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DOCK ENGINEERING.
of the wall, and covered with a thin veneer of cement. Or if their ends
be not considered unsightly they may be simply sawn fiush with the surface
of the concrète.
Where the base of the wall lies below the ground level, the earth may be
excavated at any suitable slope until the required depth is reached. If the
strata will admit of it, it is preferable to bench out the ground in a series of
steps to avoid the formation of a possible plane of rupture between the
filling and the natural earth. The steps may even with advantage be sloped
downwards away from the wall. Fig. 130 is an illustration of a masonry
dock wall built under a combination of the foregoing circumstances. The
ground in front of the wall had previously been excavated to the proposed
depth ; that at the rear of the wall is partially sloped and partially benched.
The projection from the back of the wall near the coping level is to form the
floor of a trench for hydraulic and other pipes.
Fig. 130. —Dock Wall at Liverpool.
Construction in Trenches.—The means adopted for obtaining the required
depth for the base of a wall by means of timbered trenches is illustrated in
fig. 131, which exhibits the actual strata passed through in a definite
instance on the banks of the Mersey. The vertical series of shores are
placed at intervals of from 10 to 12 feet. The width of the trench at the
top is, of course, greater than the assigned foundation width, by the sum of
the thicknesses of the timber settings. The small “ grip,” or trench, in the
bottom is for drainage purposes. The method of construction presents no
essential difference from those already indicated. The shores and walings
which, together with the sheeting piles, are withdrawn as the wall is built,
offer facilities for the support of concrete moulds. By this system the earth
in front of the wall is excavated at a later stage. In the meantime, any
space between the front of the wall and the side of the trench is occupied by