framing on the opposite side. When a length has been put together and securedby iron bolts, they may be drawn, and the same framing advanced another length, and socontinued until the entire shore is out of danger.